Prop speeds

[Mark]

I read somewhere on here that the record holder for an electric boat had the motor spinning 48,000rpm. Is it that higher prop speed with smaller props makes more boat speed or is it just that electric motors make power at that rpm? I used to race electric cars years ago and the motors in general depending on how much money you spent made more power with the engines that could spin more revs. But you had to gear them so they could spin fast. If you geared a modified class motor like a stock motor it wouldn't run well and would eventually overheat. :blink:

 

[TimD]

Mark,

I believe that props are more eficient at higher rpms but I may be wrong. I'm sure someone will correct me if I am B) This post might be better answered on the electric forum.

Tim.

 

[Mark]

Tim,

I was wondering if cavitation would become a problem.

 

[nitrotoys]

I would think if your boats going that fast and the prop is able to get clean water for each revulition, then it should cavitate.

I would think there would be slippage or something with spinning them that fast.

Someone??

NT

 

[lohring]

Actually, a larger diameter prop is more efficient than a small diameter one. All of our props are ventilated on their forward side so cavitation at speed is not an issue. The problem for top speed is what pitch is available. The same propeller, the Octura 2170, is used for both nitro and gas straight line runs. The nitro record is 120 and the gas record is 94. Even when this prop is pitched up, the rpm sets the limit on speed. Electric motors are not as rpm limited as internal combustion engines, so they run faster with a given prop pitch.

Lohring Miller