T-Pain Is On A Boat: Re: [Electric Boats] Amp draw vs speed for 37ft sailboat with 10 ft beam, displacement 13,000 lbs

Wednesday, July 3, 2019

Re: [Electric Boats] Amp draw vs speed for 37ft sailboat with 10 ft beam, displacement 13,000 lbs

I'm curious what motor/reduction you are using, and if that should even make a difference. I suspect your boat, like mine, is on the edge of 10KW versus 20KW. If these numbers are with a 10KW motor, would we expect them to be significantly different with a 20KW motor? Perhaps only at the top end?

Cheers,

On 7/2/19 8:14 AM, armyofpenguins@gmail.com [electricboats] wrote:

I completed my conversion a couple of months back and am loving it. It's time to start sharing what I've learned. ;)

I've collected data during a couple of outings under relatively calm conditions (65F, 5-10 kt winds), and I used excel to generate a trend line and a formula (using a power series if you're into math) that provides a pretty reliable estimate of how much speed I can expect for a given amp draw. This is really easy to do in excel and if anybody needs help I am happy to show how to do it. Here's the formula (keep in mind the formula would be different for a boat with different characteristics than those in the subject line of this post):

Speed (in kts) = 1.3728 X Draw (amps) ^ 0.2704

Some examples:

At 20A, my s peed would be about 3.1kts.

At 40A, my speed would be about 3.7kts.

At 50A, my speed would be about 4.0 kts.

And at 100A, my speed would be about 4.8 kts.