Circumnavigating using Electric Propulsion

[DeepFrz]

I was wondering about your figure of 8 gals. per mile, so I did some googling.

It appears that the QE2 runs about 1 gal per 40 - 50 ft. So, 5,280/50 = 106.6 gals per statute mile or 5,280/40 = 132 gals per statute mile. These are approximate of course.

snopes.com: QE2 Fuel Efficiency

He is asking about a boat, not a plane. A commercial plane uses 1 gallon of jet fuel a second, even cruise ships don't do that (8 gallons per nm). And he isn't looking to go hundreds of miles per hour, 100% of the time.

An older ship like Zaandam burns more fuel - even though she is small. 150 tons a day would put her at 1050 tons per 7 day cruise.
Her younger and slightly larger sisters burn a bit less; around 900 -1000 tons per 7 days.

The much larger ships - even though new - tend to burn a bit more.
The large RCCL Ships and QM2 are in the 1300 ton range, depending on itinerary and weather.

[DumnMad]

Good maths Stumble. Solar only is viable for all your electronics & fridge etc. Must rely on wind for traveling. In a v small boat could use it for propulsion to move out of the doldrums but only for a few hours per day and you'd have to be careful not to do in your batteries.

[simonpickard]

Thanks all for the replies. Based on the numbers it seems clear to me that this tech isn't really there yet for long term cursing.

Regards,
Simon

[jongleur]

...but...but:

PlanetSolar

They did it already.

[Stumble]

Originally Posted by jongleur

...but...but:

PlanetSolar

They did it already.

Lol they did. With enough money, time, and will power it is possible. But it certainly isn't practicle yet, possibly it won't ever be. Remember PS went around the world in something like 2 years, with an installed power plant of about 25hp. Which wouldn't be bad for a 35 foot boat, but this behemoth is 30 meter, and 15 wide... And the entire top is covered in solar panels.

[simonpickard]

I guess the compromise would be to have a generator on board with a few jerry cans.
For those times when you really needed to motor and the battery bank was dead you could charge it that way.

I guess then my question is... How much do you cruisers use your engines? If it's just getting onto and off moorings, and the old hour here and there, maybe Electric would work out just fine- and then have a backup generator with a few fuel cans lined up if you're doing a crossing, etc. What do you think to that?

[NYCSavage]

Wait till I find the money to patent my idea Will change the face of boating forever!!!

[skipmac]

Originally Posted by simonpickard

I guess then my question is... How much do you cruisers use your engines? If it's just getting onto and off moorings, and the old hour here and there, maybe Electric would work out just fine- and then have a backup generator with a few fuel cans lined up if you're doing a crossing, etc. What do you think to that?

Like many boat questions the answer depends.

Went I brought my boat down the coast from CT to FL I motored about 80% of the total trip. The sections in the ICW I motored about 95% of the time.

Long ocean passages I have made in the past I sailed 90% of the total trip but on occasion might motor or motor sail for a day or two during various parts of the trip. Times you motor on a long passage:

- dead upwind when you don't want to tack for days I would motorsail to cut my passage time in half.

- dead calms when I wanted to power through the calm zone or get to a port in anticipation of bad weather coming in behind the calm.

- had a schedule to meet and needed to make better time that sailing permitted.

On the other hand there are boats that sailed around the world with no engine at all.

So like I said, the answer depends on you, your boat, your preferences and life style. I would say for the great majority of sailors that cruise long distances their preference is for a range under power of at least a couple hundred miles if not more. That might be an interesting question for a poll.

[Stumble]

I have read estimates that in the Carribean cruisers motor or motor sail about half the time on passages. In my experience this would be about right.

The problem with diesel electric systems (electric drive plus a generator) is that to have a generator large enough to provide any real power to the drive leg you have to massively oversize the generator for the house loads. So the best answer here is to have two generators, a small one for the house loads, and a large one for propulsion.

Using our mythical 40' sailboat this would generally work out to be something like a 30kw (40hp) generator for propulsion, and a 5kw for onboard house loads. Is pretty easy to see, that the 5kw is just too small to add meaningfully to propulsion. And the 30kw shouldn't be run as lightly loaded as having it on for just house loads would require.

[SunDevil]

It all depends on what your household loads are. I don't need AC if I'm by the water and can wear a swimsuit, heat would be the biggest draw sometimes of the year, but there are ways to reduce that. My laptop, lights, and other electronics wouldn't be very much. You don't need a 5kW generator, you need a 230W solar panel...

