Todd,
The dyno graph MARS published for the motor shows efficiency at various rpm and current levels. Note that once you are up to several hundred rpm the motor efficiency does not change very much.
The prop efficiency is much more significant. Pick the largest diameter you can fit to the boat (assuming you do not care about drag under sail), pick the rpm that produces the prop hp at your max current. Prop pitch is chosen based on expected boat speed at max power. Pick a drive ratio reduction that has motor turning at rpm shown on the dyno chart for your chosen max current.
Denny
----- Original Message -----From: toddbates99Sent: Sunday, January 24, 2010 1:58 PMSubject: [Electric Boats] Re: Efficiency of mars motorA better way to ask my question might be "Is there an efficiency advantage to operating the motor at a higher rpm for a given KWh output?".
--- In electricboats@yahoogroups. , "toddbates99" <toddbates99@com ...> wrote:
>
> I'm trying to use the spreadsheet to estimate the best gear ratio. Its got a lot of info but a steep learning curve. Finally figured out how to match the required HP to the HP for a given diameter/pitch. So now I think that my best propeller RPM should be 1020. So is there a best RPM to operate the 72 volt mars motor at? Best in this case would be RPM rather than maximum power.
>
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