Electric Boating

[bobkart]

"Men tend to sell their boats to keep their wives happy because the boat usually costs more to maintain."

The good news for me is that she has been wanting this more than I have. My two reasons are not wanting to burn any more gasoline than I 'have to', and of course the high costs usually associated with boating. Once I tested the waters last year with an approach that avoids both of those downsides, and seeing potential for more, I was much more fully 'onboard' with the idea.

Here's an example of the kind of workups I've gone through. Take the Boston Whaler 110 Tender, their smallest boat, and the only one I see that you can buy (new) without a motor:

https://www.bostonwhaler.com/family-ove ... 10-tender/

There's a very affordable 20hp electric motor by Stealth. Never mind that the 110 Tender is only rated for 15hp; their Sport model is the same boat and rated for 25hp. I think the difference is tiller versus remote control. One could buy a 110 Sport with the smallest motor they force you to buy it with, then sell the motor (at a big loss no doubt) and not have to build your own console/steering setup onto the Tender.

The weight capacity on the 110 Tender is 845 pounds. Take off the 400 pounds for motor and battery (per earlier calculations) and you have 445 pounds remaining. There's a four-person capacity, but you're not squeezing four people into 445 pounds. So the batteries have taken up about 1.5 persons-worth of capacity. I.e. after the ~360 pounds for us two, there's less than 100 pounds left over. Dropping to 15hp gives back 100 pounds and thus a third person is then an option. Of course now top speed has suffered. This is the big challenge I'm facing with this project.

[GetOffYourGas]

My boat is powered by a Torqeedo Travel 1003. It is a 1kW motor which produces thrust equivalent to a 3HP gasoline motor. It has an integrated 520Wh lithium battery which I charge at home. You can also charge via solar panels if you wish.

The Travel series is nice, but for any larger boat, I would go with the Cruise series instead.

When I bought the motor in 2011, Torqeedo was the only real game in town. Minn Kota had trolling motors, but as I had mentioned, I tried that. A trolling motor is not good enough for my needs. Today there are certainly more options that I would evaluation. Frankly, Torqeedo has not really improved the technology nor the price of their small outboards; a Travel 1003 costs the same $2k it did back in 2011, and comes with a 532Wh battery over my 520Wh one. I was really hoping to see much more significant improvements over the course of a decade!

"Men tend to sell their boats to keep their wives happy because the boat usually costs more to maintain."

There's one I haven't heard before

[bobkart]

My boat is powered by a Torqeedo Travel 1003.

Ah, I should have seen that in your signature . . . sorry!

I find this website to be a good reference for electric outboard motors:

https://plugboats.com/electric-outboards-more-than-5kw/

That's their page for 5kW-and up outboards.

I have the Torqeedo Cruise 10.0 on my list. It has a few downsides: heavy for its power level, and definitely more expensive than other options.

One thing I don't agree with in the descriptions of many outboard motors is the 'horsepower equivalent'. I get that electric motors have more low-end torque, but for my purposes I need to compare the maximum power output, and (for example) Elco rating the 8.8kW motor at '20hp equivalent' seems deceptive. (In the comparison you made to 3hp, it was appropriate, as you compared thrust.)

I really want to like the Pure Watercraft entry: https://www.purewatercraft.com/product/pure-outboard/

Great power-to-weight ratio, but it's not available yet and you have to buy their batteries (at very high prices). I might still be considering that route but I was in discussion with a salesperson there and I discovered that their batteries can't be recharged while in use, and even when not in use, the recharge rate isn't very high until you get more than one of them involved. That killed solar panels and/or a propane generator as range extension options (never mind that I can build the same capacity battery for 1/4 their price).

[bobkart]

If they made a powerable version of this (no sail), I'd be very interested:

https://iflysail.com/

This seems like the ultimate in terms of decent speed being achievable from not a lot of power.

[LeftieBiker]

It would need to be completely redesigned to delete the sails, but put a motor in each side along with the batteries, and maybe a long motor shaft passing through part of the pack to get the weight balance right...

[GetOffYourGas]

One thing I don't agree with in the descriptions of many outboard motors is the 'horsepower equivalent'. I get that electric motors have more low-end torque, but for my purposes I need to compare the maximum power output, and (for example) Elco rating the 8.8kW motor at '20hp equivalent' seems deceptive. (In the comparison you made to 3hp, it was appropriate, as you compared thrust.)

