Hi James,
Thanks for that info.
Although my original thinking for a minimal 'get away from the dock and
back up to it' system was for 500watts, (using Eric's figures as a
starting point) I am procrastinating (while spending the summer getting
the boat to float!) over going to 1000watts right from day one. Mainly
due to thinking more in the way of a portable generator rather than
carrying a 2 stroke outboard for when longer running might be needed, -
especially bearing in mind my cost driven and solar charging
minimalistic ideas regarding batteries.
I intend using a main mounting plate, and lightweight belt drives, so
that more motors can be added, bearing in mind I am guessing rather than
calculating what will actually be needed. Once in the water, I prefer to
change belts rather than props. Once I have some benchmarks on what it
does, in what conditions, I can later change, if I prefer to, to one of
those nice looking single motor drives all clean looking, in a white
painted 'engine room'.
The prop pitch and load gets more critical with the use of less power.
Never did get my 15 foot testbed dinghy going, the yacht club pointed
out that it was a bit too big to be a sailboat tender, and I had to
agree, as it was too heavy for one person to manhandle. Another winter
project created, a homemade 8 or ten foot one.
So, I figure that I will start with low prop rpm, and see where the
motors are as far as slowing down and heating.
For the low prices intended, if I test a motor to smoking destruction,
all will not be lost.
But I expect all will be well, with care. I will keep that 5 minute idea
you just suggested in my mind though.
Thanks,
John
1.3. Re: power requirements - predicted vs observed
Posted by: "James Lambden" james@toolboat.com jameslambden
Date: Mon Aug 22, 2011 9:28 am ((PDT))
John,
A properly powered system will be able to run continuously at full
throttle with the correct gear ratio for the propeller.
During acceleration and deceleration a system might surge up to twice
the continuous ratings. Most controllers and motors have this surge
capability.
Whatever surge capability you plan to use, it is best to be surge
capable for at least 5 minutes before the motor / controller will
overheat.
James
Propulsion Marine
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