Category Archives: Marine

Engelmann VS 5 side

Versuchs Schnellboot 5 (VS 5) Semi-submersible Attack Boat

By William Pearce

In the early 1930s, Rudolf Engelmann of Berlin, Germany began investigating designs to improve the hull shape of seagoing ships. Engelmann felt that a new hull shape could be devised that would significantly improve how efficiently a sea-going ship plowed through the water. At the time, the fastest ocean liners and destroyers were capable of around 35 mph (56 km/h) and 46 mph (74 km/h) respectively. Engelmann’s goals were to increase speed to 46–58 mph (74–93 km/h) with the same amount of power and enable ships to maintain higher speeds through rough seas.

Engelmann patent drawings

Rudolf Engelmann’s original concept of a semi-submersible ship is illustrated in Fig 3 and Fig 4 from his first patent (651,390). Fig 10 shows the updated design from his second patent (651,892), with the exception of line 14. Line 14 indicates the chines that were added in the third patent (651,893).

Engelmann used models to test various hull shapes. On 25 March 1934, Engelmann applied for a German patent (no. 651,390) that outlined his design. Engelmann’s ship had a shape that was very similar to a modern-day submarine—a cigar-shaped (fusiform or spindle-shaped) hull with a propeller at its end and a superstructure in the middle. However, Engelmann’s ship was not fully submersible. The hull traveled beneath the water’s surface, but the superstructure sat above the waterline. The hull’s cross section was pear-shaped, with the narrow part in the middle positioned at the waterline. The submerged hull increased the ship’s efficiency and improved the ship’s stability in rough seas. The superstructure had a streamlined form to cut through the water and slice through waves.

After the first patent, Engelmann continued to develop the semi-submersible design. He applied for two other patents in 1935 that detailed an updated hull shape. The difference between the two later patents was detailed in German patent 651,893, which included a chine added to the superstructure. Tests indicated that in rough seas, the superstructure of the previous designs had a tendency to build up a bow wave. In addition, the design’s minimal reserve buoyancy caused the ship to plow under waves. To correct these issues, the thickness of the leading edge of the superstructure was reduced, and chines were added above the waterline. The chines tapered back and were blended into the sides of the superstructure. They directed water down from the superstructure rather than over it. The additional area created by the chines increased the ship’s displacement and buoyancy with the wave action.

Engelmann VS 5 drawing

A drawing of the Versuchs Schnellboot 5 (VS 5) shows the ship’s profile as very similar to what was depicted in Engelmann’s second and third patents. Note how the ship narrowed at the waterline, which is where the hull and superstructure joined.

Engelmann’s experiments caught the attention of the Kriegsmarine (German Navy), which felt the hull design had military applications. Having the superstructure as the only part of the ship above the water decreased the ship’s detection range and also presented a small target for an enemy to hit. Combined with its high speed, a ship of Engelmann’s design could get very close to an enemy ship undetected, launch torpedoes, and then quickly retreat to a safe distance. Around 1938, the Kriegsmarine ordered a proof-of-concept prototype be built.

The prototype was designated Versuchs Schnellboot 5 (Experimental Fast Boat 5 or VS 5) and was also referred to as the Engelmann-Boot. The ship was a semi-submersible, fast-attack torpedo boat for use in coastal waters. The VS 5 was built along the lines specified in Engelmann’s third patent. Rudders and stern planes at the rear of the ship provided control. The VS 5’s armament consisted of two forward-firing, 21 in (533 mm) torpedo tubes in the bow of the hull and two 20 mm cannons atop the superstructure. However, it is not clear if the weapons were ever installed in the prototype.

Engelmann VS 5 front

The VS 5 in dry-dock, most likely before it was launched in January 1941. The completed ship looked very much like a submarine with an odd sail. Note the chines on the superstructure. Engelmann stated in his patents that the top of the superstructure could be built with an overhang so that its leading edge was angled back to the hull. This configuration would further reduce the tendency of waves to pass over the superstructure.

Power was provided by four MAN (Maschinenfabrik Augsburg-Nürnberg) L11Z 19/30 diesel engines. The L11Z 19/30 was an 11-cylinder, double-acting, two-stroke, inline engine capable of reverse operation. Each of its closed cylinders had a combustion chamber at the top and bottom of the cylinder. A single intake manifold brought air into the cylinders, where the air was directed either above or below the double-sided piston, depending on its stroke. Separate exhaust manifolds collected exhaust gases from the upper and lower combustion chambers. The engine had a 7.48 in (190 mm) bore and a 11.81 in (300 mm) stroke. Since the piston was double-acting and there was an upper and lower combustion chamber, the engine’s displacement was nearly doubled, as if it had 22 cylinders. However, the connecting rod passing through the lower combustion chamber took up around 40 cu in (.66 L) of volume. Total displacement for the upper combustion chambers was 5,710 cu in (93.56 L). Total displacement for the lower combustion chambers was approximately 5,269 cu in (86.35 L). The L11Z 19/30’s total displacement was around 10,979 cu in (179.91 L). The engine had a maximum output of 2,000 hp (1,491 kW) at 1,050 rpm and a continuous output of 1,400 hp (1,044 kW) at 900 rpm. The four L11Z 19/30 engines were installed in two rows in the middle of the VS 5 and were connected to a common gearbox that drove a single propeller.

MAN LZ 19-30 engine side

The VS 5 was powered by four MAN L11Z 19/30 double-acting, two-stroke, 11-cylinder engines. Note the upper and lower exhaust manifolds separated by the single intake manifold. The gap under the lower exhaust manifold is where the two fuel injectors for the lower combustion chamber were installed. A covered connecting rod passed through the center of each gap. (Hermann Historica image)

The VS 5 was 160 ft 3 in (48.84 m) long and 9 ft 3 in (2.82 m) wide. The keel sat about 11 ft 10 in (3.6 m) under the waterline. The superstructure was around 66 ft (20 m) long and rose about 12 ft 6 in (3.8 m) out of the water. The VS 5 displaced some 292 tons (265 tonnes) and had a forecasted top speed of 58 mph (93 km/h). The ship had a full crew of 17. Some sources state the VS 5 could sink in shallow water to hide from enemy ships. Once submerged, it could not move (other than surfacing), as the ship did not have batteries or the capability to run its engines while underwater. However, the ability to intentionally sink is not mentioned by all sources.

Engelmann VS 5 side

For normal operation, the hull of the VS 5 was completely submerged, and only the superstructure sat above the waterline. The 12 ft 6 in (3.8 m) tall and 66 ft (20 m) long superstructure was a small target for enemy ships to detect and hit.

Construction of the VS 5 started on 1 April 1940, and the ship was built by Deutsche Schiff- und Maschinenbau Aktiengesellschaft (Deschimag) in Bremen, Germany. Deschimag was a conglomerate of eight German shipyards. The VS 5 was launched on 14 January 1941, and trouble was encountered soon after testing began. Despite the changes in Engelmann’s design, the VS 5 still had a tendency to plow under waves in heavy seas. In addition, torque from the single propeller caused the whole ship to list around 14 degrees as full power was applied. The issue was so severe that a speed of 32 mph (52 km/h) could not be exceeded because of the tilt.

The VS 5 project was apparently abandoned in 1942, and what happened to the ship is not known. Plans for a larger 661-ton (600-tonne) ship were cancelled. Twin propellers were planned for the larger ship, and their configuration would have cured the list issues caused by the single-propeller. Engelmann’s design concept was passed over as the Kriegsmarine focused on submarines and fast boats, rather than a combination of the two.

Engelmann VS 5 rear

The chine on the superstructure can easily be seen in this image of the VS 5. The VS 5 had a severe list under full power, an issue that would have been corrected if other ships of the same type had been built. The VS 5 combined elements of both a fast boat and a submarine but did not really offer any advantages over other types of ships.

“Schiff” German patent 651,390 by Rudolf Engelmann (granted 23 September 1937)
“Schiff” German patent 651,892 by Rudolf Engelmann (granted 30 September 1937)
“Schiff” German patent 651,893 by Rudolf Engelmann (granted 30 September 1937)
“Improvements relating to the construction of Ships” GB patent 455,466 by Rudolf Engelmann (granted 21 October 1936)
“Improvements relating to the Construction of Ships” GB patent 470,907 by Rudolf Engelmann (granted 20 August 1937)
“High Speed Seagoing Ship” US patent 2,101,613 by Rudolf Engelmann (granted 7 December 1937)


Mercedes-Benz 500 Series Diesel Marine Engines

By William Pearce

Daimler-Benz was formed in 1926 with the merger of Daimler Motoren Gesellschaft and Benz & Cie. Prior to their merger, both companies produced aircraft engines under the respective names Mercedes and Benz. After the merger, the Daimler-Benz name was used mostly for aircraft engines, and the Mercedes-Benz name was used mostly for automobile production. However, both names were regularly applied to marine engines. For clarity in this article, the name Daimler-Benz will refer to aircraft engines, and the name Mercedes-Benz will refer to marine engines.


