Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

(locate the through-hull at least 2 feet or

0 .6 m below the waterline). Even this can’t

absolutely ensure that these problems won’t

occur. The deeper the shared sea suction and

the larger its diameter, the better.

Sea Chests

Probably the best way to get a large-diameter

inlet opening as deep as possible is by using a

sea chest. These are boxes or chambers built

onto the inside of the hull, with large open-

ings to the outside water. The openings are

covered with grates, and several sea valves or

seacocks are installed in the top or side of the

sea chest as convenient. Sea chests are not

required on any boat, but they offer a number

of advantages if used:

• A sea chest gets the water inlet opening
  as far below the waterline as possible
  to maximize inlet head and minimize
  the chance of sucking in air when the
  boat rolls.


• Its outside opening(s) has a total area
  far larger than all the suction pipes
  attached to it.


• The grate at the sea chest’s opening (or
  openings) provides an added coarse
  filter element to protect internal
  plumbing.
  
  
  • With the grates let in flush, water flow-
    ing past the boat tends to keep debris
    from fouling the grate.
  
  
  • A sea chest in a box keel can be
    two-sided (open on both sides) and
    thus ensure full water flow even when
    a plastic bag is stuck against one side.
  
  
  • A sea chest centralizes inlet/suction
    plumbing fittings.
  
  
  
  

Figures 17-11 through 17-14illustrate a

two-sided sea chest in an aluminum motor

PART SIX: PLUMBING SYSTEMS WITH NOTES ON FIRE SUPPRESSION

Figure 17-10.
Self-cleaning sea
strainer (Courtesy
Groco)

Figure 17-11. Sea chest seen from inside a

motor cruiser