Electric motor sailer of the future

[Paul Scott]

After experiencing the joy of electric propulsion after a refit of our uldb sailboat 40er, with a Torqeedo 48-5000 and a cruise 10.0 it has become really apparent that to use light air and tide to effectively boost range, some things have become very apparent :

-upwind ability like really really high pointing ability

-lower to medium speed hull efficiency

-a really clean rig aerodynamically, in zero wind when motoring only

which begs some questions, initially at least:

furling jibs too much drag? hassle?

freestanding or stayed rigs?

rotating wing masts? freestanding or stayed, say like an a class cat rig?

aero resistance of hull? and how to keep this low with solar panels?

prismatic coefficient?

turbine style prop for regeneration?

folding prop for less drag when going back and forth between motorsailing and sailing?

bunch of questions about style vs efficiency, ease of switching gears while keeping efficiencies going, as well as keeping things seamless and not fiddly.

Boat of the future sort of question- the differences that lead to a boat that can average 5 knots for 6-8 hours vs 60 minutes as easily as piloting a motorboat while playing wind and current. (And current! ).

I’m leaning towards a streamlined Lawley 225 (or is it 224?), a big version of an Int 110 with a single wing sail, unstayed, modern foils under water. Or maybe a bigger Admiralty 30.

Oops? The terrier is telling me it’s time for a walkie!

anyway, any brainstorms?

 

[rwatson]

Why not go for Electric Sails then and never have to trim your sails, while getting optimum pointing, low wind performance, squall proof sailing, reduced heeling

 

[Paul Scott]

How much power to spin? Drag vs wing mast w/ no wind? FR does make everything quite automatic, which might appeal to motor boaters- use the turbine blade to repower all the time, which might really extend range, but slow things down sailing only.

patience required both ways! Change in mindset-

 

[philSweet]

Light isn't in the cards yet. You need about 20,000 pounds of displacement to have a smallish e-cruiser with decent range. If you had an ULD, you know how little of the interior is actually living space, to save weight. That's good, because electric takes up a lot of space. Think Hans Christian or Baba 40 sunk down about 6 inches below design lines. L/D about 350 for a 40' LOA double ender. This can work today. The propulsion electrical footprint is the size of a medium car, but heavier. The battery compartments require heating and a/c (or forced ventilation in cool climates) to get nameplate life and performance. The chargers will fill a closet. The above will handle a 10kw emotor pretty well for half a day. If the boat comes standard with a 35hp diesel, you will want to up that to 40-45 hp with the electric system so you can charge batteries while motoring. This arrangement can cut the engine hours by 2/3 while cruising. You need an extra $4k of alternators as well. But no need for a night genset - the main bank chargers can load the engine at 1200 rpms with the correct alternators. You can run a/c all night on the batteries.

Propulsion batteries - three strings of eight L16 400Ah 6V lead carbon such as SWE-6 for 1200 Ah at 48 V.
House batteries (12V or 24V) - four L16 400Ah.
Battery box - three feet by nine feet, sealed from occupied spaces, with room for wiring and cooling.
Alternator - twin Balmar high gain
Chargers - one Victron Skylla 48/50 TG, two Victron multibus 48/2 kVA 120, one 48V - 12V(or 24V) DC-DC charger
Battery switches - four Blue Sea 6006.
Relay/contactor - Trombetta Bear 225 Amp (for combining banks, mostly for shore charging 3 banks with the two Multibus 48/2s.)
Fuse blocks - four 100 A

Warm climates may require changing from L16 to a slab type battery footprint because they can be cooled much better. But their lower Ah rating makes it difficult to build efficient battery banks for a 10 kW motor.

The above specs were what I came up with to fit an off-the-shelf Beta Hybrid with 10 kW e-motor and 5 kW built-in charger in the controller.

 

[rwatson]

How much power to spin? Drag vs wing mast w/ no wind? FR does make everything quite automatic, which might appeal to motor boaters- use the turbine blade to repower all the time, which might really extend range, but slow things down sailing only.

patience required both ways! Change in mindset-

I am working on a 3 metre, .56 m diameter, spinning at 400 rpm, in a 15 mph wind, producing 5 hp ( ~ 3500 watts) at maximum, using 600 Watts of power.

Flettner Rotor for small craft - Design and Build Prototype https://www.boatdesign.net/threads/flettner-rotor-for-small-craft-design-and-build-prototype.67600/#post-941796

 

[Rumars]

which begs some questions, initially at least:

furling jibs too much drag? hassle?

freestanding or stayed rigs?

rotating wing masts? freestanding or stayed, say like an a class cat rig?

aero resistance of hull? and how to keep this low with solar panels?

prismatic coefficient?

turbine style prop for regeneration?

folding prop for less drag when going back and forth between motorsailing and sailing?

