200130 Building solar-electric 20' pontoon boat system with option to plug into home wiring when not boating

[Ivar Ivarson]

Self introduction on 200130 to https://diysolarforum.com/forums/newcomers.4/

I have a 20' pontoon boat, the "S.S. Hole In The Water", which I like to take on lakes in S. Ohio and on the Ohio River. I would like to construct a tiltable 20' X 8' awning on the pontoon boat. The awning could be lowered by a cable and pulley system and winch onto the boat rails for trailering and/or foul weather. The awning would have a >1500 watt PV array controlled by an MPSolar LV5048 with battery bank consisting of 2 Battery Hookup BYD 24vdc approx. 4.5KWH ABSSM LiFePO4 packs for a 48vdc system. The batteries and/or the solar panels would power a Minn-Kota eDrive 2 HP outboard electric motor (originally, a bank of four 12v 115 amp/hr lead acid batteries powered the motor but endurance on a full charge is usually about 7 hours at 1/2 speed) .

The LV5048 would act as onboard 120vac power and as 48vdc battery charger when attached on the water to "shore power" or via the PV panel array. Max motor current draw at full speed has been measured at 48vdc at 39-40 amps; 1/2 speed current draw is 11 amps. When at home, the pontoon would be parked on its trailer with the PV panels South facing to both charge batteries and feed power into the house and garage. This feed into the house would be via an pre-existing 240 vac six-circuit generator panel wired into six 'essential' circuits meaning refrigerator, freezer and lights etc. to use surplus power to offset the electric bill. However, there would not be any grid-tie as the old generator power switches have the choice of 'generator only' (or solar plant), 'off' and grid. I believe the combination of "houseboat" and/or PV residential array qualifies for the 30% Federal Income Tax credit. Of the above solar plant, only the two BYD battery packs and the generator panel have been purchased. Of course, the outboard eDrive and its speed controls came with the pontoon. Somewhat complicating our house wiring is a Generac 20kw propane powered emergency generator which automatically isolates the wiring and runs during power outages. No control interlinks between this generator and the proposed solar plant are contemplated.

I'm 70 years old, male, and fairly handy with tools and wiring but my solar experience is limited to installing a solar thermal hot water system. Eventually, I want to replicate a Wisconsin college professor's 1000 mile 1893 voyage* from near Pittsburg on the Monongahela River and down the full length of the Ohio River to Cairo, IL on the Mississippi River (although, having visited Cairo IL by car on 12/1/19, I should change the endpoint to something else).

* https://archive.org/details/afloat_onthe_ohio_1208_librivox

Comments?

 

[SolarRat]

I can't wait to see the progress. I'd like to do something similar with my 21' pontoon, but I'm still in the design stages.

First, I need to make a hardtop. I thought about making it tiltable, but it really complicates things...not that it can't easily be done, but I'm worried about the strength (i'll be using heavy glass solar panels, and we get frequent storms here in Florida). I'm probably going to limit the top to half the boat so we can still get some sun. I could fit about 2000w if I covered the whole boat, but 1000-1250w ish is probably where I'll end up.

Right now I just have a 36v 101lb thrust MinnKota with 115ah of lead acids. It cruises about 3.5mph at 2/3rds throttle drawing 20 amps. I want something bigger! I've looked into the E-drive but it's pricey for what I think is about 140-160 lbs of thrust? I'm probably going to end up either getting one of the 2-5kw motors off Ali-express, or make my own from an old ~15hp outboard converted to electric.

I'd also like to tie it into the house. It's parked at my dock about 100ft from the house, and I already ran a few extra 10ga wires in buried conduit that should handle whatever I'm producing. It will probably be more of a backup power system as I don't think grid tying it would pass my county's sniff test.

Please keep me updated on your progress and I'll do the same!

 

[45North]

Could it work the other way too? If you get a run of cloudy days (impossible in Florida, I know!) could you charge the boat's battery from the house mains?

