AFT Air Venting

Vent hose is probably your best bet. You should be able to get shorter lengths from W.M. or even your local marine shop. Even Drier vent hose should work. That comes in 8' lengths and comes in foil or alluminum.

I also have pondered the importance of these vent structures during replacing the aft deck. The original boxes were made of wood and masonite-like material. I think the masonite material can be improved.

One thing to consider might be air flow rate to the engine compartment with the original design versus flow with flexible hose. I would want to try and keep the flow rate into and out of the engine compartment at least at the level found with the original design.

Can a couple of flexible hoses provide this amount of flow without increasing flow impedance?

After replacing the deck on my 1966 37', I added a couple extra 4" bilge blowers (Why? because I had them and plenty of extra hose). My feeling is that more ventilation and air flow is better than less.

I think that the purpose of those vent boxes is to funnel water that enters through the scuppers back out of the boat. If the hose is at least the diameter of the scupper you should get full air flow. Blowers are a wonderful idea however.

NYC - Unlike a dorade, these are straight boxes from the deck scoop straight to the bilge. There is no tortuous path that can re-route the water out to a drain. When traversing rough seas, I am sure some water gets funneled to the bilge.

Here's my question: can there be too much flow of air into the engine room? I can't imagine why. Is the air exchange rate in an engine room carefully engineered?

Regarding the flexible hose, I doubt it would be a problem as long as the cross-section of the airflow is maintained with the new arrangement, all will be fine.

In any case, as long as the vent hose is at least the capacity of the scupper and doesn't crimp, it should let in the same amount of air. Also, can't imagine too much clean air ever being a problem.

Hi,

The unfortunate answer to that question as basic as it seems is often NO.

That's why you'll often see the go-fasts with their engine hatches open when they're slow cruising. K1W1, you're probably the best person I can think of to answer the question "can there be too much flow of air into the engine room?" my answer was not based on calculations, just experience. Can there be too much?

If you're getting so much flow into the engine room that it cannot properly exhaust and it pushes vapors past the hatches and into the vessel itself, perhaps you have too much... That's my unscientific guess.

My scientific, at least according to OSHA, guess is that 1:1 air exchange is desirable and the more times per hour that exchange occurs the better - provided, of course, you're not creating a hurricane in the engine room to do so.

NB: Neither guess is based on adequate engine room experience nor on engineering education.

Whoa! You just added a big variable:

Get ye some blowers. Those gas fumes have to be expelled BEFORE you turn the key. Passive air venting won't do it for you.

I suggest you refer to ABYC Standard H-2, Ventilation of Boats Using Gasoline rather than internet hearsay and wishful thinking.

If you can't find it locally or on the net, contact me and I will send you a copy.

I always thought it was because they were guido idiots who thought it was flash to drive around with the engine hatches up, and got inordinate jollies from their electric hatch lifts.

Cap, although your perception is not far off the mark you might want to rethink that guido thing . As an Irishman married to a Donna Marie Franchesca .... i. I can tell you it's not a term of endearment. Raising the hatch is to release the heat. The mirror under the hatch is for the rest.

How does the heat get released when they are running fast with the hatches down

Air forced through the engineroom vents like most boats, but it's more the volume of air than just the heat. Those motors are hungry.

So what you are saying is that when the engines are not running hard they are generating more heat and need to have the hatches open .. I am assuming because the cross sectional area of the engine room vents are inadequate ... but when they are running hard the hatches can be closed and for some reason there is now enough cross sectional area of the engine room ventilation system?

No longer worth discussing. Unsubscribed.

I was hoping a son of DaVinci would chime in