T-Pain Is On A Boat: [Electric Boats] Re: Torque

Monday, July 27, 2009

[Electric Boats] Re: Torque

--- In electricboats@yahoogroups.com, "Jerry Barth" <shredderf16@...> wrote:
>
> With the recent hp equivalency discussion I was wondering if you
> could use torque as a valid measure. For example in my case could you just
> look at the torque curve for a Yanmar 2GM20, find out how much torque there
> is at about 2800 RPM or so (cruising speed), then take that value and find
> an electric motor with the same torque at whatever you're going to use for
> cruising RPM? I guess you might be able to bias it a little bit toward a
> smaller electric motor since I do plan on using a bigger, slower turning
> propeller than on the diesel installation. Any thoughts?
>
> Thanks,
>
> Jerry Barth
>
>
>
Torque alone does not sufficiently define the propulsive power input. The power is directly related to the product of torque multiplied by rotational speed (RPM). For an electric motor having the same torque as the Yanmar Diesel at 2800 RPM, the real output horsepower would only be the same if the electric motor is also rated at 2800 RPM. If the electric motor is only running at half this speed (say 1400 RPM), then the electric motor is putting out half the power of the Yanmar.

Yes, you can bias (in favor of the electric) a little if you have a more efficient propeller (generally lower RPM, larger diameter propeller). But then you could also provide the proper propeller and proper propeller RPM with the Yanmar, and eliminate the bias.