 

[Ivar Ivarson]

Could it work the other way too? If you get a run of cloudy days (impossible in Florida, I know!) could you charge the boat's battery from the house mains?

Well yeah, that's my current option with the lead acid batteries. I understand that the LV5048 can be set to do this automagically. I even carry an 1800 watt quiet generator on board to recharge in an emergency. It's not much use since the Minn-Kota onboard charger (draws about 950 watts at first) says not to use the system when charging (altho I've done so at 1/4 throttle; eDrive system and charger is 10 years old so there's no warranty to preserve). However, the current charger takes about 10 hours to get back to full charge. Once on the Ohio River, I really ran into impossible headwinds and barely made it back to the launch site. In the event of an on-board generator recharge, I'm probably stuck on the river or lake overnight.

 

[Ivar Ivarson]

I can't wait to see the progress. I'd like to do something similar with my 21' pontoon, but I'm still in the design stages.

First, I need to make a hardtop. I thought about making it tiltable, but it really complicates things...not that it can't easily be done, but I'm worried about the strength (i'll be using heavy glass solar panels, and we get frequent storms here in Florida). I'm probably going to limit the top to half the boat so we can still get some sun. I could fit about 2000w if I covered the whole boat, but 1000-1250w ish is probably where I'll end up.

Right now I just have a 36v 101lb thrust MinnKota with 115ah of lead acids. It cruises about 3.5mph at 2/3rds throttle drawing 20 amps. I want something bigger! I've looked into the E-drive but it's pricey for what I think is about 140-160 lbs of thrust? I'm probably going to end up either getting one of the 2-5kw motors off Ali-express, or make my own from an old ~15hp outboard converted to electric.

I'd also like to tie it into the house. It's parked at my dock about 100ft from the house, and I already ran a few extra 10ga wires in buried conduit that should handle whatever I'm producing. It will probably be more of a backup power system as I don't think grid tying it would pass my county's sniff test.

Please keep me updated on your progress and I'll do the same!

Since I've been thinking about this since August of 2018, a month after getting the pontoon, I'm pretty embarrassed at my lack of progress.

If I had my druthers, I wouldn't invite the trouble and expense of a hardtop that can be raised and lowered, let alone one that tilts. However, I like to trailer the pontoon to various lakes and the Ohio River. I would like to be able to button it up by lowering the top smack down on the rails and seat back cushions for the road or really bad winds. I've considered getting electric screw jacks, some of which can extend up to 52", lift 160 lbs and support 300 lbs statically. These are of course from China and run about $200 each. I figured that the jacks could be left low on one side and high on the other for tilt. Some sort of sliding joint would be needed to handle the increased distance (hypotenuse in a right triangle) when tilted. I want the tilt up here at about 40 degrees latitude to improve panel performance when parked next to the detached garage. I'd be using the six essential circuit panel at the end of a long ten gauge cable (this will be about 50' for me) instead of trying to convince American Electric Power to accept my installation. The MPPSolar LV5048 doesn't have a UL approval yet although it rumored to come through this Spring. Anyway, the LV5048 can use and automatically switch between grid power, battery or solar inputs to pipe 240 volts AC to this panel. It'll always be isolated from the grid by either the LV5048 itself or emergency Generac generator transfer switch.

Like you, I plan on using rigid glass aluminum framed panels. Since they all run about 40" X 85" (ish) for the wattages I want, I have room for about six (think of the Jinko 400 watt models). At about 50 lbs each, that's a load of 300 lbs just for the panels but evenly distributed. I'd love to use the light semi-flexible ones but very few are above 100 watts apiece. That's an additional expense to buy comparable wattage and a giant interconnection headache as I see it.

