N38143 Chapter 1 Engine room ventilation The engine room must be ventilated for two reasons: To supply the engine with air for combustion. To provide a flow of air through the engine room to prevent an excessive temperature build up, which may cause components such as the generator to overheat. In most applications in temperate climates, the engine will draw air from the engine room. If this is the case then, as a rough guide, it can be taken that every horsepower produced by the engines requires, as a minimum, 0.25 sq.ins. of vent area. If the boat is likely to be used in hot climates, and if engine room ventilation fans are fitted, then a vent area of 0.5 sq.ins.
per horsepower should be provided, (see the table below). Wherever possible a flow of air through the engine room should be encouraged by using forward facing intake vents to take advantage of ram airflow, together with other vents to allow hot air to escape. With an effective ventilation system the engine air intake temperature will be no more than 10 Centigrade degrees higher than the outside air temperature.
Page Minimum cross section of air duct per engine Engine For hot climates For temperate climates 415GM 103sq.cm (16sq.ins) 52sq.cm (8sq.ins) 422GM 422TGM 700GM 135sq.cm (21sq.ins) 71sq.cm (11sq.ins) 4GM 200sq.cm (31sq.ins) 103sq.cm (16sq.ins) 4TGM 348sq.cm (54sq.ins) 174sq.cm (27sq.ins) 4.4GM 213sq.cm (33sq.ins) 106sq.cm (16.5sq.ins) 4.4TGM 275sq.cm (42.6sq.ins) 139sq.cm (21.5sq.ins) 4.4TWGM 358sq.cm (55.5sq.ins) 181sq.cm (28sq.ins) 4.4TW2GM 474sq.cm (73.5sq.ins) 240sq.cm (37sq.ins) 6TG2AM 477sq.cm (74sq.ins) 240sq.cm (37sq.ins) 6TWGM 626sq.cm (97sq.ins) 316sq.cm (49sq.ins) Note: This is in addition to the ventilation needs of the main propulsion engines.