Adding engine ventilation

jibes138 · Aug 10, 2015

Why? The engine can pull air from the cockpit locker cover and the bilge that is open near the mast. Why do you feel you need this?

Tally Ho · Aug 10, 2015

njlarry said:
I would like to add ventilation to my engine compartment for better air flow to the engine and the refrigeration unit. Would like to not clutter up the transom. Any suggestions of size and location to drill for a vent? Also would the engine noise factor increase much? Smooth sailing.

I have an O322, and have contemplated how to add ventilation to my engine compartment also. The rear berth, right next to the engine, gets hot after the engine is shut down and I would like to introduce fresh air (or pull hot air) into/out of the engine compartment.

I see a lot of engine rooms with a 3 or 4" hose that terminates in the engine compartment, and I assume that is the purpose. I imagine that also have an in-line fan in the hose somewhere.

My issue is there is no room from the engine to the transom...the area around the shaft already has lots of other hoses in there... I don't think I can squeeze even a 3" vent hose in there. I intended to put some sort of clamshell on the outside of the transom to vent the hose.

Curious what other sailors suggest.

Greg

Sefuller · Aug 10, 2015

Possible vent location and comment on engine noise

Maybe in the rear section of the cockpit - directly behind the helmsmen's legs?

On a perhaps unrelated note - I think the Universal M25 in our 34 is the loudest sailboat engine I have ever heard. We motored 4 hours yesterday on a return trip and it is so loud as to almost make conversation in the cockpit impossible. It seems adding sound proofing would be futile since so much of the engine compartment is open to the cockpit locker.

What to other 34/35 owners think?

jzuk · Aug 19, 2015

I'm pondering this issue as well with my 35.

I've been holding off on drilling holes for air circulation and engine bay (and refrigeration unit cooling).
I did make a shelf for the refrigeration unit raising it up above the hot water tank (port side under winch coming). I know this puts it in the upper/hotter area, but was thinking of making the shore power inlet (which is nearby) into a inlet vent and moving the shore power somewhere else (ideas?).

The refrigeration was moved as it was right above the stuffing box that needed attention. If need be the refrigeration unit can be moved again if there's a better spot.

Planning on making an engine blower (I know not needed on diesel) that would suck air near engine out to transom. Would wire to run when the engine and or refrigeration unit are running. This would help create neg air pressure that would pull air in the yet to be done air inlet near the refrigeration unit (also pull air from cabin so no diesel smell in there).

Right now I have to replace the air filter, so researching on new filters and making an air intake with an air silencer to cut down on some of the noise. Just have to make sure its sized right to not to effect the engine. I'll post a separate question asking if anyone has made an air silencer, to keep this tread focused.

jibes138 · Aug 20, 2015

Why not put a hole in the bulkhead at the end of the quarterberth. Think of the size of the pipe on the air intake on the engine. Your hole will only need to be this big to flow the same amount of air as the engine. This will pull air out of your cabin and suck it through the engine and out the exhaust. You could easily make this so it could be closed off. This avoids putting holes in the topsides of your deck that might be a source of leakage.

wufibugs · Nov 7, 2015

If you are reluctant to drill another hole in the transom, perhaps you could tie the engine vent line to one of the cockpit drain hoses using a check valve to prevent water to the blower..

jzuk · Nov 7, 2015

There's a thread regarding engine noise, so as to not mudle the issues.
In it I mention I added a better air filter setup, which helps with noise (think the air silencer on your car air filter). iPhone app showed a difference in sound. Sound proofing is next. can't sound proof the cockpit floor easily, but can reduce the sound bouncing off the surrounding fibreglass.

My refrigeration deck is in a poor spot for cooling. Hoping that a cooler engine compartment will help it run better (less power).

