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)

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 he shaft with the aid of a heat gun (bronze has a thermal expansion coefficient of 12 compared to 7 for steel) in conjuction 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.