TPD1317e Chapter 5 Engine Cooling Systems 5.1 Raw Water Systems 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. The water intake fitting 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 flow problems at high speeds. If desired the rear edge of the water intake may be allowed to project more than the front, by no more than 6mm (0.25”) to give a slight scoop effect, but if this is done it is necessary to locate the fitting so that it cannot be inadvertently partially rotated.
The intake fittings and pipework should have a minimum bore of 25mm (1”) (see figure 1). Inboard of the intake fitting a sea cock must be provided. This should be of the full flow type giving unobstructed passage to the water in the open position, with a minimum bore of 25mm (1”). Between the intake fitting and the sea water pump on the engine, there should be a strainer which should be easily accessible for routine examination, and should be easily removable. From the sea water strainer a pipe should be run to the sea water pump inlet connection on the engine (see figure 1).
The pipe may either be mainly rigid, of for example copper or cupro-nickel, or flexible, but only flexible hose which is reinforced to prevent collapse should be used. Rubber hose connections in the sea water system should be kept as short as possible and should be reinforced with a minimum of three layers of canvas. The system must be sufficiently flexible to permit the engine to move on its flexible 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 electrolytic 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. A typical system is shown in figure 1. Page 25