Electric Propulsion on Catamarans

[Oliver L.]

I am tickled by the fact that this subject keeps coming back up. And let's face it -I love solar power. After finally sizing the wires correctly on my panels I can live on the hook indefinitely with sun and (alternatively) wind just use the generator for water making and the washing machine.

But for propulsion it simply is not there yet - and I doubt that it will get there in my lifetime - let alone my cruising time. One kg of Diesel "stores" 11,8 kWh of energy. My battery at 500 kg stores 12 kWh - but I am not allowed to use them all, or bad things will happen to the battery...

So assume you can use 6 kWh. That is as much as half a kilo of Diesel. The ratio is 1:1000! And no, Moore's law does not apply here...even if you improve it by a factor of 10 you still will be worlds apart.

Yes, I recognize the fact that my engines weigh something - definitely more than Torqueedos. But then they have a combined output of 106 horsepowers, and I vividly can remember times when I really needed them.

I guess this is the real difference: If you can pick and choose if and when you want to leave the dock for a daysail, electric propulsion might work 90+%of the times. If you go cruising and you can't be picky about the weather, the tides or any other factors, you need a lot more power and a lot more stored energy than you currently will get from an all electric system.

Oliver

[nimblemotors]

Yes you pretty much got it.

However, the boat with acres of laundry flapping off giant poles and miles of ropes or wires hanging about has its own problems. Can only go slow when the wind is just right.
Or maybe one enjoys the stinky, smoky, polluting vibrating diesel.

The thing is, the electric boat will only get better.
The hanging laundry boat pretty much is as good as it will get.

The devil you know, you know.

Originally Posted by cwjohm

This has been very interesting. I enjoyed the link. It appears that a solar boat is feasible if you:-

(a) Make the boat light
(b) Use the full area of the boat for solar panels
(c) Are prepared to tootle along at low speeds - 5knots or so
(d) Do not wish to make long passages on any given day

This is definitely a technology which will see the light of day sometime in the future, but unless you are a very slow cruiser and want your boat to look like a Chinese junk, this will not be applicable to cruising for a few years. Better motors, batteries and solar panels will see this as standard fitout in cruising boats some day, but I doubt I will be alive to see it unfortunately.

[mbianka]

We are talking sailboat here aren't we? From my experience electric propulsion is thoroughly compatible with long distance cruising provided you have the right sized sailboat. It even offers some advantage. It's often you read about boats calling for rescue because something happened to their engines either fuel or mechanical issues. Could not charge the batteries because the engine died. With EP you could charge with solar, wind turbine, on board generator and regen via the props if you are sailing fast enough. Plus when you get to your destination you don't have to pick one because of how close it is to a fuel dock. You could use the wind and solar to charge things up as you rest up. Are there limitations to EP sure but, it opens up other ways to sail too. For example in light winds just a little prop spin negates any prop drag and gives a nice 2 knot bump up in speed without turning on a noisy vibrating diesel for hours. It will keep you moving along until the wind picks up with the noise fatigue of a diesel engine making you sleepy. With my diesel 5 knots was about as much noise and vibration I could tolerate and also have reasonable fuel consumption too. The sweet spot for EP system is about 4 knots and with a little wind added and I'm a very happy sailor. I know I won't convince the doubters who love more speed so here you go:

THE BIANKA LOG BLOG: ELECTRIC BOATS ARE FUN

[domenica]

I think we should all be grateful for the early adopters. Everyone knows the infant technology is difficult, and if it were a business, unviable. But investment funds research, and research drives improvement. Sooner or later the sails will be the panels, and then diesel will be dead in the water.

Sent from my GT-I9210T using Cruisers Sailing Forum mobile app

[mbianka]

Originally Posted by domenica

I think we should all be grateful for the early adopters. Everyone knows the infant technology is difficult, and if it were a business, unviable. But investment funds research, and research drives improvement. Sooner or later the sails will be the panels, and then diesel will be dead in the water.

Sent from my GT-I9210T using Cruisers Sailing Forum mobile app

I think it is going to be sooner:
The official site of UK Sailmakers Lofts Worldwide

[Stumble]

Originally Posted by mbianka

We are talking sailboat here aren't we?

