Tuesday, September 20, 2016

[Electric Boats] Re: Decibels

 

My gearbox is virtually silent.. motor is not. I get some prop noise at higher speeds but practically none at low speed.

I don't find folding props to be very efficient. Too many design tradeoffs to make it slippery in the water. Many guys say the bigger the better, and within reason I have to agree. A two blade folder with the typical willow leaf blade shape, even if it is of greater diameter, is not going to match a typical 3 blade fixed prop. At least, I don't believe so. Folding props are worth considering on a sailboat, precisely for the reasons that they have that design.

And it is quite true that on smaller sailboats, regen is insignificant. On bigger boats where hull speed is in the double digits, it is good to have the option. Drag can be minimized if the regen is not needed, simply by setting regen near zero, meaning the motor is allowed to turn or being turned at an energy neutral power level. I don't know if my explanation makes sense, but tthat's the way I see it. On a sailboat over 50' or so I definitely would still go fixed rather than folding.

One irritation of folding props is the CLUNK sound they make when turning very slowly, under power, or sometimes even freewheeling. At a reasonable speed this is not an issue.

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