My final word (I Promise) you would be surprised at how may insurance claims i attend for engine room equipment failures and how many are thrown out on THE GROUNDS of not meeting the manufacturers ambient operating temperatures,
I stress again it's not ONLY about the Turbo or not requirement, Engine-room ventilation falls into two categories, those required for cooling the space, and those needed for combustion. The air used to cool the compartment improves not only the combustion efficiency, but also the longevity and efficiency of gear in this space, including engines, generators, compressors, and electrical and electronic components (and also makes it a more comfortable place to work). Where generators are concerned, while the engine portion is typically liquid cooled, the electrical generation end relies on air from the engine-room for its cooling (a small number of generators rely on liquid cooled stators). When engine-room temperature is excessive, generator manufacturers will often lower the unit’s rated output.
Additionally, heat takes a toll on “soft goods” such as generator couplings, belts, motor mounts,torsional vibration dampers, transmission damper plates, hoses, insulation, voltage regulators, and other electrical and electronic components, as well as batteries.
As a general rule of thumb, (these apply to wet exhaust engines) to determine the necessary air flow rate, in cubic feet per minute, use this formula (2.75 x hp) – 90. Having said that, it’s wise to defer to requirements established by engine manufacturers, or whichever is greater.
Caterpillar’s standard guidelines for forced ventilation call for 2.5 ft3 (.07m3), per horsepower, while one generic rule of thumb for passive combustion air inlet surface area specifies 0.55 in3 (9cm3) per horsepower (including generators). The Cummins guideline for passive vent surface area size uses the following formula, rated engine air intake, specific to each model, in cubic feet per minute, multiplied by 0.272, equals required area in square inches. Failure to follow these formulas is a common violation for new builders, particularly where designs evolve to accommodate larger engines with no changes made to intake size. It’s important to note that the cross section must be measured at its narrowest restriction (and louver area must be subtracted); it’s not unusual to find large louvers that supply air via significantly constricted duct work.
Due to the nature of my position as a (MIIMS) Lloyd's Maritime surveyor -(NZ Chief End 1)specializing in engineering installations/refits, I get to see a host of so called "Professional Installations" that dont meet manufacturers specifications and have spent CONSIDERABLE TIME in courts as an "Expert Witness" facing well known international boat builders out lining there failures and the belief in there systems.
"You can lead a horse to water but you cant make it drink"