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

Saturday, July 30, 2016

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

You only need about 10-15 kw per side of power for 8 knots from a 80
feet hull.
This 50% variance can change another 50% based on windage, mass, or hull
shape.

Current best solar panels are about 21% efficient => 330 W / panel, or
210 W / sq meter of hull area.
You might get, at best (imho), 12 kW of direct PV input.
Forget 70 kW, totally unrealistic.

12 kW / 0.21 (W/sq m) => 57 sq m.
Panel array between the hulls.

You need a light, strong, frame for the panels.
Spaceframe from commercial stuff would be best - something alu or carbon
fiber.
You need to start with
1. how to arrange the panels, and where.
2. size of same
3. Then power control electronics for 12 kW, with potentially 50 kw (?)
power runs.

Note spaceframe is lightest suitable structure, and even then it likely
to be 1-5 metric tons in mass.
500% variance based on how the open space is constructed, and what the
span is.
Rigidity is cube of span.

Note wracking stresses (huge, enormous) in widely spaced structure,
where the hulls want to twist and bend about 30-40 cm, wrt each other,
continuously.
Thus, mounting of frame and panels is a critical item.
Soft mount (ie non- structural) is an option, with it´s own issues.

Parts 1., 2., 3. are all critical.
Hulls are trivial.
Motors etc are trivial. Cots, easy and cheap.

There are no cheap large cats in the recreation market.
Use current cats for inspiration, and look at howto/where mount panels
on them.
Use current costs for estimation.

If you build in alu, estimated cost about 1-1.5M U$D, and 20.000+ work
hours.
Thats for a bareboat, no electronics and entertainment.

Note difficulty of making hull, almost no professional work being done
in this size, ie it´s very expensive due to practically no competition.
The pro yards don´t and wont want to do a cheap-ass build (liability,
lack of profits).

It is not, technically, hard to do alu hulls.
It´s just that there is almost no-one doing them to this size, and they
charge $$$.

A semi-pro approach would/could be to have 2 alu hulls made by those
doing large alu sailboats.
Again, the next step up is a major undertaking.

Examples:
Alu will need, for example, insulation, as its a huge heatsink.
Cost of insulation, perhaps 30-50k.
(About 20-25k per hull.).

Major power wiring.
Cost of same, perhaps 30k.
(15 k per hull, with suitable mandatory marine isolators etc.)

My point.
Running 50-100 kW power wiring, long distances in complex structures, is
a major cost.

Project management is a major cost.
Who will do this ?

I could think of 5 ways to drop 100-200 k each out of total build costs ..
but all will need significant specialist skills from someone.

CNC cutting the major elements in a cheap location (could be asia, or
anywhere, with a huge router) is one way.
Shipping the pieces is only 10k vs easily 100k+ extra cost delta to
getting them cut in the USA, for example.
Who will check them ? and how ? and authorise payment.

Example:
Who will build the 3D model, and with what sw ?
Note correct sw can easily cost 100-200k in extra work, vs "better" sw.
Ie cheap Rhino 3D can easily make pretty models, but wont drive
manufacturing processes, today, as-is.

Thus revisions in Rhino are not a manufacturing solution.
IE you cannot derive manufacturing prints from a single model- and thus
every hull revision costs 1000+ work hours extra in other stuff.

Cost of panels.
Sunpower panels are more efficient (21% vs 16%) but twice the cost at
say 1.2$/W shipped vs 0.6$ for containerload.
Thus Sunpower panels might be 14 k$ for 12 kW, vs 6 k for china panels.
Add 100% for bos, and a 12 kW system might be 24 k $.
Relatively low cost, in context.

The range is huge in terms of $$, mostly due to how the marine industry
works, in terms of business.
Thus, getting 2 hulls built and a cat based from them, is relatively
easy in engineering terms, and could potentially be not-expensive.
But based on economics, it will cost 3-5x more than it "should".

So technically, if I needed no certifications, I could probably get a
cat done for 200k in alu.
But, practically, a cat with "marine" stuff would cost around 800-1M$.
(These costs with no engineering or systems).

The same could be done, in a marine yard, for under 200 k in steel.
Steel is about the same in terms of mass (yachts over 15 m), but 1/3 -
1/4 the cost.

--

-hanermo (cnc designs)