When comparing the two motor types, you really should look at thrust. That is what moves your boat forward, and ultimately what matters.

Strictly in terms of power, 1kW = 1.34HP

HOWEVER, propellers are more efficient at low speeds. In order to drive a prop at low speeds with lots of power, you need a that low-end torque. That can be done with a gas motor to a degree with gearing, but an electric motor naturally shines at low speeds. So most (all?) electric outboards have a large prop driven at slow speeds whereas all gas outboards have a small prop driven at high speeds. This is why you can get more thrust from less power (again, better efficiency).

One downside that I have is my lake is particularly shallow and weedy. A large, slow-moving prop does an excellent job of collecting weeds. I end up cleaning the prop often, especially if I am fishing (i.e. intentionally in the weeds).

[bobkart]

When comparing the two motor types, you really should look at thrust. That is what moves your boat forward, and ultimately what matters.

I mostly agree, as you're using 'thrust' as opposed to 'static thrust'. But Elco (for example) is quoting the static thrust of their '20hp' motor at 390 pounds, but the input power is only 8.88kW:

https://www.elcomotoryachts.com/wp-cont ... -EP-20.pdf

I get that 390 pounds of static thrust is probably comparable to what a 20hp gas engine can produce (for the reasons you outline). So that part is fair, and if you're pushing a barge with this motor, that will be the primary consideration. But at cruising speeds, the Elco won't compare to a 20hp gas outboard. Assume 8kW of that 8.88kW input power makes it to the propeller shaft, that's only 10.7hp. If we again assume that the propeller on the Elco is comparable to that of a 20hp gas outboard (appearances would suggest that), there's no way to get the 'high-speed thrust' (as opposed to 'static thrust') of the gas engine from not much more than half the power to that same propeller.

Thrust ('propulsive force') will be a factor of prop shaft RPM and torque, times the efficiency of the propeller *at that RPM and boat speed*. A propeller's efficiency will be different for a static thrust situation (100% slip) versus at cruising speed (10%-20% slip). Where it gets more interesting is when the electric outboard has abandoned traditional 'gas outboard' propeller parameters (RPM range, diameter, pitch, rake, ...), and instead tried better to maximize efficiency for an electric motor's torque/power curve. Torqeedo and ePropulsion (for example) do this, and achieve more propulsive force ('thrust') for the same prop-shaft power as a result. Lower propeller RPM is a big part of it (as you mention).

I'm not trying to be disagreeable, more trying to peel back a technical layer on the subject. Also not trying to be an authority on this subject; I'm by no means a propeller or propulsion expert. But I am a student of physics, and have built the above understanding up as part of my exploration into this area over the last year. So I could easily be off on some parts of that understanding. Feel free to correct/clarify.

[bobkart]

A power catamaran looks to be a good choice for practical-yet-efficient hull configuration:

https://electrek.co/2017/10/18/electric ... -outboard/

[GetOffYourGas]

Your post triggered a memory for me. A few years ago, I met a gentleman who had built his own solar electric trimaran. He had a bank of batteries charged exclusively by on-board solar panels, driving a Torqeedo outboard. He named his boat "Ra" after the Egyption sun god.

He took the boat around the "great loop" - basically up the ICW (intracoastal waterway) to NY, then up the Hudson/Erie Canal to the Great Lakes, and finally back down the Mississippi river to the Gulf of Mexico. I live close to the Erie Canal and met him when he was waiting for one of the locks.

https://www.passagemaker.com/destinatio ... great-loop

[jjeff]

Your post triggered a memory for me. A few years ago, I met a gentleman who had built his own solar electric trimaran. He had a bank of batteries charged exclusively by on-board solar panels, driving a Torqeedo outboard. He named his boat "Ra" after the Egyption sun god.

He took the boat around the "great loop" - basically up the ICW (intracoastal waterway) to NY, then up the Hudson/Erie Canal to the Great Lakes, and finally back down the Mississippi river to the Gulf of Mexico. I live close to the Erie Canal and met him when he was waiting for one of the locks.

https://www.passagemaker.com/destinatio ... great-loop

Interesting read, thanks I had no idea, he must have passed through my city(Minneapolis) within 5 miles from me
They didn't say but using their numbers it would have taken 240 days and then they said they did stop for a while, so maybe close to a year in total? impressive though to do it all with the power of the sun