In article
"Tony Kenny" writes:

So, a 12v 140 Amp-hour battery on a 4kW motor will last 0.336 hours?
Or have I made a tits-up of the calculations there? At half speed
that would give 1.344hours? Seems like I'll need an extension lead in
the water with me

My bout is deep vee hull, 13' 6" long, 5' 6" beam I don't know what
LOA, BWL and Draft are, sorry, I'm new to the whole boat thing, I
usually stick with canoes and computers.

If you have a displacement hull of those dimensions then the maximum
theoretical speed would be 5.2kts. This speed would require an 800W
motor to move it at that speed (assuming a reasonably efficient
propellor.

I think my outboard is worth about £200 in its current state so it
would be nice to be able to do all this within that budget or a little
more, is electric going to prove v.expensive to get the same times on
the lake that i do now? Ideally I'd like to get 10mph for 5 hours...
mission impossible maybe?

If you need to do that sort of speed at least a 4kW motor is needed.
For that sort of duration then be prepared to put in a battery of
about 20kWh capacity. This could be achieved with six Elecsol 270Ah
batteries wired for 24 or 36V powering a LEM170 motor through a 4QD
300-36 motor controller.

So the mission is possible only if you are into doing some quite
intense engineering. I am sure you will find a suitable prop from
the Piranha range. Angle gear-box need not be that complex. It will,
though, all come at a price. The battery, motor, controller
combination above is what I have on my 7 metre 2.1 beam 4-berth
cruiser. I am not aiming for your high pace of travelthough and am
expecting two days travel at a gentle 3 to 4 kts on most canals and
rivers. The cost was about UKP2400 for all that including the bottom
end of a Johnson 65 outboard leg. Mind you, I did get a good deal on
the batteries.

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