Diesel/Electric Propulsion for Sailboats

I have been involved with numerous remote pumping stations, which are basically a diesel generator, switchboard, VVVF drive, electric motor, and a pump. They are simple proven systems which operate continuously with minimal issues. In a boat the pump is replaced with a propellor and the system would very similar and the technology is tried and proven.

Some of the issues I see in a small boat (say a 50ft displacement cruising boat)
1 - Cost: The switchboard, VVCF drive, and electric motor, are all additional items not required with a traditional propellor directly driven by a propellor, (but there are savings with deleting the gearbox)
2 - Efficiency: VVVF drives (say 97% efficient) , electric motors (say 92% efficient) , and cabling (say 5% voltage drop) all produce losses, and would not take much to produce a 15%-20% loss. This can be reduced by using latest DC technology.
3 - Efficiency: One of the claims is that generators can operate continuously at the optimum rpm. A good diesel system should be design so that at cruising speed, the engine should also operate at optimum rpm by correct selection of engine, gearbox, prop etc so this argument really only applies to poorly engineering systems.
4 - Quiet operation on batteries: Yes, but what is the range on batteries? It is not very far before you need to turn the generator on.
5 - Solar contribution: Solar cells can produce some electrical contribution, but the solar energy a boat can produce in one day again would not get you very far. 1000W of PV cells might produce 5kWh electricity on a good day, ie the same a 50kW electric motor consumes in 6 minutes before the generator has to be started. Moving slowly you might draw 10kW, so that would be 30min which is ok for short distances, moving the boat etc.
6 - Deleting traditional generator: Is it appropriate to remove a say 5hp generator and then have to operate a 100hp generator at night to produce electricity running at very light load. To make this work you would need to ensure you have a large battery bank.

Technically it would not be difficult to make a reliable system, but for a typical cruising vessel s I doubt it would be an economical solution.

One option might be to size the generator for cruising load, with a larger electric motor and a large battery bank. Typically a engine is only loaded at 40% load at cruising speed, so a 100hp diesel engine could be replaced with a 50hp diesel generator and 100hp electric motor and use the batteries for short periods when 100hp is actually required. This would offset some of the additional cost required for the electrical items.

 

For those interested, a freshly new magazine on these matters is on the market:

"Electric & Hybrid Marine Technology International"

http://www.ukipme.com/mag_electric_marine.htm

 

Thanks Guillermo, I was going to mention that. I just got my copy, and have not finished reading it.
Brian

 

Thanks Guillermo !

 

Don't Throw Out the Baby with the Bath Water

...from another forum

This diesel-electric subject thread has certainly raised some lively and controversial discussions. Many want to claim that converting diesel engine mechanical power into electricity, and then back into mechanical power by an electric propulsion motor, just isn't economically feasible. Therefore chuck the whole idea aside when contemplating DE propulsion systems for boats.

I say don't 'thrown out the baby with the bathwater'. This technology is still in its infancy, and there are many more developments to explore....and some may come with other emerging technologies.

One of these new technologies will likely be the ever-increasing capabilities to store electrical energy....new 'batteries', or other such devices and mediums. This capability to store large amounts of electric energy is a technology we sorely need for our future in all sorts of endeavors, and I'm sure there are presently 100's of experimenters around the world working on this major technology.

I agree Innamore. For a strictly powerboat application that spends a small amount of time idling about or maneuvering at docks, etc, and subsequently mostly at speed on the open water, D-E does NOT make sense.....too many energy conversions between main motor and the prop. Thus many powerboats are not applicable DE candidates.

But one thing those DE systems do is break the mechanical link between the engine and the prop. This opens up a whole lot of possibilities for locating the main engines apart from the drive-props, and even the variety of prop-drives that might be employed.

For vessels with big house loads, a DE systems approach makes sense, as well illustrated by the big cruise ships.

Special maneuvering desires can be accommodated with DE systems. A diesel electric system can be shifted from fwd to reverse and back much more quickly than a conventional transmission. In addition the electric motors develop full torque at any speed, even down to 0 rpm. In conventional propulsion installations, the idle speed of the engine will be between 700-1000 rpms. With a typical displacement hull reduction-gear ratio of approx 2.6 to 1, the slowest propeller speed is 270rpm or more. By contrast, a DE propeller shaft can be turned as slowly as 1-rpm!

Furthermore DE systems are much more adaptable to 'steerable prop-drives. Talk about maneuverability!!