I've been experimenting with an old design I'd half remembered seeing in a 1970s Popular Science or Popular Mechanics for fiberglass reinforced triangular spars they were promoting for windmill or TV towers. I've taken 16 gauge 2" aluminum flagpole sections as the central core. You run long wooden (better quality furring strip) stringers the length of the aluminum tubing with one end rounded over to prevent sharp corners, and the tubing side routed to sit flat with sort of a "U". (pictures attached)

As for the fiberglass reinforcement, the old PopSci article envisioned a machine tightly winding a strong glass yarn at a 45 degree angle over and over on a triangular form until you had a dense mesh that acted like virtual triangular reinforcement. I think that I've found a cheaper way that may just work. I bought a few rolls of the extra strong fiberglass drywall tape. It has slightly tacky adhesive to stick to drywall and more or less stays tight when I wind it around at an angle. On one test piece, I stapled this drywall tape to the wooden stringer top as I passed it over each one, but I don't think that's necessary. Once I had about three layers, I then put on what resin I had and the result seemed pretty strong. I put a long row of filled 1 gal water bottled on top this 10' test section and got only about a 2" defection for 200 lbs evenly distributed. There's no reason the main "spar" in the middle, about which the hardtop would pivot, couldn't be surrounded by four stringers at 90 degree intervals to make a box beam rather than my test beam which was triangular at 120 degree spacing.

This constructed rectangular or triangular spar would be the main center beam and there'd be two more outside beams but these would probably have just two stringers at 180 degrees spacing to fight sag. Connections between the main center beam and the outside beams would be 8' plywood cross beams with the spaces between each cross support X-guy wired to the next so the roof would stay square. There's thin weather and UV resistant "patio liner" paneling to make the entire 8' X 20' rain proof. Fixing rigid solar panels atop that would add further rigidity to the structure. The center beam would terminate in the reinforced 2" aluminum tubing left bare which would ride in the pivots on the bow and stern. The pivots would be atop standards that I want to crank up and down via an electric winch. Lightweight telescoping poles would be attached on the roof sides port and starboard to fix the tilt or keep the roof flat. The bases of these poles would snap into tracks mounted on the little stubby bits of exposed deck outside the pontoon safety rails. Finally, another pair of guy wires would run under the length of this hardtop roof over a pair of stays holding them out and down so that when tightened, the guy wires would correct sag. Those stays wouldn't be very long as I don't want to bash my head on them when moving about the boat or garrote myself on any of those guy wires. I also figure that, if I can't make this hardtop light, non-sagging and strong, I can always tolerate a center support pole in the exact center of the pontoon.



I don't have drawings yet.

 

[Ivar Ivarson]

I can't wait to see the progress. I'd like to do something similar with my 21' pontoon, but I'm still in the design stages.

First, I need to make a hardtop. I thought about making it tiltable, but it really complicates things...not that it can't easily be done, but I'm worried about the strength (i'll be using heavy glass solar panels, and we get frequent storms here in Florida). I'm probably going to limit the top to half the boat so we can still get some sun. I could fit about 2000w if I covered the whole boat, but 1000-1250w ish is probably where I'll end up.

Right now I just have a 36v 101lb thrust MinnKota with 115ah of lead acids. It cruises about 3.5mph at 2/3rds throttle drawing 20 amps. I want something bigger! I've looked into the E-drive but it's pricey for what I think is about 140-160 lbs of thrust? I'm probably going to end up either getting one of the 2-5kw motors off Ali-express, or make my own from an old ~15hp outboard converted to electric.

I'd also like to tie it into the house. It's parked at my dock about 100ft from the house, and I already ran a few extra 10ga wires in buried conduit that should handle whatever I'm producing. It will probably be more of a backup power system as I don't think grid tying it would pass my county's sniff test.

Please keep me updated on your progress and I'll do the same!

