How feasible is 100% renewable electric cruising right now?

[Stumble]

Originally Posted by StuM

It did quite a few revs - he used it for re-gen. But that was only feasible to keep because of his low power requirements and because he averaged well over 10 knots. Not practical for your average cruiser.

Fair enough, I should have said output RPM. But the point was he never used the electric motor for propulsion.

[Snyper]

Remember it is a sailboat engines and electric are luxuries

[roland stockham]

A point of note with any hybred drive but especially a retrofit one. Normal shaft/transmission is not designed for side loading. Adding a small generator to the prop shaft, say 10A used to be common. It reduced the life of shaft and gearbox bearings but not seriously. Adding even a 5hp drive motor is an order of magnitude greater. You will need to add extra bearings (needle rollers would be ideal). You also need to consider whether they need to be in sealed waterproof housings as they are deep in the bilges.

[roland stockham]

Interesting thread. I think it is missing some important points. On a sailboat we already use renewable energy as are primary motive power. That's what the sails are for! In terms of propulsion the engine is a safety backup for those occasions when sailing is not practical or possible and for maneuvering. The critical safety one is situations like powering off a lee shore. Getting 'embayed' or stuck not being able to get upwind past a headland is the classic example. This is why so many wrecks are to be found either side of major headlands. Modern lightweight diesels have made a major contribution to the safety of sailing boats and I, for one, would be reluctant to give that up. For maneuvering most harbours are no longer set up to accommodate sailing and it is frequently forbidden which makes some form of auxiliary pretty much essential.
I think this tread shows that electric propulsion is perfectly capable of acting as a maneuvering engine it is not, at present, an economic alternative for either passage making or safety at sea unless you have a diesel engine as well, i.e. diesel electric or hybrid drive. Currently these are very expensive options.
What is missing is the obvious element of improving the efficiency of the sails. The most effective way to reduce fossil fuel use is to use the sails more. How many boats have you seen motoring in conditions where sailing should be a perfectly viable option? So I would say that for most of us spending the bucks on better sails and sail controls may be the way to reduce our carbon footprint. Ask yourself whether you could change the rig to sail in 7/8kn instead of 10/12kn before turning to the engine? Would a few extra deg of pointing save significant time motor sailing to windward? Would practicing anchoring under sail reduce motor use? The answer for most of us would probably be yes.

[Peregrine1983]

Originally Posted by roland stockham

Interesting thread. I think it is missing some important points. On a sailboat we already use renewable energy as are primary motive power. That's what the sails are for! In terms of propulsion the engine is a safety backup for those occasions when sailing is not practical or possible and for maneuvering. The critical safety one is situations like powering off a lee shore. Getting 'embayed' or stuck not being able to get upwind past a headland is the classic example. This is why so many wrecks are to be found either side of major headlands. Modern lightweight diesels have made a major contribution to the safety of sailing boats and I, for one, would be reluctant to give that up. For maneuvering most harbours are no longer set up to accommodate sailing and it is frequently forbidden which makes some form of auxiliary pretty much essential.
I think this tread shows that electric propulsion is perfectly capable of acting as a maneuvering engine it is not, at present, an economic alternative for either passage making or safety at sea unless you have a diesel engine as well, i.e. diesel electric or hybrid drive. Currently these are very expensive options.
What is missing is the obvious element of improving the efficiency of the sails. The most effective way to reduce fossil fuel use is to use the sails more. How many boats have you seen motoring in conditions where sailing should be a perfectly viable option? So I would say that for most of us spending the bucks on better sails and sail controls may be the way to reduce our carbon footprint. Ask yourself whether you could change the rig to sail in 7/8kn instead of 10/12kn before turning to the engine? Would a few extra deg of pointing save significant time motor sailing to windward? Would practicing anchoring under sail reduce motor use? The answer for most of us would probably be yes.

Nice post. I agree. Surprised to see this thread is still going. To your point... we actually just placed an order just minutes ago on a new main and mizzen from Mack sails. They gave us a great deal on a high end cloth and have been great to work with so far.

[GrowleyMonster]

Originally Posted by roland stockham

A point of note with any hybred drive but especially a retrofit one. Normal shaft/transmission is not designed for side loading. Adding a small generator to the prop shaft, say 10A used to be common. It reduced the life of shaft and gearbox bearings but not seriously. Adding even a 5hp drive motor is an order of magnitude greater. You will need to add extra bearings (needle rollers would be ideal). You also need to consider whether they need to be in sealed waterproof housings as they are deep in the bilges.

