Proper direction of engine air cowl vent on Cape Dory 25D

Sea Hunt Video · Post by **Sea Hunt Video** » Feb 3rd, '16, 18:09

I was doing some research on diesel engine maintenance and came across some photos that showed engine air cowl vents. Most seemed to show that if there were two (2) engine air cowl vents then one was positioned to "scoop in" air (facing forward) and the other was positioned to "expel" engine compartment "air", that is, facing the opposite direction - aft.

On S/V Bali Ha'i (a 1982 Cape Dory 25D) I have always positioned both air cowl vents so that they "scoop in" air. Both vents are attached to a flimsy 3" diam (approx.) wire vent hose (3' - 4' in length) that goes down into the engine compartment on either side of the engine. I have always assumed that because both air cowl vents have this wire vent hose that both vents "scoop in" air for the engine.

Is this correct or should one of the air cowl vents be positioned to expel "air" from the engine compartment

If one should be positioned to expel "air" it would seem that the flimsy wire vent hose is unnecessary and may hinder removal of engine compartment "air"; the "air" only gets out if it can finds its way to the hose and works it way up 3' - 4' of a flimsy wire vent hose.

Yes, I know, one of the burning, hot topic issues of the winter season.

But, in my defense, I cannot spend all of my time thinking about Super Bowl 50, beer commercials, and girls in bikinis on the beaches of Miami - now can I

Steve Laume · Post by **Steve Laume** » Feb 3rd, '16, 18:21

Do you rotate them when you are running down wind? If you do not do this regularly, you may be sucking all the air out of the engine compartment. Steve.

Jim Walsh · Post by **Jim Walsh** » Feb 3rd, '16, 18:22

I face one cowl forward and one cowl aft. I replaced the original "clothes dryer hose" with this stuff in the picture. It's real good stuff. You can lay on it and flatten it out and it resumes its shape. Guess how I know?

Steve Laume · Post by **Steve Laume** » Feb 3rd, '16, 19:15

Sorry for being such a wise arse.

Contrary to convention it probably doesn't make much difference which way they are turned. Most of the time a forward facing cowl should allow more flow in. I keep the port side forward and the starboard side facing aft most of the time. The exception to this would be if there is heavy wind and rain or spray and then they are both turned aft. The reason the port side is treated as the intake is that I run a long hose forward in the engine compartment to end somewhat close to the alternator. I am hoping to create an air flow around the engine and then have the hot air exit on the starboard side where I have a very short hose that is kept as high as possible. I installed a power vent on the exhaust side. The idea was to run it for a while before and after shutting down the engine to help keep things cool and exhaust any odors that might linger in there. In practice, I don't use the fan all that much because it is loud and obnoxious.

The hose on Raven was the typical, nasty, dryer vent, type, stuff. I happened to have some dust collector hose in my shop that was the right size. It is some sort of black, rubber with a wire reinforcement. If you look up dust collector hose, you will find all sorts of material in a wide range of prices. Any of it should work better than the original stuff.

When you go to install the new hose, think about what you are trying to accomplish. You want cool air to enter and hot air to leave the space. You also want any water that might happen to enter the hose to be able to drain into the bilge without doing any harm.

You really can't mess this up and it probably doesn't really matter which way the vents are facing, Steve.

Sea Hunt Video · Post by **Sea Hunt Video** » Feb 3rd, '16, 22:21

Jim and Steve:

Thank you both for the information, advise and photo.

Jim, do you happen to remember the name of the mfg. of the blue hose

Steve and Jim and all, is there any benefit to having any hose on the "exhaust" air cowl hanging down into the engine compartment:?: Steve you mentioned your exhaust hose was "short" and "high". Why not just eliminate that hose and have "exhaust" air flow directly into the cowl

I would think less clutter and more direct exhaust air flow out.

Thanks again for all of the helpful information.

RC James · Post by **RC James** » Feb 3rd, '16, 22:45

Lower vented hose facing Windward
Upper vented hose facing Aft

Not that it makes much difference to the Tractor-engined 1GM-Yanmar,
but I just figure that cold air should come in the lower hose, and heated warmed air should exhaust thru the somewhat minimally placed upper hose.

For what it's worth, I usually leave the engine cover off when motoring....just to be able to hear the perhaps "off-sound" of the engine's performance.
But then, there are the always present Gremlin sounds that make motoring so much more stressful than sailing.

RC

Jim Walsh · Post by **Jim Walsh** » Feb 3rd, '16, 23:10

Roberto,
Trident makes the blue "blower" hose. They are the same people that make all the exhaust and waste line hoses among other stuff. Instead of a wire helix it has polypropylene, hence you can drive your truck over it and it pops back into shape. I haven't driven over it but I just lay on it if I'm under the cockpit and it goes right back to shape in a couple minutes.
I keep one down low and one a little higher to promote air movement. I also turn the cowls away from spray in real crappy weather. I've only done that a couple times and that was offshore.
http://www.defender.com/product3.jsp?pa ... &id=732033

tjr818 · Post by **tjr818** » Feb 3rd, '16, 23:43

I am sure there was a post on this topic before. The recommended way in that post, if I remember correctly, was the intake hose was longer and led down near the alternator to help cool it, the exhaust hose was shorter and its only function was to provide suction from the engine room.

Sea Hunt Video · Post by **Sea Hunt Video** » Feb 4th, '16, 13:04

RC, Jim and Tim and all:

Thanks for the additional information and advise and the sourcing for the blue hose.

joemerchant · Post by **joemerchant** » Feb 4th, '16, 14:49

On our 300 CD, I added a blower that runs when the engine is running or when using the oven/stove with the gas on to keep the bilges clear. Worked so well, it is on the list to install on our Island Packet as well. With a potentiometer (speed control) and 12 volt timer ($10 on ebay) block off the inlet and it will run a couple minutes every hour or so to pull the warmer heated air down into the bilge from the cabin and keep everything from freezing up in our climates where a bilge heater is overkill. No hose on the inlet, but long hose into the bilge for the outlet.

Maine_Buzzard · Post by **Maine_Buzzard** » Feb 4th, '16, 21:35

You'd be surprised to see how much air the diesel needs when running... Well just about as much as it exhausts out. The cowls need to feed that too, unless you have a very leaky compartment.

I was all set with a shaggy dog story about diesel submarines using schnorkels to run underwater, but realized it was only because I would be able to use the word "Schnorkel"

Just try to say it out loud without smiling.

"Schnorkel".

Happy Winter. The skiing stinks up here.

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