LETTERS TO THE EDITOR
to potential energy. The dynamic
losses mentioned—flow in the pipe or
hose and various fittings—are called
minor losses. Each is a function of the
velocity head (kinetic energy changed
into length units), and coefficients for
each are well established. The hose or
pipe loss is a little more complicated,
since it is a function of length divided
by diameter times the internal friction
term. However, all materials do have
well-established coefficients. The
bottom line is that all of these can be
easily calculated for any given setup.
The article made me think through
my boat a little more closely. It is
a catamaran, and one might think
less pumping capacity is needed for
every 10 feet of length in each hull.
But that would be incorrect. Each
hull has the same risk associated
with it as a monohull.
I greatly enjoy Steve’s work in
PMM. I was in the heavy-duty truck
and construction equipment world
before getting an MS and PhD
in hydrodynamics. Boating is a
wonderful blend of machinery
and hydrodynamics.
Bill Fleenor, PhD
Davis, California
Thanks for your note, Bill, and for
pointing out the pumping capacity
error. If I’m going to be corrected on
an article about pumps, it might as
well be by a doctor of hydrodynamics!
I couldn’t agree more with your
statement about boating being a
“wonderful blend”; it includes so
many disciplines.—Steve D’Antonio
MORE ON OVERHEATING
SHOREPOWER CORDS
I’m writing in response to
the letter to the editor about
overheating shorepower cords
(“Shorepower Cord Safety,” PMM
April ’09). The problem mentioned is
not all that uncommon on trawlers
with two shorepower cords, and I
have encountered it on two occasions
on older boats. In both cases, the
neutral for one of the power cords
was compromised. This happened
not at the plug, but at the breaker.
What then happens is that both
power cords’ hot leads feed their
respective loads, but one of the
neutrals handles the return duty
for both cords.
To troubleshoot, use a clamp-on
amp meter at the back of the
shorepower receptacle on each
wire individually (the black and
the white), and make sure what is
coming in through the hot black
wire is the same as what is going
out through the neutral white wire
for each shore cord. You will then
find the guilty circuit. Then, follow
