Hybrid speedboat

Marine serial hybrids have been in use for decades: tug boats, ice breakers, submarines, and other working ships. Use in a recreational speedboat is new. Some sailboats are starting to use electric motors for auxiliary propulsion, sometimes with an ICE, sometimes without.

Tom

 

I'd imagine a boat is probably similar to a plane where a hybrid system wouldn't really make much of a difference on mileage. These type of applications typically require the engine to run towards the top of it's RPM range for long periods of time. This is in contrast to the typical stop/go/sit at traffic lights way a car typically lives it's life.

I can see these in some marine applications as an electric motor (that's powered by a generator) is useful because it limits the amount of space a drivetrain would take up in a ship.... in addition an electric motor in these applications can rotate close to 360 degrees which allows better handling during slow speed operation.

 

Exactly. The electrical system replaces all of the complexity of a transmission, and allows multiple engines to be coupled to one or more screws as needed. For low speed cruising you can use one engine. For maximum thrust you can bring more engines on line. Using an electric motor also allows nearly instantaneous shifting from forward to reverse.

The old icebreaker Mackinaw uses two 5,000 Hp electric motors for main propulsion - one for each screw.

You are also correct about the steady loads on a marine engine. There isn't a lot of stop and go. Besides, most big marine engines are diesel. Our sailboat has a 10 Hp single cylinder marine diesel that weighs almost 500 pounds. I don't think that engine would work well in a motorcycle or airplane.

Tom

 

Oh great! Now a 'hybrid' hole in the water to dump money into.

 

An auxiliary sailboat is kind of a hybrid hole in the water, into which we dump money. We get to spend money on the sails and the engine, although with current fuel prices sailing is getting better and better.

Tom

 

Problem with a boat is you won't get much in the way of
regen, since water viscosity pretty much makes a boat fall
flat on its face and slow down immediately as soon as you
stop pouring on the coals. A recovery system of any sort
would be infeasibly inefficient if it could work at all.
.
_H*

 

Interesting. So basically they use the electric motor to drive the boat at low speeds, where the big engines would be inefficient. Then rev up the big ones to go fast. It does make some sense, particularly for a boat that lives in a marina or canal and has to travel a ways at slow speed to reach open water. Planing powerboats get lousy mpgs no matter what you do, though, and the hull shapes that are efficient at speed are terribly inefficient when going slowly.

it is going to be interesting to see if there are less huge powerboats out and about this summer because of the fuel costs. I wouldn't mind a few less gigantic wakes to deal with!

 

There is no need for regen, since there is no stop and go. As you point out, drag stops a boat very quickly without any need for brakes, but boats don't stop very often.

Some sailboats use a towed turbine to generate electricity. It's not that common, but is sometimes used by blue water sailors to generate enough electricity to power electronics and some lighting. Solar panels are becoming more common, as well as wind turbines.

Tom


Tom

 

Hybrid makes far more sense for sailboats. They can make power while under sail and have it for cruising in and out of port. The weight of the batteries can be put in low and not effect the boat badly.

In a hybrid sailboat you entirely replace the diesel with electric. The boat is powered by wind and electricity exclusively.

 

What we need is a battery shaped like our keel, then we could have a 5,000 lb battery. With my luck, the battery company would upgrade to Li-ion and our boat would float upside down.

It would be great to get rid of the diesel. We have a fabulous diesel engine, but it's still big, smelly, and noisy, plus it requires a big tank of fuel.

Tom

 

The battery pack for the Tesla Roadster is an extremely irregular shape, specifically designed to fit into the shape of the space available for it. Since it's constructed of small laptop batteries, it's a fairly simple matter to build it in whatever shape is wanted.

So, for your keel boat, it would be easy to build a Li-Ion battery pack shaped to fit in the keel. Since you probably have ballast in there now, there would be no weight penalty. The Tesla requires liquid cooling because those laptop Li-Ion batteries (unlike the LiFePO4 pack in my Xebra) are subject to thermal runaway and must be cooled. But in your sailboat, cooling would be easy as the keel is surrounded by sea water, and if conduction through the hull is inadequate, a small pump could deliver cool sea water to a circulating cooling system without the need for a refrigeration unit like the Tesla requires.

Of course, when you are becalmed you have no way to charge the batteries. You'd want to design your BMS to conserve some charge for emergency use during calms. Or maybe a small propane-powered Stirling cycle engine (clean and quiet) as an emergency generator.

 

I like the idea. I have kicked around thoughts like that for a lot of years. I may build another boat along these lines sometime in the future, when I feel like having another big project. Often times a small genset is used for auxiliary power. They are small, self-contained, and reasonably efficient. It doesn't take much power to move a sailboat.

As for a weight penalty, as you point out, we have a lot of ballast. Our boat carries 5,000 lbs of lead. Li-Ion batteries are not as dense as lead, so you would need a lot of them, or perhaps a combination of ballast and batteries, but it is certainly possible.

There is a power boat on the market that uses this sort of system for propulsion. It has a large coach roof covered with PV panels, which are alleged to provide enough power to move the boat at cruising speed with only the sun. For night, or higher speed, you kick in the genset. It's too new to know how well it works, but the idea is attractive.

Tom

 

I would anticipate that lithium batteries would not entirely replace your lead ballast. My point was merely that since you already have so much ballast, unlike an electric car, which pays a weight penalty for the batteries, your sailboat would not.

I am extremely skeptical of the solar boat. I believe it takes far less energy to move a car on level ground at moderate speeds, than a boat, considering the enormous drag of the water. And we know that a conventional car has not nearly enough surface area for solar panels to provide more than 1 or 2 percent of the energy it needs. But there are plenty of grandiose claims in the EV world, ranging from dreams to scams.