This website is saying that the hp numbers of electric motors is a little higher. Products | Electric Boat Motors
But it is a trade off. And I think the boats need to be designed around the electric motor instead of in place of the diesel one. You might not be able to cruise in the same way that a normal sailboat could, but not everyone would need to go as fast from Point A to Point B as possible. I have a 4-5 year plan for a trip around the world. I would be in no rush to leave someplace except for bad weather.

transatlantic21: The world's first crossing of the Atlantic on a solar boat
Here is another boat that is more in the 'normal' length that has crossed the Atlantic. And the Atlantic crossing is the one where you will be the farthest out from the coast. They did it from December - February for storm reasons probably, but the solar power potential is lower then too. They could have easily added some wind turbines or a kite sail to the boat to help move things along.

Technology has advanced quite a bit from 2007 as well. The Lithium batteries of 2012 weight 1/4 as much and last 10 times longer. In the next 5 years, there are some big ideas that could change things even more. Solar panels are becoming better too, but adding wind turbines and a sail rig that can be used during the night or on stormy days would be a good idea.

[mcarling]

I'm new here, but I do know something about electric propulsion. Several points if I may:

1. The efficiency of electric motors/generators has improved dramatically in the 21st century due to developments with permanent magnets and other advances with materials. Using the latest (expensive) motors and generators, it is more efficient to go diesel -> electric -> propeller than to go diesel -> gearbox -> propeller. The diesel-electric arrangement is more reliable and allows free placement of the genset.

2. In a conventional arrangement, one has a diesel for propulsion, a second diesel for the genset for household power, and a third diesel for the dinghy. In a diesel-electric arrangement, one needs only a single diesel genset (assuming electric propulsion for the dinghy).

3. In a solar/diesel/electric arrangement with a single genset, it's important to size the genset and battery bank such that neither will be damaged during charging. An intelligent charger can protect the batteries, but the genset also needs to be able to operate at reduced load -- down to the load of the safe charging current.

4. Obviously, a cat or tri will support a lot more solar panels than a similarly sized monohull.

5. If the solar panels and (lithium phosphate) battery bank are sized sensibly, it's probably realistic that as long as one can sail i.e. doesn't need to motor, the household load can be sustained from solar power. I would not expect to be able to do any significant motoring without using the genset. Increasing the size of the battery bank won't help much here because the solar panels wouldn't be able to recharge it at a reasonable rate. Charging in port could help somewhat.

6. If the solar panels can generate more kilowatt hours per day than the household usage, then the motoring range would be higher for a given hydrocarbon fuel capacity. On the other hand, if the household load includes frequent use of an electric stovetop, hairdryer, clothes dryer, etc. in excess of the kilowatt hours generated by the solar panels, then the motoring range would still be more than with a conventional arrangement because the diesel genset would anyway have been consuming a lot of fuel. The addition of solar panels will reduce the fuel consumption.

7. I would want to carry a towable generator as an emergency backup for charging the batteries under sail if the genset were to fail. Don't attempt to use it at the same time as trawling for fish.

In summary, I think the question of whether or not one can circumnavigate without using primordial hydrocarbon fuels probably reduces to the question of whether or not one can circumnavigate without motoring (except briefly to get in and out of port). Obviously, circumnavigation without motoring has been possible since Magellan and Drake did it, but is that the sort of sailing one is looking for?

If the experience one wants would normally be described as cruising, then I would recommend an electric motor and a genset in combination with the solar and battery solution. However, if one wants an adventure, then a sailboat with only wind and solar power would definitely make circumnavigation an adventure.

The OP asked specifically about 400-600W of solar panels and a 40' boat. On average, 400-600W of solar panels will provide between 1 and 2 kilowatt hours per day, depending on season, latitude, and weather. Some days will be less than 100 watt hours and some days might be over 4 kilowatt hours. I suggest figuring out one's daily household load and size the battery bank to provide that for at least 72 hours without sunshine.

[skipmac]

Originally Posted by mcarling

I'm new here, but I do know something about electric propulsion. Several points if I may:

1. The efficiency of electric motors/generators has improved dramatically in the 21st century due to developments with permanent magnets and other advances with materials. Using the latest (expensive) motors and generators, it is more efficient to go diesel -> electric -> propeller than to go diesel -> gearbox -> propeller. The diesel-electric arrangement is more reliable and allows free placement of the genset.

To be precise it would be diesel -> electric -> electric -> propeller if you count first generating the electricity and then converting the electricity back into mechanical energy. From research I've read diesel electric can be more efficient if running within a fairly narrow, optimal range but in general usage the traditional diesel / gearbox is more efficient.

