Eric and anyone else
Still lots to think about. Now I would like to determine prop pitch and gearing. Some of the electric conversion web sites say that because of the torque produced by a electric motor you should go to a large pitched prop. The largest prop I could fit is a 13 inch dia prop, obviously the more pitch the more torque required to turn it at a given RPM and the more boat speed. Aprox boat speed can estimated by pitch x prop RPM, but how would you determine the amperage draw to achieve that RPM. Of course gearing would come into the picture but that's easy to deal with. I guess my question boils down to, is it more efficient to run a electric motor at medium or high RPM? i.e. If I want to motor at 4 knots would I gear the motor to turn at 2400 RPM (max) or at 2000 RPM. Since I would be using 4 knots as an common speed I would pitch the prop to be most efficient at that speed. Yes
this is starting to wander but both issues are connected.
And to really highlight my ignorance is the speed of AC motors regulated by voltage like DC or by amperage or both.
Glenn
--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
>
> Glenn,
>
> I wouldn't go smaller than a 90 or 100Ah Li battery bank, small banks have bigger issues with Peukert's Effect, they lose more power under high load rates. You could also consider 4 group 31 AGM (105Ah) to begin with, they would weigh about 280 pounds, but you should get about an 8Nm range at 4Kts to 80% DoD. Then after you win the lottery, you can upgrade to the latest Li batteries. :)
>
> If you're thinking generator, Mike has been successful with his Honda 2000 and a charger, I think that he can put about 15A into his system when the generator is running, that is about half of your 4kt load, so your batteires should last twice as long at that speed. There are some chargers available that can deliver more than 20A at 48V running on a Honda or Yamaha 2000 generator. The generator should be on deck while running. But the good part is that you don't need to set it up until you think that tyou need the range. If it's truly a day sail, you can leave the generator ashore.
>
> It sounds like your getting your head wrapped around this project. Let us know if you need more info as you do more research.
>
> Fair winds,
> Eric
> >
>
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