Concept electric drive

[duluthboats]

Attached is an image of an idea for an inboard electric drive. It is very simple using a LEM200 from Lynch Electric Motors, http://www.lemcoltd.com/ , a pipe as a main body, and a timing belt for power transmission. The motor is capable of approximately 10 hp using 48 volts. It could be easily built as an outboard by changing the packing gland to a transom bracket and putting a cover over the motor. The finished motor should weigh less than 50 lbs. Comments on this idea would be welcome.

[marshmat]

Interesting concept, duluth. Looks like a nice, simple design; easy to build and install. The belt drive is an interesting idea; would make it quite tolerant of vibration and misalignment I would think. How much of the leg is 'dry'? (I wonder what a timing belt would think of water...) A nice inexpensive unit like this could be pretty useful.

[FAST FRED]

A hp in 12 v is about an 80A load , 10hp would be 800A .

Battery sets dont like to be drawn down much faster than 10% of capacity,
so you would need 8000A of batterys .

Battery sets cost about a buck a pound and produce about an amp a pound.

So your boat will have an 8000lb battery set at $8000 a shot.

Recharging will be interesting!

FAST FRED

[Danielsan]

For as far as I saw the specs, Fast Fred is right, You will need a whole lot of bat power
when having a litle gen set on board it could work for emergency prop or when the normal prop or drive is out of order, on the other hand I don't like to play with that amount of current into wet (salty) environment.

[Sander Rave]

The amount of power will be a bit tricky 80A at 12V would be 20A at 48 V right?
10hp as an electric propulsion will be a whole lot of power and not very practical.
I like the concept of this idea. The configuration of components... A rudder won't be nessecery anymore, would it?
In combination with the Volvo Penta IPS concept this could be a great sollution for a small boat, I like this!

[yokebutt]

Duluth,
I've been kicking around thoughts along similar lines for a couple of years, but I haven't gotten around to doing any experiments, mostly because I primarily do composites and not that much metalwork.

A couple of ideas I've come up with are to use a large spreader extrusion for building the drive-leg, or, simply cannibalizing the bottom end from an outboard and pasting the motor onto the drive-shaft. The benefit of the second approach is that most outboards have a 2:1 or thereabout gear-down in the bottom.

In either case, since electric motors hardly vibrate at all, it should be possible to mount the assembly rigidly without any complicated rubber-bushing solutions.

The Lemco motor is great, when we replaced the GE motor with one in a fantail launch we built, the draw at cruising speed dropped from 30 to 23 amps.

Let me know how the project goes in the future, I'm very interested in the concept.

Yokebutt.

[Danielsan]

Yokebutt, how did you power the motor as 23 amps seems low? and what hp rating did you get?

greetz,

[duluthboats]

There are already boats using this motor for propulsion. I am only trying to adapt it for use on my boat without breaking my bank account. The cost would be comparable to an equal sized 4cycle outboard and far less than a marine diesel. A genset and/or solar panels would be extra. As with all systems there are advantages and disadvantages.

The intension is to have a dry leg but this type of belt is used widely in extreme conditions with little effect. If the boat is designed for the weight of the batteries they can be useful ballast.

[artemis]

In the Pacific Northwest of the USA there are many people working with the electric boat concept and, I understand, a few are working with LEM motors. I think the idea is sound and definitely should be explored. Based on your "public profile" you have the knowledge, skills, and tools to build this unit, so DO IT!

If you make the "guide tube" for the unit tall enough that the top is well above the LWL then you'll not need a packing gland and, with a "tiller" extension, the motor can "steer" as well. Since it's DC, reversing is no problem. You might consider an oval shape for the "below hull" extension, not so much for reducing "resistance" as for providing better water flow to the propeller. And the neat thing about batteries is that they can be placed where ever they trim your boat best.

The most enjoyable part will be the "quiet" cruising - sneaking in among waterfowl at 2 or 3 mph, trolling for fish at under 5 mph, and always being able to talk to others. Those of us into "hobby steamboating" find this one of the great pleasures and you'll have the same capabilities - with less hassle.

[stevel]

I like the idea. My untrained eye says the design could benefit from a streamlined fairing over the pipe and a longer prop-shaft to make room for the trailing edge of the fairing. The tradeoff between hydrodynamics and the stroger bearings that may be required with the longer shaft may not be worth it, but its an idea to think about.

[duluthboats]

My first drawing doesn’t show it but the whole unit will rotate inside the glad for steerage. I have been wondering about the below the water line profile. The max speed will be slow, up to 7.5 knts on a 26’ boat, and the forward side will be against the keel. Would I gain much performance from fairing the leg or just complicate the construction?

[artemis]

Originally Posted by duluthboats

Would I gain much performance from fairing the leg or just complicate the construction?

I think "Westy" Farmer would tell you that "fairing" the afterside of the vertical "drive" tube would promote better water flow to the propeller and thereby increase efficiency. If you're mounting the drive tube against the existing keel, you might shape the keel to fit partway around the drive tube to create a "smooth" water flow, then fair the after part. There is a shape that is hydrodynamically best - someone here should be able to point you in the right direction.

[yokebutt]

Duluth,
I think you do want to fair the tube, round shapes have quite high drag. If you are making the tube from stainless, one approach is to roll a sheet of metal to the desired curvature and then bending it length-wise in the middle until the edges meet at the trailing edge. Drill two rows of holes where the sheet bears on the tube and spot-weld it through them onto the tube, then weld the trailing edge together. If you are using aluminium, just make the strut from a spreader-extrusion for a big boat.

You don't neccessarily have to make a perfect foil-shape, just a hand-waving effort to somewhat streamline it will make a big difference.

Danielsan,
The boat was a Phil Bolger designed fantail launch, 23 feet long. Instead of the intended wooden construction and diesel inboard, we built it from glass and divinycell and used the weight we saved in the budget for 16 large six-volt batteries wired for 48 volts, we were still 300 pounds below target when all done.

Reflecting on it after building and using the boat for a while, I realized that the reason why the steam-launch style of boat from a hundred-odd years ago is such a good match for electric power is because the power-plants available at the time were low on horsepower, and thus they needed a skinny and efficient hull-shape. Nothing new under the sun.

Yokebutt.

[cyclops]

Frontal drag KILLS, compared to any other. Sub, boat, car, plane, always long and lean with a point or sharp leading edge to shear the medium. I have the same sun as you.

[stevel]

Frontal drag requires sharp leading edges at high speeds. At lower speeds, a teardrop shape is fine. The rounded leading edge can push the water out of the way in a somewhat smooth flow, but a rounded trailing edge would not be able to pull the water back in behind itself without creating a lot of turblance. At low speeds, the sharp trailing edge is much more important than the sharp leading edge. Compare the wings on a Piper Cub, a 747, and an F-18, and you will see what I mean.

Water is much denser than air, so you don't need to go supersonic before a sharp leading edge is important, but I think this experiment is definitely in teardrop territory.