Three more addenda:

a. Minn-Kota advertises pounds-thrust ratings on all their trolling motors even the ones they sell to attach to an outboard motor swash plate. However, the eDrive, which is very pricey usually $3000, is just rated at 2 HP. BTW, for your $3000, you just have the outboard unit and a remote infinite speed control which includes a graphic "fuel" gauge and digital 'battery hours left at this throttle setting' LCD display. You still have to buy batteries and a $900 charger if you go with Minn-Kota's offerings.

b. I'm searching for a Minn-Kota serviceman in my general region to rebuild the eDrive. The underwater motor bulb is OK, but I know damn well that I'll twist the long bolts that hold it together in half if I try to open it. The tiller bearings on which the outboard pivots are in need of replacement as well as the lower one is usually in the water and is gone. The rather thin shaft going from the speed control head down to the prop and motor runs through a pretty sturdy aluminum extrusion in which I've stuffed sections of PVC pipe to support the shaft. I feel like I can hear the motor bearings grating a little and would like to see this 10 year old outfit refurbished with new bearings and brushes. FWIW, an entire motor, bulb and shaft is $550 so the serviceman had better not exceed that in his estimate.

c. I might need two sets of custom canvas sides, one for cruising with the roof raised and flat with screened windows, and another blank one for buttoning the pontoon up for the Winter at a tilt towards the sun. These would both snap onto the roof and to the aluminum extrusion that surrounds the deck, or maybe the cruising one just to snaps on the safety railing. It's not been a big problem, but the present canvas cover only goes down to the middle of the rail system. Rain soaks the carpet from the exposed outside 2" in. It's all marine plywood and indoor/outdoor carpeting but I'm not very happy about the whole carpet getting wet every time it rains. That cover is about worn out anyway. Right now, it's all tarpped up for the Winter down to the top of the pontoon logs.

 

[SolarRat]

I've rebuilt many of those MinnKotas and never had one snap the long thru bolts. I did have a small bolt holding the brush plate snap on one though, and had to drill a small hole in it then used acid to eat out the rest of the screw and cleaned it up with a tap.

Good place I found for motor parts is here . I had actually thought of buying that E-drive lower unit to install on a 80lb thrust motor I had laying around. I called up that store and the guy was helpful, saying they have the same shaft diameter and threads, but he wasn't sure if the composite shaft would be strong enough.

My 101lb thrust had bad control boards, so I made my own and installed them in and under the dash. They will handle a much larger motor in the future. I mounted the controls into a waterproof box installed where the AM/FM radio used to be. The momentary DPDT switch controls the steering and the knob the throttle:

 

[SolarRat]

I like that main spar idea. What does it weigh when all done? At your latitude tilting is a good idea. I'm not going to bother tilting being closer to the equator but I would like to have it lower down to the side rails for storms or the very rare towing I do (or very low bridges). I thought about the design some older pontoon hardtops used, where the supports were hinged at the rails and just "flopped" forward until it sat flush on the rails. If I went this route I'd have to stiffen up the side rails first. With a bit of geometry on spacing the hinges the whole top could tilt forward or backwards, but it would never sit flush with the rails unless two different hinge points were used. Still thinking about this design, and I could reuse much of the current bimini frame and hinges.

The old pontoon hardtop style, similar to what I'm talking about but with lower hinge mounts:

 

[SolarRat]

Rain soaks the carpet from the exposed outside 2" in. It's all marine plywood and indoor/outdoor carpeting but I'm not very happy about the whole carpet getting wet every time it rains.

My carpet was always getting moldy from being wet, and it was wearing thru in spots too. I ripped it all off and used non-skid topside deck paint. But my deck is aluminum, which is getting harder and harder to find on these toons and the main reason I will probably never sell the boat. It saves a lot of weight over waterlogged plywood. In your case, vinyl flooring is a great option.

I also stripped out all the couches, as they don't last long in the sun down here anyway. I just use those aluminum padded boat/deck seats and a few cooler seats. I figure with limited electric power, weight savings is important, and what is stopping me from just slapping on some 4x4 wood supports with a 2x6 framed roof.

I still have the 50hp fuel injected 4 stroke on the back, so my electric motor is up front. I still use both, but would someday like to get a big enough electric to ditch the gas engine and gas tank and save some more weight.