Kinda like the hole in the quarter berth idea, but the desire is to get the heat from the engine out which requires more volume of air be sucked out. A good vent from the engine compartment (with fan) will move a better volume of air, the added Benefit would be negative air pressure stopping engine smell going to the cabin. This may require a bilge blower like gas engine boats have.

centerline · Nov 7, 2015

the heat from the engine will rise to the upper parts of the engine compartment, so probably up into the coaming ares of the cockpit...
you need to suck or blow the hot air out of the boat, NOT into the cabin of the boat, because it may have an engine/bilge smell that may be unpleasent at times.
The asperation of the engine will ventilate it a little while it runs, but will not stay ahead of the heat that is produced in the summer months.
For some of us In the winter, the heat is welcome.

The fresh air should not come out of the cabin either... if one is trying to maintain some heat inside the boat, it does little good to have a draft of many cubic feet of air per minute being displaced thru the space thats trying to be heated.

But The fresh air WILL most likely is already being pulled in thru the many little cracks and holes from the cabin space anyway, so there is no need to cut another hole...
Some may have a bad gasket on the lazerette or cockpit settee hatch that allows air in to the engine, but it should be repaired so it seals out the weather

I live in the northwest, so If i were to ventilate my engine compartment, i think i would take the time to install the ductwork in such a way that the hot air could be blown outside the hull ln the summer, and redirected to blow towards the helm in the winter... maybe a shuttered vent in either the transom or coaming. Or possibly up and our a riser tube at the taffrail with an adjustable weatherhead.

rajhnsn · Nov 8, 2015

Sounds like the concerns are for heat in the cabin/refrigeration and noise of the motor. We have noticed that the heat in the cabin during the summer around the motor is higher than normal during times of prolonged motoring but it's hot down there anyway during the summer. Most of the time it can be cooled to a tolerable level with fans in the saloon and a cool anchorage. We have no air conditioning.
Regarding the noise of the M-25, I've always thought that it was louder than other sailboats that I hear go by but it's hard to tell what they are hearing on their boat. I wonder if our motors can be too loud related to exhaust issues? The air filter idea sounds like it is worth looking into. I always assumed that the loudness of these motors was because it was a 30 year old motor. I think NJ Larry's motor is only a few years old however. I have sound proofing material on the access board in the saloon, the bulkhead and the 1/4 birth access board. It is foam with aluminum foil on the outside. The removable access panel in the port locker is vented. There are chrome air vents on the deck on the port stern. They seem to sufficiently vent this area. Adding a blower to this may be helpful but it has not been a priority for me.
The PO of my boat had redone the refrigeration on Graceful-lee. The box seems to be pretty well insulated without a drain hole and the mechanics are under the sink. We have always been able to maintain temperature after motoring, on the hook or at the dock.

jibes138 · Nov 8, 2015

Why not install a coaming box and then connect your intake and exhaust hoses to the inside of the coaming box? That would keep the rain out and nothing would be sticking out above the surface to be an inconvenience. You could put one on each side and have the intake on one side and the exhaust with a fan on the other to get a good cross flow of air.

centerline · Nov 8, 2015

jibes138 said:
Why not install a coaming box and then connect your intake and exhaust hoses to the inside of the coaming box? That would keep the rain out and nothing would be sticking out above the surface to be an inconvenience. You could put one on each side and have the intake on one side and the exhaust with a fan on the other to get a good cross flow of air.

the problem with this is, if you have guests seated in the cockpit while motoring in the summer, the amount of heat blowing on them would be very uncomfortable to say the least.... in the cold of winter they would all fight for the "hot spot"....

Panta Rei · Nov 10, 2015

I advise against using an axial fan like the ones they use for boats withgasoline engine. They are so loud they are not useful in cooling the engine compartment once you anchor. I would suggest you find a squirrel cage fan. I have a 12 volt motor control I will install next spring. I hope this will help with the noise as I feel I don't need a lot of airflow when the engine is off, just enough to remove the heat that comes off the engine as it cools down. That's is is few hours on my boat

seadaddler · May 10, 2016

I have a factory installed exhaust fan hook up to air dryer type hose which exits out the rear cockpit and run the fan when ever motoring and stays on until maybe a hour after anchored here in Florida.
Nick