Hi Chris--
I took a pair of partly waterlogged and partly sand filled 16 ft Prindle hulls (Say 110 lbs each) and joined them by a pair of 8 foot treated waterlogged 4 X 4s (say 30 lb each) and put a sheet of waterlogged 3/4 inch marine plywood on top (say 80 lbs) on which I placed a group 29 Wal-mart deep cycle battery (say 65 lbs) and to which by means of various fixtures (say 15 pounds) I mounted a T-34 motorguide trolling motor with modifications to the underwater part and weighing say 15 pounds. Total weight--I estimate about 455 lbs. With just me on it, it ran 4.7 mph drawing 30 amps at a total displacement estimated at 635 pounds. Without the battery or motor, I estimate weight was about 375 pounds, and I could move it around on level ground easily by teetering it on 2 inch PVC pipe.
I have fixed and lightened the hulls, found a mast to cut for replacing at least one of the 4x4s, and I am in the process of building a bridge for replacing the front cross-brace and serving as a motor and battery platform and for mounting a T-top. I haven't weighed the hulls yet but I think they are less than 100 pounds. I am guessing the bridge will weigh about 50 pounds. The aluminum mast sections for the cross pieces weigh maybe 10 pounds each. So I am look at a hull weight, without motors, or battery, of about 260 lbs.
I intend to power it with a pair of modified T-34 motors and shafts, but will discard the mounting brackets to save weight and replace the heads with remotely mounted Motorguide Varimax heads for 45 pound thrust motors for efficiency and to enable skid steering. I will use the rest of the Varimax motors if I cannot make the heads work with the T-34 motors, but they are much heavier and not as streamlined. I estimate the powertrain will weigh about 20 pounds.
With a 30 pound battery, estimated weight would be about 310 pounds. A 200 watt solar panel mounted on an aluminum tubing T top would probably add another 60 pounds, up to 370, which I think is right on the edge of what can be dragged up on a gentle bank or beach.
With a 130 pound battery, I think it would be over that line.
John Casperson
--- In electricboats@yahoogroups.com, Chris Witzgall <chris@...> wrote:
>
> John;
> If you outline the entire system you are considering, I am sure folks here
> can make some suggestions. The Lifebatt cells are quite expensive for the
> power they provide, but are good stuff, and support high charging and
> discharge rates. Headway makes similar cells that are cheaper, and there are
> prismatic cells that are much better economically if you don¹t need the high
> discharge rates.
>
> Chris
>
>
>
> On 4/1/11 12:41 PM, "john_casperson" <john_casperson@...> wrote:
>
> >
> >
> >
> >
> >
> > The target weight for a boat I am constructing is 300 lbs, so it can be
> > dragged up on the beach.
> >
> > I asked a vendor for a quote on a 12V 200 Ah Life battery. He asked what I
> > wanted it for. I told him to replace a pair of Wal-mart group 29 deep cycle
> > batteries and save 100 pounds in weight. He then recommended
> >
> > "My take on your project would be to use (1) 12V / 30Ah LiFeBATT Lithium
> > prismatic cell battery. Cost = $ 550.00 plus $150 shipping. Weight = 13
> > LBS."
> >
> > A 12V 45Ah lead acid battery weighs the same as what he quoted, and only costs
> > 1/5 to 1/4 as much. If I wanted woefully inadequate capacity, I'd do that.
> >
> > What are these batteries for?
> >
> > John Casperson
> >
> >
> >
> >
> >
>
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