Engine Room Ventilation

One of the often overlooked, yet what we at Pacific Motoryachts have found to be of prime importance, is proper engine room ventilation which is to often neglected.

Quite apart from human comfort, constant high engine room temperatures can have a profound effect on engine H.P. ratings. Most engine makers quote their H.P. ratings at an ambient temperature of 25oC (77oF). This is quite unrealistic except for vessels operating in cold climates. The engine room temperatures in the tropics are more likely to be 50oC (122oF). This increase in ambient temperature will result in a 4.5% fall in engine output (i.e. a 13 HP drop in output for a 300 HP engine).

Obviously the cooler the engine rooms air the better. Most engine makers stipulate the maximum allowable rise above ambient. Typically this is 17oC (30oF).

This requirement means a forced ventilation system is always required, generally a fan. The fan capacity has to be carefully calculated to supply enough air for:-

(1) Engine Air Consumption - A 300 HP engine for example uses 1.2 tons of air per hour.
(2) Sufficient air changes per hour to limit above ambient rise to 17oC.

We have found that the most effective are aerofoil fans either electrically or hydraulically driven. Also, to avoid the possibility of salt laden air reaching the engine room and possibly, over time causing problems, that the fan intakes should always be located high in the deckhouse structure and have effective spray excluding jalousies and water tight fire covers fitted.