The MB 501 shows the close family resemblance to the DB 602, but the engines had Vees of different angles and completely different valve trains. The tubes for the pushrods can be seen on the outer side of the cylinders. Note the two water pumps on the rear sides of the engine.

As Germany began its rearmament campaign in the 1930s, high-performance marine diesel engines were needed to power various motorboats. The Kriegsmarine (German Navy) turned to Mercedes-Benz to supply a series of high-speed diesel engines. These engines were part of the MB 500 series of engines that were based on the Daimler-Benz DB 602 (LOF-2) engine developed to power the LZ 129 Hindenburg and LZ 130 Graf Zeppelin II airships. The 500 series diesel engines were four-stroke, water-cooled, and utilized a “V” cylinder arrangement.

The first engine in the 500 series was the MB 500 V-12. The engine’s two cylinder banks were separated by 60 degrees. The MB 500 used individual steel cylinders that were attached to an aluminum alloy crankcase. About a third of the cylinder was above the crankcase, and the remaining two-thirds protruded into the crankcase. This arrangement helped eliminate lateral movement of the cylinders and decreased vibrations. The crankcase was made of two pieces and split horizontally through the crankshaft plane. The lower part of the crankcase was finned to increase its rigidity and help cool the engine oil.


The crankcases of the wrecked MB 501 engines on Crackington Haven Beach have completely dissolved over the years from constant exposure to salt water. Only the engine’s steel components remain. Note the fork-and-blade connecting rods. The engine’s gear reduction can be seen on the left side of the image. (gsexr image via

Each cylinder had two intake and two exhaust valves. The camshaft had two sets of intake and exhaust lobes per cylinder. One set was for normal operation, and the other set was for running the engine in reverse. The fore and aft movement of the camshaft to engage and disengage reverse operation was pneumatically controlled. Bosch fuel injection pumps were located at the rear of the engine and were geared to the camshaft. Each injection pump provided fuel to the cylinders at 1,600 psi (110.3 bar). Fuel was injected into the center of the pre-combustion chamber, which was in the center of the cylinder head and between the four valves. For low-speed operation, fuel was cut from one bank of cylinders.

The MB 500 had a compression ratio of 16.0 to 1. The engine used fork-and-blade connecting rods that rode on roller bearings fitted to the crankshaft. The camshaft also used roller bearings, but the crankshaft was supported by plain bearings. Speed reduction of the engine’s output shaft was achieved through the use of bevel planetary gears. Two water pumps mounted to the rear sides of the engine circulated water through the cylinder banks. Each pump provided cooling water to one cylinder bank. The pumps were driven by a cross shaft at the rear of the engine. The engine was started with compressed air.


With the exception of the different intake manifolds, the MB 502 was nearly identical to the DB 602. Note the Mercedes-Benz emblem on the rear of the V-16 engine.

The MB 500 had a 6.89 in (175 mm) bore and a 9.06 in (230 mm) stroke. This cylinder size directly corresponded to the cylinder size used on the DB 602. The MB 500’s displacement was 4,051 cu in (66.39 L). The engine had a continuous output of 700 hp (522 kW) at 1,460 rpm and a maximum output of 950 hp (708 kW) at 1,630 rpm. Fuel consumption was .397 lb/hp/hr (241 g/kW/hr). The MB 500 was 9.6 ft (2.93 m) long, 3.2 ft (.98 m) wide, and 5.7 ft (1.73 m) tall. The engine weighed around 4,784 lb (2,170 kg). MB 500 engines were installed in Schnellboote that Germany built for Bulgaria. A Schnellboot, or S-boot, was a fast attack boat and was referred to as an E-boat (Enemy boat) by the Allies.

For more power, the MB 501 was built with two rows of ten cylinders, creating a V-20 engine. The MB 501 was similar to the MB 500, but it also had a number of differences. A 40 degree angle separated the cylinder banks, and the engine used two camshafts positioned in the upper crankcase, one on each side of the engine. Rollers on the lower end of the pushrods rode on the camshaft. Two pushrods for each cylinder extended up along the outer side of the cylinder bank to operate a set of duplex rocker arms for the two intake and two exhaust valves. The fork-and-blade connecting rods were attached to the crankshaft with plain bearings.


The MB 507 was based on the DB 603 inverted V-12 aircraft engine. Although the engine’s architecture was similar, the MB 507 had a completely different crankcase and reduction gear than the DB 603, and it was not supercharged.

The MB 501’s bore and stroke were increased over the MB 500’s to 7.28 in (185 mm) and 9.84 in (250 mm) respectively. The engine displaced 8,202 cu in (134.40 L). The MB 501 had a continuous output of 1,500 hp (1,119 kW) at 1,480 rpm and a maximum output of 2,000 hp (1,491 kW) at 1,630 rpm. Fuel consumption was .397 lb/hp/hr (241 g/kW/hr). The engine was 12.7 ft (3.88 m) long, 5.2 ft (1.58 m) wide, 5.6 ft (1.71 m) tall, and had a weight of 9,303 lb (4,220 kg). Three MB 501 engines were installed in each 1937 class Schnellboot. Six engines were installed in each of the U-180 and U-190 submarines. However, the MB 501 engines proved unsuitable in the submarines, and they were soon replaced by MAN diesels. The remains of three MB 501 engines can be found on Crackington Haven Beach in southeast Britain. The engines belonged to Schnellboot S-89, which was surrendered to the British after World War II. S-89 slipped its tow on 5 October 1946 and was wrecked upon the shore.

The MB 502 was essentially a Daimler-Benz DB 602, except it had water jacketed intake manifolds that protruded above the engine’s Vee. The rest of the MB 502’s specifics mirrored those of the DB 602. The MB 502 was a 50 degree V-16 with a single camshaft located in the Vee of the engine. The engine had a 6.89 in (175 mm) bore and a 9.06 in (230 mm) stroke. The MB 502 displaced 5,401 cu in (88.51 L) and had a continuous output of 900 hp (671 kW) at 1,500 rpm and a maximum output of 1,320 hp (984 kW) at 1,650 rpm. The engine was 9.9 ft (3.02 m) long, 4.0 ft (1.22 m) wide, and 6.2 ft (1.90 m) tall. The MB 502 weighed 5,952 lb (2,700 kg) and had a fuel consumption at cruising power of 0.37 lb/hp/hr (225 g/kW/hr). Three MB 502 engines were installed in each 1939 class Schnellboot.


The MB 511 engine on display in the Aeronauticum museum in Germany. Note the finning on the lower half of the crankcase. On the front of the engine (left side of image) is the gear reduction with the supercharger above. The square connection above the engine is for the induction pipe. (Teta pk image via Wikimedia Commons)

The MB 507 was based on the Daimler-Benz DB 603 inverted V-12 aircraft engine, but some features from the DB 602 were incorporated. The normally aspirated MB 507 was an upright V-12 diesel engine that used monobloc cylinders and had a compression ratio of 17 to 1. A new finned crankcase was fitted that was similar to those used on other MB 500 series diesel engines. For the initial MB 507 engines, the bore was decreased from the 6.38 in (162 mm) used on the DB 603 to 6.22 in (158 mm). The stroke was unchanged at 7.09 in (180 mm). This gave the MB 507 a displacement of 2,584 cu in (42.35 L). The DB507 weighed 1,834 lb (850 kg). The engine had a continuous output of 700 hp (522 kW) and a maximum output of 850 hp (634 kW) at 2,300 rpm. An updated version of the engine, the MB 507 C, reverted back to the 6.38 in (162 mm) bore, which increased its displacement to 2,717 cu in (44.52 L). The MB 507 C produced 750 hp at 1,950 rpm and 1,000 hp at 2,400 rpm. The engine was 6.0 ft (1.83 m) long, 2.6 ft (.79 m) wide, 3.5 ft (1.06 m) tall, and had a weight of 1,742 lb (790 kg). Two MB 507 engines were used in a few LS boats (Leicht Schnellboot or Light Fast boat), and the engine was also installed in some land vehicles, such as the Karl-Gerät self-propelled mortar.

The MB 511 was a supercharged version of the MB 501 V-20 engine. The bore, stroke, and displacement were unchanged, but the compression ratio was decreased to 14 to 1. The supercharger was positioned at the front of the engine, above the gear reduction. With the supercharger, output increased to 1,875 hp (1,398 kW) at 1,480 rpm for continuous power and 2,500 hp (1,864 kW) at 1,630 rpm for maximum power. The MB 511 was 13.1 ft (4.00 m) long, 5.2 ft (1.58 m) wide, and 7.6 ft (2.33 m) tall. The engine weighed 10,406 lb (4,720 kg). Three MB 511 engines were installed in each 1939/1940 class Schnellboot. An MB 511 engine is on display in the Aeronauticum maritime aircraft museum in Nordholz (Wurster Nordseeküste), Germany. Also, the MB 511 engine was built by VEB Motorenwerk Ludwigsfelde as the 20 KVD 25 in East Germany in the 1950s. Two 20 KVD 25 engines were installed in an experimental torpedo boat.


