Rick,

In the Monte Carlo cup (very interesting by the way) are the boats using batteries in addition to the solar panels?  It occurs to me that the solar panels are mostly for show and that the boats would be lighter and faster without them.

Solar racers are usually not permitted large batteries.  A small battery is usually required to stabilise voltage.  The E340 race has no restriction yet on battery size or solar array.  There are talks of setting limits to prevent high speed boats and keep costs down.  Solar cells are extremely light so pack a lot of power to weight.  The 2.2kW panels on the E-340 boat weigh 40kg and when/where the race is run, average sunlight day is equivalent to 7.5 hours full sun.  This results in 410Wh/kg over the day.  A good lithium battery gives about 100Wh/kg for a single charge so it is better to get more solar panels than battery if going long distances.    The Monte Carlo race Day 1 was an endurance event where greatest distance over a set time won.  Large batteries would be detrimental particularly on a foiling boat where power to weight really counts.

Your solar race boat design looks really nice and I am curious. It seems to me that the hulls rocker shape will cause the bow to lift, reducing the waterline length of the boat and with the bow out of the water the front plate surface area will increase, further raising the bow and lowering the stern increasing the drag there. The design also appears to have a sharp edge chine which causes a lot of drag.

This hull shape  is the product of about 30,000 iterations of a drag minimisation routine.  So that will be the lowest drag hard chine hull for the design speed and design weight.  Remember that this is a displacement hull with some dynamic lift.  It is not a planing hull.

The linked photo shows Twin-8 as a light hull sitting on the water.:

It has a concave keel line.  Again the shape is a product of 30,000 to 40,000 iterations to target minimum drag for its design displacement and speed. One of these hulls is being paddled as an OC2 and the owner believes it is the fastest OC2 he has ever used but has not raced it yet - it will be used in a shootout some time in April so we will see how it goes:

I figure this will be the first hard chine OC2 to be raced and maybe first ever hard chine OC2.    

I would be curious at what the difference would be if the entire hull was flat (eliminate the rocker) and the chine was a nice radius curve. I bet the wetted surface would be very similar (increased a little), but the frontal flat plate area would be reduced, the waterline would be increased, the drag from the chine would be reduced, and the drag from the stern would be reduced. I think it would improve your L/D by a third.

And while I am ranting, it might be worth your while to round the edges of the deck and bow for improved aerodynamic efficiency. Airflow and water flow hate sharp edges.

The deck is a wing profile with prospect of adding wings extending sideways to use ground effect to get it to fly at low speed.  As it is it has quite a tendency for aerodynamic lift. In a good head wind it will semi-fly to reduce water drag. 

But and this is a big but, at lower speeds, below 4 knots or so, none of the 'improvements' I suggested will make any difference at all and the increased wetted surface will increase the initial drag. Fun choices eh?

It will have enough battery on board to hold 6mph overnight but should be close to finishing the race in daylight as there is typically a 4mph current to add to speed over water.

Talador

• Privacy • Unsubscribe • Terms of Use