Electric propulsion - stops or stalls - any experience ?

[Murraybrowne]

Yes, solid split coupler.
https://vmdafoe.com/couplings/
We may install a rubber knuckle flexible coupling in the future but so far (touch wood) we haven't needed it. The Thunderstruck came with a chain coupling. I showed the chain coupling to a few machine shops and they strongly advised against using it. Maybe they're fine but we decided against it and went with the solid split coupling. The motor sits on rubber engine mounts.

[Emoyeni]

Thanks for this detailed post on your conversion. How many hours has this taken? Also, why does almost everyone do what you did with the belts connecting the shaft to the motor and not connect the motor to the shaft directly?

Originally Posted by Skipper Lee

I have done the Thunderstruck conversion, I used the 5 Kw kit with 2-1 reduction spinning a 13rh11 prop for my 27 ft sloop at 4900 lbs. I was told by Thunderstruck that it would be as powerful as the Yanmar SB8 that it came with. I have yet to finish the conversion as it is winter here in central Canada but will be running in spring.
I do know a friend with the same boat as mine in Nevada who used the 5 kw kit as well. He is up and running he is well satisfied with the conversion but chose poorly imho regarding the batteries (Walmart) and he only gets about 1.5 hours run time on lake Mead.
I suppose it is enough for a lake boat left at a dock every night with power or just an overnight now and then.
I just purchased 6X12 Volt 110ah Firefly group 31 batteries.(2 house and 4 Drive) and that's likely the best you can do. Of course you can go Lithium as well if you choose but during other endeavors I have had them catch fire and burn the counter I was charging them on so I am slightly scared of them after replacing the countertop. I also purchased a 2000 w suitcase generator for use if needed while out on the water or charging at anchor. I saw your boat on sailboat data and like mine there's not much room for Solar panels though you might fit a few to assist or perhaps you'll add a tower for more or add a wind generator. not to many people actually get enough Regen on slower electric boats, or any boat, even big bucks professionally set up systems (like Jimmy Cornell recently found out). I suppose it all about how and what your sailing goals are.
I really enjoy the quiet life and will be listening to the meanderings of my mind while I learn how to get the best of my E-Powered backup drive system on my SAILBOAT.
I also had a 26 ft sailboat for 3-4 years without any aux power so yes you can do it with electric power.
Good luck and merry Christmas.

[Murraybrowne]

I have no idea about how many hours. Lots. A lot of grinding and fibreglass work to refit the engine bed mounts. Regarding belts, I think it is a requirement due to gearing ratios. There is no transmission. We experimented and found we needed a 3:1 ratio to drive our 20,000 lb. boat with our 18x12 prop and the 18KW motor at 48V.

[Skipper Lee]

If I recall the T-struck motor spins max at 2500 rpm with 48 volts and the Yanmar SB8 spun at 1050 or 1100 (I cant remember exactly) rpm max,
I wanted to use the existing prop so I used the 2-1 Thunderstruck reduction plate and cogged belt system so should spin at 1250 max which is close enough and the prop wont just cavitate. There's a formula someone told me but don't remember where I got it from. I didn't have to chop or grind anything and used the existing SS engine beds that the Yanmar sat on just redrilled and set on rubbber so was able to tweak the shaft alignment with compressing the rubber to the exact spot.
Took about a day to install the motor itself but will probably take a few to get the batteries installed in a good looking holder setup.
Get the best batteries you can and have fun. I will post a few more pix later today.

[PineyWoodsPete]

Originally Posted by Emoyeni

Thanks for this detailed post on your conversion. How many hours has this taken? Also, why does almost everyone do what you did with the belts connecting the shaft to the motor and not connect the motor to the shaft directly?

Since most of the motors used are re-purposed industrial types, I doubt that they were designed with bearings taking several hundred lbs of shaft fwd/rev thrust in mind - only rotary stresses of gearing or belts. My little Torqueedo OB states 33lbs thrust @ 0.4kW input...

[tomsnrg]

You want the system perfectly balanced vibrationswise which cannot be done with elastic couplings.

[carstendenmark]

Thanks, guys !
I will soon revert more in details, to your replies.

Skipper Lee and Murraybrowne, nice setups and nice photos !!

Amazing to see, that your "monster" diesel engines has been replaced with tiny electric motors, providing same power as the diesel did !
And with much more flexibility.

I think most buyers of secondhand yachts are thinking "oh, wow, that's an electric powered yacht, then the owner must be an electrical engineer, so we will not buy that sh**".
(But again, what do the average sailor know in-deep about diesel engines ? :-)

The problem for this nice and clean, and maintenance free technology is, that when we face a problem, not any backyard mechanic can solve it. Then we're pretty much on our own, so far.
Like driving an electric car. That is why they still don't have a breakthru.
Any garage can pick up your car and fix your Toyota Corolla 2008, but NOT your Tesla 3.

So we're just doing it for the fun and joy of quiet sailing, definitely not for the resale value of the boat !!!
However, in case that your boat has some economic value, and you may need to sell her one bad day, try to keep your existing engine bay and setup intact, when making a conversion, so a new owner can throw in a new diesel, if they want to.
If still functional, use any existing engine frame bolt threads to mount your own DIY frames for motors and batteries, etc.
Just a thought...

