(ouch!) in order to give your pump an
outlet. This is unnerving, but trust us, it’s
100-percent necessary. Choose a thru-hull
that matches the diameter of the pump’s
port size. Obviously, this will also determine
the diameter of the discharge hose you use.
Locate a spot on the hull that’s far
enough above the waterline that it won’t
become submerged when the boat is fully
loaded or heeling over. It should also be
as close as possible to the pump, because
long runs and bends in the discharge line
will reduce the pump’s capacity. The natural loss of pumping ability due to “head”
(height above pump level and friction in the
discharge hose) can cut a pump’s capacity
by as much as a third of what’s advertised.
On top of that, long runs can result in lots
of backflow when the pump shuts off, and
in extreme cases, enough backflow to restart
the pump — so keep the plumbing as short
as possible.
The boat’s gelcoat is less likely to
splinter if you drill from the outside-in as
opposed to the inside-out, but if nearby
bulkheads, wires, or plumbing makes it
imperative for you to get the exact location
perfect, you may need to first drill a tiny
pilot hole from the inside, so you can iden-
tify the specific spot while standing outside
the boat. Remember, you’ll minimize gelcoat
splintering if you run the drill at full speed
at all times (slower speeds only encourage
the bit to grab and break off chunks of gel-
coat). Okay, it’s time to grit your teeth and
drill, baby, drill!
STEP 4 INSTALLING THE
DISCHARGE HOSE
When you cut the hose to length, allow
enough room to install a loop in it, just
above the discharge. Make it a fairly large
loop, which rises well above the thru-hull fit-
ting, and secure it to the hullside with cush-
ioned clamps. This is called an “anti-siphon
loop,” and although this bend will increase
the head your pump must overcome, it also
prevents water from back-flowing through
the discharge hose — an imperative feature,
if your discharge ever dips below the water-
line. With the hose in place, secure it to the
pump’s discharge and the thru-hull’s barb,
using stainless-steel hose clamps. Then use
cushioned clamps to secure the hose along
its run.
Lenny Rudow is the electronics editor
of BoatU.S. Magazine.
TECH TIP: YOU’LL HAVE TO CHOOSE BETWEEN CORRUGATED AND SMOOTH HOSE. GO WITH THE SMOOTH
HOSE. THE CORRUGATED MIGHT BE LESS EXPENSIVE, BUT THOSE RIDGES ALSO CAUSE TURBULENCE AND
FRICTION, WHICH ADD TO THE HEAD THE PUMP HAS TO OVERCOME, THEREBY REDUCING ITS CAPACITY.
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