Mokai boat

[alaskamokaiman]

I have a Honda gc190 in this boat I would like to increase its speed.
Any suggestions?

You can see this boat at mokai.com

 

[patprimmer]

Fit a more powerful motor that develops the same torque but makes more power by making more rpm.

Apply standard hot rodding technique to your engine, ie bigger valves and ports, higher compression, higher lift and longer duration camshaft, tuned low back pressure exhaust, bigger carby and manifold runners.

If you increase the torque to much, you will also need to change the jet unit to gain speed.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dcasto]

What I've seen with squirted boats is the pump is matched to the engine. Tuning the engine will get you faster accelleration, but not more top speed. If you increase the RPM of the engine, the pump (fan laws) kick in. If you double the RPM, the power required to run the pump is increased by rpm^3, so a small increase in rpm requires a big increase in HP.

 

[mishar]

It looks pretty slow on those videos, so I assume that you would like it at least twice faster. Probably even more than that. It can’t be done with existing engine and pump. Even if you double the power it will be only 25% faster, but only if you match the pump. To make it twice faster you would need about 50HP with matching pump.

Conclusion is that you need engine and pump from one of those skidoo’s. In order to stay alive in that think you would need to make that boat strong enough for that speed. At least two longitudinal stiffeners all the way. Another problem is: will it float with all that additional weight. Good luck.

 

[dcasto]

I looked at the web page. That boat doesn't look like it has a hull that will allow much more speed.

 

[alaskamokaiman]

I can add stiffeners to the inside. I believe that the pump is designed to turn 6000rpm and is only using 3600rpm so there is wiggle room.

The real problem is finding a motor that maintains torque at a higher rpm.

Find the answer to this problem and I can line people up to purchase your solution.

 

[patprimmer]

A turbocharger or supercharger could give you the desired results.

The power band from a turbo instalation will more accurately match existing pump, so long as the pump will handle the torque.

If it is rated to higher rpm, it should be rated to the torque required to obtain that rpm under load. The water inlet will need to cope with the extra inlet water flow to avoid cavitation.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mishar]

If pump will work at 6000 rpm, which is quite probably, it can consume 25-30 HP. Original engine can’t be blown to that power. You need bigger engine: air cooled, light, 30 HP @ 6000 rpm. There is a bunch of them for ultralight planes. Rotax 370, Kawasaki 340 … Round $1500 new. Used can do. You are not going to fly it. Hopefully.