Peter
Judging by the number of responses, I think the final combination is the result of experimenting and seeing what works the best. I'll certainly share whatever performance data this generates.
At the moment, I'm trying to find out if a 48v charger with 15 amps per 12v bank is enough for deep cycling 250 Ah batteries.
Victor
--- In electricboats@yahoogroups.com, "sailingpm" <sailingpm@...> wrote:
>
> Victor: I'm also beginning a conversion in a Union Polaris with the ET-RT 709 motor. A heavy displacement 36'.
>
> If you have the original transmission from the extracted engine, you can use that reduction box as a guide. As I understand it the big unanswered question is how fast does you prop need to turn to bring it up to hull speed? and then match that with the maximum rpm of the mars motor. This number floats with different prop pitches and sizes. To get the right combo is all math, (if you have plans to the boat, that is. Mass resistance through the water, hull shape, displacement etc...).
>
> In my reading experience so far, it's all trial and error. Shoot for 800rpm for the prop (total guess) to get the boat to hull speed (that changes with different props). Your motor turns 3000rpms at max efficiency. So that means start with a 3.5:1 ratio. You may not use the motor at max but now it's a start to adjusting the ratio to getting efficient. My numbers aren't accurate, just an example of what I'm trying to do as well.
>
> If you are go going full bore at 3000 rpms then your prop is turning 800 rpms. Will this bring the boat to hull speed? If you leave everything the same and change the prop size, what does that do to speed? Change the pitch, same question. If the prop is turning too fast then you go change the ratio. Back to the store for another gear, etc...
>
> I'm using the heavy s/v ??? in the early photos section, the one with all the solar panels in Vallejo.
>
> If you find out anything I'd love to hear it.
>
> Peter M
>
>
> --- In electricboats@yahoogroups.com, "vjmtymo" <vjmtymo@> wrote:
> >
> > Okay, I'm up to my armpits in this conversion and still going. What is the "typical" gear reduction range for the Mars 709 motor to the prop shaft? Again, I've got a heavy 36ft sailboat. Just need a number to start with.
> > Also, am I aiming for hull speed with the prop calculation or do I aim for 2/3 or 1/2 of it, which is probably the more expected speed? Wouldn't mind trying one of those urethane props if I can get some advice.
> > Thanks again.
> >
> > Victor
> >
>
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