If we move beyond ' strictly powerboats', then we might see a use for DE systems aboard wide variety of other type vessels. I'll just give two examples where I wish to use them:

1) Sportfishing Vessels.
Whether pleasure or commercial types, these vessels spend considerable time in the 'trolling mode', usually quite a bit below their cruising speed. This trolling speed might well be accommodated with a DE system.
Gamefishing Catamaran


2) MotorSailing Vessels.
In light airs, running one engine often is all that is needed to bring the apparent wind forward to make the sails work harder, and the combination provides much better results than either motoring or sailing alone…… sailing synergy/harmony, the motor taking over in the lulls and the rig taking over in the puffs

Motorsailing offshore is by far the most pleasant way to make passage, most of the time. With the engine barely above idle and a moderate amount of sail set, there is a synergy created by the apparent wind which generates more forward thrust than either one alone, with the bonus that you don't have to set large areas of canvas, which will have to come down in a hurry if the wind increases. The boat rides better, makes a better average speed and the batteries are always full. The beneft of using a much smaller sailplan can only be appreciated by someone who's been caught offguard in a squall with too much sail up. "Adventures" like that might be fun for weekend sailors and short coastal passagemakers, but on a long ocean passage they're something to avoid, even if it means a slower passage.
Motorsailing Catamaran

3) Etc

 

Nice post, Brian.
I agree with your vision of the DE thing. Highly adequate for some applications where big hotel loads, silent running and/or high torque and long times at low revs are a must, but not the boating propulsion Panacea.

 

There's a rather good EU funded report on Hybrid systems here.

The conclusions are rather interesting - in the majority of cases DE drive will burn more fuel than direct drive.
However, they also point out that a significant fraction of the running cost of an engine isn't in fuel but in running hours - and a large proportion of these are for battery charging or manoeuvring short distances at low speed in/out of harbour. If these could be consolidated into significantly fewer run hours, large savings could be made (and, in the process, reduce local pollution levels in harbours, etc.).

Hence, their conclusion was that a parallel hybrid with a direct drive diesel coupled to a sub-5kW motor/generator was the optimum, along with a larger battery bank (sufficient for 5-10 miles or so, and automatically charged whenever the engine was running and not at full power).

 

I wonder if a motor/generator plugged into the top of the saildrive would give you a gen set and a direct drive engine or both for extra power
Could make for a very nice package.
You gain a gen set on a boat where you dont have room for one.
To me thats where this technology should head

 

I think there are two completely different ideas being floated.

One, it must be a cheaper and universal fix for everything.

Two, DE can be a better installation for many uses, but not all.

Until we decide which question we are asking/answering, it is difficult to get to a solution.

I think the Engine/Electric has some great advantages not even mentioned. And a motor sailer is where many of the advantages come into play.

But, I do not think cost savings is one of the advantages.

 

I guess the only viable Hybrid drive for a small to mid size yacht (max 70') would be a parallel drive with a variabvle pitch prop fitted so the low power electric drive can be used to its full potential and also be used as windmilling generator...the electric motors could also supply that extra energy boost in an emergency..if props are chosen correctly...does that make sense?

 

Solar Electric Sailing_ James Lambden and Jean-Michel Cousteau

http://www.youtube.com/watch?v=BgH5EW7Zngo

What do you think?

 

I like the invisible propeller and all the idea of adding micro-power. Thanks.

 

For many boats, 24 hours per day at full speed is NOT the modus operandi. Commercial vessels go go go, time is money.
But PLEASURE vessels, except for long distance cruisers, are primarily daylight voyagers, holing up for the nights. And many boaters are underway full power, only a few hours at a time, example: high speed to the fishing grounds, drift, slow troll, or anchor to fish, then high speed home.

A smaller, cheaper, better fuel economy, lighter weight diesel makes sense for these folks. Combined with a battery bank and a substantial electric motor, allows higher speed to be obtained driving propeller directly from diesel AND electric motor simultaneously. If 3 hours of high speed was planned, then the batteries would need that capacity.
A number of hybrid cars use this double-up assist tactic, for climbing grades that neither the electric motor nor the gas engine, could manage alone while maintaining speed.
For slower speeds such as trolling, use either diesel or electric, depending on later demands on or availability of electricity at destination.
Trolling or still fishing, a quiet running diesel that doesn't frighten fish is good, equipped with engageable multiple alternators (solenoid clutches), to recharge the batteries for the days-end dash home.

My point being, FIRST determine most common use, and use factors, for propulsion system, and design accordingly. Any possible addons for versatility, redundancy, or rare extraordinary uses, need to be a much lower priority. Preaching to myself!

 

ski boat that needs to pull deep water starts doesn't need that power once the skier is skiing

 

Good example. Add an electric assist to IC engine for power to get skier up, then electric motor shuts off and battery recharging recommences on cruise speed.