The sectional and cylinder drawing are for the MB 518 but were basically the same for the MB 501 and MB 511—all were 40 degree V-20 engines with individual cylinders. Note the pre-combustion chamber, valve train, and two camshafts.

The MB 512 was a supercharged version of the MB 502. Its compression was decreased to 14 to 1, but its output increased to 900 hp (1,398 kW) at 1,500 rpm for continuous power and 1,600 hp (1,864 kW) at 1,650 rpm for maximum power. The MB 512 was 10.0 ft (3.05 m) long, 4.2 ft (1.28 m) wide, and 6.3 ft (1.92 m) tall. The engine weighed 6,834 lb (3,100 kg). MB 512 engines replaced MB 502s in some Schnellboot installations.

The MB 517 diesel engine was a supercharged version of the MB 507. Returning to its DB 603 roots, the engine was inverted, but it retained the 6.22 in (158 mm) bore and 7.09 in (180 mm) stroke of the early MB 507. The supercharger boosted power from the 2,584 cu in (42.35 L) engine to 1,200 hp (895 kW) at 2,400 rpm. The MB 517 was installed in the Panzer VIII Maus V2 tank prototype.


The MB 518 was the last development of the V-20 engines. This image shows the large intercooler installed on the engine’s induction system.

The MB 518 was a continuation of the MB 511 and featured an intercooler. The large intercooler was positioned in the intake duct, above the engine and between the supercharger at the front of the engine and the intake manifolds in the engine’s Vee. The first MB 518s had a continuous output of 2,000 hp (1,696 kW) at 1,500 rpm and a maximum output of 3,000 hp (2,237 kW) at 1,720 rpm. After World War II, updated versions of the engine went into production starting in 1951. The MB 518 B had a continuous output of 2,275 hp (1,696 kW) and a maximum output of 3,000 hp (2,237 kW). The MB 518 C had a continuous output of 2,500 hp (1,864 kW) and a maximum output of 3,000 hp (2,237 kW). A turbocharger was added to create the MB 518 D. It had a continuous output of 2,900 hp (2,163 kW) and a maximum output of 3,500 hp (2,610 kW). The MB 518 engine was 14.8 ft (4.52 m) long, 5.2 ft (1.58 m) wide, and 8.0 ft (2.44 m) tall. The engine weighed around 11,332 lb (5,140 kg). MB 518 engines were used to power several different vessels for the German Navy and were also exported to 35 countries. Some of the engines are still in use today.

Schnellboot S-130, the only remaining German S-boot from World War II, was originally powered by three MB 511 engines. After the war, S-130 was reengined with two MB 518s, and one MB 511 was retained. S-130 is currently part of the Wheatcroft Collection and undergoing restoration. Four MB 518 C engines for the restoration were obtained from the Arthur of San Lorenzo, formerly known as the S39 Puma and originally built as a German Zobel Class fast patrol boat in the early 1960s.


A number of MB 518 engines under construction show many different details. The lower crankcase half is on the floor, while the upper half is in the engine cradle; note the two camshaft tunnels. The crankshaft and its fork-and-blade connecting rods can be seen. Farther down the line is an engine with cylinder studs installed, and farther still is an engine with studs and pushrod tubes installed.



Brayton Ready Motor Hydrocarbon Engine

By William Pearce

With the proliferation of steam power in the late 1800s, many inventors looked to create a simpler and more efficient engine. Rather than having combustion occur outside the engine, as with a steam engine, designers sought to create an internal combustion engine, in which the piston was driven by the expansion of a volatile gas mixture after it was ignited. George Brayton of Boston, Massachusetts was one such inventor, and while his designs would forever influence the internal combustion engine, he never achieved the same level of recognition as many of his contemporaries.


Patent drawings of George Brayton’s 1872 engine. Gas and air was drawn into cylinder C, compressed by piston D, and stored in reservoir G. The mixture was then released into cylinder A and ignited as it passed through wire gauze e. As the mixture combusted and expanded, it acted on piston B.

Brayton was an inventor, engineer, and machinist who had experience with steam engines. Some of his internal combustion engine experiments date back to the early 1850s, but he began serious development around 1870. In 1872, Brayton patented a new type of engine, the first in a series that became known as the Brayton Ready Motor. The name “Ready Motor” described the fact that the engine was immediately ready for operation, unlike a steam engine. The Brayton engine was also called a “Hydro-Carbon Engine.” The engine used fuel (hydrocarbons) mixed with air as the working fluid that directly acted on the piston, rather than the fuel heating some other working fluid, as with a steam engine. The theoretical process by which the Brayton engine worked became known as the constant-pressure cycle or Brayton cycle. The Brayton cycle in a piston engine involves the pressure in the engine’s cylinder being maintained by the continued combustion of injected fuel as the piston moves down on its power stroke. The constant-pressure Brayton cycle is used in gas turbines and jet engines and is also very similar to the Diesel cycle.

Brayton’s 1872 patent engine was a two-stroke that had two pistons mounted to a common connecting rod. The smaller of the two pistons acted as an air pump, compressing the air to around 65 psi (4.5 bar). A gaseous fuel, such as illuminating gas or carbureted hydrogen, was mixed with the air entering the compression cylinder. Alternatively, an oil fuel, such as naphtha, could be vaporized and added to the air entering the compression cylinder. The air/fuel mixture was then compressed, passed through a valve, and stored in a reservoir. An engine-driven camshaft opened a valve that allowed the pressurized air/fuel mixture to flow from the reservoir and into the large combustion cylinder. Before entering the cylinder, the air/fuel mixture passed through layers of wire gauze where a small pilot flame constantly burned. The pilot flame was kept lit by a continuous, small supply of the air/fuel mixture. As the charge passed through the wire gauze and entered the cylinder, it was ignited by the pilot flame. The combusting and expanding gases created around 45 psi (4.1 bar) of pressure that forced the large piston back in its cylinder, creating the power stroke. At the same time, the small piston was moved toward top dead center in its cylinder, compressing another charge of air for continued operation.


Brayton’s 1874 patent illustrating a double-acting engine. The upper side of piston B compressed air as the lower side was exposed to the combustion process of air and fuel being mixed and ignited in chamber H. Reservoir C only stored compressed air.

Brayton’s experience with steam engines and how steam expands into the cylinder to smoothly act on the piston probably influenced his desire to have the fuel burn in the cylinder. Gas expansion created by burning fuel acts smoothly on the piston, whereas the sudden ignition of fuel by a spark creates more of an explosion that exposes the piston and other engine components to high stresses. The combustion (motor) cylinder was about twice the volume of the compression (pump) cylinder, and the reservoir was no more than twice the volume of the combustion cylinder. The pressure in the reservoir was always greater than the pressure in the combustion cylinder. A water jacket surrounded the combustion cylinder to provide engine cooling.

The 1872 patent clearly illustrates a single-acting engine in which only one side of the piston acts on the working fluid. Brayton explains in the patent that the same principles of his engine could be applied to a double-acting engine. In a double-acting internal combustion engine, one side of the piston compresses the working fluid, while the other side of the piston is used for combustion of the working fluid. The patent drawing also shows a flywheel mounted to the camshaft. Engine power would be distributed from a driving pulley on the opposite end of the flywheel. However, images of early Brayton engines show an articulated rod mounted to the connecting rod that drove the flywheel and drive pulley.


Brayton Ready Motor vertical engine with a double-acting cylinder. The air reservoir was housed in the rocking beam support column. Note the ball governor.

Around 1873, Brayton installed a 4 hp (3.0 kW) engine in a streetcar in Providence, Rhode Island. The streetcar could obtain a speed of 15 mph (24 km/h), but it would barely move with a full load and had difficulty climbing an incline. A larger 12 hp (8.9 kW) engine was substituted, as it was the most powerful Brayton engine that fit in the space available. The engine took up the space of one passenger and enabled the streetcar to climb a 5 percent grade. All total, the streetcar was tested for 18 months. However, the tests indicated issues with wheel slip on the rails, especially in snow or ice, and financial issues brought an end to the experiment.

A drawback to the 1872 engine was the storage of the volatile gas mixture in the reservoir. If any flame were to get past the wire gauze and continue to burn back to the reservoir, the contents of the reservoir would explode. A safety valve prevented damage to the engine, but such an event was very disconcerting to anyone near the engine. The use of light, gaseous fuel exacerbated the issue. In 1874, Brayton switched to a heavy petroleum oil fuel and patented a refined engine in which only air was stored in the reservoir. A small supply of petroleum fuel was pumped into absorbent, porous material contained in a chamber that surrounded the induction pipe. The top of the chamber formed what was basically a burner. As the liquid fuel was heated by the engine and vaporized, it joined with the air charge being admitted into the cylinder via a camshaft-driven valve. The mixture was then ignited as it flowed through the burner section and into the cylinder. The burner stayed lit by residual fuel from the absorbent material mixing with a small amount of air from the reservoir that constantly passed through the burner.