To make STALL / STOP clear :
When I mean a stall or a stop, it is not just related to the electric motor drive itself, so please read it like this :
A STALL is a system breakdown, so you are unable to continue motoring during the cruise. The failure could origin in any part of the system (wiring, motor, transmission, controllers, battery bank, etc.), but you were UNABLE to run the motor again on that trip.
A STOP means any malfunction of the system that stopped your motoring, but could be fixed, so your cruise could continue.


Electric motors are in general weak in their construction.
Not supposed to support or withstand anything, just made to provide radial forces. And they do so very well, for the bucks.
When an electric motor is connected via radial belt or chain drive to a shaft, it is flexible with great tolerance, and such a setup will not damage the motor and the motor shaft. Just look into your car engine bay, and take a look at the setup.
It also makes it possible to make easy adjustments to the gear ratio, when the gear wheels are exchangeable.
As we all have different boats, the tuning of each system (prop diameter and pitch/gear ratio/motor rpm/motor torque) all takes, that it is very convenient to be able to change the gear ratio in a smooth way ;-)
So, bottom line - it is BAD to connect an electric motor direct and axial to the shaft.
Never ever do it ! Even with flex couplings etc, you'll never end up happy with that !

[tomsnrg]

Solid and tested solutions can be had from a series of suppliers in Europe, a good reference is Kraeutler Elektromaschinen GmbH of Austria (i'm biased, do your research). The motor and controller are the easier part to define, they will generally perform so well you forget about them.
The equipment which requires attention is the battery, much like the old combustion engine. Think about voltage level (probably 48V), consider the charging power available, forget lead acid batteries which will not make you happy, learn well what a BMS is and does. On the occasion redesign and simplify your electrical system using only one traction battery plus perhaps some redundancy for the VHF.
Cost of a correctly dimensioned system will be around 25% to 50% higher than a new Diesel engine. The near absence of parts subjected to wear and tear means very little maintenance is required. This will make up for the extra system cost in about 5 years time. The resulting better reliability and availability should be factored in.
And enjoy the best possible add-on to a sailboat.

[tomsnrg]

The weakness in electrical motor construction is by no means a technical necessity. The directly rigid coupled inboard motor should have a rotor designed for the important mass of shaft and propeller attached. In exchange you get a nearly vibration free and highly efficient system.

[Pete7]

Originally Posted by Skipper Lee

Does anyone mechanical know why this idea would suck?

I have turned you photo round, I hope its orientated correctly.

I would certainly move the electric motor closer and remove some of that shaft. Looks like the shafts either side of the chain coupler are slightly out of alignment. Do you think you could adjust this out? One of these might help:

https://shop.tnorrismarine.co.uk/collections/r-d-marine

Alternatively there is the Sigma drive, but they are eye wateringly expensive:

https://www.bruntonspropellers.com/sigmadrive

[Pete7]

Originally Posted by tomsnrg

The weakness in electrical motor construction is by no means a technical necessity. The directly rigid coupled inboard motor should have a rotor designed for the important mass of shaft and propeller attached. In exchange you get a nearly vibration free and highly efficient system.

If you look back at the first page you can see Skipper Lee has a remote motor with a belt drive. Is this enough to give a nearly vibration free system?

[Skipper Lee]

Hi tomsnrg,
So do you think I could/should just have one shaft from the prop all the way directly to the bearing on the reduction plate and get rid of the shaft coupler of any type?
I'm thinking there would be less drag, noise, vibration. Based of course on a true, balanced shaft to begin with.
The bearing on the reduction plate has a lock to stop the shaft from wanting to creep forward with the push of the prop and the belt should not carry vibration through the system.

[Skipper Lee]

Thanks Pete,
Yup it looks poorly lined up but it is quite in line.
I am a millwright and spent time getting it as straight as possible.
First I lined it up without the motor and clamped the shafts into a SS angle iron then bolted it in place and used the compression of the rubber pads to set the final position.
I then removed the angle and checked it at 45 degree intervals around the shafts circumference with a metal rule to confirm, then a few more tweaks here and there compressing or releasing the rubber mounts. Hope its good but when I recoupled the shafts together I could get it to keep spinning a rev or so on its own with a spin by hand so just looks funny your right.
I think since I am doing it on a trailer I will recheck the alignment when I float the boat though as there may be twist when on the trailer, who can say but I worked for 40 plus years building and installing drive systems on oil rigs and other mining equip.
I'm just a DIY guy doing as best as I can to keep it quiet and true.
Super thanks for spinning my photo.

[Skipper Lee]

Jeepers, I dont know why my photos come upside down or sideways?
The red knob is the throttle in a teak disc so it wont get bumped on or off.

[Skipper Lee]

One more thing, can anyone say if there is a bit of clearance in Cutlass bearings?
I had my shaft reworked, rewelded, straightened at a machine shop to 1 inch OD exactly, verified with a micrometer. there is a few thousands clearance in the bearing/bushing. Is this normal? I used a new Cutless bearing as well. Hmmm.