Blower motor venting seems all wrong!!

[Second Star]

On the 28+ the inlet and outlet are port and stbd, right aft on the outboard side of the cockpit combing. They were originally removable "scoops" with a screw in plug (like a fuel deck plate only about 3 inches across) if you weren't using the system. I have replaced the broken scoops and missing plugs with vent covers. The blower is located aft stbd mounted on the inside of the transom and a removable panel provides access to the blower. As above, there are two original power switches, one big turn switch on the main panel and one simple switch on the engine panel, although they are 3 way switches so don't have to be "aligned" to function. I raised the exhaust hose to above the engine with a metal home furnace vent piece of ducting to remove hot air from the compartment for the reason many have stated above - this also lowers the temp on the inboard side of the icebox.
WRT the vent covers that replaced the scoops and waterproofing plugs I must say that a couple of knockdowns have concerned me about the high potential of flooding in through the vents! I am designing a way to run the vents horizontally directly inboard along the inside of the transom to midships with a trunking hose that could take the weight of water in them. I think this will act as a a kind of schnorkel or stand pipe to prevent flooding when extremely healed over. Anyone else done something similar?

 

[Prairie Schooner]

On the 28+ the inlet and outlet are port and stbd, right aft on the outboard side of the cockpit combing. They were originally removable "scoops" with a screw in plug (like a fuel deck plate only about 3 inches across) if you weren't using the system. I have replaced the broken scoops and missing plugs with vent covers. The blower is located aft stbd mounted on the inside of the transom and a removable panel provides access to the blower. As above, there are two original power switches, one big turn switch on the main panel and one simple switch on the engine panel, although they are 3 way switches so don't have to be "aligned" to function. I raised the exhaust hose to above the engine with a metal home furnace vent piece of ducting to remove hot air from the compartment for the reason many have stated above - this also lowers the temp on the inboard side of the icebox.
WRT the vent covers that replaced the scoops and waterproofing plugs I must say that a couple of knockdowns have concerned me about the high potential of flooding in through the vents! I am designing a way to run the vents * horizontally directly inboard along the inside of the transom to midships with a trunking hose that could take the weight of water in them. I think this will act as a a kind of schnorkel or stand pipe to prevent flooding when extremely healed over. Anyone else done something similar?

* When you say the "vents", do you mean the vent hoses? And I'm not sure what you mean by "trunking hose". I'm having trouble visualizing what you're describing.

 

[Second Star]

When I say vents I mean the holes in the boat that let in (or out) air and the trunking hose the large diameter "dryer hoses" that direct that air around. Currently, the vents are directly connected to the trunking hoses and run down to either the bilged (intake hose) or above the engine (exhaust hose). If the boat is hard over on its side, or nearly, water can pour in through the vents and is directed by the hose into the bilge or over the engine. If I were to run something like 3 inch PVC sewer pipe from each vent horizontally to midships, connect the trunking hose to that, then when the boat is on its beam. water would have to rise up in the pipe to midships level before it could get into the bilge or engine space.
Kinda difficult to explain without drawings or pictures ....

 

[Christian Williams]

I would put in the vent plates when sailing the boat hard enough to cause ingress. Which in my world would be rare.

As far as I'm concerned, passive vents are adequate for diesels and I find no need for hose systems and blowers. Any vent hose actually requires a blower, since they don't work passively.

There are various opinions on this, but as usual all dissenting opinions are wrong.

 

[Kenneth K]

On the 28+ the inlet and outlet are port and stbd, right aft on the outboard side of the cockpit combing.

If you're running the blower, then I'd say you're correct about the inlet and outlet ports. But without the blower, it's just passive ventilation. When pressure is greater inside the boat than outside, air flows out, and vice versa. If you have some port windows or a hatch open when sailing into the wind, air is likely venting out of both the cowls.

The 32' and larger boats typically have a dorade vent forward of the mast. The airflow is then generally thought of as IN through the dorade and OUT through the cowls. But again it's all passive, so it's more sensitive to pressure than to collecting "wind" through the small vent openings.

 

[Kenneth K]

a couple of knockdowns have concerned me about the high potential of flooding in through the vents! I am designing a way to run the vents horizontally directly inboard along the inside of the transom to midships

I suppose a horizontal hose that faces mid-ships becomes a vertical stand-pipe when the boat is on its side, but it's still going to fill with water. So once the boat is righted again, whole vent system is filled with water and would need to be pumped out.

Sounds a lot easier to just try to avoid knockdowns, or if you anticipate them, to screw in the cover plates first.

 

[Second Star]

A very good point about flooding the hose Kenneth. If I had cover plates I would use them but they have disappeared into the mists of time!
I do try to avoid knockdowns but there are some very rough places like Middle Channel and Admiralty Inlet when I've not had much choice but to go for it ...

 

[Prairie Schooner]

Considering the arrangement of the aft vents on our boat, I was thinking you must be doing some really hairy sailing. But a search on the web turned up this picture. Is the placement like yours? If so, I see the problem.

 

[Second Star]

Yes very similar