Electric propulsion thumbs up or down?

olsalt · Apr 27, 2011

The current issue of Good Old Boat has a nice article about an electric conversion. The author reminds us that its cleaner, not as smelly, safer and takes less space (more stowage!).

BobM · Apr 27, 2011

website

olsalt said:
The current issue of Good Old Boat has a nice article about an electric conversion. The author reminds us that its cleaner, not as smelly, safer and takes less space (more stowage!).

Woody...if you go to the Good Old Boat site they actually have most of the article up. Just in case you aren't a subscriber. The guys set up was cheap, at a couple of thousand, but it really seems underpowered for a boat that displacement. It was good for about 4 knots for three hours or so, if I recall correctly. I'd certainly consider doing it for something I was daysailing under 25 feet, but I don't think I'd do it for my 30 footer or if I intended to cruise. Of course I could put larger batteries in my bigger boat (his were relatively small).

Roger Long · Apr 27, 2011

If you are thinking about this, I suggest you search out all the recent threads on batteries. A set up like this is one in which you are going to either need a huge battery bank or be drawing your batteries way down. Battery management is going to be a challenge and battery life is apt to be very short. It may not be all that green by the time you factor in the lead and shipping the batteries over from China.

It's a very different situation with cars where regenerative breaking can put a lot of power back into the batteries. Hybrid cars would probably not exist if cars went uphill all the time which is essentially the propulsion profile of boats.

sailaway78 · Apr 27, 2011

For a smaller day sailer

For a smaller day sailer, the electric might be OK. But for a bigger boat, don't think this is a good idea. For any extended use, the battery bank would have to be huge, and expensive. The power output that works fine for getting into and away from a slip, probably isn't going to cut it if you get into a situation where wind/tide is against you. I keep thinking of some of the inlets on the gulf coast, and how I could possibly manage them with less power. When the tide is running usually am wanting more, even with the diesel.

JohnShannon · Apr 27, 2011

The consensus seems to be that electric is a wonderful technology so long as you don't need to go anywhere. Suffers the same problems as the electric car, to whit limited range and slow recharge.

As far as the solar array for recharge, hmm 6 hrs of light motor sailing what size boat? call it 7kw (about 10hp) so you use 7x6 42kwh if that is 80% DOD on the battery pack then you have a 53kwh battery, dividing by 12 to get to amp hours works out to about 4000Ahr battery. Kind of large. Anyway we go forward, charge on 4000 Ahr pack maybe 10% of rating or 400A, so that works out to about a 5kW solar array for a 10hr charge, (not including night)

On the other hand I know somebody that has electric propulsion on his boat, powers out of the harbor about 1/2mi sails, powers back in, plugs in recharges, wonderful quiet solution for that use.

Bill Roosa · Apr 27, 2011

To answer the questions:
If you had a very large 400 watt solar panel it would be putting out 400/13.6=29.4 amps at peak sun. The bad thing is you get peak sun only about half an hour a day. Using the hourly profile (each hour has a different % of the peak sun output) starting with 0600 and going to 1800 hours (.1, .2, .45, .6, .75, .85, 1.0, .85, .75, .6, .45, .2, .1) you get 203 amp hours per sunny day. This is about the most you can ever expect without actively aiming the solar panel at the sun all day long. BTW you will surly almost never get that amount due to the panels being mounted on a boat and there will in almost all cases be shadows cast on the panels.
203 AH is about 1/2 of a 400 AH bank so you could recharge (not really but suspend disbelief for a second) a 400 AH bank discharged to 50% every day. That is a very healthy solar capability!
203 AH driving a motor would last as follows:
@ 10 amps 20.3 hours ---> 120 watt motor (yawn, most electric trolling motors are bigger)
@ 20 amps 10.2 hours ---> 240 watt motor = ~ 1/4 HP
@ 40 amps 5.1 hours --> 480 watt motor = ~ 1/2 HP
@ 80 amps 2.6 hours --> 960 watt motor = ~ 1 HP

You can see where the numbers are headed. The biggest solar panel I've ever seen was around 400 watts worth and they had them EVERYWHERE. They ran out of space for more panels. This is not much of a capability when you consider using it for powering a motor. And we have not even addressed battery acceptance which will only make the numbers worse.

Course you could use a small genset to charge the batts and have a slightly more efficient system but then all you are really doing is replacing the transmission with wires between the motor and the prop.

The real problem with electric propulsion is not that it is not doable it is the storage of enough power to allow you to return safely to port.

A sail drive has about the same drag as a shaft and prop.

Bill Roosa · Apr 27, 2011

Generating power from the prop spinning while the sails drive the boat is an option. However, there are some very significant losses using a fixed prop in the "wrong direction" With that said if you mostly sailed and only used the motor for minor docking maneuvers this could actually kill a couple of birds with one stone. The prop driven motor/generator could supply all your electrical power while under sail (cost is boat speed is reduced) and could charge the batts also. This would get you out of buying a wind generator or solar panels or running the engine to charge the batts. However when you are becalmed or at anchor you have NO charging capability....... so you still need some way to charge the batts as needed……. And you will not have a motor till you do!

Now if you had a “Mr. Fusion.” Why you could just put your table scraps in it and you could tear a…s around the Bay all day long. Might even become a “power boater” with that kind of “battery”
1.21 Gega watts is 1.5 billion HP BTW

kenn · Apr 27, 2011

caguy said:
I agree that it may not be a good idea for larger boats but what about my Cat 27?

Electric or hybrid propulsion seems to be akin to religion around here, with believers, doubters and heretics.

To declare my own bias up front, I happen to be a believer in hybrid (electric plus IC engine) powering. I don't necessarily think that the ideal solution is commercially available, but I do believe that all the right technical pieces are now available, and it's now down to trying and refining different combinations to find the most efficient and practical system, and have it produced in sufficient quantity to get the price down.

