[Rhodes22-list] Bill Effros - Electric Drive

[Peter Thorn]

Bill,

You might be interested in Jobst Vandrey's auxiliary tolling motor and solar
powered electrical system for his Compac 19 .  Some of the references on his
reading list look helpful as well.  At about half the weight of an R22, the
Compac 19 is probably the largest practical size for trolling motor.

http://www.geocities.com/Yosemite/Forest/2727/trailersubweb/trailer_outboard.html

PT

----- Original Message ----- 
From: "Bill Effros" <bill at effros.com>
To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
Sent: Sunday, September 26, 2004 7:27 AM
Subject: Re: [Rhodes22-list] Bill Effros - Electric Drive


Bob,

Thanks for saving me a lot of time.  In my heart I knew it wouldn't work,
but my head kept hoping.  It's still hard to give up the idea of an R-22
with a bow thruster.

What if you mounted 4 electric motors?  What if you put batteries into the
keel instead of lead shot?  What if you ...

How is the Honda 1000 watt generator in the marine environment?  Is it on
board all the time?  Fresh water or salt?  It's a neat little rig.  No
wonder people kept talking about it.

Bill


----- Original Message ----- 
From: Robert Skinner
To: The Rhodes 22 mail list
Sent: Saturday, September 25, 2004 2:08 PM
Subject: Re: [Rhodes22-list] Bill Effros - Electric Drive


Roger Pihlaja wrote:
> ...
> I looked in the 2004 issue of the West Marine Master Catalog on pp. 223.
> The most powerful transom-mount electric trolling motor listed is a Minn
> Kota M/N RT101/S-3X...
  This trolling motor is rated to deliver 101 lbs of
> thrust at 36 VDC and 37 amps.  To power this load, you would need:
> P = V * A = 36 VDC * 37 amps * 1 watt/VDC-amp / 1000 watts/kw =  1.33 kw
> ...
> The horsepower ratings of outboard motors are on the basis of power output
> at the crankshaft...  Assuming
> you are willing to trust my estimated power transmission efficiency, you
> would need an outboard rated at:
> 1.33 kw / (0.746 kw/hp * 0.72) =  2.48 hp
> So, in big round number, this 101 lb thrust trolling motor would be
roughly
> equivalent to a 2-1/2 hp gasoline powered outboard...

Roger -

Your calculations produce results roughly in line
with my experience.

My electric outboard rated at (perhaps a bit hopeful)
1.5 hp draws 28 Amps at 12 VDC and produces 28 lbs of
thrust.  In actual use, this cross-checks with my
4-hour endurance at full power from a fully charged
105 AH 12 VDC deep cycle gel cell marine battery.

The Honda 1000 watt generator 125 VAC drives a 20 Amp
battery charger, not quite able to keep up with a
constant WFO motor output, but quite adequate for
1/2-3/4 throttle gunkholing all day long.

I usually don't have to use the generator, as the
4-hour battery life is more than adequate to get me
out of the marina and assist if the wind dies down.

One problem:  My smaller sailboat is only 15' long
with a tiny cabin, but the 28 lb thrust is not enough
to push it directly upwind against more than 12-15
MPH winds.  In those conditions, I use a 3 hp Tanaka
air-cooled 2-stroke that weighs only 24 lbs, but
wails like a banshee.  However - it will push the boat
at hull speed against a 15 MPH wind.

Hope this actual experience will convince people that
a Rhodes 22 is too big to push with a trolling motor.

At the last Annapolis sailboat show, I saw a $50,000
25' double-ender pilot-house sailboat with an inboard
electric drive.  There were 10 big 12 VDC batteries
in the bilges - power and ballast.  The motor was
about 10" in diameter with a 1" shaft.  Looked as if
it would do the job.  But it had no generator, and
would therefore be tied to shore power.

Retrofitting such propulsion would be all but
impossible in an R22, and is they made such a rig in
outboard format, I'd be terrified of the huge
flexible 125 VDC cables that would be required to
connect with the battery farm.

The 9.9 hp outboard is cheaper, more effective,
easier to keep repaired anywhere in the world, and
simpler.  It is also quickly replaceable if ripped
off.

Keep the pointy end up,
/Bob Skinner
__________________________________________________
Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
__________________________________________________
Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list