Center Cockpit Engine Room Ventilation - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance
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Old 12-19-2006
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Center Cockpit Engine Room Ventilation

Some counsel please. I own a Cape North 43 center cockpit cutter with pathetic engine room ventilation. All it has is a 1.5 inch hole, leading to a 1 inch by 3 inch conduit, which is connected to a cowl vent on the aft deck. This conduit is too small of an area to connect to a blower and connecting a pipe to this vent isn't a good option (runs through the aft head). The designer has told me to plumb a 4 inch pipe from the engine room and vent at the highest point into the cockpit. His reasoning for this are two-fold: harder for seawater to enter in all but the worst conditions and (2) to be able to smell the warm air coming out of the engine room. Don't want to smell it; don't want to feel it. He shot down my idea of a vent on the seaward side of the cockpit seat backs (yes an entry point for seawater) and a long run to the transom (seawater entry). Any ideas or opinions to the designer's comments? Thanks in advance.
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Old 12-19-2006
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Concordia...why exactly do you feel the engine room NEEDS to be ventilated better? If the engine isn't starving for air, why the concern on a boat that is designed that way and obviously has survived for a long time the way it is?
The warm air in the engine room shouldn't smell like anything but warm air...but I think that providing a passage for a boarding sea or a flooded cockpit directly into your engine space is a ridiculous idea.
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Old 12-19-2006
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venting

On our Brewer center cockpit, the engine room vent is outboard of the cockpit on the port side. It is approx 4" above the deck and has a ABS cowl vent: http://www.westmarine.com/webapp/wcs...12407/12406/12

with a bilge blower inline:
http://www.westmarine.com/webapp/wcs...1/12111/302/12

Works great! Running your flexible duct pipe higher that the vent at some point in the run will minimize the chance of water into the engine room.

Roger
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Old 12-19-2006
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"His reasoning for this are two-fold: harder for seawater to enter in all but the worst conditions and (2) to be able to smell the warm air coming out of the engine room. Don't want to smell it; don't want to feel it."
Life is full of compromises. Ordinarily I'd say to trust the designer...but if they only gave the engine a 1.5" hole to breath through, I'd have to rethink that trust.

Without seeing the boat...there are often two vents into the engine spaces. One facing forward, the other facing aft, so there's always some pressure difference between them contributing to ventilation. Seawater should not be a major issue unless you are waverunning. One vent opens high in the engine room (the exhaust) and the other drops down low (the intake) so it is vented from bottom to top as well, contributing more to the cooling. And there would be an extraction blower in the exhaust vent.

Short simple runs are also of some value, so the question is, what are two reasonably dry locations with reasonable short pipe runs that can make this work for you?

On many sailboats both vents are simply mounted on top of the transom. I can't see your location being any more likely to ingest seawater than those are. If you're taking green water...there should be some provision to close off those vents, i.e. pull the intake hood and snap in a deck plate as part of your foul weather checklist. When you do that, you can open up a separate deck plate [sic] to let the engine room breathe from the main cabin. That's a reasonable compromise all around, and only requires buying one more 4" deck plate and cutting one more hole.
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Old 12-19-2006
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Camaraderie - Air starvation isn't the issue - heat is. The engine room becomes incredibly warm, which affects refrigeration, warms up the cabin, etc. Not something I want to deal with in the tropics. Plus, I believe currrent ABYC guidelines stipulate active, rather than passive, engine room ventilation.
Roger - What you describe was the direction I was headed, until I talked with the designer. Was your arrangement factory installed? Concordia is also a Brewer design. Does your vent pipe have run above vent? Has anyone ever seen a vent that includes a flap that closes under water pressure ... sort of an anti-siphon for air?
Regards - Craig
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Old 12-19-2006
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"Has anyone ever seen a vent that includes a flap that closes under water pressure ... sort of an anti-siphon for air?"
Sketched--but not in the flesh. Then again, you could install two dorade vents. In theory they dump the seawater on dump and only pass air. And, again, one pops off the vent hood and installs a deck plate, or pulls down the line from below, to close them off before foul wx hits.
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Hellosailor - There is just one vent, unless you count air leaking out of the lazerette. I think you've answered my delimma, however: Install a cowl vent that can be replaced with a deck plate during storm conditions (when that occurs excess heat in the engine room isn't high on the list of worries). My shortest run is to the port side cockpit sette backs. The upside is I wouldn't have to leave the cockpit to snap in the plate, unlike the 10-foot distant stern - Craig
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Craig

All of the Whitby and Brewers that I have seen have the vent. Yes, the pipe does loop above the vent. Also, the supply side of the hose opens below the engine in the bilge. If any water does enter the vent, it will dump straight into the bilge.

If you have a bilge area below your engine and begin the vent in that area or put in a loop above the vent, I see no way that water into the engine room via this vent could possibly be a problem.

Also, your idea of a flap is a good one.....like a residential dryer vent.

Roger
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Old 12-19-2006
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Contact Delta T Systems. They specialize in engine room ventilation and are now working on smaller boat systems. I don't know if they would have anything suitable for a sailboat or not.

Also check out newer high quality yachts in your marina to see what they are doing. You should be able to get a good idea of what the "best practices" are from looking at these boats.

http://www.deltatsystems.com/page9/page13/page13.html
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Old 12-20-2006
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cockpit vent

we have 2 3 inch vents in our cockpit.
one runs when the enfgine is running on 12 volts and the other runs on 220 volts when the genset is running.
they both vent into a sideways vertical plenum on the cockpit side. it is arranged so se water never enters . it is a standard feature on all amels.
it is built under the amel logo on the port side of the boat.
we were pooped this trip south and did not have a drop of water in the engine room.
heat in the engine room also shortens the life of your alternators and generator.
fair winds,
eric
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