Myles,
I can see how motor specs are important for someone that is creating their own drive system from components like you described. For someone that is looking for a more turnkey solution, the motor specs don't tell much of a story.
I guess the problem is that with so many different people with different goals, finding a single set of data that is helpful to most is very difficult. I found the data supplied by Torqeedo and Propulsion Marine to be really helpful, others have stated that data from different types of boats from their own is meaningless to them.
So I guess that each vendor can provide whatever info they find helpful to generating sales with their own target market. Unfortunately, this means that some vendors will sell more hype and less real performance. I guess that this is a side effect of trying to combine such a disparate community into a single conversation.
Fair winds,
Eric
--- In electricboats@
>
> Another perspective:
>
>
>
> As one who converted his own outboard to electric several years ago now,
> when it comes to spec'ing new drive motors (i.e. drives without props), I
> don't want to see performance rated as "used only 2kw to make a 4k#
> super-dyno-whatsit hull reach 4knots". Sure, give me that information, but
> if you're developing a motor, I want to see motor torque, voltage, speed and
> efficiency specs at a minimum. I would not change out my existing brush-
> ETEK motor for anything different without such information. In fact, that's
> the best way to compare motors given an existing plant. Say for example you
> had an ETEK that was driving thru some or none gearing a thru-hull prop
> shaft and an optimal prop. You have the spec'd performance curves for the
> ETEK. You hear claims that MARS or AMeP or other brushless motor is the
> cat's meow. Would you invest thousands of dollars in a new motor after only
> receiving 1 or two performance datapoints from the manufacturer that claim
> that this motor drove this boat this speed and consumed just this amount of
> power? Yeah? Not me. I know that my ETEK has a fairly wide sweet spot for
> efficiency. I have the speed/efficiency/
> for it. For me to decide to dissect my system, extract the motor and
> replace with another that is claimed to be so great, I need to see released
> performance curves that are credible and verifiable. With such information,
> I can quickly judge whether any claimed improvement is really there and if
> so, is it enough to justify the money and the hassles of changing. And with
> a wide 86-88% efficiency peak for the ETEK, I'd need to see at least a 92%
> efficiency curve for a motor to entice me to switch. And even then, that 5%
> reduction in power is on paper. Reality is that each motor will vary
> somewhat within or even outside the specs. MOST important however is this:
> That 5% savings in power by increasing efficiency could easier be had by
> simply reducing boat speed by a miniscule fraction of a knot---and that
> costs nothing.I quickly realize that changing motors for efficiency reasons
> at this point borders on irrational. Now, it would be a different case if
> the realized motor efficiency in my setup were merely 75%. Why? Well, not
> just because there's so much to be gained on the topside, but the big reason
> is thermal. That 25% loss is to heat. And with a 6HP peak power in my
> setup, a 25% loss to heat would be 1500watts of heat---that'
> rid of under an outboard cowling! Even at 87% efficiency, the loss to heat
> is not insignificant at 6HP, with nom. 550watts or so lost to heat. Should
> I ever desire to cruise for lengths of time at 6HP of power, it's the heat
> buildup that would really motivate me to look at alternatives. But again,
> I'm not buying any motor that doesn't have published standardized motor
> specs.
>
>
>
> Caveat emptor-
>
>
>
> -MT
>
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