Potential electric propulsion systems?

[pamakela]

Hi,

for a motorsailer, what would be the best propulsion method that is electrically powered? I was considering water jet(s) because of their handling capabilities. But then I researched on their efficiency and other issues involving weight and wasn't so sure anymore.. Was also thinking there might be benefits running a water jet with a electric engine which could run in reverse by itself.




Ps. this is for concept exploration, not a real boat building project

[mitiempo]

The real issues for electric propulsion are battery capacity and charging. Range will be short without an auxiliary engine/generator for charging or a hybrid of some sort.

[pamakela]

Originally Posted by mitiempo

The real issues for electric propulsion are battery capacity and charging. Range will be short without an auxiliary engine/generator for charging or a hybrid of some sort.

According to some research papers, battery packs (and electric motors) should become much more common in the future in marine use. Remember, this is about a future concept and it's use in a electric powered sailing boat. Aux power is always a necessary consideration though..

[mitiempo]

For someone who doesn't travel far and returns to the dock at the end of the day and plugs in a shore charger it works well usually. But for longer distance cruising with the desire to anchor out instead of tying to a dock it is not as workable. 10 gallons of diesel is hard to replace with batteries.

In this area, the B.C. Coast, due to light summer winds motoring is common - often the only way to get anywhere, especially with our sometimes strong currents and narrow passes. A 2 week vacation and anchoring out would be unworkable with pure electric propulsion, you would have to go from dock to dock. In a hybrid it could work.

A motorsailer should be able to both sail and power fairly long distances.

[TropicCat]

Originally Posted by pamakela

According to some research papers, battery packs (and electric motors) should become much more common in the future in marine use. Remember, this is about a future concept and it's use in a electric powered sailing boat. Aux power is always a necessary consideration though..

I don't think you understood mitiempo. Electric motors work just great when couple to a marine propeller. No question about it.

Now, here's the ....but...... to have any kind of meaningful propulsion in a cruising boat, this electric motor would need several kilowatts to move ( I believe it's 767 watts are = to 1 HP). Even the large catamarans with over 1000 amp hour battery packs can only 'motor' for 20 minutes. In other words the batteries haven't been invented to make this meaningful. Any extrapolation of this concept is science fiction.

As mitiempo pointed out, the alternative is a genset powering the electrics. This is how it's done these days. As an aside, if a visit to the tropics is planned, you should understand the chances of a boat lightning strike are great and would render any electric system inoperable.

In short, electric propulsion for pleasure boats holds great promise, but isn't ready for prime time.

[mitiempo]

It would work with a jet drive, hell it would work with a paddlewheel as well. But both are even less efficient than a propeller.

[beej67]

Originally Posted by mitiempo

It would work with a jet drive, hell it would work with a paddlewheel as well. But both are even less efficient than a propeller.

This.

People use propellers because they're efficient.

If you're looking for a magic, completely sustainable means of boat propulsion, it's already been invented. They're called "sails."

[ewdysar]

Originally Posted by TropicCat

I don't think you understood mitiempo. Electric motors work just great when couple to a marine propeller. No question about it.

Now, here's the ....but...... to have any kind of meaningful propulsion in a cruising boat, this electric motor would need several kilowatts to move ( I believe it's 767 watts are = to 1 HP). Even the large catamarans with over 1000 amp hour battery packs can only 'motor' for 20 minutes. In other words the batteries haven't been invented to make this meaningful. Any extrapolation of this concept is science fiction.

As mitiempo pointed out, the alternative is a genset powering the electrics. This is how it's done these days. As an aside, if a visit to the tropics is planned, you should understand the chances of a boat lightning strike are great and would render any electric system inoperable.

In short, electric propulsion for pleasure boats holds great promise, but isn't ready for prime time.

I would have to disagree with some of this. I have a Cheoy Lee Bermuda 30 with a 5.5kW electric drive installed with 8kWh (160Ah x 48V) of Lithium batteries. My boat will go 3kts while consuming only 500W of power and hits 4.2kts at about a 1200W load. At 4.2kts, my usable range (to 80% depth of discharge) is over 20nm (5 hours). Of course, raising the sails will extend the range...

This "7.3hp" electric drive pushes the boat at 6kts, compared to 5.5kts with the Yanmar SVE12 at full throttle. While diesel powered, I used less than 6 gallons of fuel per year doing local coastal and offshore trips. So my "2/3 gallon" electric fuel tank meets my particular needs. As a backup to my auxiliary (tertiary backup?) I carry a portable Yamaha 2000 generator that can fully charge the batteries in less than 5 hours while on the hook, or drive the boat at almost 4.5kts if needed. However I've never needed to fire it up under way, though I have done a test run as a POC.

The bottom line is that electric drives are an excellent alternative for some sailors, it all depends on how you use your boat.

Fair winds,
Eric

[JimsCAL]

Waterjets are only efficient at high speeds. Nothing is more efficient at driving a sailboat than a well designed and properly selected propeller. Other than the sails of course.

[TropicCat]

Originally Posted by ewdysar

I would have to disagree with some of this. I have a Cheoy Lee Bermuda 30 with a 5.5kW electric drive installed with 8kWh (160Ah x 48V) of Lithium batteries.....

Eric, I have to admit that I'd never heard of lithium batteries used on a boat , so I had to look em up this afternoon. My hat's off to you as you've obviously made a substantial financial commitment to your electric drive.

I will gracefully accept this correction, but would just like to point out that the average guy won't spend more on an

• electric drive


• motor controller


• genset


• those gorgeous batteries


• optimized propeller

than his boat is worth, just to make electric propulsion work at reduced performance levels.

Would you say the path you took is viable?