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Hi Bill, I remember living aboard during
winter-time on the bay. I lived in Deal, Md. for a few years.
(Ice eaters outside and glycol in the bilge)<br><br>
You may not need to mess with belts(and lose eff
=miles)The lower unit is a gear reduction(you'll have to
check it out) and saildrives used higher reductions
then the standard outboard...could be 3 or 4:1 which
would be a good start for an electric
converision.<br><br>When you do the Speed/Drag you can enter the data into
a sperad sheet like excel and graph out the curve.
What happens is the drag curve increases along with
speed (more or less together)until you hit the hulls
displacement limited speed, then speed flattens and drag goes
up like a rocket. Use the calculation to find hp
needed at a given speed...It's fun to do really, but
maybe not in the cold....<br>Joe

Thanks for the Idea about a hull drag test. I may
try that as soon as it warms up here on the
Chesapeake. I'll post any data so that other can follow along
with the repower story. Should be fun.<br>FYI
currently the boat is powered by a 15hp Saildrive and has a
12x9 prop, loaded displacement is +/- 6000lbs. my
cruise speed is 7kts and max is 9.5kts. My intent is to
keep the saildrive leg and simply remove the block and
adapt the existing shaft to a belt and pulley system.

To figure out what electric HP you need first
start with the motor that WAS in the vessel. Usually
the manufacturers are pretty good a determining the
appropriate fossil fuel HP. Then divide by 3 for a coarse
guestimate. If you have enough room to size the prop up a
little, say from 14" to 16" then you can usually reduce
the HP to 1/4 instead of 1/3. If you list the current
engine HP, prop size, and displacement I could help you
even more. After gauging HP you can then use the
aperage/voltage to determine a burn rate and get the battery pack
sized right. This will require you to guess at a motor
technology and the voltage. It your trimaran is over 16,000
lbs you will probably need to call Solomon
Technologies and get an Electric Wheel motor. There aren't
many people producing marine motors much over 4 Kw.

You could do a "Hull drag" test with the help of
a friend and a second boat. You will need a "good"
knotmeter(0~10 Kt ? ) and a calibrated scale (0~100lbs. maybe
150 lbs the kind with hooks on both ends). The idea
is to measure the pounds of "pull" (on tow line)at
increasing speeds. Like 4kts. 25lbs, 5kts. 32lbs, and so on.
Then if you want to calcualte the power your hull is
dissipating (power your going to need also) then multiply the
speed (in knots) times the drag (in pounds) times
0.003068 (corrects for differences in units). Collect as
many data point as you can and make the "runs" inboth
directions to lower the errors.(wind~current)<br>Have
fun<br>Joe<br>ECB

Hi group, I am currently planning to repower my
35' trimaran to electric and need to find someone
with direct experience sizing motors and other
important considerations for such a project. Anyone with
this type of knowledge please post or email me. Also
if Oconaill has the Motor System which was posted on
11/28 I would like to discuss how that might work for
my conversion.