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MetroMPG 05-03-2010 10:09 PM

Electric sailboat motor: new conversion project (update: project shelved)
2 Attachment(s)
On impulse, I started a new project this week:
  • Out with a 30 year old, smelly, smoky, noisy, sometimes unreliable, inboard gas engine!
  • In with a quiet, odorless, underpowered, limited range, homebrew electric system! :p
The back story:

I've got a sailboat with an inboard, 2-stroke, 15 hp gas engine. For the last 10 years I've had a love/hate relationship with this engine.

My biggest beef with it is actually the stink. Even with proper ventilation and intact plumbing, the slight smell of fuel and exhaust is ever present inside the cabin after it's been running for more than a few minutes. I spend a lot of time on board in the summer, so that sucks to put up with. (Various strategies have been developed to minimize it, but it still sucks.)

Reliability is my secondary beef. It has been an on and off again engine, though most years have been trouble-free.

But not last year - it started leaking (dribbling) cooling water due to some seals going bad. So in preparation for this spring's launch, I pulled the engine a couple of weeks ago, fully intending to tear it apart, replace the necessary gaskets and o-rings and reinstall it.

Changed my mind. Going electric instead.

Here's the wee beastie: it's an OMC "Sail Drive" setup. (I've got a great service manual for it...)

Step 1 is already done: the engine has been pulled.

I completed step 2 this evening: shaped a plastic plug and epoxied it into the lower unit at location (12) - the cooling water intake. No longer need to pump cooling water into the boat. Cooling leak problem solved!

The boat goes in the water, motor-less, this Wednesday or Thursday. The rest of the conversion will take place afloat, at the dock.

I've played around with electric boats before. This is a little more involved than my last "project" :D ...

I'll keep you posted.

Silveredwings 05-03-2010 10:26 PM

It's the next best thing to an Azipod.

MetroMPG 05-03-2010 11:23 PM

SW - very cool. A ship sized Minn-kota trolling motor!

The Sail Drive doesn't swivel though - flow over the rudder is how I steer under power or sail.

And it goes without saying that this conversion project will be typical Darin style: ie. making best use of available resources...

I still have a pile of left over parts from project ForkenSwift:
  • 2 motors to choose from,
  • a sizeable collection of golfcart batteries,
  • contactors,
  • 2 spare controllers (I may just do a contactor controller),
  • and a selection of battery chargers.
As usual, the hardest part will be coming up with a coupler to connect the motor to the input shaft of the transmission (lower unit).

Daox 05-04-2010 08:18 AM

Sounds like a fun project to me. Looking forward to hearing and seeing more about it. :)

MetroMPG 05-04-2010 09:34 AM

1 Attachment(s)
I should have gotten a photo / video of the ICE in the engine compartment before I started ... but when I took it out I didn't know at the time I was going this route.

But here it is out of the boat, the 67 lb stinkpot:

(shown in the same orientation as the diagram in post #1)

Coincidentally, the entire engine is almost the exact same weight as one 6 volt golf cart battery.

Which always drives home to me how much power there is in petroleum fuel...


MetroMPG 05-04-2010 09:51 AM

1 Attachment(s)
And here's option 1 of the two e-motors on hand:

This is the permanent magnet power steering pump motor from the forklift.

5.5 inches diameter, 11 in. long, 32 lbs.

It's only rated .88 hp, continuous duty at 48v.

Consider: the ICE is rated 15 hp, peak. But for perspective, the vast majority of the time I run the engine, I'm basically putting around at 1/4 throttle, just to get in and out of harbours/docks/anchorages. Probably using about 3 hp.

Of course, we all know electric motors can be run at outputs well above their ratings, provided you don't melt them. Since the motor won't be used in the boat for extended periods, I'm thinking a small one may be OK.

Option 2 is the twin / "backup" motor to the one in the ForkenSwift, though it's actually overkill in terms of power and weight (8 in. diameter, 15 (?) in. long, 110 lbs).

It's a bit of a Goldilocks situation: the ideal motor, the one that's juuuuuuuust right, is probably somewhere in between these two.

Maybe I'll drop by the forklift place and see if the guys have something else on hand that's surplus/headed to the scrap yard.

bryn 05-04-2010 10:51 AM

for what it's worth
on my cal' 27 the only motor i had last summer was a 47# thrust whisper guide (and a long paddle)
i could cruise aprox 3 knots without the wiring getting hot to the touch. into the wind went ok, up to 10+ knots, then i had to get the paddle out. i think our boats are probably about the same drag. mine is a 27' poptop disp. 5500#

unless you actually need to get to hull speed, against wind and current, i think any motor with 1+ hp should be enough, especially if you can play with prop pitch/size at all.
have you thought about regen/recharge under sail?
i'm looking foreward to seeing progress

MetroMPG 05-04-2010 11:55 AM

That's good info, bryn. Funny too! (backup paddle) You sail on one of the finger lakes?

Yeah, the boats sound similar. This one is ~5000 lbs.

Just for kicks I have tried my Minnkota 17 lbs thrust electric trolling motor on it a few times. At high power, on calm water and in zero wind it will go along at the equivalent of a slow walking pace. Maybe a knot or a knot and a half.

To be practical, I'll need something capable of about 4-5 knots max. I'm on the St. Lawrence, and currents around here are 1-2 knots. And of course the prevailing wind is the same direction as the current...

The actual motor I played with (attached to a more appropriate hull :P):

The idea of regen has occurred to me, particularly if I use the per mag motor. But to be honest, I spend more time aboard at anchor or tied to docks than I spend sailing, so it's not a priority.

DonR 05-04-2010 12:43 PM

Do you plan on solar charging the batteries while on the water? I know nothing of sailing or boating, but when your batteries dead, it's dead.


MetroMPG 05-04-2010 01:24 PM

I do have a 35w solar panel on the boat, yes. But even without that, I'm not worried about dead batteries and not being able to get home.

An auxiliary electric motor in a sailboat isn't going to come with the same set of concerns as an electric car.

I never used the gas motor just to "drive around", and I won't be using the electric motor to do that either. It's mainly for getting in and out of the harbour ... to go sailing for the afternoon when there's a decent breeze. So electric "range anxiety" really isn't a big issue.

Also, there's 110v, 20A electrical service ("shore power") at the dock to use for charging (among other things). So the batteries can always be 100% topped up at the start of each outing.

But what if the wind dies!!?

As it happens, my favourite areas for sailing are up-river from where I usually dock, so if the wind completely dies, drifting back towards the harbour on the current before switching on the motor to come in is an option. (Drifting in the current is actually a pretty popular thing for boaters to do around here on calm days).

And there are paddles. And there's an anchor. And a kayak on board. Lots of options.

Sort of like worrying about what happens if an electric bicycle runs out of juice. Well, you could pedal. And what if the chain breaks!!? Well, you could get off and walk it. Several options.

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