Jason,
I applaud your desire to convert your cat to electric drive, and look
forward to hearing about your future progress. You didn't mention whether it
is a sailing catamaran or a power cat.
Having cruised for seven years on my 33' (now 36') Seawind sailing catamaran
with two 9.9 Yamaha HiThrust outboards, let me simply say that there are
times when serious long-term motoring or motorsailing becomes a necessity.
Examples are the Baja Bash from Cabo to San Diego, going round Point
Conception, or simply having to motor a few hundred miles when the wind
becomes non-existent when crossing the Tasman - and wanting to get it over
with before the next front hits!
This is quite a different scenario than using one's boat for a daysail out
of a marina or for short coastal hops.
That said, I've also been very keenly following electric drive and
lightweight battery progress and think there is "green" merit to the concept
of having an electric drivetrain as, in my case, either an addition to the
two gas outboards or else replacement of one of the outboards, simply to
significantly reduce reliance on fossil fuels.
I can readily rationalize additional batteries in terms of increasing my
house bank (thus further reducing my nightly DOD). In considering, e.g., a
48v Torqueedo, there are alternatives such as appropriate relay/contactor
switchovers (disconnecting four 12v paralleled batteries and putting them in
series) or maybe leaving them at 48v and using appropriate dc-dc
converters/chargers in both directions. Lots of possibilities. In my case,
having onboard 500+W solar panels and a windgen, I can envision all the
batteries usually being fully charged and available when needed - after all,
I really do sail most of the time.
Motorsailing to windward with the engine at very low rpm is a very effective
technique for dramatically improving VMG, and motoring at ever-lower speeds
results in significant range improvements. When you are cruising, boatspeed
becomes somewhat unimportant unless you're trying to beat/escape a weather
system. In your example, say your five hours at five knots (25nm) could
perhaps increase to 20 hours at two knots (40nm). Need to do the math...
Yes, also having the Honda generator adds another measure of peace-of-mind,
and would be a great range extender. Glad to see you continue using two
drivetrains - wonderful for marina/anchoring maneuverability, and of course
reliability through redundancy. Perhaps outboards such as the Torqueedo
would be much lighter and more efficient than converting a conventional
outboard?
BTW, other than wanting to be green about it, I think you may be
hard-pressed to justify the cost-effectiveness of installing an electric
drive system, especially with Lithium batteries of whatever flavor in
today's dollars.
Bottom line, I like what you're thinking of doing if you can afford it, but
would suggest having a decent gas outboard as an emergency backup, with
enough gas for, say, 12 hours of hard motoring (all depending on your
cruising venue).
Wishing you all the best,
Joe Siudzinski
--
http://www.KatieKat
> From: jason_d_s_uk <jason_d_s_uk@
> Reply-To: <electricboats@
> Date: Wed, 09 Dec 2009 16:57:14 -0000
> To: <electricboats@
> Subject: [Electric Boats] Re: Electric Catamaran
>
> Hi, i've been watching this group as I'm hoping to do a conversion in the
> future on my 30ft cat.
>
> I'm realistically upbeat that this can be done and have the following as my
> concept.
>
> 13*200ah Thundersky Lithium Batteries
> 94.9 KG, 9.75 KW ( 200ah * 3.75v)
> 2 motors attached to twin outboards as replacement for the engines.
> 2 Controllers, BMS etc.
>
> Based on a previous post, using 1.5kw /h @ 5Kts, this would give me:
> 9.75/1.5 = 6.5 hours continous use. Limit it to 80% DOD = 5 1/4 hours.
>
> As reserve, I would have a small generator (honda 2kw) which is about 25kg and
> a couple of gallons fuel. This would provide me with at least 12 hours
> running in an emergency situation.
>
> This also excludes the 1 x 200W solar panel and 400w Wind Generator which main
> use would be recharging for free.
> My requirements at the moment are for sailing a couple of days, then stopping
> at a harbour overnight. Having done this recently, the most time I used the
> engine for was 2.5 hours in a day and more likely 1.5h which would easily be
> recouperated by the wind/solar gen.
>
> The two motors this setup would replace would match weight wise (50kg x 2).
>
> Any comments?
>
> Regards, Jason.
>
>
>
>
> ------------
>
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