I think the aerodynamic drag is not a big problem and in that last 10% to optimize. Moving at 5kn in zero or very low winds doesn't generate significant drag, if there is some wind the sails are out and contributing to the driving force.
The only time air drag is a problem would be punching to windward under motor alone in heavy air, but that is not a good strategy for an electric motorsailor.
The ideal rig would completely dissappear under deck, or at least be able to reduce mast height, so either a kite or some form of telescopic mast.

To keep the solar panel windage low, you can use walkable panles glued to the deck and cabin. Custom shaping to accommodate the deck profile and hardware installation is available. Flexible solar glued to sails has been tried, maybe it's going to be solved in the future.

The ideal prop would have full variable pitch and a feathered position for sailing. Commercial solutions are available off the shelf. Next best thing is to have a normal folding or feathering prop.

Hull shape is always going to be a compromise. To maximise solar capacity you want the widest deck possible, wich leads you down the path of the modern scow bow wide stern boats. These boats are also fast, making regeneration actually useful for propulsion. To maximize range you want as little wetted area as possible, wich means narrow waterline and generous overhangs.
In order to get both you need a multihull.

Ultimately it comes down to how much batteries you can carry, and how you define the operating parameters of the boat.

 

[Paul Scott]

I think the aerodynamic drag is not a big problem and in that last 10% to optimize. Moving at 5kn in zero or very low winds doesn't generate significant drag, if there is some wind the sails are out and contributing to the driving force.
The only time air drag is a problem would be punching to windward under motor alone in heavy air, but that is not a good strategy for an electric motorsailor.
The ideal rig would completely dissappear under deck, or at least be able to reduce mast height, so either a kite or some form of telescopic mast.

To keep the solar panel windage low, you can use walkable panles glued to the deck and cabin. Custom shaping to accommodate the deck profile and hardware installation is available. Flexible solar glued to sails has been tried, maybe it's going to be solved in the future.

The ideal prop would have full variable pitch and a feathered position for sailing. Commercial solutions are available off the shelf. Next best thing is to have a normal folding or feathering prop.

Hull shape is always going to be a compromise. To maximise solar capacity you want the widest deck possible, wich leads you down the path of the modern scow bow wide stern boats. These boats are also fast, making regeneration actually useful for propulsion. To maximize range you want as little wetted area as possible, wich means narrow waterline and generous overhangs.
In order to get both you need a multihull.

Ultimately it comes down to how much batteries you can carry, and how you define the operating parameters of the boat.

I agree with most^ of this. Funny thing, when I kept on motoring after I took down the furled jib, I had more minutes at the same speed- 3.5 knots engine only, and that was taking off a blade jib, same tidal flow and wind. This was on the 40er, with a prismatic in the .53’s (she’s designed as a light wind flyer), 36’ lwl, 8’ wlb. The old pinhead main has only 2 full battens at the top, the new one will be full battens with a smallish squarehead, so maybe a difference there as far a luffing goes, at least.

I know this isn’t terribly scientific, but it got me thinking.

It was a real wake up call concerning electric with our L7 tri- I could literally paddle the thing as fast as an economic electric speed- wetted surface is prominent drag, and when wave resistance starts to rise, efficiency and range go out the window. That’s what got me thinking about a double ended box hull with fairly low prismatic- think a lowrider skinny double ended moth hull 3 times as big with a lead fin, single sail, Torqeedo 48-5000, and cruise 10.0 drive, camber induced sail about 250 - 300 sq ft, l/d 80 or so? Flared hulls get pretty wonky as far a wave drag heeling, so there are conflicting things going on. Motoring on solar cells, not battery, introduces wetted surface in air and water- so right now I’m more interested in the smaller spiral, which I realize goes against the bigger spiral going on right now in sailing and motoring- bigger sails, wider hulls, and more motor power.

 

[Rumars]

I'm not surprised to hear removing the furled jib gave you more minutes, the question is how much more. Five more minutes motoring time is probably not worth loosing the convenience of a furler, 30 minutes probably is. Furling is also an easy thing to change, you might even save money by not having it. Changing the rig from stayed to unstayed is a different game, as is going for even more exotic options like a telescoping mast.

For a double ender I would choose an inboard with shaft or a pod drive instead of an outboard, and use a folding or feathering prop. Oceanvolt also has the option of variable pitch, if that interests you.

 

[Paul Scott]

I'm not surprised to hear removing the furled jib gave you more minutes, the question is how much more. Five more minutes motoring time is probably not worth loosing the convenience of a furler, 30 minutes probably is. Furling is also an easy thing to change, you might even save money by not having it. Changing the rig from stayed to unstayed is a different game, as is going for even more exotic options like a telescoping mast.

For a double ender I would choose an inboard with shaft or a pod drive instead of an outboard, and use a folding or feathering prop. Oceanvolt also has the option of variable pitch, if that interests you.

