The Propeller Handbook would be another source - it talks about losses in
gearing and thrust bearings and such.
Will
On Wed, Sep 2, 2009 at 12:25 PM, toddbates99 <toddbates99@
>
>
> If you measure the strain on the thrust bearings or motor mounts you could
> get the actual efficiency of the whole system. There might be greater gains
> in improving the prop than in the rest of the system. Well, other than the
> Peukert effect.
>
> --- In electricboats@
> Arby bernt <arbybernt@.
> >
> > I'm working on a shaft mounted strain gauge to measure output toque to
> the prop. It will hook-up to a shaft mounted power supply/transmitter with a
> USB dongle or a hand held battery powered display to receive the signal. The
> RPMs can be read with a optical tachometer. Other conditions like wind and
> tidal forces would be part of the data log as well. Calibration would be
> required each time a strain gauge is epoxied to the prop shaft, but that can
> be done with a pair of vise grips and a fish scale. Gauges are $10 each. The
> transitter would be able to spin on the prop shaft, and be re-usable (I
> hope!!$$). I'll loan the system out in exchange for data added to the the
> forum.
> >
> > Arby
> >
> >
> >
> >
> >
> > ____________
> > From: ewdysar <ewdysar@...
> > To: electricboats@
> > Sent: Monday, August 31, 2009 1:55:10 AM
> > Subject: [Electric Boats] Re: Problems with the Marine EV industry
> >
> >
> > Arby,
> >
> > This is the type of conversation that I was hoping would develop. We can
> already identify a couple of constraints that need to be acknowledged. Lead
> acid batteries weigh about 60-65 pounds per kWh. Therefore, a 10kWh
> batteries pack will be around 650 - 700 pounds with cables, platforms, and
> tie downs. Lithium batteries are about 35% of the weight of lead acid
> batteries.
> >
> > My boat is around 5 tons displacement and I'm targeting a 48v system that
> can pull up to 125A, resulting in a 6kW drive. I hope that the boat would
> perform sufficiently running at around 2.5kW with the rest of the power held
> as reserve. Given a 24' LWL, the estimate of 500W per ton would result in a
> cruise speed above 4kts at 2.5kW.
> >
> > I'm interested how you would dyno the shaft power of an installed system.
> I'm pretty sure that you're on the eastern half of the country, I wonder if
> there's anyone in SoCal set up to perform a similar measurement. If we could
> collect this type of metrics, it would go a long way towards objectively
> measuring the efficiency of some of the various drives available. While
> total thrust measured with a bollard pull may be more relevant to the end
> user; the variations from hull shape, shaft angle, and propeller design
> would skew the results towards the installation and away from the drive's
> performance.
> >
> > Given that the weight of the battery pack seems like a limiting factor to
> me, and that displacement keelboats already carry thousands pounds of
> ballast, the elegant solution would be to make some of that ballast
> "active". I will attempt to do that with my second battery bank after the
> drive is installed and running. I think that the best solution would be a
> boat built with vertical battery racks running into an internal keel or a
> battery filled bulb at the bottom of a fin keel. A power bulb my be able to
> be retrofitted, but I would want to remove some of the original ballast to
> keep the boat sailing as designed.
> >
> > Fair winds,
> > Eric
> > Marina del Rey, CA
> >
> > --- In electricboats@ yahoogroups. com, Arby Bernt <arbybernt@ ..>
> wrote:
> > >
> > > Keith has raised an interesting question...How much power should a boat
> have to consider it safe? I've read that 2.5kW per ton will allow a boat to
> reach hull speed. For your Hunter, that would be a 10kW system. 70% of hull
> speed requires but 500W per ton, however, so a "3hp" (2 kW) system would
> move your boat just fine.
> > > Please suggest a standard, in shaft power, not controller input. I'll
> be glad to dyno your system if you would like an actual curve for your
> Mars/Sevcon system. Knowledge is power.
> > > I will agree that 3hp on a 10,000lb boat can provide manuevering power,
> but would be hard pressed to buck heavy seas and headwinds. By the same
> token, installing a 15kW motor and expecting to support it with a 100kWh
> battery pack is not reasonable.
> > > If other members would care to suggest power to displacement ratios,
> and the batteries to match, we could help to build a database of working,
> marginal, and disfunctional boat repowers.
> > > By creating a standard, we help not only folks like ourselves, we help
> the boating industry in general to accept a greener option.
> > >
> > > Be Well,
> > > Arby
> > >
> >
> >
> >
> >
> > [Non-text portions of this message have been removed]
> >
>
>
>
[Non-text portions of this message have been removed]
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