T-Pain Is On A Boat: Re: [Electric Boats] Repowering Macgregor 26x

Saturday, June 13, 2009

Re: [Electric Boats] Repowering Macgregor 26x

Glenn wrote:
>
> The Myall River was only an example, we would like to repower and keep some of the performance of a 40-70HP outboard, performance is one of the reasons that we were attracted to the Macgregor.
>
>
If you hunt around this list (Is it archived anywhere ?), I think you
will find other people have done the sums and found it won't work -
electric and planeing speeds are not there yet. The power required to
push the boat over the displacement hull speed and get it up on the
plane are so high that the batteries required would make the boat too
heavy to plane in the first place.

My E-Boat will run for 4.5hrs using about 1.5Kw into the motor ( You
need may be 30Kw ?). The batteries that do this weigh in at just under
200kg. They are 'old tech' flooded lead acid, but they are relatively
cheap, easily looked after and were easily locally available. Scale that
all up 20 times. Could you shed 4 tonnes of ballast to replace with
batteries ? (

The design on my boat was done on the basis of of the old 5.5hp two
stroke it used to have (4kw). It's interesting to note that maximum
speed is reached with less than half the hp that was previously
available. (Not quite true - I can extract very small amount of extra
speed using MUCH more power, but the range is dramatically cut back -
with the old engine you didn't worry about wasting power so much and it
was easy to just leave it running hard and inefficiently!)

The motor I have will run to about 13kw peak according to it's spec
chart (half that continuous), but they can be 'stacked'.

Motors and the controllers are easy for your power, but even with LiPO4
batteries, I don't think you can pack enough in to run for any sensible
amount of time and still float.

Electric boating is still the preserve of the slow (and efficient)
displacement hulls, it's not really there for 'power boating'.
The maximum speed of my boat is about 9.5km an hour. I can sustain
20km/hr on my bicycle for about an hour on flat ground. Human powered
cycling will get you there faster!

There are some exotic electric power boats available in Europe - but
they are extraordinaryly expensive and built from the ground up with
expensive exotic high power batteries integrated into the hull and even
then they can only run a couple of hours.

I'm ignoring the electric sprint boats here - they don't have to worry
about range. They only have to last long enough to do their run and get
back to the dock.

I've just realised looking at the Macgregor site, that I've seen one of
these at Apple Tree Bay in Sydney. I was amazed at the size of the boat
being carried on a single axle trailer, and the size of the car towing it.

They also say they go well with 5-10hp engines. That sort of power is
certainly doable with electric, but forget planing speeds. You could
just double what I have (400kg) and possibly remove some of the ballast
to compensate, although given where the fixed ballast is and the water
ballast system, getting it all right down there could be difficult.
(Water and electricity don't mix)