basskisser wrote:
K Smith wrote in message ...

wrote:

If they can make a car go 70mph with an electric motor, why not an
electric motor asist for large yachts,(50-60 ft) run off batteries
that are charged off a solar array situated on the canopy.

Seems like any assist would be worth while considering large yachts go
thru 1000's of gallons of fuel.

Just a thought.

Solar panels only put out tiny amounts of power, a standard large one
is good for about 80 watts, in the very best of circumstances i.e. at
noon in the tropics under a clear sky, it would take 10 to make 800
watts or about 1 HP.

Ten of the big panels would be as big as a reasonable sail area, as if
not more difficult to mount & keep oriented straight at the sun, cost
much more, weigh much more.

Then once you got 1 Hp out of them on the rare times when everything
was perfect, you'd need a huge bank of heavy, bulky expensive batteries.
They'd need at least 666 amp hours of battery capacity just to be able
to with stand a continuous charge at that level.

The electric motor is reasonably inefficient also so double all
calculations.

We had a solar powered boat here some years ago, who claimed to set
some world record or other (what BS:-)), but it was running very slowly
up & down a very protected river (we have lots of sun:-)) but it was
purpose built, other peoples' money no object, virtually a floating
battery box & not much else space left for anything else.

K


That's odd. We have a solar car race here, with cars developed from
the engineering schools around the U.S., and they do quite well. And
666 amp/hours isn't a "huge bank of batteries".

We have a similar race from Darwin to Adelaide!!! mostly local cars or
from Japan etc & yes they do perform well. However they don't make any
real power. I don't know what the accepted numbers are on a cyclist, but
I do know a good oarsperson:-) can only make a max of about a 1/4 hp
over any length of time. So that gives you some idea. I used to have an
exercise bike with a meter which read in watts & I couldn't make any
real power at all even in a burst, so given how push bikes perform
pedaled by the tiny power humans can generate, it's no real surprise
that light purpose built solar cars can also be OK.

We're a bit like batteries, we take time accept, convert & then store
the charge & then you can't draw down on it too quickly or the
reconversion bringing it out of storage will make you over heat, you can
have a quick burst then allow some time to cool & reconvert some more
charge out of storage & you can have another quick burst.

Rolling, stop, start, up, then down hill cars can use this with
batteries to advantage; not so a boat.

The "solar cars" are very light almost push bike technology. As the
original poster commented electric cars do work with nothing much more
than wind resistance to overcome on the flat but they do need overnight
plugged into the mains just to give an hour or two city type driving.

However a boat has a high & constant resistance from the water, 600
times more so than air. Even to go very slowly pushing water out of the
way takes much more HP that a car.

I agree 666 amp/hours capacity isn't that big a bank, but that's just
to be able to withstand the charge rate & not be overheated or damaged.
If ever fully charged (not likely); you now have to reconvert & draw on
it & drawing 800 watts continuously out of say 3 x 120 amp/hr batteries
will trip the inverter cutout in about 3/4 of an hour or less, leave it
a while so the batteries can recover (no added charging, just a rest to
cool) & you'll get a while longer etc.

Now imagine the numbers of solar panels & batteries you'll need to
actually draw any real HP continuously over any length of time, even
just for a couple of hours like the overnight mains charged cars do.

K