Going with the Torqeedo folding prop (looks like a Flexofold) for now, on the 40er, but still have the regen prop that came with the saildrive, so I can experiment. The cool thing about the folding prop is when I throttle into neutral, the prop folds, and the glide is phenomenal compared to the diesel.

I’ll have figure a way to document differences in drag/minutes. It’s pretty fascinating. The whole experiment feels like riding a kick bike- the smallest declines make for a long glide, and vice vera, as well as subtle aero, while technique (or lack thereof) on flats is exaggerated.

Maybe all this is too subtle for sensibilities seduced by immediate brute power? The art of light wind sailing is almost always underrated.

 

[Clarkey]

Interesting thread. I can imagine something with a relatively small, very clean upwind motorsailing-focused rig that can drop down to the deck completely out of the way - maybe something like a Wharram wingsail rig (exploiting modern mast/sailcloth materials)? Then a large kite for reaching and downwind that can power loads of regeneration. With the decks cleared of the upwind rig there would be plenty of space for unshaded solar and kite control?

 

[Paul Scott]

Interesting thread. I can imagine something with a relatively small, very clean upwind motorsailing-focused rig that can drop down to the deck completely out of the way - maybe something like a Wharram wingsail rig (exploiting modern mast/sailcloth materials)? Then a large kite for reaching and downwind that can power loads of regeneration. With the decks cleared of the upwind rig there would be plenty of space for unshaded solar and kite control?

a better modern version of this?

 

[Clarkey]

a better modern version of this?

Something like that, yes. I might be tempted to mount it off centre, maybe on the rail, rather than the centreline to clear the deck.

 

[Paul Scott]

Something like that, yes. I might be tempted to mount it off centre, maybe on the rail, rather than the centreline to clear the deck.

With walk on solar panels on the deck?

How to pull in a mainsail enough on one tack of a side mounted mast?

I’m beginning to detect a sliding scale twixt motoring and sailing? Would a sliding Gunter (not folding) camber induced top mast sail on a foiled lower freestanding wingmast stub afford enough upwind ability? Or get out of the way of the sun enough?

 

[Tim N]

I just signed up again after a number of years absent as I having just converted my 45 year old Freedom 40 to electric power and thought my experience might be pertinent to this thread . I converted the boat last summer and left Toronto in July bound for Nova Scotia but only made it to Newport Quebec south of the Gaspe . We left the boat there as a hurricane was approaching, and made it to our place in Mexico where we live in the winters. I am now back on the boat about to complete our trip. We were able to make 40 nautical miles on a charge at five knots last summer . The boat has an 18kw motor that runs on 72 volts I made the batteries from 48 3.2 300 amh cells I bought on Alibaba for $8000 ca. The motor ,controller, bms and 72v charger were another $5000 . I have 1kw of solar running through a 72 volt Midnight Classic mppt controller. I plan to add another kw. I ended up buying a small portable gas generator that enabled me to extend my range to about 50 nautical miles. Unfortunately this winter I forgot to remove the drain plug and water from melting snow flooded the boat above the floor boards and destroyed most of my battery cells . I have ,I hope salvaged 24 cells and have managed to charge the battery to 80 volts but the BMS can't quite seem to keep the cells balanced. I am hoping now, that with half the cells, and those degraded at that, (by how much I have no idea) I can still make 15 miles which should be enough as from here I should be able to sail more and the winds should be favorable. I would never go back to diesel. I will get rid of the generator as soon as I add more solar. If I was younger I would build an electric ultralight multihull motor sailor with an extremally high aspect telescoping freestanding wing sail.

 

[Paul Scott]

I did a gunter folding main- the top mast was sleeved like a Laser sail, and the bottom mast was a rotating wing mast, which could be thought of as an old school telescoping mast. It was fiddly beyond belief, although it did lower the center of gravity reefed, and became a more bendy rig as wind increased. It needed many more generations of design before it would be considered a good sail, but as usual with development, I wound up spending that money on other things….. it did have moments of brilliance, but the wetted surface of a trimaran defeated the Torqeedo outboard, and the sail needed to be taller and higher aspect ratio to really be effective upwind in the light. Looking at some of the German lakeboat rigs, though, I think it has possibilities. But at the low speeds electric needs for range, I’m wondering if multihulls would really be efficient.

At the motorboat end of things, I think a telescoping FR might actually provide the seamless convenience necessary for non sailors? The top part might be skinny enough to have a low re and rotation speed that would be advantageous in light air, and then lower it inside the lower tube where higher re might work better in higher velocities? Kind of a sliding Gunter FR?

kind of like this crude cartoon;

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collapsing to this:

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egads…..could be much taller…and the tall part in the first one won’t cooperate when I hit the change button. I’ll do a better sketch tomorrow.