Usage:
A completely separate sea water system should be provided for each engine to prevent a blockage resulting in the need to shut down more that 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.
The intake fittings and pipework should have a minimum bore of 25mm (1") (A). 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 A). 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 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.
A typical system is shown in figure (A).
NOTE: Where possible mount the strainer so that the top is just above the waterline to facilitate cleaning.
Keel Cooling or Skin Cooling
Keel cooling or skin cooling is a closed circuit method of cooling that uses only coolant with 50/50 antifreeze mix.
A properly designed and installed cooling system is essential for satisfactory engine life and performance.
Keel cooling is a cooling system that uses a group of tubes, pipes or channels attached to the outside of the hull below the waterline as a heat exchanger. Keel coolers are used in preference to the standard raw water cooled engine mounted heat exchanger when operating in areas that have heavy silt and debris in the water that would erode the heat exchanger tubes or block them.
Keel cooling is used in Arctic conditions to avoid the problems of freezing that is experienced with the raw water circuit on the heat exchanger cooling system.
Keel coolers are available in standard designs from several manufacturers. These units are simple to install and are sized by the manufacturer for the engine model and boat application. Commercial coolers are made of erosion resistant materials and have a relatively high heat transfer efficiency.
The disadvantage of external keel coolers is that they are vulnerable to damage and therefor must be guarded. An alternative to the commercially available coolers are fabricated keel coolers manufactured by the boat builder as part of the hull construction. These coolers are not as efficient and must be designed oversize to allow for a decrease in performance that follows the formation of rust, scale and marine growth on the keel cooler.
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If the genset is a replacement package and the original cooling system, keel cooler and expansion tank, is to be reused, then it is essential that the system thoroughly flushed to remove sludge that may be in the system. Failure to remove sludge could block air bleeds leading to the engine overheating. |
Sizing the Coolers
Commercial keel coolers are manufactured in a variety of sizes and shapes. The keel cooler manufacturer will recommend a keel cooler when provided with the following data:-
- * Engine model and rating
- * Engine data sheet
- * Heat Rejection (see table below)
- * Engine Coolant Flow
- * Max. coolant temperatures from grid cooler
- * Maximum raw water temperature
- * Pipe connections - Min. 44mm (1.75") o.d; Min. 38mm (1.5") bore
- * Coolant - 50/50 antifreeze mix
- * Engine data sheet
Figure (A) shows the connections (A1) and flow (A2) for the 4 cylinder engines to the keel cooler (A3). The size of the connections (A1) are both 38mm (1 1/2" inches).
Figure (B) shows the connections (B1) and flow (B2) for the 6 cylinder engines to the keel cooler (B3). The size of the connections (B1) are both 45mm(1 3/4" inches).
Keel cooler should be installed below the waterline far enough to avoid the aerated water close to the surface. Recessed and shielded coolers must allow for unobstructed flow around the coolers. The keel coolers should be installed so that air pockets are not present during the initial fill. Vents at all high points along the connecting of the pipes will be necessary.
Keel coolers should not be fitted where they would be exposed to pounding seas or hull flexing. The bow of the vessel is not considered to be a good location whereas adjacent to the keel, where it is the strongest area of the vessel, is the preferred location.
De-aeration
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Air in the engine coolant can cause the following problems:
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Expansion Tank
The expansion volume in the tank must be large enough for the entire cooling system. Since the engine coolant expands about 5% between cold and hot engine operating temperatures, the expansion tank must have a volume equal to 5% of the entire cooling system volume.
The plastic expansion tank supplied is just large enough for commercially available coolers used with short pipe runs and therefore in most applications a remote expansion tank with a larger capacity is recommended especially where fabricated coolers are used.
When designing the larger expansion tank the following allowance should be made:
- * 3% to 5% of total system capacity for expansion losses
- * 10% of total system capacity for volume loss on hot shut down
- * 5% of total system capacity for working volume
- * 10% of total system capacity for volume loss on hot shut down
The illustration (A) shows the allowances required when designing a larger expansion tank.
Engine Bleed (Vents)
The engine bleed system provides a continuous flow of water through the expansion tank as a method of removing air from the engine coolant. Depending on the model of the engine there can be up to three bleed pipes which need to be connected to the top of the expansion tank. Each bleed must be connected to the expansion tank without using tee's or other fittings that would join the bleed pipes together in a common vent.
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Joining the bleed pipes into a common vent will reduce the total water flow and may result in aerated water flowing back into the engine resulting in the engine overheating and possible failure. |
Remote expansion tank
A remotely mounted expansion tank is recommended where longer pipe runs are required and where fabricated coolers are used. A remote cooler expansion tank kit can be fitted using the following procedure.
1 Figure (A) shows draining the engine coolant (A1), cutting, removing and discarding the bleed pipes (A2), and removing the existing expansion tank (A3) and disposing of the rubber elbow (A4) at the base.
2 Mount the remote expansion tank in a position where the bottom of the unit is no lower than where the filler cap was (B1) on the original expansion tank, as shown in figure (B).
3 Connect the new bleed hoses (B2) to the tank and the original fittings on the engine.
4 Connect the main inlet hose to the engine (B3).
5 Secure the inlet hose (B3) the front of the engine in the position shown in (B4) with the hose clip.
6 Fill the remote expansion tank with 50% antifreeze solution (C1) to the maximum position on the sight glass (C2).
7 Switch on engine (D1).
8 Start engine (D2).
9 Run engine until normal working temperature is reached, between 82 to 88°C (D3).
10 Stop engine (D4).
11 Switch off panel (D5).
12 Check coolant level in the sigh glass (E1)
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Hot coolant is under pressure and can cause severe burns when removing the pressure cap. First release the pressure in the system by loosening the pressure cap. |
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13 Top-up with 50% antifreeze to maximum level (F1).
