Hi
I think this is my first post after lurking for a while
The first thing to do is to buy a good book on propellors
With a good book you can work out the power curve of your present props
with this you will be able to work out how much power is needed to drive the
boat at a particular speed
The other thing you need if you can get it is the SHP graph of your engine
gearbox combination
SHP is shaft horse power and is the real horse power coming out of the back
of the gearbox and is what the prop is being fed with
SHP takes in to acount all the losses of your engines and gearbox plus the
loses of driving the water pump alternator etcetera
There is a lot of smoke and mirrors with engine horse power as some figures
are for a fully configured engine while
Some figures a while ago didnt even include the power drain drain of the
engine water pump!
As stated before in a previous post a petrol engines output depending on the
cam it has can be a really peaky figure with the half max rpm output being
way down on the max rpm output
This means it may take a lot less power to drive a boat than at first
appears at a still decent speed
After all how many planing boats are actually driven at Max rpm?
The other thing to consider is that displacments boats drag goes way up as
you approach hull speed
A planing boats drag drops once it gets on the plane
My fantail launch will do 5 Knots at 2200rpm at 3600rpm which is allmost
twice the horsepower it allmost does 6 !
The last thing to consider which someone has allready mentioned is the
weight saving
This should not be underestimated
As
the racers say
Adding lightness adds speed
my boat <http://www.flickr.
A boat I do a lot of work on (not
mine)<http://www.flickr.
A boat I do a real lot of work (not
mine)<http://www.flickr.
> > I just found this site today. I too am interested in converting my
> > boat to electric. It is a 47 foot river cruiser with a shallow draft
> > with a Volvo v8 sterndrive that I would like to remove. We plan on
> > using solar and wind for our house power but am getting lost on all
> > the electrical options or non-options. This a go slow boat. Are
> > there any viable options out there?
> >
> > --- In electricboats@
James Sizemore <james@>
> > wrote:
> > >
> > > I see a lot of traffic on this list for smaller conversions
> > replacing
> > > A4's and such on 20-30 foot sail boats. Are there any folks that
> > have
> > > replaced larger motors on cruisers/trawlers?
> > > I will be replacing two 427 fords (350hp gas engines) on a 41 foot
> > > Chris-Craft. This if for a number of reasons including not wanting
> > > the ongoing expense of buying gas, second I really hate the
> > monstrous
> > > complexity of combustion engines. I have a computer science/
> > > electrical background so I am much much more knowledgeable and
> > > comfortable with electrical systems. And not to mention the smell
> > and
> > > noise of combustion engines. The knowledge I lack right now is boat
> > > related: prop size pitch ...etc...etc. I don't need the boat to
> > plane
> > > at 17 knots or anything like that, although if it does all the
> > better.
> > >
> > > My current thinking is to replace the fords with a pair of (Netgain
> > > Warp 11'' or Transwarp 11'')'s. The part I can not rap my head
> > > around is if I go direct drive with the Transwarp's will they spin
> > the
> > > props to fast? Or should I keep the transmissions that the fords are
> > > bolt to now and go with the Warp's. I would prefer not to have the
> > > extra complexity of the transmissions. The Netgains can move a large
> > > truck at freeway speeds 70+ MPH. My understanding of the
> > conversion of
> > > electrical hp to combustion hp is at 144v these motors should be
> > about
> > > the equivalent of a 150-200 hp gas motors with considerable more
> > > torque at the low end.
> > >
> > > The boat will soon have a fairly large solar array and already has
> > > 7.5 KWH generator. So keeping the battery bank feed should not be a
> > > problem. I know finding a solar charger/inverter for a 144v battery
> > > pack will be a real challenge. Any recommendations are welcome. I
> > > would also be very curious of other conversions of larger plaining
> > > hull boats, and what motors you use and performance you get now.
> > Also
> > > any recommendations on motors/charges/
> > > this size would be most welcome.
> > >
> > >
> > >
> > >
> > > [Non-text portions of this message have been removed]
> > >
> >
> >
> >
>
>
>
> [Non-text portions of this message have been removed]
>
>
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