Hi Kerry,
Nope, all I was comparing was the Gerr power prediction at the propeller shaft for my boat and 3kts - 3.98hp and my known energy consumption through my electric drive - 500W. Since we know that my drive is not 100% efficient, then we know that my boat is using less than 500W of power at the propeller shaft to drive the boat at 3kts. But adding in my drive (controller, motor, gearbox) losses, the math gets even worse, the Gerr prediction is even farther off.
Anyway, I think that we've all agreed that the Gerr formulas don't work for our boats at our speeds.
I'm working on some ideas about how to accurately predict the power neede to drive a boat at a given speed. I'm working on the formulas first and then checking the results to see if they're reasonable. I plan on sharing my results with Gerr, once I've worked out some of the kinks. I exchanged a few emails with Dave before the release of the "AGM vs. Lithium in the Real World" article in the May 2011 issue of Practical Sailor.
If anyone wants to build/acquire the approriate measurement equipment and collect discrete data from various parts of a driveline, then by all means, go for it. I don't think that it's neccessary for what I'm trying to do. I'm just looking to get into the ballpark, I don't need two sigma accuracy.
Fair winds,
Eric
--- In electricboats@yahoogroups.com, "Kerry Thomas" <kjthomas@...> wrote:
>
> Hi Eric
>
> .... Looking at the numbers behind Gerrs predictions I think the data base was
> for higher speeds. The relatively low speeds used for most EP setups are in
> a different ball park.
>
> Are you comparing the real power output of the ICE at 3 knots to the real
> output of the EP?...
No comments:
Post a Comment