EV EXODUS      
 7.3M (24 Ft) Solar Electric Vessel
By Bruce Hannam
(Last up-dated 15/7/03)

This is a chronical of the design and development of the first known exclusively solar powered electric boat of this size. Originally, the hull was a fibreglass life boat from a sea going merchant ship, and manufactured by Viking Marine Co. Ltd in Southampton, England in 1971.
I purchased the hull and trailer, removed the diesel motor and canopies, and then set to work designing a superstructure and roof. The idea was to have a live-aboard boat that could re-charge its batteries from its own solar panels. This turned out to be harder than first envisaged, but with careful placement of the solar panels (laminates actually), I managed to get 1700 Watts (peak) worth of solar. This is a combination of BP SOLAR brand; 8 of the 85W and 6 of the 170W laminates, wired to produce a 48 Volt system.

The hull was a canoe stern type which I thought would be a more streamlined hull for easy movement through the water.
The negative from an efficiency point of view, was the greater weight than a ply hull, and the wide beam. Beam is important for electric vessels to maintain that all-important slipperyness through the water. I have a water line aspect ratio of LENGTH to BEAM of approx 3:1, but would recommend any other EV builder to try and get aspect ratio of 4:1 or higher.

Early on, and before removing the diesel engine, I needed to get some figures on the vessel's performance in the water by a 'dead' tow test (i.e. thrust required). I scrounged an old spring balance (0-150 lbs) and a GPS handheld unit from a neighbour, plus a length of rope and another powered boat (10ft dinghy with a 5HP outboard).

With a few eager helpers, I hooked the spring balance onto the front of Exodus, and then via a rope to the other boat. The GPS was powered up, a notepad produced to record the results, and Exodus's motor shut down. I should mention here that advice was to remove the prop from Exodus for this test, but I left it on to maintain full control of the vessel when leaving and returning to the boat ramp and also the extra resistance of the prop helped to compensate for the extra weight of the completed vessel. Three people were aboard Exodus and two in the runabout, and this should be regarded as a minimum for a satisfactory outcome.

After much ado trying to get Exodus to follow straight behind the runabout, before the runabout lost it completely and skittered far off to the beam, we finally started to get some figures. Result was perhaps 10 measurements of spring balance reading at different speeds up to the maximum achievable with this runabout of 4.2 Knots.
These were graphed, and from it a fairly consistant curve was produced. Extension of the curve up to 5 Knots showed that thrust of 50 Kgs would be required for Exodus to achieve the desired cruise speed of 5 Knots. The Viking hull seems to have a maximum speed of 7 Knots, but at this speed has its bow right up in the air and the stern dragging, and great amount of wash being produced. At 6 Knots the boat is better but still shows that its not happy, but at 5 Knots the boat slips along with very little problem. So 5 Knots it is.

So how much power is required to provide 50 Kgs of thrust at 5 knots (9 kph)?
Apply the equation:     Power (Watts) = Speed (Metres/sec) x thrust (Kgs) x 9.8

In this case, Watts = 2.5 x 50 x 9.8
                            = 1225

We have installed a 1500 Watt continuous motor, which still allows some margin for inefficiencies.

Roof was sub-assembled and then lifted on to the bulkheads - the forward bulkhead only has the doorway at this stage. Work progressed quickly then and the forward cabin area completed. Next came the motor and thruster tube. Thruster tubes replace the rudder, but do a similar job by directing the propellor water flow to one side or the other. Their big advantage is the boat steers in reverse!

So here we are now to July 2003, and work is progressing. Watch this chronical for the frequent updates.