Some boats have very little ventilation air leaving the machinery space. The air consumed by the engine
air intake is pretty much the only way air can exit the space unless there is some active ventilation. Auxiliary diesel
engines on sail boats are not "required" to have these powered ventilators but gas/petrol boats are required to have positive ventilation in most jurisdictions. But in the case of petrol the ventilators are not for cooling
but just to reduce the concentration of explosive vapors.
If you have an automatic fire suppression system the ventilation system has to have some means of automatically shutting down the influx of forced air if fire is detected along with an automatic engine
shutdown. So it is a bit of system engineering to have forced ventilation but still avoid making a fire worse.
I have heard the argument in the case of diesel
sail boats that it's best to not actively ventilate the machinery space due to increased risk of a fire more quickly getting out of control. The theory being that the engine's own air consumption
will be replenished with fresh cool air and that's good enough as far as cooling
goes. Any fire suppression system will starve the fire (and engine) for O2 thus shutting the engine off without any particular change to the engine controls.
I have also heard the argument that forced ventilation is mandatory to reduce the temperature in the machinery space.
What is the conventional wisdom here? Is high temperature in the machinery space a greater hazard than the risk of a fire that is force fed air by a ventilator fan? Are some engine types less affected by ambient temperature or are all engines negatively impacted by high ambient temps?