 

[kernel]

Well yeah, that's my current option with the lead acid batteries. I understand that the LV5048 can be set to do this automagically. I even carry an 1800 watt quiet generator on board to recharge in an emergency. It's not much use since the Minn-Kota onboard charger (draws about 950 watts at first) says not to use the system when charging (altho I've done so at 1/4 throttle; eDrive system and charger is 10 years old so there's no warranty to preserve). However, the current charger takes about 10 hours to get back to full charge. Once on the Ohio River, I really ran into impossible headwinds and barely made it back to the launch site. In the event of an on-board generator recharge, I'm probably stuck on the river or lake overnight.

Use a different charger. The inverter charger and solar chargers will operate seamlessly amd charge while running full throttle if you like. Generator limitation, but how often for how long, in a generator backup situation would you be at full throttle. Either way you should be able to sail hybrid no issue with the right inverter charger and generator combo.

If your array is large enough, you should have the ability to cruise 24/7. Boats and ships have much success with solar electric drive no fuel.

I have designed these. Motor efficiency is key. Get the best you can afford.

 

[SolarRat]

My on-board 3 bank charger (ProMariner) also said it's not to be used while under load. The only problem I can see is if the charger has trouble going from float or CV back down to CC, like if you started your genny with a near full battery when the charger is in float or CV mode, and then drew down the battery. If you only start the genny in a lower battery situation it should stay in the CC bulk charge stage and not confuse the charger. Unless it tries to compensate for load by overvolting...but I doubt that would be the case...

The problem is most of these on-board chargers don't put out enough amps (mine is 5+5+5) to run full speed off the generator, so you have to reduce the speed. Plenty of ways around that, like using a larger golf cart or forklift charger. Or adding solar plus the genny/on-board charger.

 

[kernel]

Three more addenda:

a. Minn-Kota advertises pounds-thrust ratings on all their trolling motors even the ones they sell to attach to an outboard motor swash plate. However, the eDrive, which is very pricey usually $3000, is just rated at 2 HP. BTW, for your $3000, you just have the outboard unit and a remote infinite speed control which includes a graphic "fuel" gauge and digital 'battery hours left at this throttle setting' LCD display. You still have to buy batteries and a $900 charger if you go with Minn-Kota's offerings.

b. I'm searching for a Minn-Kota serviceman in my general region to rebuild the eDrive. The underwater motor bulb is OK, but I know damn well that I'll twist the long bolts that hold it together in half if I try to open it. The tiller bearings on which the outboard pivots are in need of replacement as well as the lower one is usually in the water and is gone. The rather thin shaft going from the speed control head down to the prop and motor runs through a pretty sturdy aluminum extrusion in which I've stuffed sections of PVC pipe to support the shaft. I feel like I can hear the motor bearings grating a little and would like to see this 10 year old outfit refurbished with new bearings and brushes. FWIW, an entire motor, bulb and shaft is $550 so the serviceman had better not exceed that in his estimate.

c. I might need two sets of custom canvas sides, one for cruising with the roof raised and flat with screened windows, and another blank one for buttoning the pontoon up for the Winter at a tilt towards the sun. These would both snap onto the roof and to the aluminum extrusion that surrounds the deck, or maybe the cruising one just to snaps on the safety railing. It's not been a big problem, but the present canvas cover only goes down to the middle of the rail system. Rain soaks the carpet from the exposed outside 2" in. It's all marine plywood and indoor/outdoor carpeting but I'm not very happy about the whole carpet getting wet every time it rains. That cover is about worn out anyway. Right now, it's all tarpped up for the Winter down to the top of the pontoon logs.

I would look at minkota motors that connect to the lower unit of your gas engine.

The twin motors mounted to your engine are way less expensive and you get to steer normally regardless of drive selection.

 

[SolarRat]

I would look at minkota motors that connect to the lower unit of your gas engine.

The twin motors mounted to your engine are way less expensive and you get to steer normally regardless of drive selection.

The drag from the gas lower unit is HUGE. So not a great option when trying to run on electric only efficiently. Fine for occasionally moving your boat from fishing spot to fishing spot, but not much else. The trim tab mounted ones that tilt out of the water are a better option, but there's nowhere to mount them on a pontoon boat.

