[Rhodes22-list] electric motor selection

[David Rasberry]

Bob,

I have done a lot of research into electric conversions. You would need
around 240lbs thrust to equal a 9.9hp gas engine. This can be obtained from
a 6hp electric at 48v. There are primary electric outboards made by several
firms now that fit the bill, the least expensive being Amemco at about $2500
<www.amemco.com>. The real problem is range and weight requirements for the
battery pack. With lead/acid based batteries (wet cell,absorbed glass mat,
or gel cells) it takes about 540lbs of batteries to equal the energy content
of 3 gallons of gasoline. You would need the equivalent of four 4D size
batteries for 48v, which would provide about 18 mile range at 4 knots on a
Rhodes, about 9 miles at 5 knots or 3-4 miles at 6 knots. Fine for short
haul use on an inland lake. Compared to a 9.9 outboard and fuel you would be
carrying around a 375lb weight penalty. Total cost for the installation,
including premium Lifeline AGM batteries and a 48v 3 stage automatic shore
power charger would be around $6000.00
 The actual horsepower at the prop required to push a Rhodes to 6 knots in
calm conditions is about 6hp.  Thrust required works out to about 150lbs
based on 50% prop slip. Electrics are more efficient because they can turn a
larger prop that would stall a gas engine at idle. The amemco motor
mentioned above generates 13 lb/ft torque from 0 to 2800 rpm. The Yamaha
generates 13 ft/lbs at the motor shaft at 2500-5000rpm and requires 3:1
reduction gearing to get useful torque at practical prop shaft speeds.
Subtract the losses from the 10 amp alternator and the gear box and the
actual power at the prop for the Yamaha is about 8HP. Based on an 11x8 prop,
a Yamaha 9.9 hi-thrust should do about 240lbs of thrust flat out wide open
with 62% slip. Good for about 7 knots in calm water on a Rhodes. How does
this jive with real world experience for you Yamaha owners?

Razz

-----Original Message-----
From: rhodes22-list-bounces@rhodes22.org
[mailto:rhodes22-list-bounces@rhodes22.org]On Behalf Of Robert Dilk
Sent: Tuesday, November 05, 2002 3:21 PM
To: rhodes22-list@rhodes22.org
Subject: [Rhodes22-list] electric motor selection


I am confused. If I have a 8 hp gas outboard motor, what size THRUST
electric motor do you need? Is an electric trolling motor a good idea?

I guess any motor will push me out into the river, But....

Or what size (thrust) electric motor would be good for a Rhodes 22. Assume
I want to be able to drive the boat to 5 knots.

Any help is much appreciated.

Bob Dilk

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