4wings.com Hovercraft development 47751 Michigan ave., Port Isabel - 78578 - Texas, US Tel.: (956)943 5150


Hovercraft development
47751 Michigan ave. , Port Isabel, TX, 78578
Tel:(956) 943-5150

Mazda Wankel 13B Engine for Hovercraft  Use

Michael Dolezal - 4wings.com 

The following is a summary of adaptations made to accommodate a Mazda Rotary engine for Hovercraft  use. It is provide free for education purposes with the assumption that the reader is fully aware of the risks involved. The author assumes no responsibility or liability for its use or consequences of its use by others. 

The Mazda Wankel 13B engine is unique in that it employs two rotors with 3 faces on each rotor which are similar in function to a reciprocating engines pistons. The total displacement of the engine, as conventionally measured, is 80 cubic inches. However, because each rotor face completes a cycle of intake, compression, combustion and exhaust every revolution and there are two rotors with a total of six faces, the engine produces a very high amount of power given its small displacement.   As seen in the torque curve. The typical horse power range in automobile applications have ranged from 150-250 HP. In highly modified race applications over 350 HP has been achieved ( with reduction in reliability). The RPM red-line for normal automobile application is 8500 RPM. In this adaptation for Hovercraft  use the upper limit is 6500 RPM which is an operating range well within its limits. 

Reliability and Safety Benefits of the Design:
The design is inherently more reliable than reciprocating engines in that there are fewer moving internal parts. There are no Cam shafts, valves, valve springs or keepers, no valve rocker arms, no connecting rods or piston wrist pins. 
Furthermore, there are a number of other features which contribute to reliable and safe operation. The rotors which revolve on an eccentric shaft (crankshaft) are of a iron alloy while the housing ( or chamber) they rotate in is of an aluminum alloy. 
Loss of coolant and resulting overheating resulting in the aluminum housing expanding faster than the iron rotors, this increases the clearances between moving parts (rotor) and stationary parts (the housing) which greatly reduce the potential for engine sizing due to over heating which can quickly occur with loss of coolant in reciprocating engines.( In fact, one installation of a 13B in an aircraft did lose all coolant and while the temperature red-lined, the engine continue to function until the pilot could land. A subsequent tear down and inspection of the engine revealed no damage other than a number of rubber seals were damaged due to the excess heat and required replacement.) The Wankel engine has been used in automobile race events for a number of years and has a wide spread reputation for durability under extreme operating conditions. 
The Wankel engine is inherently smoother than a reciprocating engine in that there are no linear to  rotational translations as exists in a reciprocating engine. This greatly reduces vibration and inertial loads caused by pistons reversing direction in a cylinder several hundred times a minute. Additionally, the power pulses are more frequent, but of a much lower magnitude that a typical four cylinder automotive / marine / aircraft engine. This reduces frame and component fatigue effects and also reduces pilot and passenger fatigue. It also lowers the magnitude of the propeller torsion response to the power pulses. The relatively small dimension (  side view with basic dimensions ,   end view with basic dimensions  and  actual engine as received ) makes it a desirable power plant.

Given a first class remanufactured engine costs from $1600-$3200, the wankel adaptation is cost effective.

Engine remanufactured
Complete Dual Electronic Ignition system
Oil Pan & pickup
12 volt with internal voltage regulator
New water pump 
Light weight water housing 
Holley carb set up, marine carb & spark arrestor
Starter remanufactored. unit - top mount 
Exhaust plate 
Shipping and handling - a bit hefty 
Total expenses - marinized B 13 
"This prize included the engine , invoice and 0 documentation - it would be wise to print this file and all other relevant info to have a successful application - personal opinion Michael Dolezal"
B13 Rotary engine used in Hovercraft

To compare to other marinized engines in short :

  • 270 lb for 180 hp = 1.5 lb per HP
  • 4,334.- for 180 hp = US $ 24,07  per HP
Information status with July 2001


Lubrication of moving parts is as crucial for this engine as a reciprocating engine. However, even in the case of lubrication subsystem failure the failure mode is gradually, with the engine actually slowing down to a stop as the friction increases rather than suddenly sizing as piston engines are inclined to do. 
The internal design does require oil to be injected into the rotor chamber for lubrication. In automotive use the engine draws on oil from the crankcase for this purpose. A closer look at the system is  available here.
This is not a desirable feature for hovercraft usage in that it can result in exhaustion of lubricating oil in the crankcase, if not frequently checked, and the carbon deposits from combustion of automobile engine oil causes internal wear of the seals of the rotors. 
Some alternatives to the above system are :