THE BIANKA LOG BLOG: ELECTRIC BOATS ARE FUN

No. We are talking about someone who wants to build a pure solar powered boat.

Solar + Sails + backup generator = doable, restrictive, but doable.
Solar alone = really silly at this point in the battery and PV life cycle for anything but a stunt.

[deckofficer]

Originally Posted by Stumble

The transatlantic21 is using twin 8kw motors and has a top speed of 7kn. The Torquedo 4 is a 4kw motor. So right off the bat you are down to 1/2 the available hp of the Transatlantic21.

The TS21 has an installed 10kw of solar panels taking up 65sq meters. I couldn't find exactly which ones, but that is a pretty large array.


Like I said, an electric only boat is perfectly possible if you accept short range hops between harbors. Or use hyper-specialized boats with tens of thousands of dollars in batteries and solar arrays.

A new suit of sails is $10K, on a powerboat 2000 nm is $10K in fuel. So why not $20K in solar and batteries? On this cat 8 kw of solar gave 6000 miles of cruising the first year.
Boat - SolarWave

[valhalla360]

Originally Posted by deckofficer

A new suit of sails is $10K, on a powerboat 2000 nm is $10K in fuel. So why not $20K in solar and batteries? On this cat 8 kw of solar gave 6000 miles of cruising the first year.
Boat - SolarWave

I think your numbers are exagerating things a bit.

Sails for a similar boat would likely be on the order of 30% less (depends how high tech you go of course).

Motoring that boat at 4kts is likely going to result in under $1/mile in fuel. Maybe as low as $0.50/mile.

Someday but still not there.

[Stumble]

I would easily buy that the sails for a 46' catamaran would run $10,000 for performance sails. What I wouldn't buy is that a 46' lightweight cat would have an average passage speed of 4kn.

And frankly like most electric boats Solarwave is massively underpowered. 2 10kw motors is not enough power to make any headway into waves and wind. It would work fine in calm weather, but it's missing about 40kw of installed power. Just as a quick comparison the Gunboat 40 (6500lbs max load) uses 20hp (15kw), which seams reasonable... Except that Solarwave is bigger, longer, and displaces 24,000lbs.

Why electric boats always seem to under power is beyond me. One upside to electric motors is they are just as efficient at low power draw as at higher draw. It probably has to do with wire size and battery capacity, bust still.

Oh and SolarWave has a 9kw solar array and a 10kw diesel generator.


As for powerboats... My old 54' 32 tonn cruising sailboat motored at 8kn burning 1 gallon/hr. Even at $5/gallon that works out to $0.63/mile. At 5kn it was likely more like $0.30/mile.

[deckofficer]

Originally Posted by Stumble

Why electric boats always seem to under power is beyond me. One upside to electric motors is they are just as efficient at low power draw as at higher draw. It probably has to do with wire size and battery capacity, bust still.

Oh and SolarWave has a 9kw solar array and a 10kw diesel generator.


As for powerboats... My old 54' 32 tonn cruising sailboat motored at 8kn burning 1 gallon/hr. Even at $5/gallon that works out to $0.63/mile. At 5kn it was likely more like $0.30/mile.

Sounds like you are defeating your own argument. You say electric boats are underpowered but then state your 54' 32 ton boat could run at 8 kt on 1 gallon per hour. 1 gallon per hour works out to about 13 hp.

SolarWave has 8 kw of solar and a 10.6 kw DC gen set that they needed for certification but do not use.

15 years ago when I was racing EVs against ICE, I believed we would have electric cars on the highways. Among these motorsport competitors I was alone in this belief. This is a bit like deja vu for me.

Greg, give it some thought, cruising at a leisurely pace is in fact a perfect candidate for solar-electric propulsion. It is already being done, I'm not trying to re-invent the wheel.

[Cotemar]

My 36 foot cat uses one 30hp = 22,000 watts to move it at 7.5 knot hulls speed.
If I were to go with a hybrid Diesel/Electric, I would want to use the same power.
30hp = 22,000 watts. It works well.