Engine speed was controlled by an admission valve that regulated the amount of air passing into the cylinder. Although the fuel quantity supplied to the chamber was metered and dependent on engine speed, making changes to engine speed proved to be difficult. Any change in the amount of air supplied meant that there was a brief period of either too much or too little fuel, and this would occasionally extinguish the burner flame. By 1876, this issue had been resolved by implementing a new fuel injection process. The incoming air passed through the absorbent, porous material that was saturated with injected fuel. A jet of air coincided with the injection of fuel and helped distribute the fuel throughout the absorbent material. This injection technique proved more responsive than the earlier vaporization process.

Other changes incorporated in the 1874 engine were the use of both sides of the piston, making the engine double-acting. A rod connected to the compression side of the piston extended out of the engine. The rod decreased the volume of the compression cylinder to less than that of the combustion cylinder. The rod also provided a means to harness power from the reciprocating movement of the piston. Although the rod was mounted on the compression side of the piston, it was the power stroke of the combustion side that provided the motive force.


Circa 1876 Brayton inverted rocking beam engine. The combustion cylinder is on the left, and the smaller compression cylinder is at the center of the engine. Two air reservoirs made up the engine’s base; one was used for operating the engine, and the other was used for starting. The engine is currently in storage at the Smithsonian. (Paul Gray image via John Lucas /

Development of the Brayton Ready Motor continued, and by 1875, the compression cylinder was completely separate from the combustion cylinder. Both cylinders had the same bore, but the stroke of the compression cylinder was about half that of the combustion cylinder. A number of different engine styles, both vertical and horizontal, were built, and the engines used different ways to harness the power of the compression cylinder. Some engines used the compression cylinder to actuate a rocking beam; other engines had the compression cylinder connected to a crankshaft that turned the power wheel.

By 1875 (and possibly as early as 1873), the Pennsylvania Ready Motor Company in Philadelphia had been established to sell Brayton’s engines, but the engines were built in the Exeter Machine Works in Exeter, New Hampshire. The Brayton Ready Motor may have been the first commercially available internal combustion engine. Engines based on the Brayton cycle were also sold by a number of other companies, including the New York & New Jersey Motor Company (by 1877) and Louis Simon & Sons, in Nottingham, England in 1878.


Drawing of the 10 hp (7.5 kW) vertical Brayton Ready Motor displayed at the Centennial Exposition in Philadelphia, Pennsylvania in 1876. This is the same engine that inspired George Selden. The compression cylinder was mounted above the combustion cylinder. The column supporting the rocking beam also contained the reservoir.

In 1878, John Holland used a 4 hp (3.0 kW) vertical Brayton engine in the first submarine powered by an internal combustion engine, the Holland I. While functional, this submarine was not a true success. Holland’s second submarine, the Fenian Ram, used a 15 hp (11.2 kW) horizontal Brayton engine and was launched in 1881. This submarine has been preserved and is displayed in the Paterson Museum in Paterson, New Jersey.

Also in 1878, a vertical engine was tested in an omnibus in Pittsburgh, Pennsylvania, but local authorities would not permit its use to transport passengers. Scottish engine pioneer Dugald Clerk converted a 5 hp (3.7 kW) Brayton engine to spark ignition. This engine was the first two-stroke, spark ignition engine ever built. Horizontal engines were installed in a few boats that operated on the Hudson River. In 1880, the USS Tallapoosa was fitted with a Brayton engine capable of 300 rpm. Other Brayton engines were used for industrial purposes such as powering pumps, cotton gins, or grinding mills. These Brayton engines were the first practical oil engines and were noted for their ease of starting and steady operation.


George Selden and Ernest Samuel Partridge in the Selden automobile in 1905. The vehicle was built in 1903 to prove the viability of Selden’s patent design. Between the front wheels is a three-cylinder Brayton-style engine, which ultimately led to Selden’s patent claims being dismissed.

George Selden was inspired by the 10 hp (7.5 kW) Brayton engine he saw at the 1876 Centennial Exposition in Philadelphia and felt the engine could be adapted to power a practical wheeled vehicle (automobile). In 1879, Selden applied for a patent on his three-cylinder Road Engine, which powered a four-wheel carriage. Selden continued to delay his patent with minor modifications until 1895, when the patent was finally granted despite the fact that Selden had never built the actual vehicle. That did not deter Selden from claiming he invented the automobile and demanding royalties from all automobile manufactures—suing those who refused to pay. Henry Ford led the rebellion against Selden and lost the court case in 1909. However, that ruling was overturned on appeal in 1911. For the successful appeal, Ford demonstrated that Selden’s automobile used an engine based on the Brayton cycle (two-stroke and a constant-pressure cycle), while Ford and others used engines based on the design of Nicolaus Otto (Otto cycle: four-stroke and a constant-volume cycle). No automobiles were built with a Brayton cycle engine; therefore, the automobile manufacturers were not infringing on Selden’s patent.

By the late 1880s, it was becoming clear that the Brayton cycle for piston-driven internal combustion engines was outclassed by the more efficient Otto cycle. The main issue facing the Brayton engine was its relatively low pressure (60–80 psi / 4.1–5.5 bar) combined with excessive friction, pumping, and heat losses between the compression and combustion cylinders.


Horizontal Brayton Ready Motor marine engine that was very similar, but not identical, to the engine used in the Fenian Ram submarine. The combustion cylinder is in the foreground, and the compression cylinder is in the background. The bevel gear powered the propeller shaft.

Brayton continued to develop his engine and applied for a patent in 1887 that outlined a horizontal, fuel injected, four-stroke engine. The cylinder was closed at both its combustion (hot) and non-combustion (cool) sides. Exhaust from the hot side of the cylinder passed through a water-cooled condenser that opened to the cool side of the cylinder. As the piston moved up on the exhaust stroke, the vacuum created in the cool side of the cylinder helped draw exhaust gases out of the hot side of the cylinder. An exhaust valve on the cool side of the cylinder was sprung to open at just above atmospheric pressure. As the piston moved toward the cool side of the cylinder on the intake stroke, the exhaust valve opened to expel the products of combustion. When the intake valve was opened, it brought fresh air into the cylinder and sealed the condenser. The intake valve then closed, and the piston moved toward the hot side of the cylinder to compress the air. Brayton stated in his patent that the cylinder’s cycle provided an abundance of fresh air to increase the engine’s power and efficiency.

Once the air was compressed, fuel was injected into the cylinder. The act of injecting the petroleum oil under pressure converted the fuel to a fine spray that was easily ignitable. The fuel injection pump was controlled by a follower riding on an engine-driven camshaft, and engine speed was controlled by the quantity of fuel injected. Once injected, the fuel was ignited by an incandescent burner made from a coil of platinum wire. This concept is very similar to a hot bulb in a much later semi-diesel engine. Brayton’s fuel injection was ideally suited for the use of heavy fuels. This engine was built with a 7 in (179 mm) bore and a 10 in (254 mm) stroke, displacing 385 cu in (6.31 L). Running at 200 rpm and driving a 30 in (762 mm) fan at 1,500 rpm for 10 hours, the engine only consumed 3.5 gallons (13.2 L) of kerosene.


Patent drawing showing the cylinder of Brayton’s horizontal, four-stroke engine of 1887. Passage d was used for both intake and exhaust. Passage d1 harnessed the vacuum created under the piston to help draw the exhaust gases out of the cylinder and through the condenser (C). The exhaust was expelled via valve g1. Fresh air was admitted via valve e1, which sealed the condenser. Fuel was injected via “Oil-jet” F and ignited by a platinum coil.

In 1890, Brayton patented his last engine, a vertical four-stroke that featured fuel injection. As the piston moved down on its intake stroke, a valve in the piston head opened and allowed the slightly pressurized air in the crankcase to enter the vacuum in the cylinder. As the piston moved up on the compression stroke, the exhaust valve opened for a short time to evacuate any remaining products of combustion. With all valves closed, the remaining air was compressed, and fuel was injected in a combustion chamber space above the piston. A connecting rod attached the piston to an inverted rocking beam, and the opposite end of the rocking beam was connected to a crankshaft. A small air pump was driven from a rod connected to the rocking beam. The air pump provided the pressure for the fuel injection system, enabling a blast of air to disperse the fuel into a fine spray as it was forced into the combustion chamber. The fuel was ignited by an incandescent burner and continued to burn as more fuel was injected and the piston moved down on the power stroke. Brayton’s last engine worked through a similar process as the engines Rudolf Diesel began developing in 1893, but Diesel used much higher cylinder pressures.

While traveling in England and still experimenting with engines, Brayton passed in 1892 at the age of 62. Production of his engines had already decreased by the time of his death but may have continued until the early 1900s. While names like Otto and Diesel are known to many today, Brayton’s is relatively unknown despite his pioneering work. Brayton’s engines were used in land vehicles, boats, and submarines before Otto’s or Diesel’s engines successfully ran. Undoubtedly, Brayton’s engineering contributions helped pave the way for many who followed. Out of the hundreds of Brayton Ready Motors that were made, only around six original engines are known to survive today.