 

[kernel]

Not bad without a prop, which is how i would do it. Gut the lower unit amd use it for mounting and steering. At that point its basically a rudder and eminently more rugged than most options

 

[kernel]

Maybe not gut his lower...... spensive engine!

 

[SolarRat]

Maybe not gut his lower...... spensive engine!

Those E-drives he has usually come on boats that are electric only, no gas engine. Mine still has the gas engine, but when I finally convert to a bigger electric I want to sell the engine for a few grand to hep fund the project.

Mounting an electric is no problem, so no need for the gas engine. I've even read where people have added cowls to the round motor shaft of their electrics to reduce drag and gain over 0.5mph. I didn't believe it at first, but after doing my own tests on motor height I found I gained a few tenths of a MPH by just raising my motor as high as it would go without cavitating, to have less shaft in the water. Now I'm believer! And when I move from fishing spot to fishing spot with my electric, with the gas lower still in the water, I lose 1/3rd of my top speed. Drag kills when trying for every last tenth. The back of my pontoons are flat which creates a lot of turbulence and drag...but that's a problem for another day...

 

[kernel]

Torqueedos are spensive too. I liked the e drive, but at that price point, id have to build something converted. There are some nice drives, the sailboat stuff is astonomic in cost but what is needed in that persuit.

The thing about efficiency and hydrodynamic drag is drag has a heck of a progressive increase with speed. The same setup has un-proportionately different drag at 3-5 knotts than it does at 20. People want to go 30mph or more and that costs efficiency.

 

[Ivar Ivarson]

I like that main spar idea. What does it weigh when all done? At your latitude tilting is a good idea. I'm not going to bother tilting being closer to the equator but I would like to have it lower down to the side rails for storms or the very rare towing I do (or very low bridges). I thought about the design some older pontoon hardtops used, where the supports were hinged at the rails and just "flopped" forward until it sat flush on the rails. If I went this route I'd have to stiffen up the side rails first. With a bit of geometry on spacing the hinges the whole top could tilt forward or backwards, but it would never sit flush with the rails unless two different hinge points were used. Still thinking about this design, and I could reuse much of the current bimini frame and hinges.

The old pontoon hardtop style, similar to what I'm talking about but with lower hinge mounts:

Don't know about the weight of my spar design. I'll certainly weigh all the components or use a portable luggage scale I have for a completed spar. So far, I've only built 5' and 11' experimental lengths and they're pretty light. The aluminum tubing comes as 20' - 25' flagpole kits as UPS ship-able lengths with a swaged end to slip inside the next length and secured with pop rivets. The strength of the center tube is not very important as its only 2" diameter with 16 gauge walls. It basically forms the center of the triangular form work with fiberglass tape over and around it. That's what bears the load and has the effect of triangular reinforcing. By the way, I put a countersunk screw through the wooden stringers into the center aluminum tubing every 3' or so just to keep them in place during wrapping.

 

[Ivar Ivarson]

Those E-drives he has usually come on boats that are electric only, no gas engine. Mine still has the gas engine, but when I finally convert to a bigger electric I want to sell the engine for a few grand to hep fund the project.

Mounting an electric is no problem, so no need for the gas engine. I've even read where people have added cowls to the round motor shaft of their electrics to reduce drag and gain over 0.5mph. I didn't believe it at first, but after doing my own tests on motor height I found I gained a few tenths of a MPH by just raising my motor as high as it would go without cavitating, to have less shaft in the water. Now I'm believer! And when I move from fishing spot to fishing spot with my electric, with the gas lower still in the water, I lose 1/3rd of my top speed. Drag kills when trying for every last tenth. The back of my pontoons are flat which creates a lot of turbulence and drag...but that's a problem for another day...

