I have to concure, it only works in dead calm with no wind or current and stopping is a problem too. I rigged an 82# thrust White Shark on the Arc. once. In our very early development stage I was thinking of rigging 4 of them on stern but our test with the one was so anemic I abandoned that approach in favor of figuring out a way to incorporate a motor into my existing drive train. My final solution was inspired by the DragonFly, (www.slowboatcruise.com), after we visited with Bill and Cynthia in Vero Beach as they where doing the great loop.
The Arc is also 20 tons and with the 82# thrust motor strapped to side of the boat at the stern we actually made 2 mph with about about a 7 mph tail wind and we where thinking Woo Hoo, this is great. Then I turned the boat around into the wind and we started going backwards at 1/2 mph and I knew it was no way. Since then I have concluded that .5 hp/ton is the absolute minimum you're going to get by with if you want to maintain control of your boat in most conditions. You should be able to get about 80% of hull speed in calm weather but if you run into any kind of wind or current, you won't be getting anywhere fast at that power level although it should be enough least control the boat, albeit in slow motion. Of course every boat is different and the more supersturcture and/or draft you have, the less you get. The generally accepted rule of thumb of 1 kW/ton is a better target and even a little bigger doesn't hurt but if all you want to do is move your boat across a calm marina, you can push some pretty big boats with a pretty small motor.
Carter
From: stmbtwle <stmbtwle@yahoo.com>
To: electricboats@yahoogroups.com
Sent: Monday, December 17, 2012 1:28 PM
Subject: [Electric Boats] Re: Using a MinnKota 55 as a thruster
To: electricboats@yahoogroups.com
Sent: Monday, December 17, 2012 1:28 PM
Subject: [Electric Boats] Re: Using a MinnKota 55 as a thruster
I see no reason it wouldn't work and I don't think any modifications would be needed, as trolling motors are already designed for high thrust, low speed.
Some years ago I tried pushing my 35', 9 ton houseboat with a 24# thrust Minn Kota (stock prop). I got 1mph both ways per GPS, in a dead calm. I had no problems with control, but if there had been any wind it would have been a different story.
Biggest problem I could see would be stopping.
Bill
--- In electricboats@yahoogroups.com, Robert Schulke <robert.schulke53@...> wrote:
>
> My neighbor uses an MK 55 as a thruster to maneuver his 20 ton boat around
> the marina, like to the haulout dock. Does anyone else out there do
> something like this? Have you changed props to deal with the high thrust,
> low speed requirement? Any other tips?
>
> Thanks!
>
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