Engine Bay Temperatures.

[oldsaltoz]

Re: No fans to be used at all.

G'day Steve,

Could not agree more re weight as close to centre as possible, also keep both ends as light as possible, makes a huge difference on some hulls.

When we were looking for a Cat we managed to take out two of the same brand and year of manufacture, the one that had the engines mounted at the bottom of the steps into each hull was so much better on all points of sail and all else was pretty much the same.

Avagoodweekend......

 

[boatmike]

Re: No fans to be used at all.

Agree that that's a good place for batteries so long as thay are adequately vented but beware of hydrogen gas build up in the bilges.
The air duct for the engine does not need to be anywhere near the engine intake though. You are preoccupied with feeding cool air for combustion. This is important but not as important as keeping the engine as cool as possible generally, especially the alternator. If you keep the engine room temperature down the engine can breathe from the air in the engine room. What you propose will feed cooler air to the intake but the engine will still have a cooling problem as the air around it is gonna be hot! I know it is a water cooled engine but the cooling system is generally designed to keep the temperature down when it is near ambient around it. The biggest sources of heat are the exhaust and manifold and drawing fresh air over these is just as important as feeding cool air to the intake.
Personally, if your boat is remotely the same as the other Bav shown I would do what he has. Fit an in and out vent high up in the transom where the noise escaping won't bother you. Have the intake bigger than the outlet on the engine intake side and lead the ducting from it forward to somewhere below and forward of the alternator. Fit a fan on the outlet on t'other side with the ducting as far aft and high up in the engine room as possible. Easy to do, and will ensure the engine is happy and air circulates around the room naturally. If you want to get clever have a thermostatic fan but personally I would not bother.