T-Pain Is On A Boat: Re: [Electric Boats] AC vs DC motors

Wednesday, August 3, 2016

Re: [Electric Boats] AC vs DC motors - new EC cat

Well said really. One of the biggest lessons I learned easily was to purchase the smallest boat possible to begin with. The facts are pretty basic when Hannu tears them all down the way he has. When you consider the previous two comparisons between the unrealistic solar catamaran and the Sun 21 which was realistic be sure to consider something as simple and elegant as the "Black Hole Sun" catamaran that I outfitted.

LOA 26.3'

LWL 25.5'

Beam 14.5'

Displacement 5300 lbs. Loaded.

With two simple Ray 48v electric outboards I have more than enough power to get where I'm going and just the right amount of solar (2160 watts) to charge my lithium batteries in a day or two if wanted or needed. Redundant high amperage gasoline generators provide ample amps to run directly off generator if need be. All without breaking the bank or the brain in one of the most stable family cruising catamarans ever made.

If you want horse power for electric then check out how that translates over at Electric Seas where on person relates to building his Tesla Boat that just literally rips - but then only for an hour at top speed. I'm pretty confident that if I wanted to cross the Atlantic with mine I could do it easily as well even at my ideal 4.1 knot cruising speed. Admittedly I'll probably get 4 more 180w panels to bring the total up to 2880 w of solar and anywhere from 20-30 amps at 48v nominal charging being realistic.

As it sits now I can motor around and make 20-25 amps I'm sure! Just never had the opportunity to completely experience that luxury yet. The extra 4 panels would be pushing the limits on the standard rating for the wire for the panels themselves but then again they will never see STC conditions. It would only serve to guarantee more solar yield.

Go small, go slow go efficient. That is after all what electric is all about. Why reinvent the wheel again? The original post is so far gone now I forget the reasoning or need for the large catamaran. Ideally what you would want to do is buy the one I have and make a template from it in real life out of aluminum and then just extend the hull length some and call it done (that is if you want to spend money). Low wind profile and ultra light with more electric thrust than you know what to do with and all the regenerative solar you can incorporate. Or keep as is and enjoy!

I'd never recommend going with tesla batteries. Most of it is marketing FUD designed for sales. When in comparison you can have a much better batteries with some of Winston Chung's offerings. http://en.winston-battery.com/

I really don't think the mega take your money battery factory that tesla proposes will prove to be better that what the preceding company is offering. The tesla batteries are an exercise in over complexity. Not something you want on a boat. Winston battery is where it is at - they are years ahead of anyone else. Still waiting to see some real life cruising numbers from James Sizemore and how he is enjoying and using his solar electric craft with the 1000ah batteries.

From: "Hannu Venermo gcode.fi@gmail.com [electricboats]" <electricboats@yahoogroups.com>
To: electricboats@yahoogroups.com
Sent: Wednesday, August 3, 2016 6:01 AM
Subject: Re: [Electric Boats] AC vs DC motors - new EC cat

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)