The hybrids you linked to, with an electric motor/generator coupled to the propshaft of a conventionally-powered boat, seem to me like the first iteration that could gain widespread adoption. It's not optimally efficient from an energy point of view, but it has the potential to bring the advantages of electric propulsion (strong torque, quick direction change - great for docking, reduced need for short-running a cold engine) while still retaining the reliability and efficiency of direct IC engine drive for long running. It requires only a modest increase in battery bank size, dependent on how many minutes of sustained electric running you want to have. For the casual sailor who can be on shorepower every night, and just has a short run to get clear of the marina, they might never need to start the combustion engine, except for sustained running (eg a weekend cruise).

Sadly, I haven't yet seen an off-the-shelf hybrid offering for saildrives, but I haven't looked much into that.

Disclaimer - I have some electrical engineering in my background and I'm a hopeless optimist. Also, our boat isn't a candidate for hybrid, unless I find a cheap electrical outboard or build my own.

tommays · Apr 27, 2011

Hunter has done it with the 27e and i dont know that is has or has not been a big seller

Alerion did a 33e and i do not believe it has gone beyond one hull as its cost was a good bit more than the standard diesel

FourPoints · Apr 27, 2011

Hunter has a 27' electric drive they were showing off at the Annapolis boat show last year. It has a massive solar array (about 8' x 8') over the bimini , and a wind generator.

I don't recall specifics, and I am not finding them on their website, but I think it was rated with a 10hp electric motor and the battery bank (with no sun or wind power generation to extend the charge) it would power the boat for about 6 hours at cruising speed, or 2 hours at full throttle. I believe they said the solar and wind combined should fully recharge the batteries from completely dead in about 1.5-2 days if I recall correctly.

btw, even the stove in the galley was electric on the demo

dscribner · Apr 27, 2011

I have always dreamed of building an electric car, so naturally projected that into my sailing. So piture this. You're 16 km from home, about 3 hours of motoring due to the dead calm that just settled. But, you've been on the water for a couple of days, motoring in and out of those cute little coves that the Admiral find so romantic (I'm dreaming). Of the three hours of possible motoring on your battery bank, you've already used 2 hours. Would it be easier to:

A) Wave somebody down and request to raft up for a day or so while you recharge off their diesel?
B) Call SeaTow and have them meet you 1/3 of the way home
C) Pour another gallon in the ourboard.

When I can charge a battery the size of a coffee cup and motor for 12 hours, I'm on it. Or when I can screw another can of hydrogen onto the fuel cell, I'm all over that. Otherwise . . . . Besides, electric may be "cleaner" on the water, but there are still smog-belching, coal-burning power plants pulking carbon emissions into the air to fill refill the lead batteries your floating around. (unless they're glass mat or something).

I'm all for the Mr. Fusion thing Doc! Great Scott! What and idea. I mean it's really heavy if you think about it!

redhead78 · Apr 27, 2011

Hey all, the concept is just that,a nice thing, but in a boat not really practical. As it was already stated, we are going uphill all the time in a boat, there is just too much drag in water, even plain still water. We in boats have power issues with things like lighting, cooking, everyday issues we are still trying to make better. Its one of the 3 main items a cruiser or sailor needs , water, power, food. I drive practical cars civics, accords, I have been recycling since the mid 70,s, I really am getting tired of the political machines using the word green, green,green, bull, look at ethanol/corn, I will not apoligize for using a little diesel, which by the way they are screwing me for anyway. just my 3 cents Red

Johnb · Apr 27, 2011

Yep - a pound of diesel burned at 30% efficiency represents as much energy as you can store in about 120 pounds of batteries.

If you really want to save, drive a more efficient vehicle to the marina.

JVB · Apr 27, 2011

My Catalina 250 WK got caught in a squall in the Charleston, SC harbor last Thursday afternoon. Being way overpowered my crewman and I should have dropped the mainsail, partially furled the genoa and started the outboard engine. If that wasn't enough to at least prevent losing ground downwind then we should have completely furled the genoa, dropped the anchor, and gone in the cabin to warm up. What we did was drop both sails and rely on the outboard. The 9.8 hp outboard wasn't enough to prevent losing ground due to hobby horsing and the resulting propeller cavitation. I could not "tack" across the wind either. We did have enough control to duck into a somewhat protected lee shore marina after "jibing" to partially downwind. A weaker motor would have allowed us to be blown into the retired aircraft carrier Yorktown. It is permanently aground there.

If you want the equivalent of a 10 hp gas engine look at (expensive) 24 volt trolling motors or electric outboards with around 200 pounds thrust and several golf cart batteries. Golf cart batteries have solid plates. They are made for deep discharging. "Marine" batteries with their coarse grained plates are not tolerant of such treatment. See http://batteryuniversity.com/

BobM · Apr 27, 2011

My friends rented a hybrid (small diesel genset and twin electric motors with batteries) Catamaran down in the BVI. They hated it. In order to keep the batteries charged they said the gen set was running all the time, which was annoying and they claimed that they actually burned more diesel than they had the year before when they rented a conventional boat.

Roger Long · Apr 27, 2011

BobM said:
they claimed that they actually burned more diesel than they had the year before when they rented a conventional boat.

The physics would support that, in fact make it inevitable. There are losses anytime you convert from one form of energy to another and significant losses charging batteries. The engine driving a prop is going to be way more efficient than driving a generator, charging batteries, and then running an electric motor.

Absent huge solar panels or frequent plug ins, a "hybrid" has to burn a lot more diesel for the distance covered than a conventional drive.

Even diesel electric where the generator directly drives the electric motor has a significant fuel consumption penalty.