T-Pain Is On A Boat: Re: [Electric Boats] SEVCON BRUSHLESS SAILBOAT KIT

Wednesday, March 9, 2011

Re: [Electric Boats] SEVCON BRUSHLESS SAILBOAT KIT - 8.5kw

Thanks Josh, I didn't have the numbers to explain it so eloquently like you have. I was just reading on yahoo news that it takes the Queen Mary 2 one gallon of diesel to move the ship six inches. Proud to have gone electric

Don

On Wed, 09 Mar 2011 07:32:02 -0000 "jrmdive" <josh@massie.org> writes:

I'm in the middle of my conversion. Just a few numbers for you to keep in mind when considering whether or not electric will work for you. Numbers are for a Catalina 30, which is 10k lbs and change, so about 2/3 your displacement.

It takes about 100 lbs of thrust to move my boat through calm water at 5 knots, or about 3.2KW with the geared system and optimized prop. So to get 8 hours at that speed, I'd need 25.6 KWh, or 533 Ah at 48V. The string of 4D AGM batteries (4 of them) has about 200Ah @ 48V, but at 60% depth of discharge leaves about 120Ah usable. Assuming no Puekert (and that's a huge assumption) it would require 5 packs of 4D batteries (20 total). Mind that at 129 lbs per battery, you've got nearly 2600 lbs of battery. Kick that up even to the Super 8Ds @ 275Ah each and it would still take 4 packs (3.2 if you could get .2 packs). Those bad boys are 161 lbs each, about the same weight at 2576 lbs. At $750 each, that's $12,000 just in batteries. It's starting to make Lithiums look better (I have no experience with them, so I'll leave that exercise to others)...

Your boat being significantly heavier is going to require more energy than mine to achieve the same speed. So what is $12 grand for me is going to be a lot more for you. As you can see, it is theoretically possible, but not really practical for other than research/PR. However, if I am willing to drop down to 4 knots, I can achieve that with 1.5KW, an 8 hour total of 12KWh, or 250Ah at 48V. I can do that with 2 packs. So dropping a knot of speed basically doubles my range. Again, your boat is larger, but the same principle applies.

It doesn't really matter what motor you choose (other than to be less efficient and thus require even greater energy) or what vendor. You can't beat the physics. Anyone who says otherwise is selling something. At that speed and range requirement, an ICE engine is much more cost and weight effective, so if you are set on electric, perhaps a hybrid system.

Josh

-- we'll see if I know what I think I know or whether I've been breathing too much acetone lately...

--- In electricboats@yahoogroups.com, "Greg. Postnikoff" <aircharterscanada@...> wrote:
>
> Donald,
> Just a short question. What type of electric motor would you pick to power your vessel 8hrs? I also currently have the 35-II Ericson same tonnage.
> Greg from Kingston Canada
>
> Sent from Tripnic's iPhone.
>
> On Mar 7, 2011, at 11:48 AM, "Bill Tucker" <bill@...> wrote:
>
> > Donald,
> >
> > I am also thinking of the system for an Ericson 35-2 11600 lbs. a couple of questions; What reduction did you use 2 to 1? What batteries do you have? and how long can you run on a charge?
> > I am thinking of a 1 to 1.5 or direct drive system to get 5 knts. Do you have any problem with tork?
> >
> > My goal is to run for about 8 hours at 5 knts. (1200 rpm.) I am thinking of using 2 sets of 48 volt batteries, and switch off and charge one with a generator while running on the other.
> >
> > What do you think?
> >
> > Thanks
> >
> > --- In electricboats@yahoogroups.com, Donald M Swanson <postal6@> wrote:
> > >
> > > Not sure who you got your kit from Carlos, but I have an Ericson 27 that
> > > has been on the system for going on two years and I have no complaints.
> > > I might add that I am using wet cell batteries too. The only advice I
> > > can give you is don't push your speed. It will get you out of a quick
> > > jam with a little burst of speed, but try to keep it at one half of hull
> > > speed, in my case 3 knots or less, which will give you a couple of hours
> > > of cruising without any problems if you are in a bay. Depending on your
> > > boat, you will need to probably go with a three blade prop like I did,
> > > and with that said, you will do fine. Don
> > >
> > > On Sun, 06 Mar 2011 01:05:40 -0000 "Carlos Silva" <pahuac@>
> > > writes:
> > >
> > > I am about to start my conversion with this kit and therefore would very
> > > much appreciate comments on actual experiences and tips.
> > >
> > > Thanks,
> > >
> > >
> > >
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