Re: [Electric Boats] Re: Arrival of Motor and Controller

James - Exactly.

4.3 kW @ 6.
111/6 = 19.3 hours
x 4.3 = 93 kWh

Also agree with the rest of the comments.
But.. on equestion.

With what size propeller is the tartan for example ?
And compared to the original on a 34 foot sailboat ?

As, I am pretty sure, that the best propeller choice for this, would
likely increase the efficiency hugely (30%),
as would going at 5 knot (my example) (another about 20-25%%, from 6
knots to 5, for 34, by estimate).

As 30% efficiency gain is a tremendous BOS cost and total power budget
reduction, this would make a lot of sense.

Today, NOS, or best prices, for batteries, 200$ * 90 kWh == 18.000 $.
A 30% reduction = 6000 $ savings in battery costs.

If the 6-5 knots reduction is also correct..
And the 30% + 20% = 50% total energy expenditure is correct, we are
lookng at around 2.7 kW (realistic) for 5 knots, with optimised propeller.
Now the total battery needed is only 45 kW, and the BOS cost is reduced
9000 $.

By around 2018-2018, the total system costs will make this a better
option than ICE solutions.

James - one more comment.
I looked at your "sailor" electroprop system.

I highly suggest you try a new modern ac brushless servo drive for the
motor- as a test if nothing else.
They are near 100% efficient, and thus DONT HEAT (well of course they
do, but very much less).

They are also probably 20-30% more efficient than whatever commutation
and drive technology your current version uses.
This can then drive interesting results with your oem component providers.


Example.
My 2.5 kW continuous output servo, under upto 300% overload (3 secs),
does not get hot at all, with no forced ventilation.
Is also about 1/3 the size of an industrial ac motor of 1.5 kW output
(220V).
Output shaft is 17 mm, and torque is 10 Nm continuous, 3000 rpm.

Some low rev high torque versions exist, with 17 Nm from similar, from
memory.

Heat = lack of efficiency.
Cool motor outputting power = efficient.

(I am not selling products - just suggesting a technology path. We wont
build servo motors).

Interesting to hear about the propeller data.

One more, perhaps inetresting, option:
I will soon be able to make propellers, at will, in 1 day.
The larger cnc mill will be able to handle large props (1200 mm squared
work area).
Alu will work fine for test props, and might work long term- since alu
sailboats last indefinitely.

The ability to generate props "free" (materials cost only), might allow
fast, cheap, development of much more suitable shapes, curves, and sizes.

I scratch built a large VMC CNC milling machine, of industrial type.
As I dont plan to make commercial products, 24x7, on it, as its mostly a
demo for cnc kit (servos, ballscrews, instruments, metrology), some
other type of product development might be interesting.
(The machine is slated for video demos in january).

Its possible to mill anything else, but large steel billets are out of
my comfort range re: materials handling.
Bronze is expensive for development purposes, but the machine will
easily do it.

Table can theoretically support 25.000 kg, but I never expect to do more
than a hundred (200) kg or so.

Best,
Hannu


On 14/12/2015 18:53, James Lambden james@electroprop.com [electricboats]
wrote:
>
> The best way of arriving at the correct propeller for EP at this time
> is by looking at boats that are currently working with EP.
>
> EP closes the gap on diesel because of efficiency. Efficiency is very
> closely related to how much slip a propeller has. I liken it with a
> car stuck in snow…. the tires spin but the car doesn't go anywhere.
> A large propeller has traction and does not waste power.
>
> Our standard propeller with a 5 KW drive unit has 14 inches of pitch,
> about 85% blade area ratio, and cupping on the propeller. This
> results in top speed achieved at 750 rpm compared to a diesel top
> speed of 1200 rpm. With almost half the slip, you can see why we
> can achieve such great overall efficiencies.
>
> The fact is that an electric motor is far better suited to turn a
> propeller than a diesel can ever be, because it takes torque to turn a
> propeller, which is where electric motors with speed reduction rule.
> It is impossible for a diesel of gas motor to turn the big propellers
> we can use with Electric. They simply do not have the torque or
> rotational momentum to turn a big propeller. We commonly use a
> propeller on our electrics that is meant to be turned by a diesel of
> 20 times the horsepower!

--
-hanermo (cnc designs)



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