Marine Fouling - MerCruiser GM4 Service Manual

The bottom is referred to as having a "hook" if it is con-
cave in the fore-and-aft direction. A hook causes
more lift on the bottom near the transom and forces
the bow to drop. This increases wetted surface and
reduces boat speed. A hook, however, aids in planing
and reduces any porpoising (rhythmical bouncing)
tendency. A slight hook is often built in by the man-
ufacturer. A hook also can be caused by incorrect
trailering or storing the boat with support directly un-
der the transom.
a - Hook
A "rocker" is the reverse of a hook. The bottom is con-
vex or bulged in the fore-and-aft direction. It can
cause the boat to porpoise.
a - Rocker
Any hook, rocker or surface roughness on the bottom,
particularly in the all-important center-aft portion will
have a negative effect on speed, often several miles
per hour on a fast boat.
Index
90-816462 2-695

Marine Fouling

Fouling is an unwanted build-up (usually animal-veg-
etable-derived) occurring on the boat's bottom and
drive unit. Fouling adds up to drag, which reduces
boat performance. In fresh water, fouling results from
dirt, vegetable matter, algae or slime, chemicals, min-
erals and other pollutants. In salt water, barnacles,
moss and other marine growth often produce dramat-
ic build-up of material quickly. Therefore, it is impor-
tant to keep the hull as clean as possible in all water
conditions to maximize boat performance.
Antifouling paint, if required, may be applied to boat
hull observing the following precautions.
IMPORTANT: DO NOT paint anodes or MerCa-
thode System reference electrode and anode, as
this will render them ineffective as galvanic cor-
rosion inhibitors.
72004
Avoid corrosion damage. Do not apply antifouling
paint to MerCruiser drive unit or transom assembly.
IMPORTANT: If antifouling protection is required,
Tri-Butyl-Tin-Adipate (TBTA) base antifouling
paints are recommended on MerCruiser boating
applications. In areas where Tri-Butyl-Tin-Adi-
pate base paints are prohibited by law, copper
base paints can be used on boat hull and boat
transom. Corrosion damage that results from the
improper application of antifouling paint will not
be covered by the limited warranty. Observe the
following:
Avoid an electrical interconnection between the
MerCruiser Product, Anodic Blocks, or MerCa-
thode System and the paint by allowing a mini-
mum of 1 in. (26mm) UNPAINTED area on transom
of the boat around these items.
72005
a - Antifouling Paint
b - MINIMUM 1 inch (26 mm) UNPAINTED Area
! CAUTION
a
b
GENERAL INFORMATION - 1A - 5
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