Patent drawing illustrating Brayton’s 1890 inverted rocking beam (D) engine. Air slightly pressurized in the crankcase (A) passed through a valve (b1) in the piston to fill the cylinder (B). Fuel was injected (via g) and ignited by a burner (G) in a combustion chamber space (B1) at the top of the cylinder. A smaller cylinder (J) acted as a pump to power the fuel injector.

Correspondence with John Lucas
“Improvement in Gas Engines” US patent 125,166 by George B. Brayton (granted 2 April 1872)
“Gas Engines” US patent 151,468 by George B. Brayton (granted 2 June 1874)
“Gas and Air Engine” US patent 432,114 by George B. Brayton (applied 15 September 1887)
“Hydrocarbon Engine” US patent 432,260 by George B. Brayton (granted 15 July 1890)
Internal Fire by C. Lyle Cummins Jr. (1976/1989)
The Gas and Oil Engine by Dugald Clerk (1904)
A Text-Book on Gas, Oil, and Air Engines by Bryan Donkin Jr (1894)
Pioneers, Engineers, and Scoundrels by Beverley Rae Kimes (2005)
“The Brayton Ready Motor or Hydrocarbon Engine” Scientific American (13 May 1876)
“Brayton’s Hydrocarbon Engine” Scientific American Supplement, No. 58 (10 February 1877)
“Selden Patent Not Infringed” The Automobile (12 January 1911)
“Road Engine” US patent 549,160 by George B Selden (applied 8 May 1879)
“Events Which Led Up to the Formation of the American Street Railway Association” by D. F. Longstreet The Street Railway Journal (November 1892)

Zvezda M503 Rear

Yakovlev M-501 and Zvezda M503 and M504 Diesel Engines

By William Pearce

Just after World War II, OKB-500 (Opytno-Konstruktorskoye Byuro-500 or Experimental Design Bureau-500) in Tushino (now part of Moscow), Russia was tasked with building the M-224 engine. The M-224 was the Soviet version of the Junkers Jumo 224 diesel aircraft engine. Many German engineers had been extradited to work on the engine, but the head of OKB-500, Vladimir M. Yakovlev, favored another engine project, designated M-501.

Zvezda M503 front

Front view of a 42-cylinder Zvezda M503 on display at the Technik Museum in Speyer, Germany. Unfortunately, no photos of the Yakovlev M-501 have been found, but the M503 was very similar. Note the large, water-jacketed exhaust manifolds. The intake manifold is visible in the engine Vee closest to the camera. (Stahlkocher image via Wikimedia Commons)

Yakovlev and his team had started the M-501 design in 1946. Yakovlev felt the M-224 took resources away from his engine, and he was able to convince Soviet officials that the M-501 had greater potential. All development on the M-224 was stopped in mid-1948, and the resources were reallocated to the M-501 engine.

The Yakovlev M-501 was a large, water-cooled, diesel, four-stroke, aircraft engine. The 42-cylinder engine was an inline radial configuration consisting of seven cylinder banks positioned around an aluminum crankcase. The crankcase was made up of seven sections bolted together: a front section, five intermediate sections, and a rear accessory section. The crankshaft had six throws and was supported in the crankcase by seven main bearings of the roller type.

Each cylinder bank was made up of six cylinders and was attached to the crankcase by studs. The steel cylinder liners were pressed into the aluminum cylinder block. Each cylinder had two intake and two exhaust valves actuated via roller rockers by a single overhead camshaft. The camshaft for each cylinder bank was driven through bevel gears by a vertical shaft at the rear of the bank. All of the vertical shafts were driven by the crankshaft. The pistons for each row of cylinders were connected to the crankshaft by one master rod and six articulating rods.

Zvezda M503 Rear

Rear view of a M503 on display at Flugausstellung L.+P. Junior in Hermeskeil, Germany. The upper cylinder gives a good view of the exhaust (upper) and intake (lower) manifolds, and the engine’s intake screen can just be seen between the manifolds as they join the compounded turbosupercharger. The exhaust gases exited the top of the turbine housing. (Alf van Beem image via Wikimedia Commons)

Exhaust was taken from the left side of each cylinder bank and fed through a manifold positioned in the upper part of the Vee formed between the cylinder banks. The exhaust flowed through a turbosupercharger positioned at the extreme rear of the engine. Exhaust gases expelled from the turbosupercharger were used to provide 551 lbf (2.45 kN / 250 kg) of jet thrust.

The pressurized intake air from the turbosupercharger was fed into a supercharger positioned between the turbosupercharger and the engine. The single-speed supercharger was geared to the crankshaft via the engine’s accessory section. Air from the supercharger flowed into a separate intake manifold for each cylinder bank. The intake manifold was positioned in the lower part of the Vee, under the exhaust manifold, and connected to the right side of the cylinder bank.

The M-501 had a 6.30 in (160 mm) bore and a 6.69 in (170 mm) stroke. The engine displaced 8,760 cu in (143.6 L) and produced 4,750 hp (3,542 kW) without the turbosupercharger. With the turbosupercharger and the thrust it provided, the engine produced 6,205 hp (4,627 kW). The engine weighed 6,504 lb (2,950 kg) without the turbocharger and 7,496 lb (3,400 kg) with the turbocharger.

Zvezda M503 Bulgaria

This partially disassembled M503 at the Naval Museum in Varna, Bulgaria gives some insight to the inner workings of the engine. The turbine wheel can be seen on the far left. Immediately to the right is the air intake leading to the compressor wheel, which is just barely visible in its housing. From the compressor, the air was sent through the seven outlets to the cylinder banks. The exhaust pipe can just be seen inside the water-jacketed manifold on the upper cylinder bank. Note the studs used to hold the missing cylinder bank. (Михал Орела image via Wikimedia Commons)

By 1952, the M-501 had been completed and had achieved over 6,000 hp (4,474 kW) during tests. The program was cancelled in 1953, as jet and turbine engines were a better solution for large aircraft, and huge piston aircraft engines proved impractical. The M-501 was intended for the four-engine Tupolev 487 and Ilyushin IL-26 and was proposed for the six-engine Tupolev 489. None of these long-range strategic bombers progressed beyond the design phase.

The lack of aeronautical applications did not stop the M-501 engine. A marine version was developed and designated M-501M. The marine engine possessed the same basic characteristics as the aircraft engine, but the crankcase casting were made from steel rather than aluminum. The M-501M was also fitted with a power take off, reversing clutch, and water-jacketed exhaust manifolds.

The exact details of the M-501M’s history have not been found. It appears that Yakovlev was moved to Factory No. 174 (K.E. Voroshilov) to further develop the marine engine design. Factory No. 174 was founded in 1932 and was formerly part of Bolshevik Plant No. 232 (now the GOZ Obukhov Plant) in Leningrad (now St. Petersburg). Factory No. 174 had been involved with diesel marine engines since 1945, and Yakovlev’s move occurred around 1958. Early versions of the marine engine had numerous issues that resulted in frequent breakage. In the 1960s, the engine issues were resolved, and Factory No. 174 was renamed “Zvezda” after the engine’s layout. Many languages refer to radial engines as having a “star” configuration, and “zvezda” is “star” in Russian. Zvezda produced the refined and further developed 42-cylinder marine engine as the M503.

Zvezda M503 cross section

Sectional rear view of a 42-cylinder Zvezda M503. The cylinder banks were numbered clockwise starting with the lower left; bank three had the master connecting rod. Note the angle of the fuel injector in the cylinder and that the injector pumps were driven by the camshaft (as seen on the upper left bank).

The Zvezda M503 retained the M-501’s basic configuration. The engine had a compounded turbosupercharger system with the compressor wheel connected to the crankshaft via three fluid couplings. The compressor wheel shared the same shaft as the exhaust turbine wheel. At low rpm, the exhaust gases did not have the energy needed to power the turbine, so the compressor was powered by the crankshaft. At high rpm, the turbine would power the compressor and create 15.8 psi (1.09 bar) of boost. Excess power was fed back into the engine via the couplings connecting the compressor to the crankshaft. Air was drawn into the turbosupercharger via an inlet positioned between the compressor and turbine.

The M503’s bore, stroke, and displacement were the same as those of the M-501. Its compression ratio was 13 to 1. The M503’s maximum output was 3,943 hp (2,940 kW) at 2,200 rpm, and its maximum continuous output was 3,252 hp (2,425 kW) at the same rpm. The engine was 12.14 ft (3.70 m) long, 5.12 ft (1.56 m) in diameter, and had a dry weight of 12,015 lb (5,450 kg). The M503 had a fuel consumption of .372 lb/hp/h (226 g/kW/h) and a time between overhauls of 1,500 to 3,000 hours.

