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transmitterdan · 15-07-2015, 22:39

The 4" fans used in gasoline engine compartments to reduce vapors when plumbed with a meter or more of corrugated hose cannot move more than about 100-150cfm. That's about the same as the air consumed by a 50hp engine.

The engine room must have a source of fresh air now else the motor would not run for long. This air has some cooling effect. Diesel engines are not much affected by the temperatures that are inhospitable to people. After all the important bits are temperature regulated by water cooling anyway. The main problems from heat are with electronic devices and alternators. Air (even hot air) blowing directly on these devices will help much more than a tiny exhaust fan. I would not punch a 4" hole through the hull for the meager amount of additional air it can vent.

downunder · 15-07-2015, 22:54

Quote:

Originally Posted by transmitterdan

The 4" fans used in gasoline engine compartments to reduce vapors when plumbed with a meter or more of corrugated hose cannot move more than about 100-150cfm. That's about the same as the air consumed by a 50hp engine.

The engine room must have a source of fresh air now else the motor would not run for long. This air has some cooling effect. Diesel engines are not much affected by the temperatures that are inhospitable to people. After all the important bits are temperature regulated by water cooling anyway. The main problems from heat are with electronic devices and alternators. Air (even hot air) blowing directly on these devices will help much more than a tiny exhaust fan. I would not punch a 4" hole through the hull for the meager amount of additional air it can vent.

To get warranty with Yanmar you will need to meet the air intake requirements. Can't imagine it is any different with other manufacturers.

transmitterdan · 15-07-2015, 23:19

The OP isn't discussing pushing air into the engine room but rather pulling it out. I agree that the engine needs air to run. But it is dangerous to pressurize the engine compartment. I don't think any manufacturer recommends doing that.

boeing1 · 16-07-2015, 07:39

my boat does not have engine room vents, I was thinking to add, I talked to someone that used to work for the company that made my boat and he told me that they only installed them on gas boats not diesel.

Scrimshaw4 · 16-07-2015, 08:04

To vent the enging room you need to provide an air intake, marine grade (ignition proof) blower and an exhaust vent. The intake should be positioned so that water, both sea and rain cannot enter. The blower should be positioned inline with the exhaust vent line, preferably at the beginning of the vent line. It has to be ignition proof to prevent vapor ignition (ABA / Insurance / Coast Guard requirement even if a diesel engine). Best to wire the blower to the on position of the ignition switch. The exhaust vent should preferably as far aft as possible, transom. The clam covers mentioned earlier work well. JMHO

autumnbreeze27 · 16-07-2015, 08:11

Thanks for all the feedback! I'm leaning towards skipping the engine room vent now. We're down to 3 months and want to get this refit over with!

We hardly run the engine anyways.

BobH260 · 16-07-2015, 08:14

Our boat came with factory installed intake and exhaust vents to the engine room. The air intake actually goes right on the Yanmar air intake. The exhaust takes air from above the engine through a blower mounted in the bilge. They both exit the boat on the transom through two clam shells as high as practical. Owners of this model have experienced knock downs without taking in any water through these two clam shells.
We find it makes a huge difference to cabin temp, often keep the blower on after we drop the hook if we have been motoring for any length of time.
I think it is safe and practical for the way we use our boat, coastal/Bahamas cruising.
Bob

adlib2 · 16-07-2015, 08:48

Quote:

Originally Posted by autumnbreeze27

Our boat does not have an engine room vent, and I want to add one.

Does anybody have any tips? I plan on exhausting out high on the port side at the same level as the fuel and waste tank vents.

Do I need some kind of dorade? or way to close it? What's the best fitting for outside the boat?

Anyhow, just thought I'd ask if anybody had any tips to share.

My question is WHY ? Is it a power vessel? I've owned a few sailboats, cruised the tropics and live in Florida & never had need of a power vent.

spraygun · 16-07-2015, 11:27

Because.....as written before.Get the engine heat out . Especially after shutdown.It can stay hot in those compartments for hours.I let mine run for about 15 minutes after shutdown.It keeps heat out of any cabin space surrounding the engine.
If we find ourselves motoring in the summer with no wind.It can be very helpful.
I have mine pulling cool air from inside the grid of my boat . I dump the cool air on top of my alternators.They love cool air.Then have the one exhaust dumping out into the cockpit.Makes a 40 degree difference in compartment temp.

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Scout 30 · 16-07-2015, 15:31

I've also considered doing this. However, most blowers are designed only for intermittent use only. What blower fan is recommended for continual use?

Sailmonkey · 16-07-2015, 15:41

Quote:

Originally Posted by Scout 30

I've also considered doing this. However, most blowers are designed only for intermittent use only. What blower fan is recommended for continual use?

Not the ones I'm using (yellowtail inline blower)I get about 500 hours out of them.
But by pulling hot air out of the engine compartment a huge difference has been made inside the boat!

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Cheechako · 16-07-2015, 16:27

Quote:

Originally Posted by Scout 30

I've also considered doing this. However, most blowers are designed only for intermittent use only. What blower fan is recommended for continual use?

They are typically used for gas power boats and are usually on all the time. Not sure about how they are rated though!

mrohr · 16-07-2015, 17:35

i owned a sailboat that the genoa sheet winch base was also a vent.

Base was fabricated of galvanized steel with a baffle that excluded water unless deck at cockpit was completely submerged to 5" depth. Never a problem ,even offshore in N. Atlantic.
Engine room always quite cool…

………………..luv you all……….mike…………………………………………………………………………………………...