An 80 feet boat has 12.7 knots hull speed.
http://www.cncphotoalbum.com/technical/hullspeed/hullspeed.htm
You could maybe, possibly, surf ie plane a cat, as many cats do so.
But the power requirement goes up about 3-400%.
The *correct*, imho, choice is forget surfing.
Even 12 knots is extremely fast, and the "right" choice is about 10.5
knots, at 1/2-1/3 the power needed.
The last 1-2.2 knots will take 50-70% more power, than the previous ones.
Fact:
99% of ALL cruising boats in the world, are small sailboats.
Avg speed for small sailboats is about 5 knots.
99% all all cruising ever done was done at less than 8 knots.
When building a new boat, for electric, the "right" choise is to get a
big, big, bigger prop, optimised for efficiency.
It will, approximately, double-triple the efficiency, compared to
"normal" props.
Current props, in the main, are extremely inefficient.
This is easily demonstarted.
A small motor can pull a hull throught the water, with a rope,
efficiency approx. 97% (non-slip).
To do the same with a prop increases needed power by 3-5x.
A good example.
A human can generate about 60 watts power, by hand (pro bicyclist about
100 watts).
This 60 watts will move a 24 metric tons, 24 meter long, steel boat, at
about 1 knot.
Anyone who has pulled a heavy hull to a pullard has experienced this.
Tons of exampes in old posts ...
using an efficient powertrain and electric drive, you would actually
only "need" maybe 6 kW total for some decent movement, circa 6-7 knots,
in my estimation.
For a 24 m / 80 feet hull.
Thus a 12 kW in-feed is realistic, for practical long-distance cruising.
Recommend:
Get 2 x 100 kW batteries from a wrecked tesla, second hand.
And get the battery conditioning/cooling, working, so they stay at 29C,
+/- 1 C, for excellent long-term longevity.
These numbers came from the service screens in a Tesla (about 39 or 30C,
iirc).
The most driven Tesla S at 140.000 miles, still has 94% battery capacity
left, and this is average for a set of 300 results, pointing towards an
expected lifetime of 10-15 years.
Note that 90-97% of the time, the boat will NOT be moving.
A cruising boat is not a taxi service.
Calculus.
10 knots (high) x 24 hours (high) x 365 = 87.600 miles.
Enough to go around the world, twice.
Or typical circumnavigation territory, in typical 8-10 years average
time spent.
A longest-trip, crossing the atlantic, say, 3000 miles, might be a
full-on trajectory.
At 240 miles / day, thats only about 3000 / 240 == 12.5 days.
Most of the time the boat will be stationary, so You can look and
something, and *enjoy yourself*.
On 02/08/2016 12:30, David Adams lonzim.adams@gmail.com [electricboats]
wrote:
>
> And it needs the whole 180kW to push it through the water at 14knots.
> And that's with a hull speed of about 10knots.
>
> So, Hannu, it looks like you're right on the money with your estimate
> of 10-15kw per side to push an 80'cat at 8kn or so.
> But if I want to put the hammer down to escape a storm or some other
> emergency, I'm still going to need a lot of power to get the boat up
> to anywhere near 15kn max speed.
> If Turanor needs 90kW a side, I don't see how I would be able to do it
> with less?
--
-hanermo (cnc designs)
Posted by: Hannu Venermo <gcode.fi@gmail.com>
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