Zvezda M503 Dragon Fire

Dragon Fire’s heavily modified M503 engine under construction. Each cylinder bank is missing its fuel rail and three six-cylinder magnetos. The turbine wheel has been discarded. The large throttle body on the left has a single butterfly valve and leads to the supercharger compressor. Note that the cylinder barrels and head mounting studs are exposed and that each valve has its own port. (Sascha Mecking image via Building Dragon Fire Google Album Archive)

M503 engines were installed in Soviet Osa-class (Project 205) fast attack missile boats used by a number of countries. Each of these boats had three M503 engines installed. Engines were also installed in other ships. A heavily modified M503 engine is currently used in the German Tractor Pulling Team Dragon Fire. This engine has been converted to spark ignition and uses methanol fuel. Each cylinder has three spark plugs in custom-built cylinder heads. The engine also uses custom-built, exposed, cylinder barrels and a modified supercharger without the turbine. Dragon Fire’s engine produces around 10,000 hp (7,466 kW) at 2,500 rpm and weighs 7,055 lb (3,200 kg).

For more power, Zvezda built the M504 engine, which had seven banks of eight cylinders. Essentially, two additional cylinders were added to each bank of the M503 to create the 56-cylinder M504. The M504 did have a revised compounded turbosupercharging system; air was drawn in through ducts positioned between the engine and compressor. The intake and exhaust manifolds were also modified, and each intake manifold incorporated a built-in aftercooler. At full power, the turbosupercharger generated 20.1 psi (1.39 bar) of boost. The M504 engine displaced 11,681 cu in (191.4 L), produced a maximum output of 5,163 hp (3,850 kW) at 2,000 rpm, and produced a maximum continuous output of 4,928 hp (3,675 kW) at 2,000 rpm. The engine had a length of 14.44 ft (4.40 m), a diameter of 5.48 ft (1.67 m), and a weight of 15,983 lb (7,250 kg). The M504 had a fuel consumption of .368 lb/hp/h (224 g/kW/h) and a time between overhauls of 4,000 hours. The engine was also used in Osa-class missile boats and other ships.

Zvezda M504 56-cyl

The 56-cylinder Zvezda M504 engine’s architecture was very similar to that of the M503, but note the revised turbocharger arrangement. Wood covers have been inserted into the air intakes. Just to the right of the visible intakes are the aftercoolers incorporated into the intake manifolds.

In the 1970s, Zvezda developed a number of different 42- and 56-cylinder engines with the same 6.30 in (160 mm) bore, 6.69 in (170 mm) stroke, and basic configuration as the original Yakovlev M-501. Zvezda’s most powerful single engine was the 56-cylinder M517, which produced 6,370 hp (4,750 kW) at 2,000 rpm. The rest of the M517’s specifications are the same as those of the M504, except for fuel consumption and time between overhauls, which were .378 lb/hp/h (230 g/kW/h) and 2,500 hours.

Zvezda also coupled two 56-cylinder engines together front-to-front with a common gearbox in between to create the M507 (and others) engine. The engine sections could run independently of each other. The 112-cylinder M507 displaced 23,361 cu in (383 L), produced a maximum output of 10,453 hp (7,795 kW) at 2,000 rpm, and produced a maximum continuous output of 9,863 hp (7,355 kW) at the same rpm. The engine was 22.97 ft (7.00 m) long and weighed 37,699 lb (17,100 kg). The M507 had a fuel consumption of .378 lb/hp/h (230 g/kW/h) and a time between overhauls of 3,500 hours for the engines and 6,000 hours for the gearbox.

Zvezda engineer Boris Petrovich felt the 56-cylinder M504 engine could be developed to 7,000 hp (5,220 kW), and the M507 (two coupled M504s) could be developed to over 13,500 hp (10,067 kW). However, gas turbines were overtaking much of the diesel marine engine’s market share. Today, JSC (Joint Stock Company) Zvezda continues to produce, repair, and develop its line of M500 (or ChNSP 16/17) series inline radial engines as well as other engines for marine and industrial use.

Zvezda M507 engine

The M507 was comprised of two M504 engines joined by a common gearbox. The engine sections had separate systems and were independent of each other.

Russian Piston Aero Engines by Vladimir Kotelnikov (2005)
Unflown Wings by Yefim Gordon and Sergey Komissarov (2013)
Ungewöhnliche Motoren by Stefan Zima and Reinhold Ficht (2010)

1939 Venturi-Mora Saimon-Fiat

Idroscivolanti and the Raid Pavia-Venezia

By William Pearce

An airboat is a vessel that has a shallow draft and utilizes the thrust generated by an aircraft propeller to drive over ice, grass, or water. The airboat concept started as a way to test propellers but evolved into a nearly indispensable form of transportation though swampy areas. In Italy in the 1930s, the concept of an airboat was taken a bit further.

1930 Mazzotti-Cattaneo SIAI-IF

The Isotta Fraschini Asso 200-powered SIAI hydroplane that Franco Mazzotti and Guido Cattaneo drove to victory in the 1930 and 1931 Raid Pavia-Venezia.

First run in 1929, the Raid Pavia-Venezia was an inshore powerboat race of around 269 miles (433 km) held in June. The course distance varied slightly by year. Starting on the Ticino River in Pavia, Italy, the race transitioned to the River Po and then through canals, finally ending in Venice. Fuel stops were incorporated along the route. Various parts of the course had many turns, hidden sandbars, and tight passageways. The Raid Pavia-Venezia was the creation of Vincenzo Balsamo, an engineer, sailor, and head of the Gruppo Motonautico della Lega Navale di Milano (Powerboat Section of the Navy League of Milan), the group that organized the race. The 1929 race was completed in 11:26:23 at an average of 22.164 mph (35.670 km/h).

1932 Biseo-Bertoli SIAI-FIAT

Attilio Biseo and Gino Bertoli won the 1932 Raid Pavia-Venezia in this SIAI idroscivolante powered by a FIAT A50 engine. (image via Three Point Hydroplanes)

The 1930 race marked the start of combining powerful Italian aircraft engines with shallow-hulled hydroplanes to create the idroscivolante (airboat). Idroscivolanti (airboats) would not only increase straight line speeds, they would also allow the boats to travel over shallow sandbars without worry. Only one idroscivolante was entered in the 1930 race. It used an Isotta Fraschini (IF) Asso 200 engine that turned a four-blade, wooden propeller. The Asso 200 was a 200 hp (149 kW), water-cooled, inline-six engine. It was mounted in a pusher configuration to the rear of a shallow-hulled boat built by SIAI (Società Idrovolanti Alta Italia or Northern Italy Seaplane Company, also known as Savoia-Marchetti). Driven by Count Franco Mazzotti with co-driver Guido Cattaneo, the SIAI/IF idroscivolante won the race with a time of 8:10:35, averaging 31.462 mph (50.633 km/h). The second place finisher was nearly an hour behind the idroscivolante.

1934 Salom-Celli Celli-SPA

The Celli hydroplane powered by an SPA 6A engine in a pusher configuration. Aldo Salom and Dino Celli campaigned this boat in 1933 and 1934. (image via Three Point Hydroplanes)

Mazzotti and Cattaneo won the 1931 race again in the SIAI/IF idroscivolante with a time of 6:52:54 and averaging 38.309 mph (61.653 km/h). However, they had competition in the form of driver Count Theo Rossi and co-driver Alfredo Stracconi in a Passarin idroscivolante powered by a FIAT (Fabbrica Italiana Automobili Torino or Italian Automobile Factory Turin) A50 engine. The A50 was an air-cooled, seven-cylinder, radial engine that produced 105 hp (78 kW). Rossi and Stracconi finished the race in second place at 33.648 mph (54.151 km/h).

Rossi and Stracconi were back in their Passarin/FIAT in 1932, but they were unable to complete the race. The only other idroscivolante was a SIAI powered by a FIAT and driven by Attilio Biseo and Gino Bertoli. The FIAT A50 radial engine was mounted in a tractor configuration on struts in the middle of the boat. Biseo and Bertoli won the 1932 race in 5:27:26 at a 47.138 mph (75.862 km/h) average speed. Biseo and Bertoli finished the Raid Pavia-Venezia 2:30:01 before the first conventional powerboat.

1934 Rossi-Cattaneo SIAI-IF

Theo Rossi and Guido Cattaneo paired up to compete in the Raid Pavia-Veneziain in this SIAI idroscivolante powered by an IF Asso 200 engine. This photo was most likely taken in 1934. (image via Three Point Hydroplanes)

For 1933, Theo Rossi and Guido Cattaneo joined forces in the SIAI/IF. The SIAI/FIAT idroscivolante was entered by driver Marcello Visconti di Modrone and co-driver Franco Mazzotti, but it did not finish the race. Rossi and Cattaneo took the win with a time of 6:37:14, averaging 40.639 mph (65.402 km/h) over the whole course. The pair averaged 56.511 mph (90.946 km/h) over the 37 miles (60 km) between Piacenza and Cremona.