Good of you to point that out, now that I read it. Yes of course any shaft pulley for a piggyback electric drive motor should have a pillow bearing between it and the ICE transmission unless the transmission is quite a bit over spec. But for those who seldom motor, not a deal killer if you keep the regen loading fairly low. If you keep charging down to 300 watts or so and don't require a lot of charging, IOW you don't suck a lotta juice from the bank, your tranny will probably not really notice it. If you are exploiting the full capabilities of the motor then add a pillow block bearing or two, yeah. Also some trannys don't tolerate a trailing spinning tail shaft very well so check with the mfgr. I remember being cussed by a Twin Disc mechanic for that once on a shrimp boat I was running back in the day.

[stevegerber]

To see a real world example of a renewable energy solar powered boat google the SoelCat 12. It's not a sailboat, it's a stand alone solar charged battery electric catamaran, but it seems like an interesting example of what is required in terms of solar panel wattage and surface area required, battery size and motor size to drive a boat. 8.6 kWp solar panels, 120 kWh battery storage, (2) 30kW electric motors. They claim it can go 6 hours at 8 knots on batteries alone. Pricing starts at $600K USD.

Of course, on a sailboat you don't have to motor all the time so a much smaller system could still be useful. But if you do want to have the option of motoring for many hours using only renewable energy you can see from this example that it does take a lot of panels which take up a lot of square footage.

[Adelie]

Originally Posted by stevegerber

To see a real world example of a renewable energy solar powered boat google the SoelCat 12. It's not a sailboat, it's a stand alone solar charged battery electric catamaran, but it seems like an interesting example of what is required in terms of solar panel wattage and surface area required, battery size and motor size to drive a boat. 8.6 kWp solar panels, 120 kWh battery storage, (2) 30kW electric motors. They claim it can go 6 hours at 8 knots on batteries alone. Pricing starts at $600K USD.

Of course, on a sailboat you don't have to motor all the time so a much smaller system could still be useful. But if you do want to have the option of motoring for many hours using only renewable energy you can see from this example that it does take a lot of panels which take up a lot of square footage.

A lot of it depends on how fast you feel you need to be moving. Moving at hull speed uses about 3 times the power to move at 75% of hull speed.

[john61ct]

Yes I'm skeptical of that 8 knots

[Adelie]

I think they could hit 8kt for 6hr but I’d like to know the conditions:
Wind, sea state and boat loading.

[stevegerber]

On their web page at this link they show pictures of calm shallow tropical waters near resorts so I guess that's their target market. They have an interesting graph if you scroll down the page which shows the ideal estimated range at different speeds with and without input from the solar panels. At 6 knots they estimate a 15 hour run time with fully charged batteries and 28 hours with full sun shining on the panels. Seems like it would start getting dark though so 28 hrs might be rather optimistic... Would be interesting to see some unbiased performance metrics in various weather conditions and currents.

[Jim Cate]

Seems like it would start getting dark though so 28 hrs might be rather optimistic...

Really, this seeming problem is easily resolved by simply teleporting the vessel to some location where the sun is still shining brightly.

Similar degree of functionality...

Jim

[StuM]

Originally Posted by stevegerber

On their web page at this link they show pictures of calm shallow tropical waters near resorts so I guess that's their target market. They have an interesting graph if you scroll down the page which shows the ideal estimated range at different speeds with and without input from the solar panels. At 6 knots they estimate a 15 hour run time with fully charged batteries and 28 hours with full sun shining on the panels. Seems like it would start getting dark though so 28 hrs might be rather optimistic... Would be interesting to see some unbiased performance metrics in various weather conditions and currents.

11.8m (39ft) LWL, 0.7m (2.3ft) draft, 6 ton (13200lb) displacement- i.o.w. a very lightweight catamaran. Covered with about 40 square metres of solar panels.

Hardly your typical cruising boat.

[StuM]

Originally Posted by john61ct

Yes I'm skeptical of that 8 knots

I'd accept that figure:

"The lightweight yet tough and durable fiberglass construction, the large solar roof and the super slender hulls

They state a Vmax of 13 kts (but it looks as though they only get about an hour of runtime at that speed).

[StuM]

Originally Posted by Adelie

A lot of it depends on how fast you feel you need to be moving. Moving at hull speed uses about 3 times the power to move at 75% of hull speed.

For a classically designed displacement monohull.

For a slender hulled catamaran, things become very different and the whole concept of hull speed is problematic.