Building the Eun Mara "Skerry"
Fitting the electric motor
Discussion
I liked the idea of using electric power for Skerry for several reasons:
- If I used a "pod" style motor (where everything apart from the wiring is contained in a pod slung beneath the boat) there would be no need for an outboard well, leading to a less cluttered cockpit.
- I want to use Skerry on Lake Burley Griffin (LBG) here in Canberra, where the local Traditional Boat Squadron (TBS) has regular sailing days. Unfortunately LBG is a bit small for a boat like Skerry so, for a casual day out without the hassle of rigging, using it under power would be convenient. However use of LBG by power boats is tightly regulated by the National Capital Authority (NCA). While I probably could have acquired a permit to use a petrol outboard on the basis of Skerry being a traditional design (most of the other boats in the TBS are restored or traditional looking putt-putt launches or steamboats), the NCA does not impose restrictions on electric powered boats.
- Electric power, particularly with the fully submersed pod design, is very quiet and free of fumes.
- Although a nice idea, "green" was not a selection criterion. I am fully aware that I will be charging the batteries with coal generated electricity!
Of course, one counter argument is the need for batteries. My intention at the moment is to run the motor on 36V, with six 6V flooded lead-acid batteries stowed amidships. (Probably arranged with two behind each centre case, and two in the cockpit against the cabin bulkhead.) The total battery weight would be 168Kg.
The motor I chose is an E-Pod 2000+ motor from Re-E-Power in the USA. It can be run at 36 or 48V. Running at 48V it is rated as being equivalent to a petrol outboard of 8 to 10 HP. As I intend running it at 36V the power will be diminished, but still more than enough to drive Skerry.
Here is the motor. It is fitted by drilling two holes through the hull, inserting the mounting pipes (which are threaded at the ends), then tightening two retaining nuts inside the hull. Of course the problem with the Eun Mara is the canoe stern - there is no convenient level surface to receive the top of the mounting block. Kevin Plank at Re-E-Power kindly customised the lengths of the mounting pipes for me.
The first task was to make a mounting pylon to provide a flat surface beneath the stern on which to mount the motor. These two shots show the plywood construction. The lamination lines form interesting contours of the hull. The whole block was sealed, glassed on the sides, and then given a couple of extra coats of epoxy.
The hardest part, as always, is to drill holes in Skerry's nice hull.
And the second hardest part is to take 40 grit sandpaper to the paintwork.
Here is the pylon dry-fitted to the hull. It's hardly a perfect fit (it crosses one of the plank lands, which made shaping it more difficult), but is adequate.
And here is the pylon epoxied in place with a couple of coats of undercoat applied.
Inside the hull the reverse problem is posed. I made a couple of mounting blocks to provide a level surface on which to tighten the retaining nuts.
The motor weighs 23kg so I was concerned about stresses on the planks. The area around the closest block will be braced by the station 8 bulkhead. I have made a station 9 part-bulkhead (similar to that at station 3), which will further brace the planks aft.
And here is the motor in place (just dry fitted for now). The bottom of the propller is 1" above the keel - less than I would have liked, but adequate. I'll have to take care not to let the boat roll onto its starboard side if I beach it. I'll give the motor a fresh coat of black paint when it's permanently attached.
Overall the effect is a bit clunkier than I would have liked, but that's only a trailer-appeal issue. When afloat only the top of the pylon will be visible.
Inside the hull is simplicity itself - a couple of heavy leads to deliver all those amps to the motor, and a small poly-pipe that will allow me to check for any water in the motor casing. (Kevin at Re-E-Power assures me that there is no recorded instance of water entering the motor due to shaft seal failure. The tube has been used only to remove water that entered the motor via the inboard ends of improperly fitted mounting tubes, or was created by condensation inside the motor.)
Of course there will also be the batteries and a motor controller box, but all these should be able to be hidden discretely around the boat.