Yep, as far as I can tell, my 'toon has always just had the eDrive. I bought it up in Michigan after finding a listing online. There was no sign that the boat had ever had a Michigan number ID sticker on it so I figured it had spent its time up to July 2018 tooling around on a fishing pond somewhere. There is some mineral deposit on the pontoons which I'm gradually dissolving off; though I never did a really thorough cleaning. I did see the name of the previous owner on the title work, and he seemed to be an engineer for GM near Dearborn according to a Linked-In profile.

Perhaps I have that eDrive prop too deep, but there's no adjustment on the depth as there's just one set of bolt holes on the little transom hull that holds the outboard. I'll have to ask the Minn-Kota service guy about shortening the shaft perhaps. The capacity sticker reads that you can put 115 hp (ha!) and 11 people on this boat which both seem pretty excessive. I've always boated alone so far; my wife won't go near it.

Yeah, the sterns of my pontoon logs are flat also. I wondered whether it'd be worthwhile to make a tapered canoe stern on each out of sheet aluminum to swing down into place. Those sterns always seem to produce a lot of turbulence and gurgling noise. By the way, that little triangular transom hull is open at the back so it lets the water in through three little slots in the bottom. I wonder if I'd get a little more flotation by stopping those slots up and trying to keep the transom hull empty of water. I mention this in connection with those little "canoe" sterns, as I'd planned to allow them to be flooded when in place. How could I seal them if they swing down into place anyway? Probably too much trouble. I also thought about underwater bulbous bows and the "hull speed" of pontoon boats as this is a displacement hull design unless you have one of those fancy set of fins and a large engine. Again, I don't think it's worth the trouble.

I feel that I'll want to minimize roof weight as much as possible that's held so high above the waterline as pontoon boats tend to have a high center of gravity. I have little trouble on the lakes, but there's usually more height to wakes on the Ohio River. Currently the lead acid batteries are right on the rear deck above that transom hull open to the back but with a sun lounger cushion on a hinged hatch protecting it from above; I plan to move the LiFePO4 batteries farther forward under one of the rear seats so it's not exposed to the sun and weather as much as well as improving the weight distribution.

I am sort of interested in one of those cowlings around the prop since I don't usually go into weedy areas (in fact I don't fish at all, hate the taste of fish, sorry). One name I've read about is the so-called "Kort Nozzle" which is apparently used on some very large tug and work boat props.

 

[Ivar Ivarson]

Torqueedos are spensive too. I liked the e drive, but at that price point, id have to build something converted. There are some nice drives, the sailboat stuff is astonomic in cost but what is needed in that persuit.

The thing about efficiency and hydrodynamic drag is drag has a heck of a progressive increase with speed. The same setup has un-proportionately different drag at 3-5 knotts than it does at 20. People want to go 30mph or more and that costs efficiency.

Yes, I priced the Torqueedos out of curiosity as well. Very pricey.

Well, my dad was an engineer for GE near Cincinnati at the Evendale jet engine plant and always said that drag increases by the cube, that is, the speed times itself to the third power and he was talking about air. Water has to be more than equally bad since it starts out so much denser than air. We spent our weekends on the Ohio River in a little 16' wooden runabout with a 40 hp outboard and did a lot of water skiing back before there was much pollution control; I'm amazed I'm still alive. It was my job each third winter to sand off the paint for repainting. Dad engineered two gigantic saw horses and slung the boat beneath to take the trailer out. I really hated holding that sander up while lying on a mechanics creeper.

I found an interesting source of AC and DC motors at https://www.electriccarpartscompany.com/DD-ES-15-6-br-48V-72V-DC-br-62-Lbs--EV-DC-Motor_p_736.html. They have all kinds of car conversion parts. The link is to a "D&D ES-15-6 48V, 72V DC 62 LBS - EV DC Motor". They handle other brands as well. If your electronic speed control is beefy enough, you wouldn't have to buy one with this motor which is about $870 by the way. They have Li batteries and just about anything you'd need.

There are at least two sources of old junk outboard lower units within 50 miles of me, perhaps one day I'll do a conversion rig myself.