T-Pain Is On A Boat: [Electric Boats] Re: Direct drive brushless DC motors now available

Tuesday, July 14, 2009

[Electric Boats] Re: Direct drive brushless DC motors now available

Motor efficiency curves won't really tell much - it's the entire system that has to cooperate to produce efficiency.

Luckily - we have a near perfect control setup. I have a 1978 Hunter 30 in SF bay with the Mars/Sevcon setup. I've got some test data (multiple runs in calm water, bi-directional, etc). I'm happy to re-do those as we agree on protocol but meanwhile I'll post the .xls to the files section.

The major variables between the 2 boats would be (IMHO)

Bottom coating
Prop (blades, size and pitch) Mine is 13x13 3-blade
Weight (I have 12 group 27 on board)
Rig (Hunter had a couple of different keel/mast combos IRRC). I have the 6' keel

If you can publish those variables, and some performance data in flat calm water I think we'd have reasonable comparisons.

My battery pack is having some troubles, but I do get full voltage (just not as long as I'd like - I think I know why Walmart batteries have a 2 year warranty...).

I use a CycleAnalyst for volts/amps so we might need to use a cheap clamp-on DC meter as arbiter (same brand/model on both coasts)

Just as one comparison, I get 4kts @40amps (that is just about 2KW...) in calm water (freshly clean hull/blade) That drops to 2.2 kts in a 15-18kt headwind (SOG measured with a GPS). I can push my rig to 130amps in a pinch (6.5KW or almost 9HP), but obviously not for long since the motor is rated 100AMP cont. - I can get to about 5.2kts at 90 amps. Hull speed is 6.3 but my diesel couldn't do that either.

I think there was a little hyperbole in some of the posts (and maybe some confusion between kts and mph). I suspect my boat might have been used as one informal comparison based on a post where I was having some trouble - but clearing some stowaways off the prop seems to have helped a bit...

The gauntlet is down :)

-Keith

--- In electricboats@yahoogroups.com, "itsdej" <itsdej@...> wrote:
>
> I understand the desire for the actual specs and real world data. It makes it a whole lot easier. Facts are facts. We are all working very hard on putting this together for the motor.
> Thanks for sharing your thoughts.
>
> DEJ