"Jeff" wrote in message
. ..
* Wilbur Hubbard wrote, On 3/28/2007 1:17 PM:

wrote in message
oups.com...

The max rating of the engines is not the point: IF the panels
produced
10 kW for 12 hrs a day straight, and there was not much loss in
storage, they could run on 5 kW 24 hours, which is 8 hp, and could
work. (I guess...)


I can tell you aren't overly familiar with photovoltaics. 10KW
represents the max output when the sun is straight overhead and the
temp is mild That same 10KW array will produce perhaps 5K when the
sun is at a 45 degree angle and even less when the angle is less. The
total wattage output of a 10KW array is probably 50-60 KW on a good
sunny day, not 120KW per 24 hour day.

You can't run motors and charge batteries and run electonics with
that paltry output.

Something's fishy here...

Maybe if you washed your hands ???

The engines and performance is no problem, at 5 knots the boat is only
being pushed to half of hull speed, so the requirement is only around
4-5 kW. With the efficient hull shape it might only be 3 kW needed.
The batteries seem to be able to stash 50 kWh, so that's about 12+
hours worth. The solar output is the bigger problem - the theoretical
output of a 10kW panel at 18N in the winter is maybe 65 kW-hours, so
pushing the boat and charging the batteries would seem to be
problematical. However, this would not be too different from a
sailboat getting less than expected winds - it would just slow down a
bit.

The biggest issue I see is that the "weight" is listed as "ca. 12
tons" which is about double what a lightweight cat would weigh. My
cat, without the engines or sailing rig would only be about 8000
pounds. Its possible that the "weight" is really the admiralty
tonnage and the actual displacement is much less. This would affect
the power needed in a linear fashion, so if the Disp is only 12000
pounds, it could be driven with possibly as little as 2 kW or even
less.

The weight is a bit obscene. The battery bank alone must weigh at least
two tons.

Then there's the array. 100, 100 watt panels at 20lb each is a ton.
That's a ton on the roof so to speak. And it looks like the roof is made
out of 2X4s - more weight up high. Must do wonders for the stability
curve. Oh, excuse me, catamarans don't have a stability curve. It's more
like a stability square. Very good stability till it gets to 90 degrees
then it's over she goes to stay over forever.


One more item: although they talk about doing 5 knots, the log is
filled with entries showing speeds as low as 3.5 knots, and very few
days over 100 miles, even though they had a tailwind much of the time,
plus a quarter knot current in their favor. Thus, they may have only
been getting 3-3.5 knots worth of power from the system.

You must remember photovoltaics make almost no electricity if it's a
cloudy day. Certainly not enough to power electric motors strong enough
to power a vessel. The could improve that thing about 50% quite easily
by being able to tilt the roof so the array was always facing the sun.
If they were really smart they could shape it like a wing sail and get
solar and sail power at the same time. Just a thought.

Wilbur Hubbard