Regarding reliability, I think one could make the argument that small boat transmissions are pretty reliable in general and the diesel electric has one more step in getting power from the engine to the prop so stating categorically that it is more reliable may be debatable.

Flexibility in the mounting location and orientation of the diesel is inarguable.


2. In a conventional arrangement, one has a diesel for propulsion, a second diesel for the genset for household power, and a third diesel for the dinghy. In a diesel-electric arrangement, one needs only a single diesel genset (assuming electric propulsion for the dinghy).

Except many boats (maybe most?) do not have a diesel generator in addition to the propulsion engine and I don't know any cruisers with a diesel powered dinghy. Are you talking about cruising sailboats or yachts?

3. In a solar/diesel/electric arrangement with a single genset, it's important to size the genset and battery bank such that neither will be damaged during charging. An intelligent charger can protect the batteries, but the genset also needs to be able to operate at reduced load -- down to the load of the safe charging current.

4. Obviously, a cat or tri will support a lot more solar panels than a similarly sized monohull.

5. If the solar panels and (lithium phosphate) battery bank are sized sensibly, it's probably realistic that as long as one can sail i.e. doesn't need to motor, the household load can be sustained from solar power. I would not expect to be able to do any significant motoring without using the genset. Increasing the size of the battery bank won't help much here because the solar panels wouldn't be able to recharge it at a reasonable rate. Charging in port could help somewhat.

6. If the solar panels can generate more kilowatt hours per day than the household usage, then the motoring range would be higher for a given hydrocarbon fuel capacity. On the other hand, if the household load includes frequent use of an electric stovetop, hairdryer, clothes dryer, etc. in excess of the kilowatt hours generated by the solar panels, then the motoring range would still be more than with a conventional arrangement because the diesel genset would anyway have been consuming a lot of fuel. The addition of solar panels will reduce the fuel consumption.

7. I would want to carry a towable generator as an emergency backup for charging the batteries under sail if the genset were to fail. Don't attempt to use it at the same time as trawling for fish.

Or a smaller, portable generator, or the solar panels mentioned or a wind charger.



In summary, I think the question of whether or not one can circumnavigate without using primordial hydrocarbon fuels probably reduces to the question of whether or not one can circumnavigate without motoring (except briefly to get in and out of port). Obviously, circumnavigation without motoring has been possible since Magellan and Drake did it, but is that the sort of sailing one is looking for?

I think there are systems available that will allow circumnavigating with electric power and have a decent cruising range, but the off the shelf systems I've seen to date are 2-3 X more expensive than a complete engine/transmission and limited to about 30 HP.

If the experience one wants would normally be described as cruising, then I would recommend an electric motor and a genset in combination with the solar and battery solution. However, if one wants an adventure, then a sailboat with only wind and solar power would definitely make circumnavigation an adventure.

The OP asked specifically about 400-600W of solar panels and a 40' boat. On average, 400-600W of solar panels will provide between 1 and 2 kilowatt hours per day, depending on season, latitude, and weather. Some days will be less than 100 watt hours and some days might be over 4 kilowatt hours. I suggest figuring out one's daily household load and size the battery bank to provide that for at least 72 hours without sunshine.

Basically, I've come to most of the same conclusions. The idea of diesel / electric is very attractive but doesn't seem ready for prime time.

[mcarling]

Originally Posted by skipmac

I don't know any cruisers with a diesel powered dinghy. Are you talking about cruising sailboats or yachts?

I was abusing the word "diesel" for which I apologize. I meant generally "primordial hydrocarbon fuel" which could be either diesel or petrol/gasoline (or even propane, CNG, etc.). In the present context, they are all equivalent to diesel or worse due to the need for carrying yet another type of (even more dangerous) fuel. The spirit of the discussion was getting away from the use of primordial hydrocarbon fuels toward reliance on wind and solar only. I'll try to be more precise in the future.

Originally Posted by skipmac

Or a smaller, portable generator, or the solar panels mentioned or a wind charger.

I meant as a backup to the solar panels for days of low sunlight. I would not suffer a wind charger on a sailboat. For me, the noise and the aesthetic of the wind charger would take some of the fun out of sailing. I would rather use a towed generator to keep the batteries charged underway if and when the solar panels might be insufficient. The advantage of the wind generator would be that it can generate electricity when the boat is in port or at anchor and there is a good wind. Your windage may vary.

Originally Posted by skipmac

Basically, I've come to most of the same conclusions.

Thank you for the confirmation.

Originally Posted by skipmac

The idea of diesel / electric is very attractive but doesn't seem ready for prime time.

