Installation Manual
N38143 Chapter 4
Page 15
A completely separate sea water system should be provided for each engine to prevent a blockage resulting
in the need to shut down more than one engine.
A typical system is shown in gure (A).
The water intake tting (A6), situated below the water line (A1), should not project appreciably below the
bottom of the hull and it should be situated well clear of other components such as shafts, logs, rudders to
prevent ow problems at high speeds.
The intake ttings and pipework should have a minimum bore of 25mm (1”) (A2). Inboard of the intake tting
a 1 inch BSP or NPT sea cock (A3) must be provided. This should be of the full ow type giving unobstructed
passage to the water in the open position, with a minimum bore of 25mm (1”).
Between the intake tting and the sea water pump (A4) on the engine, there should be a strainer (A5) which
should be easily accessible for routine examination, and should be easily removable.
Note: Ensure a separate feed for each engine. A shared supply is not recommended.
From the sea water strainer a pipe should be run to the sea water pump inlet connection on the engine (see
gure A). The pipe may either be mainly rigid, of for example copper or cupro-nickel, or exible, but only exible
hose which is reinforced to prevent collapse should be used. The system must be sufciently exible to permit
the engine to move on its exible mountings. The sea water pump connection is for hose with a 32mm (1.25”)
bore.
Care should be taken to use compatible materials in the sea water systems, to prevent excessive galvanic
corrosion. Systems incorporating copper, cupro-nickel, stainless steel Type 316, gun-metal, silver solder, and
aluminium brass will generally be satisfactory. Components made from lead, iron, steel, aluminium or its alloys,
zinc or magnesium, should be generally avoided.
Raw water systems