Why skimp on power. A 4 knot catamaran would suck exponentially. Most cruisers want a Cat for a bit of speed not for napping in transit.

Hybrid Diesel/Electric is the way to go today. An all-electric boat is just not ready yet for prime time.

[valhalla360]

Not defeating the idea at all. The problem with your 13hp calculation is that is talking about efficency under normal conditions (relatively low wind and waves). When the wind comes on the nose, he has the option to sacrafice efficency so that he can continue to make headway with the extra HP. The solar/electirc boat is far more likely to lose speed and possibly even lose ground.

We are stil a long way from a practical all use electric vehicle on the highway. The ones that are out there have major draw backs if you want full unemcumbered use. Now if we are talking a hybrid system, thats a different story but that suffers from overcomplication.

[mcarling]

Originally Posted by Stumble

And frankly like most electric boats Solarwave is massively underpowered. 2 10kw motors is not enough power to make any headway into waves and wind. It would work fine in calm weather, but it's missing about 40kw of installed power. Just as a quick comparison the Gunboat 40 (6500lbs max load) uses 20hp (15kw), which seams reasonable... Except that Solarwave is bigger, longer, and displaces 24,000lbs.

Why electric boats always seem to under power is beyond me. One upside to electric motors is they are just as efficient at low power draw as at higher draw. It probably has to do with wire size and battery capacity, bust still.

Not only are electric motors highly efficient at low speeds (which diesels are not) but electric motors produce very high torque at low speeds (which diesels do not). So it is not that solar boats are underpowered, but rather that diesels on boats are massively oversized to deal with low speed requirements.

If one wants to make a long passage on a solar-only boat, the limiting factor will be the output capacity of the solar array. LiFePO4 batteries make it easy enough to have ample battery capacity to allow for constant speed.

Personally, I would rather have a sailboat with an electric motor, solar panels, and no hydrocarbon fuels than a solar-only boat.

[deckofficer]

Originally Posted by valhalla360

Not defeating the idea at all. The problem with your 13hp calculation is that is talking about efficency under normal conditions (relatively low wind and waves). When the wind comes on the nose, he has the option to sacrafice efficency so that he can continue to make headway with the extra HP. The solar/electirc boat is far more likely to lose speed and possibly even lose ground.

We are stil a long way from a practical all use electric vehicle on the highway. The ones that are out there have major draw backs if you want full unemcumbered use. Now if we are talking a hybrid system, thats a different story but that suffers from overcomplication.

I'm quite aware of environmental factors determining the amount of energy to be expended. Currently I have friends cruising up to Alaska on their Nordhavn 43, and they have to plan passages depending on the ebb and flood tides of that area. The last ship I served on was a dynamically positioned 32,000 ton oil exploration rig that was diesel electric. It employed (6) 5000 hp electric thrusters powered by (7) 4.7 mw gen sets. During calm conditions and no currents, I would consume around 100 gallons per hour for hotel and drilling loads of about 1 mw, but if things piped up, that consumption could rise to 1000 gallons per hour just to hold position over the wellhead.

Short of crossing oceans, a solar boat that can maintain 5 kt of speed in calm conditions, complete 120 nm in a 24 hour period and can repeat after 3~4 days in an anchorage is IMHO ideal for the Great Loop, Coastal, Bahamas, and Caribbean cruising. Fossil fuels, like lead batteries, is dead in my opinion.

Haven't we mucked up our environment enough with fossil fuels? Do we still need to involve ourselves in the Middle East for access to energy? When will we learn that the Sun gives us all the energy we need?

[mcarling]

Originally Posted by deckofficer

Short of crossing oceans, a solar boat that can maintain 5 kt of speed in calm conditions, complete 120 nm in a 24 hour period and can repeat after 3~4 days in an anchorage is IMHO ideal for the Great Loop, Coastal, Bahamas, and Caribbean cruising. Fossil fuels, like lead batteries, is dead in my opinion.

Assuming this boat can do 150 nm in two days and one night and 200 nm in three days and two nights, it would be fine for cruising the Mediterranean also.