Staycation Electric Motor Progress

So we are coming to the end of our staycation. Managed several walks, one food shop, one visit to the pharmacy.


Plus Jane has made lots of progress on the cushions. She has nearly finished all the ones we have foam for. That is all the backrests for the U-shaped part of the saloon finished. Also nearly finished the cushion that goes behind the log bench on the starboard side to make the a great sea berth.

Electric Motor

Meanwhile, I’ve continued to make progress with the electric motor frame. both end frames are complete.

Front and rear motor end plates (outside faces)
Front and rear motor end plates (inside faces)

So I have been able to attach them to the motor, add the shaft, belt pulleys and belt drive (and tension it).

Motor in the frame with the belt tensioned.
Note that the back is deliberately lower as the propeller shaft is not horizontal.

Remaining motor tasks

So just a few tasks left.

While it is already very rigid (each end frame weighs about 10kg) I do want to make sure there is no twisting or other movement between the motor and the shaft).

  • so I need to cut and drill the 4 angle lengths to attach the front and back together at the corners (all but two of the bolts already fitted to the end plates)
  • add one diagonal flat bar per side.

I need to cut a keyway in the shaft to lock the large pulley to it. Then fit both pulleys with keyways.

I haven’t got the right spanner for the big bolts on the bearings yet, that will have to wait until we can get to the boat.

Once we have sorted all that we have a much larger angle length which will be for the two cross bars that rest on the engine mounts (which we have not got yet).

Of course I’ve still got to build a battery box and do all the wiring and fitting. The box for the 4 x 300AH batteries will be positioned just forward of the pulleys. As the box will drop between the original grp coated engine bearers the batteries (2 layers of 2 batteries) will end at about the same height as the motor frame.

Weight comparisons

I’ve done a quick estimate of some of the weights. I can check what we have take out more accurately later. But

Electric Motor + Frame + Batteries (1,200AH) = approx 220kg

Diesel Engine with gearbox approx = 180kg
Two huge stainless steel fuel tanks? Guess more than 80kg (will check)
All the exhaust components, fuel filters etc etc? Guess at least 30kg
Original engine bearers (not being replaced) 20kg
Full load of fuel. Guess 70 gallons which is around 220kg
Starter battery approx 30kg

Total being replaced is over 560kg

So the new Electric motor fully fuelled is 1/3 the weight of the diesel engine fully fuelled. Even compared with empty diesel tanks the electric motor system is 1/2 the weight. And that weight is all in the centre of the hull with a much lower centre of gravity than before. So our boat trim won’t vary as much.

Space gains

Beyond all the weight comparisons there is the space issue. The entire electric motor and battery bank easily fit in just the old diesel engine compartment (with space for house batteries, inverters and solar charge controllers). So we gain 1 fuel tank plus old battery box (for 4 lead acid batteries) into the cockpit locker. Plus we gain the 1 fuel tank space at the side of the corridor to the aft cabin.

And more gains

Then there is the smell! Diesel smells horrible and inevitably over 42 years there have been leaks of fuel and exhaust soot in the boat. All that is going to end up cleaned off and painted. We can already tell the difference, by the time we are finished it will be lovely 🙂

9 thoughts on “Staycation Electric Motor Progress

  1. Tristan Mortimer June 12, 2020 / 9:40 pm

    Hi David, The project is coming on. I’m interested in what arrangements you will have for absorbing propeller thrust?
    All the best

    Liked by 1 person

    • dave42w June 12, 2020 / 10:38 pm

      Hi Tristan,
      This is an area with a bit of guesswork.
      Both the bearings on the lower shaft in the frame are thrust bearings and they are facing in opposite directions to absorb both forward and reverse thrust (I did give the motor specs to the bearing supplier so hopefully they match the loads).
      I’m choosing a coupling that will connect it this shaft to the propeller shaft that can pass the thrust onto the motor frame and also cope with slight misalignment (some can’t do either of those things).
      If the thrust seems too great for one bearing then I could add a 3rd on the very back of the frame which would also be for forward thrust.
      I’m also going to add a pillow block bearing housing between the coupling and the shaft seal (that is to make sure the propeller shaft is properly supported as the new seal doesn’t provide the same support as the old stuffing box seal. I’ll try to get a thrust bearing for that too if I can.
      So all the thrust will have been handled before the belt drive connection to the motor so not of it will be transmitted to the motor itself.
      I’m pretty confident that the frame itself can cope with thrust. If we felt that the angle bar coming out of the sides to the mountings wasn’t rigid enough we can always add diagonal braces to that.

      What do you think?


      • Tristan Mortimer June 13, 2020 / 9:22 pm

        Hi Dave,

        Sounds reasonable, I just cant see how the shaft is contained within the bearings you have fitted. It looks like it is free to move axially or are there some kind of locks, shoulders or circlips that can’t be seen that locate the bearing axially on the shaft in order for the shaft to transfer the thrust to you frame/motor assembly.

        What about an Aquadrive coupling assembly in the drive line prior to the motor assembly? This type of thing would remove the need for any intermediate bearings, would cater for a degree of miss alignment and also absorb thrust?




      • dave42w June 13, 2020 / 9:24 pm

        The bearings each have 2 grub screws which tighten onto the shaft. I’ll drill small holes for these to lock into.


  2. Tristan Mortimer June 13, 2020 / 9:44 pm

    I’m not sure I like the idea of a relying on some grub screws to transfer the thrust to the hull to be honest, it just doesn’t sound too robust. I’d rather see a set up with some appreciable surface area, like a machined shoulder on the shaft or similar to absorb ahead thrust.


    • dave42w June 13, 2020 / 10:24 pm

      Yeah. It is an area where I’m limited in skills and knowledge. Couldn’t find a lot of info via Google.
      Nothing stops us using an aquadrive so maybe that would be a good idea.


  3. Tristan Mortimer June 14, 2020 / 10:07 am

    Yes, The aquadrive is very expensive and I don’t have any direct experience with it but most that you read is positive, there are other options, Python drive which is a bit cheaper. I am sure you can also come up with your own design and you don’t need the ability to compensate for miss-alignment. Maybe you could use the thrust assembly from the Python drive without all the universal joints.

    Liked by 1 person

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