In 1934, two of the three idroscivolanti entered in the race failed to finish. One of the non-finishers was a new, small SIAI hydroplane raced by Rossi and Cattaneo. It was powered by a 200 hp (149 kW) IF Asso 200 inline-six engine in a tractor configuration and housed in a streamlined cowling; the engine and propeller were probably from the previous SIAI/IF boat. The other idroscivolante that did not finish was a Celli hydroplane powered by a SPA (Società Ligure Piemontese Automobili or Ligure Piemontese Automobile Company) 6A engine and raced by Aldo Salom and Dino Celli. Their 205 hp (153 kW) inline-six engine was mounted at the rear of the boat in a pusher configuration and turned a four-blade, wooden propeller. The race was won by driver Attilio Biseo with co-driver Renato Donati in a SIAI hydroplane powered by a Farina T.58 135 hp (101 kW), air-cooled, five-cylinder, radial engine. The engine turned a two-blade propeller and was mounted in a tractor position at the middle of the boat. Their time was 5:44:08 with an average of 47.188 mph (75.942 km/h).

1934 Biseo-Donati SIAI-Farina

Attilio Biseo and Renato Donati competing in the 1934 race, which they won. Their SIAI idroscivolante was powered by a Farina T.58 engine. (image via Three Point Hydroplanes)

Four idroscivolanti competed in the 1935 Raid Pavia-Venezia. Driver Renato Donati and co-driver Federico Borromeo finished in sixth place overall. Their sleek, two-hulled, catamaran idroscivolante was designed by the Laboratorio Sperimentale Regia Aeronautica (Royal Italian Air Force Experimental Laboratory) but was most likely built by SIAI. It was powered by an air-cooled, seven-cylinder, 200 hp (149 kW) Alfa Romeo Lynx radial engine based on the Armstrong Siddeley Lynx and produced under license. The engine turned a three-blade, metal propeller and was mounted in a tractor configuration in the middle of the idroscivolante. In fourth place overall were Aldo Salom and Dino Celli in the Celli/SPA. In second place were driver Goffredo Gorini and co-driver Francesco Bertoli in the sister ship of Donati and Borromeo. However, their idroscivolante did not have a deck connecting the two hulls. Gorini and Bertoli finished the race in 5:12:30 and averaged 51.652 mph (83.126 km/h). The winners of the 1935 race were Rossi and Cattaneo in the SIAI/IF. Their boat had been modified with larger fuel tanks that bulged out above the two-hulls. Rossi and Cattaneo completed the race in 5:01:50 at 53.483 mph (86.073 km/h). They averaged 69.326 mph (111.570 km/h) over the 37 miles (60 km) from Piacenza to Cremona.

1935 Donati-Borromeo LSAR-AR

Renato Donati and Federico Borromeo in the Laboratorio Sperimentale Regia Aeronautica powered by an Alfa Romeo Lynx in 1935. Note the deck connecting the hulls. The idroscivolante sits in Venice’s Grand Canal with the Santa Maria della Salute in the background. (image via Three Point Hydroplanes)

Theo Rossi and Guido Cattaneo took another win in their SIAI/IF for 1936. Their time was 4:45:02 at an average speed of 56.576 mph (91.051 km/h), and they finished over three hours before the first conventional powerboat. Second place was won by Vito Mussolini and Carlo Maurizio Ruspoli in the SIAI/Farina. Vito Mussolini was Benito Mussolini’s nephew, and Carlo Maurizio Ruspoli was a Prince of Poggio Suasa. The third and last idroscivolante entered in the 1936 race was the Laboratorio Sperimentale Regia Aeronautica/Alfa Romeo of Goffredo Gorini and Renato Donati. While they did not finish the race, they did average 74.191 mph (119.400 km/h) over the 43 miles (69 km) between Pavia and Piacenz.

A race was also run on the Danube River between Vienna and Budapest in 1936. Which idroscivolanti participated and the results of the race have not been found. It can be assumed that the SIAI/IF idroscivolante raced by Rossi and Cattaneo did participate in this race, as it had “Vienna-Budapest” painted on its hull during the Pavia-Venezia race. At around 177 miles (285 km), the Vienna-Budapest race was about two-thirds the distance of the Raid Pavia-Venezia.

1935 Gorini-Bertoli LSAR-AR

The other Laboratorio Sperimentale Regia Aeronautica/Alfa Romeo driven by Goffredo Gorini and Francesco Bertoli in the 1935 Raid Pavia-Venezia. (image via Three Point Hydroplanes)

In 1937, driver Goffredo Gorini and co-driver Renato Donati won the race. Their idroscivolante was referred to as an SIAI, replacing Laboratorio Sperimentale Regia Aeronautica. The boat was still powered by an Alfa Romeo Lynx, but the engine struts and supports had been redesigned. In addition, a wide cord, two-blade, metal propeller was used. Gorini and Donati’s winning time was 4:47:32 with an average speed of 56.143 mph (90.354 km/h). In the sister ship, Prospero Freri and Salvatore Flamini took second place just 10 minutes behind the leader, with an average speed of 54.175 mph (87.186 km/h). Their idroscivolante was referred to as a CNA (Compagnia Nazionale Aeronautica or National Aeronautical Company), replacing Laboratorio Sperimentale Regia Aeronautica. The catamaran had new engine struts that now supported a nine-cylinder, 240 hp (179 kW) Alfa Romeo D.2 engine turning a three-blade, metal propeller. A Townend ring intended to reduce drag and improve engine cooling encircled the D.2’s cylinders. Theo Rossi and Guido Cattaneo, the previous year’s winners, placed third in their SIAI/IF.

1936 Rossi-Cattaneo SIAI-IF

Theo Rossi and Guido Cattaneo won the 1936 race in the SIAI/IF idroscivolante. Note the increased capacity fuel tanks that bulged above the deck and that “Budapest” is written on the hull. (image via Three Point Hydroplanes)

1938 saw five idroscivolanti entered in the Raid Pavia-Venezia race. Goffredo Gorini and Marco Ponzalino won the race in a SIAI/Alfa Romeo at a very fast time of 4:11:28, averaging 64.193 mph (103.308 km/h). Prospero Freri and Salvatore Flamini in the CNA/Alfa Romeo finished in second place. Vito Mussolini and Luciano Agosti took third place in the SIAI/Farina. Marco Celli and Aldo Tassinari finished in eighth place overall in a Celli catamaran powered by a 115 hp (86 kW) Walter Venus engine. On this boat, the seven-cylinder radial engine turned a three-blade propeller and was strut-mounted in a tractor configuration on the rear half of the catamaran. The last idroscivolante finished in ninth place overall; it was Aldo Salom and Bruno Rocca in a Celli hydroplane powered by an IF Asso 200 inline-six engine. The engine turned a four-blade, wooden propeller and was rear-mounted in a pusher configuration. Theo Rossi and Guido Cattaneo did not finish in their SIAI/IF.

1936 Mussolini Ruspoli SIAI-Farina

Vito Mussolini and Carlo Maurizio Ruspoli competing in the 1936 Raid Pavia-Venezia in the SIAI/Farina idroscivolante. (image via Three Point Hydroplanes)

In 1939, Goffredo Gorini and Marco Ponzalino won the Raid Pavia-Venezia again at a slightly slower pace than the previous year. They finished in 4:19:16 at an average speed of 62.264 mph (100.205 km/h). The pair averaged 79.477 mph (127.80 km/h) over the 43 miles (69 km) from Pavia to Piacenz and finished the race 3:32:44 before the first conventional powerboat. Sources list their idroscivolante as a Gorini powered by an Alfa Romeo engine. However, film taken during a speed run in August shows a catamaran very similar to the one used the previous year but powered by a Wright R-975 Whirlwind 330 hp (246 kW), nine-cylinder, radial engine that turned a two-blade, metal propeller. Finishing twenty-three minutes behind them was their sister ship, listed as a Gorini/Freri/Alfa Romeo. Driver Prospero Freri and co-driver Salvatore Flamini averaged 57.148 mph (91.970 km/h). Freri and Flamini’s idroscivolante no longer had a Townend ring around the engine; the Alfa Romeo D.2’s cylinders were exposed to the air. In addition, a two-blade, metal propeller was installed. Fernando Venturi and Paolo Mora finished third in a Saliman (some sources say Saimon) catamaran powered by a FIAT A50 engine. The engine of this two-hulled idroscivolante was mounted in a tractor configuration at the center of the boat and turned a two-blade, wooden propeller. The SIAI/Farina idroscivolante of Vito Mussolini and Luciano Agosti finished in fourth place.

1937 Gorini-Donati LSAR-AR

Goffredo Gorini and Renato Donati won the 1937 race in the SIAI/Alfa Romeo idroscivolante. Note the wide cord, two-blade propeller on the Lynx engine.