If I were specifying a new boat for myself based on today's available technology, I would get as much solar capacity as reasonably possible, lithium phosphate batteries (to about double the capacity and about 60% of the weight of lead acid batteries), LED lighting, and try to rely on solar only for household electricity. I would not yet specify diesel/electric propulsion, but that might change in a few years because the cost of permanent magnet machines (motors and generators, plus the power electronics that govern them) are dropping fairly fast. Because I would anyway need to tank diesel for motoring, I would have a very small diesel genset installed, but my goal would be to never use it (except as necessary to keep it in good working order). With the genset installed as a backup, I would not bother with a towed generator. Depending on how electricity generated from the solar panels compared with household load in practice, I might unbelt the alternator on the motor in order to reduce fuel consumption a bit.

[SunDevil]

Boat - SolarWave

transatlantic21: The world's first crossing of the Atlantic on a solar boat

I still think that since other people have done it, it is possible. I would make a few improvements myself to the amount of batteries personally. For $12,000 and 800 lbs, you could get 1725 usable amps out of LiFePO4 batteries @12 V, or 20kWh. Add in a wind turbine design to help when the wind is blowing at night, and a large enough array like the above boats, and pick your weather windows based on it not raining...I would like to try it and see.

The other option that few people talk about is if your batteries are drained, couldn't you just pull into a marina, plug in, and charge them back up?

[skipmac]

Originally Posted by mcarling

I was abusing the word "diesel" for which I apologize. I meant generally "primordial hydrocarbon fuel" which could be either diesel or petrol/gasoline (or even propane, CNG, etc.). In the present context, they are all equivalent to diesel or worse due to the need for carrying yet another type of (even more dangerous) fuel. The spirit of the discussion was getting away from the use of primordial hydrocarbon fuels toward reliance on wind and solar only. I'll try to be more precise in the future.

Sorry to make the point, just the reference to a diesel dinghy confused me, something easily done.



I meant as a backup to the solar panels for days of low sunlight. I would not suffer a wind charger on a sailboat. For me, the noise and the aesthetic of the wind charger would take some of the fun out of sailing. I would rather use a towed generator to keep the batteries charged underway if and when the solar panels might be insufficient. The advantage of the wind generator would be that it can generate electricity when the boat is in port or at anchor and there is a good wind. Your windage may vary.

I'm not in love with the idea of a pole and the big swinging blades of a wind charger perched like a giant bug on my stern but the idea has grown on me and will give one a try. In the long run I think solar will be by far the best option, just might have to add more panels to get the amps in less sunny areas. Never owned one but almost all the users of towed generators have reported lots of problems. The new style water gen used by some of the racers where the prop is on a rigid boom lowered into the water have gotten good reviews but very expensive.



Thank you for the confirmation.

Any time.



If I were specifying a new boat for myself based on today's available technology, I would get as much solar capacity as reasonably possible, lithium phosphate batteries (to about double the capacity and about 60% of the weight of lead acid batteries), LED lighting, and try to rely on solar only for household electricity. I would not yet specify diesel/electric propulsion, but that might change in a few years because the cost of permanent magnet machines (motors and generators, plus the power electronics that govern them) are dropping fairly fast. Because I would anyway need to tank diesel for motoring, I would have a very small diesel genset installed, but my goal would be to never use it (except as necessary to keep it in good working order). With the genset installed as a backup, I would not bother with a towed generator. Depending on how electricity generated from the solar panels compared with household load in practice, I might unbelt the alternator on the motor in order to reduce fuel consumption a bit.

I think diesel electric systems are viable now with a couple of limitations that mostly boil down to cost.

1. Power. The largest off the shelf system I have seen if I recall was about 25 HP. Fine for maybe low thirty foot boat but I think would be severely under powered for forty and up.

2. Cost. Checking the price from several companies making electric drive systems for the yacht market prices are generally double the cost of a similar sized diesel engine even before adding a generator. Start adding a large bank of fancy batteries and the cost can be 4-5 X more than straight diesel.

3. Range. If your cruising plans are mostly open water and power is used strictly for in/out of the harbor or marina then a minimum sized generator and battery bank will work. If your plans include ICW, canals and rivers of Europe or you want enough range to power across the Horse Latitudes or the ICZ then a larger generator is required. Assuming a mid forties boat with +/- 60 HP diesel that translates into about 45 KW electric. Of course long range motoring you would not be running the diesel at max HP so assume half or less for a cruising speed load. That's still 20 KW or so, a big and expensive generator.

4. Size. If you add the generator and a significant bank of batteries your overall system is going to be larger and heavier than an equivalent diesel powered boat.