Last update: Sep 18 2021

2021 - Going Electric

The goal - to replace this:

Watermota SeaWolf, circa. 1972

with this:

Thoosa 7000HT, circa. 2020

(OK, without the dirt either...)


The motor is a Thoosa 7000HT, rated for 7kW continuous output, running on 48V DC. It is reversible, and capable of some "regenerative braking" when under sail.

The batteries are ReLiOn RBGC248V LiFeO4 (LiPo) golf cart batteries, rated 30AH at 48V, with integrated battery management electronics and CANbus interconnect. Two batteries in parallel is the minimum to run the motor at full speed.

For shore power, there is a GX4820 48V 20A industrial charger.

For solar power, there will be ten Solarparts semi-flexible panels, nominal 100W but actually rated 74W at normal operating temperature. There is a Smart Solar 150/70 MPPT charge controller with a remote display. The panels produce 16.5V at the maximum power point, the batteries need at least 55V to charge, so there will be two strings of five panels each, producing about 80V.


11 June 2021

Sketch of motor installation (PDF)

Click thumbnails for larger image

Motor with Mk 1 temporary shaft extension

New instruments - motor and solar monitors

First two batteries under cockpit sole

Solar charge controller

Motor, controller, circuit breakers


25 July 2021

I'm in a Catch-22 - I need a motor to get Alastor from her mooring to a boatyard, but I need a boatyard to switch the motor. Or do I ?

The starter motor on the original Watermotor jammed in 2020, but I was able to remove it, take it apart and free it up. This year it did the same thing, but I'd had enough - I removed the entire mess and temporarily fitted the electric motor while at the mooring - lowered the engine onto my little catamaran with the boom, took it to shore and dragged it up the beach with my truck.

My initial idea was to make a temporary propeller shaft extension, just good enough to let me motor out to sea, and sail to a boatyard. My first attempt worked - everything ran, I was able to move under electric power (at least, after removing a heavy weed growth from hull, propeller and rudder), but the plastic broke when I applied more throttle to counter a current. Fortunately, there was favourable wind so I sailed back to the mooring. The second temporary extension was in steel pipe, but I had some wobble which would probably have damaged the stern tube if I'd gone very far. The current plan is to get a complete new shaft and coupling fabricated, which will take at least a couple of weeks, then careen Alastor to fit the new shaft. Then I can proceed to the boatyard in a more normal fashion for haul-out and painting.

I tried to remove the propeller at the mooring, using SCUBA gear. I'd made up a custom prop puller, but nothing doing. So to plan B - remove the shaft together with propeller, then replace it temporarily with the original bronze shaft I still have from around 1990 to keep the water out. Doing that in situ would probably have worked, pushing the old shaft out from inside with the even older one, but it was easier and less risky to careen the boat and do it out of the water. I managed to finally get the prop off the shaft with the aid of a heat gun (bronze has a thermal expansion coefficient of 12 compared to 7 for steel) in conjunction with the prop puller.

Solar panels temporarily mounted on mainsheet slide. The final plan is to fit a second track alongside the mainsail track so I can hoist both at once, or at least not have them interfere with each other.

Mk II temporary shaft extension

Mk II motor mounts, replacing Mk 1 wooden ones

Careening Alastor in Horton Bay to swap propeller shafts.

The propeller puller


16 August 2021

I took the motor and propeller to VM Dafoe in Vancouver, who as it turned out had fabricated the stainless shaft for me back in 1990 or thereabouts. He gave me a lot of grief about how the Thoosa shaft wasn't properly designed for a coupling, and how they didn't do metric and it would be a special job and expensive and would be at least a couple of weeks work and put at the end of their job queue. Then I got a phone message in 5 days to say it was finished, at half the price. Maybe he liked me when he found we'd both built a houses on Mayne Island, or maybe it was the challenge.

The original Watermota gearbox had a 1 inch shaft, same as the propeller, and a keyed flange secured with a nut (and really well jammed on, almost an interference fit). The propeller shaft had a mating keyed flange, secured against reverse thrust with a couple of bolts bearing on dimples in the shaft. Dafoe's new flanges are better engineered, with an alignment ring between the flanges, and secured with through bolts that engage with indents machined in the shaft. The new longer propeller shaft had the indents already in place, but they didn't want to touch the Thoosa shaft, saying it might be hardened or something. I managed to carve the indents with a file, and using a twist drill as a ream to get the right shape. I also lapped the flanges onto both shafts using a bit of polishing compound, as they were really stiff - I didn't want to have to bang them in place with a hammer.

Thoosa motor with new coupling flanges

Thoosa motor with indents filed in shaft


21 August 2021

I unloaded a few more petrol-engine related items - a gallon of new engine oil, various spares (plugs, points), the water-injection silencer and cast-iron exhaust pipe (seriously rusty, it had been leaking exhaust), a few pounds of loose rust, a pint or two of dirty oil in the bilges, to go with the spare petrol cans and the in-keel fuel tank removed earlier. Amazing how much there is. There's still the rubber exhaust hose and the fuel filler hose if I can be bothered.

My mast hardware that had been on order for a couple of months arrived, so I was able to fit that. It was made to take countersunk bolts but I wanted to use pop-rivets, so I ground a twist drill flat and used that to machine the bolt holes to a cylindrical shape.

Solar panel track with temporary spar.

I contrived to thread a cable from the engine compartment under the portside bunk and up the mast, for the solar panels. There are two strings of five panels each, sharing a common negative wire. The two strings are in parallel, each with a separate circuit breaker. That gives a suitable voltage to feed the charge controller - it has to be somewhat more than the battery voltage (50V), but less than the maximum allowed (120-odd volts I think). Each panel gives 16V at maximum power point so that's 80V per string. This arrangement also lets me hoist half of the panels and still charge. When drilling the hole in the mast, I found I'd gone into an internal conduit or pipe that contains the cables for the masthead antenna and light. I hadn't realized that was there, but it worked out OK in the end. I was able to run a fish tape down and out the bottom of the mast, and pull a steel wire through, and then the actual cable, well lubricated with washing-up liquid.

Solar power cable in mast, with connectors for two strings.

Final arrangement of four batteries in parallel, 120Ah at 50V. The batteries are lithium iron phosphate, with integral battery management. There's a CANBUS connection daisy-chained between the batteries to synchronize the BMUs and allow them to be controlled from one button. I'm hoping to get a remote monitor and switch - removing the cockpit hatch is hardly convenient. (The batteries can be turned off, and the actual state of charge monitored on a pair of LEDs, as opposed to the motor controller's idea based on being told when the batteries are full and measuring the current used).
The battery shelf is plywood, shaped to fit the hull aft, supported on wooden rails screwed to the plywood locker sides. The acrylic cover is mostly to avoid "bad things" were a metal object to fall across the terminals. (I believe the batteries have internal protection, unlike a lead-acid battery, but I'd rather not test that).

Setting up to align the motor. The weights and pulley are supposed to balance the unsupported weight of the prop shaft.

25 Aug 2021

Cleaning old oil from the bilges with slices of plastic foam

The Watermota had been leaking oil for some time (years). I hadn't realized quite how much. Most of the oil was in the bilge under the engine (the oil pan overflows with rain water that gets past the cockpit floor seal, and weepage from the stuffing box, carrying oil with it).

2 Sept 2021

Panels mounted on auxiliary track - I can hoist the panels and the sail at the same time.

I've ordered material to fit a second track on the starboard side, so I'll be able to collect power sailing east as well as when sailing west.

The Great Battery Connection Question - my investigation into whether I had connected the batteries "wrong", or whether there was a better way.