In July 1939, Fernando Venturi in the Saliman/FIAT idroscivolante set an 800 kg (1,764 lb) class speed record of 49.692 mph (79.971 km/h) on Lake Bracciano. The record was broken in August when Goffredo Gorini achieved 91 mph (147 km/h) in the Wright Whirlwind-powered Gorini idroscivolante mentioned earlier. This appears to be a new idroscivolante, as the Alfa Romeo Lynx-powered machine was also present for the speed runs. Gorini had reached 96 mph (155 km/h), but technical difficulties prevented him from maintaining that speed. Gorini’s Wright-powered idroscivolante still had “Raid-Pavia-Venezia” painted on the hull from the race two months earlier.

1938 Freri-Flamini CNA-AR

For the 1937 Raid Pavia-Venezia, Prospero Freri and Salvatore Flamini installed a nine-cylinder Alfa Romeo D.2 engine with a three-blade propeller and a Townend ring. The pair took second place in 1937, 1938, and 1939. This photo is from the 1938 race.

The Raid Pavia-Venezia was suspended in 1940 due to World War II. The race was held again in 1952, but the idroscivolanti were no longer allowed to compete. The 1952 and 1953 winners were slower than the idroscivolanti of the 1930s, but technology progressed quickly, and conventional powerboats soon outpaced the idroscivolanti. The large, powerful aircraft engines allowed the idroscivolanti to reach high speeds, but with limited fuel on board the sleek machines, more frequent fuel stops were required. Only around 12 idroscivolanti were built, but their type won all ten of the Raid Pavia-Venezia in which they participated, outpacing conventional powerboats by more than three hours over the 269 mile (433 km) course.

1939 Venturi-Mora Saimon-Fiat

Fernando Venturi and Paolo Mora’s FIAT-powerd Saliman in 1939. The idroscivolante finished the race in third place and went on to set a short-lived speed record of 49.692 mph (79.971 km/h) in July 1939. Santa Maria della Presentazione (Le Zitelle) is in the background. (image via Three Point Hydroplanes)

In August 1951, Franco Venturi, Fernando’s son, set an 800 kg (1,764 lb) class speed record of 97 mph (156 km/h) on Lake Sabaudia. The idroscivolante used for this record run was the same two-hulled catamaran used by Goffredo Gorini in 1939 to win the Raid Pavia-Venezia and establish an 800 kg speed record. However, the idroscivolante was modified with a three-blade, metal propeller attached to the Wright R-975 Whirlwind engine. With idroscivolanti banned from the Raid Pavia-Venezia, Franco Venturi eventually donated the machine to the Museo della Scienza e della Tecnologia “Leonardo da Vinci” (Museum of Science and Technology “Leonardo da Vinci”) in Milan, Italy, where it is currently preserved.

1951 Franco Venturi Gorini-Wright

The Gorini/Wright idroscivolante used to set a speed record in 1939 by Goffredo Gorini at 91 mph (147 km/h) and in 1951 by Franco Venturi at 97 mph (156 km/h). (image via Museo della Scienza e della Tecnologia)

Prospero Freri managed to save the idroscivolante that he drove to second place finishes in 1937, 1938, and 1939. Numbered 108 and later T-108, the racer had deteriorated over the years. After Freri passed away in 1965, his heirs donated T-108 to the Civico Museo Navale Didattico di Milano (Civic Museum of Naval Education of Milan) in 1967. In 2006, T-108 underwent a seven month restoration by the Dalla Pietà boatyard in Malcontenta. At the beginning of the restoration, T-108 had “XII Raid Pavia-Venezia” painted on the hull, indicating Freri had prepared the idroscivolante for the 1940 race (the 12th Raid Pavia-Venezia). After the restoration, the hull was painted “XI Raid Pavia-Venezia” (indicating the 1939 race) to eliminate any confusion. T-108 is currently on display in the Museo della Scienza e della Tecnologia “Leonardo da Vinci”.

Sadly, there is very little information on the idroscivolanti, and what information can be found is occasionally contradictory. The timeline in this article was developed by cross referencing existing information with contemporary photos and videos. While every effort was made to maintain accuracy, there is no guarantee the article is entirely correct. Most of material for this article came from Three Point Hydroplanes, a historical archive of Italian hydroplanes.

2007 T-108 Freri SIAI-AR

The Alfa Romeo D.2-powered idroscivolante driven by Prospero Freri and Salvatore Flamini to second place in the 1937, 1938, and 1939 races. It was restored to its 1939 Raid Pavia-Venezia configuration in 2007. (image via Dalla Pietà Yatch)

Idroscivolanti results in the Raid Pavia-Venezia

1) Franco Mazzotti and Guido Cattaneo in the SIAI/Isotta Fraschini
8:10:35 averaging 31.462 mph (50.633 km/h)

1) Franco Mazzotti and Guido Cattaneo in the SIAI/Isotta Fraschini
6:52:54 averaging 38.309 mph (61.653 km/h)
2) Theo Rossi and Alfredo Stracconi in the Passarin/FIAT
7:38:43 averaging 33.648 mph (54.151 km/h)

1) Attilio Biseo and Gino Bertoli in the SIAI/FIAT
5:27:26 at 47.138 mph (75.862 km/h)
DNF) Theo Rossi and Alfredo Stracconi in the Passarin/FIAT

1) Theo Rossi and Guido Cattaneo in the SIAI/Isotta Fraschini
6:37:14 averaging 40.639 mph (65.402 km/h)
DNF) Marcello Visconti di Modrone and Franco Mazzotti in the SIAI/FIAT

1) Attilio Biseo and Renato Donati in the SIAI/Farina
5:44:08 averaging 47.188 mph (75.942 km/h)
DNF) Theo Rossi and Guido Cattaneo in the SIAI/Isotta Fraschini
DNF) Aldo Salom and Dino Celli in the Celli/SPA

1) Theo Rossi and Guido Cattaneo in the SIAI/Isotta Fraschini
5:01:50 averaging 53.483 mph (86.073 km/h)
2) Goffredo Gorini and Francesco Bertoli in the Laboratorio Sperimentale Regia Aeronautica/Alfa Romeo
5:12:30 averaging 51.652 mph (83.126 km/h)
4) Aldo Salom and Dino Celli in the Celli/SPA
6:26:18 averaging 41.789 mph (67.253 km/h)
6) Renato Donati and Federico Borromeo in the Laboratorio Sperimentale Regia Aeronautica/Alfa Romeo
7:20:28 averaging 36.650 mph (58.982 km/h)

1) Theo Rossi and Guido Cattaneo in the SIAI/Isotta Fraschini
4:45:02 averaging 56.576 mph (91.051 km/h)
2) Vito Mussolini and Carlo Maurizio Ruspoli in the SIAI/Farina
5:29:02 averaging 44.967 mph (72.367 km/h)
DNF) Goffredo Gorini and Renato Donati in the Laboratorio Sperimentale Regia Aeronautica/Alfa Romeo

1) Goffredo Gorini and Renato Donati in the SIAI/Alfa Romeo
4:47:32 averaging 56.143 mph (90.354 km/h)
2) Prospero Freri and Salvatore Flamini in the CNA/Alfa Romeo
4:57:59 averaging 54.175 mph (87.186 km/h)
3) Theo Rossi and Guido Cattaneo in the SIAI/Isotta Fraschini
5:29:22 averaging 49.013 mph (78.878 km/h)

1) Goffredo Gorini and Marco Ponzalino in the SIAI/Alfa Romeo
4:11:28 averaging 64.193 mph (103.308 km/h)
2) Prospero Freri and Salvatore Flamini in the CNA/Alfa Romeo
5:34:40 averaging 48.236 mph (77.629 km/h)
3) Vito Mussolini and Luciano Agosti in the SIAI/Farina
6:37:32 at 40.614 mph (65.352 km/h)
8) Marco Celli and Aldo Tassinari in the Celli/Walter
8:13:11 averaging 32.733 mph (52.678 km/h)
9) Aldo Salom and Bruno Rocca in the Celli/Isotta Fraschini
9:25:44 averaging 28.535 mph (45.922 km/h)
DNF) Theo Rossi and Guido Cattaneo in the SIAI/Isotta Fraschini

1) Goffredo Gorini and Marco Ponzalino in the Gorini/Wright
4:19:16 averaging 62.264 mph (100.205 km/h)
2) Prospero Freri and Salvatore Flamini in the Gorini/Freri/Alfa Romeo
4:42.29 averaging 57.148 mph (91.970 km/h)
3) Fernando Venturi and Paolo Mora in the Saliman/FIAT
6:10:54 averaging 43.524 mph (70.045 km/h)
4) Vito Mussolini and Luciano Agosti in the SIAI/Farina
6:16:13 averaging 42.915 mph (69.065 km/h)

Sources: (and numerous pages, images, and videos therein)
Fernando Venturi 1939 Record Run (YouTube)
Geoffredo Gorini 1939 Record Run (YouTube)
Franco Venturi 1951 Record Run (YouTube)
Aerosphere 1939 by Glenn D. Angle (1940)
Aeronuatica Militare Museo Storico Catalogo Motori by Oscar Marchi (1980)