  • Eliminate the crankcase oil injection subsystem and instead mix 2 cycle oil in the gasoline. This has proven to be a reliable method and removes the possibility of crankcase oil exhaustion and improves the rotor seal life. It does, however, require mixing the 2 cycle oil with each gasoline fill up. 
  • Install a  metering pump adapter, as offered by  PCV Technologies  which  takes the solution one step further in allowing to still using the stock metering pump but supply it with two-stroke oil.
Heat ejection by the lubrication subsystem is crucial for maintaining engine temperature within design limits. This is accomplished through an oil cooler with a fin surface equal to that used in the automobile application. Most aluminum oil cooler as used in race car applications will provide this job.
Lubrication Subsystem Instrumentation: 
The lubrication subsystem can be  instrumented with an oil pressure and oil temperature gauge mounted in the instrument panel. 
A dipstick provides for oil quantity measurement.


Additional features relative to safety is that each rotor chamber has two spark plugs with two independent ignition coils for each plug set. There is one plug per rotor chamber referred to as the "Lead" and one referred to as the "Trailing" plug. The trailing plug in the automobile application is set to fire approximately 15 degrees after the lead plug fires. The engine will run on just the trailing plug setting for auto application, however, there is considerable power loss. While the trailing plug was designed principally to meet auto emission and fuel economy standards, it can be recalibrated to fire essentially in sync with the lead plug providing true redundant ignition for the engine in Hovercraft application. An after market ignition computer can be  used which provides two independent ignition CPUs and a feature for checking each ignition coil subsystem independently.

The electric charging is accomplished with 12 volt marine alternator ( single wire to high amp unit ) with internal voltage regulator. 

Electrical Subsystem Instrumentation: 
The electrical subsystem can be  instrumented with a High/Low voltage visual indicator as well as a voltmeter which can be switched.

Since the engine is liquid cooled the adverse effects of "shock" cooling which can cause cylinder damage on air cooled engines does not occur. Again, a positive feature. Due to the fact that this small displacement engine does produce so much power relative to its displacement, adequate cooling is a critical need to remove the excess heat from the block. Approx. 1/3 of the heat rejection (above that not ejected by the exhaust gases) is by the lubrication system through an oil cooler. The remaining (approx. 2/3 of the waste heat) is ejected through a  water based coolant system  using radiators installed in the thrust duct exit section of the craft or any location where adequate airflow is possible. 

Additionally, since the engine is liquid cooled, cabin heat can be  derived from an heat exchanger in the cockpit to transfer heat from the coolant system into the cockpit. The heat exchanger can have  a manual coolant cutoff valve as well as a manually controlled fan. This approach removes the danger of carbon monoxide leaking into the cabin through the typical exhaust muff approach to heating .

Coolant Subsystem Instrumentation: 
The coolant system can be  instrumented with both a coolant temperature gage and a coolant pressure gage. 
The coolant pressure gage will immediately indicate any abnormality and provide early warning of a leak giving time for a flight to be terminated before complete loss of coolant. 
If only a coolant temperature gage were used, considerable loss of coolant is possible before a rise in temperature would indicate a problem existed. Therefore, the coolant pressure gage is considered a crucial feature of any liquid coolant system in an Hovercraft.


A PSRU is used to reduce the engine RPM to that required for efficient and safe propeller / fan operation. 
The PSRU is provided by "GoodYear" orange eagle PD belts ( w=700mm)in a ratio 2:1 . 
Alternative  a Ross Aero PSRU designed for the Mazda 13B using planetary gears providing a 2.17:1 reduction. 

The fuel subsystem in our case is adjusted to a carburated engine. It consist of a marine fuel pump, inlet filter, outlet filter and fuel pressure regulator with return line. All fuel lines  consist of USCG compliant  hoses. The fuel system  was pressurized with air to test for leaks. 
For a more detailed file please see :  fuel system on high speed Hovercraft


In summary, I believe the engine has a number of inherently desirable features and benefits for hovercraft  use. The adaptations to make it suitable for hovercraft  use have been carefully thought out and failure modes thoroughly examined. 

4wings Main page - 4wings Yachtservice - Kite-sailer.com - Site-map


Related external links