Boat Journal

Chronicling a love affair with sailing

Month: February 2012

Engine Efficiency

I checked the engine out the other day, when I had the luxury of a winter sail. It was making some awful racket. It was rattling quite a bit. So yesterday, I pulled the panels off to take a closer look. It seems the bolts holding the engine in place had worked their way loose. So I tightened them up again and took the boat out for a spin (hey, someone has to take her out! 🙂 ). Much better! Looks like I need to put some Locktite on the engine support bolts as I did with the coupler to the shaft.

While out there, I took some measurements on the efficiency of the engine. It’s something the electric boats mailing list recommends; it’s a good way to determine how far you can go on your setup. The wind was blowing, and the tide was coming in pretty strong, so I’ll need to do this again come summer when everything is calm. But this was a good ‘first run’:

Amps vs Knots

Amps vs Knots

Not exactly a straight line, and it probably never will be, since I’m not running in a bathtub where I can control all the environmental factors.  But interesting nonetheless. However, part of the ‘hiccoughs’ are because I would run downstream, then upstream to see how the values changed.




Amps vs RPMs

20120202 – Amps vs RPMs



This is actually more interesting, because it will help me determine how far I can go on a charge. I’m guessing the formula would be:

Battery amp-hours/amps * knots/hour = knots to travel

That’s amp-hours, as in the amount of energy stored in the battery, not amps minus hours.

Using this calculation, it appears I can go about 16.5 NM on a single charge, if I stay under 2.5 knots. If I up it to 5 knots, I can only go about 2.5 NM.

As I said, I’ll recalculate this in the summer when things are a bit calmer. But it’s interesting nonetheless!