Notes from the P4W project
journal<br><br>Comparing HP:<br>In considering a replacement motor for the
Cal 29 the amount of HP required quickly became
confusing when trying to consider motor choices other than
fossil fuel, such as electric. Direct HP comparison was
not close, so the questions became why, and what
power am I loosing if I don't have matching HP?
<br><br>This bothered me for a while, especially when seeking
recommendations, I was constantly met with encouragement to stay
with a proper sized diesel or gas system. I could see
clearly that HP was and is the perceived 'common
currency' for the measure of power and a standard not to be
messed with. I agreed HP is important, but I needed a
better picture of what it was representing. So I began
to explore its role as 'common currency' in a
financial model. To me the role of HP became clearer. Treat
HP and RPM as gross revenue components and solve for
the net result (power at the prop). <br><br>This
exercise focused my attention on the role of two items RPM
and torque. I saw there was a significant difference
in the "top line" RPM number, produced at the motor
and RPM delivered to or needed at the prop, "bottom
line". <br><br>This helped build my understanding of
specifications for my new motor. In my case, the motor would
need to produce a range of 1000 -1200 RPM at the prop,
and torque of 21 foot pounds. To most experts this is
a given, and can be seen in the original boat
owners guide. But it becomes very important in searching
for a motor based on net results at the prop vs.
shopping for a motor focused on HP. <br><br>Long story
short, respect HP ratings, but focus on net results,
sustainable power at the prop. <br><br>Once motor candidates
are identified, then a separate review of fuel source
and power management can be undertaken.<br><br>I was
successful in identifying a few electric motors that met my
filter, and reduced it to one based on sustainable torque
delivery, regeneration and housing built for the marine
environment.
