Hi Julian,
It sounds like your head is in the right place. If I were in your position, I would continue the project as planned. If the speed doesn't show up, you have the option of running the motor faster than the 1000rpm target speed or removing the reduction (v-drive) to get the prop spinning faster. Obviously, the former sounds preferable. The problem here is the big leap from 2:1 to 1:1 really changes the loading on the motor.
If the motors are overloaded when installed as planned (which I think unlikely), you have the option of cutting the props down in diameter or figuring a way to get more gear ratios available to you. It's not uncommon to arrange an electric motor pointed forward, parallel over the drive shaft and using the reduction system (belt, gearbox or chain) to do a 180 and turn the shaft running right under the motor. Kind of like a v-drive, but everything is at right angles or parallel. My system uses a Browning gear box (not 180 deg) and belt drives can be very efficient and strong (they are used in many of the "professional" electric drives). Some DIY folks have used chain drives, but the feedback about chain drives isn't as positive as the info about gears or belts.
Using one of these types of reductions, you have many more ratios available and can fine tune your performance for your desired speed and power. This would also allow you to tune reduction into the big gap between 2:1 and 1:1.
So you might be fine as planned. And even if you need some tuning when you're done, there are cheaper options than an entire "rip and replace".
Eric
--- In electricboats@yahoogroups.com, Julian Webb <julian.proto@...> wrote:
>
> Hi Eric
>
> - As no prop man would guesstimate speed for my boat, maximum efficiency
> was all I could head for that they seemed able to calculate to.
>
> - I know I'm a bit on my own when it comes down to it, just didn't want to
> be at the "bleeding edge" and be first-in-my-class but hey someone has to
> do it as they say.
>
> - I'll publish/post all my results and hope I don't have to either new
> props made or the proposed ones turned down (the only cheap mod I can think
> of) as they are costing me £1000 each!!!
>
> - I know I could have had off-the-shelf guesses way cheaper but I thought
> if I went to a "proper" prop maker I would get what was optimum for my
> boat............... time will tell I guess, "a fool and his money" as they
> say.
>
> Cheers, Julian
>
>
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