Thanks Myles.
Interesting stuff indeed.
In order to compare solar boats, the UK Electric Boat Association (EBA) introduced a performance measure known as the "Solar Boat Index" (SBI).
Details on the SBI:
http://www.electric-boat-association.org.uk/forms/What_is_a_Solar_Boat.pdf
SBI = 3 (Ppv)/(Pm)
Where Ppv is the peak power in watts supplied by the PV panels, and Pm is the motor input power required to give a cruising speed of 5 mph (6.4 kph) on rivers and lakes, or 4 mph (6.4 kph) on canals. The factor 3 in the definition so that a boat giving an average 7 hours of weekend cruising in England, which is just "solar-powered", achieves an SBI of unity (1.0). This is easy to explain, discuss, and remember. A further advantage is that a boat's SBI value equals the expected number of cruising hours per day provided by its PV modules. For example, a boat with SBI = 2 gives an average 2 hours per day of solar cruising at "normal" speed.
They also publish a table with a few known boats:
http://www.electric-boat-association.org.uk/forms/Solar_Boat_Data.pdf
Sun21 has 10 000 watts of solar panels and need 3 800 watts to reach 5 mph (8 kph) on rivers and lakes.
SBI = 3 * (10 000)/(3 800) = 7.9
which is by far the highest index in the list.
The cost of speed is pretty obvious here:
3.5 knots = 4 mph @ 1 350 watts
5 mph @ 3 800 watts
That's almost 3 times more power!
Let's speculate it takes 30 kw to push Planet Solar at 5 mph.
Its SBI would be
SBI = 3 * (93 500)/(30 000) = 9.35
All yours,
Pierre
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