Vents through the deck, topsides and hull. What would you use?

[rslifkin]

Originally Posted by stormalong

I have a hidden fuel vent for my diesel tank. An idea I saw on (I think) a Hinckley.

It is a 1/4 inch stainless diameter standpipe that goes up a few inches inside a vertical stern rail tube and three tiny holes drilled near the base of that stern rail far below the inside standpipe. That makes the vent invisible and water proof. I've had it this way for about 20 years with zero problems.

I don't know about tank odors needing venting. The purpose of the vent is to prevent a partial vacuum or pressurization of the tank when drawing fuel and allowing air pressure to equalize as the fuel expands or contracts by ambient temperature or from the warming from the excess fuel return from the injection pump.

Please read the thread again. This isn't about venting the tank itself, but venting the compartment the tank sits in.

[Tusitala]

Chotu, you posted about venting the compart. Doesn't sound like you need the blower itself, but the dorades and vent hose are as you describe and are typical on gas inboards, especially stern drives.

https://www.wholesalemarine.com/boat...ntilation.html

Pat

[notiesbob]

ABYC guidance - https://law.resource.org/pub/us/cfr/....H-32.1987.pdf

That said, for proper air flow you need inlet and outlet. To enhance that you need to move air when there is no natural air flow. Continuous air flow will also aid to remove excess moisture (think mold)

https://www.proboat.com/2015/06/venting-the-engineroom/
https://www.powerandmotoryacht.com/m...ts-engine-room

Above links show larger vessels but the same principals apply.

https://www.google.com/search?rlz=1C...4dUDCA0&uact=5

[Paul Howard]

I used a clamshell vent on the slope on the outboard side of the hull, pointed down, and another vent at the bridge deck transom with 3" flexible dryer hose leading through a cockpit locker into the compartment on my catamaran

[Djarraluda]

Originally Posted by Cheechako

I would vent out the back up high, or (preferably to me) into the cockpit. Use a 3" vent with plastic hose (like used in bilge vents, kinda like dryer hose) from bottom up to the vent. That way the chimney effect will draw it out better. it's amazing how much chimney effect you get in 4-6 ft of head!

The “chimney effect” is formally called “stack effect” in vent terms and requires a difference in height between the two in/out to work. Operates on air density as basics but of course with heat or fan assistance it can be driven very effectively. We can also use it in a building to generate airflow.

In this case, trying to vent a low level locker, I query the temp there. In cooler waters especially, there will be cooling down low and warm air above so no stack effect operating. An in-line blower fan would be guaranteed to drive the air or need to seek a noticeable difference in height between inlet and outlet.

For volatile fumes such as petrol, duct inlet to low level and extract at high level, for lpg the reverse of course. So for your petrol situation, inlet vent could be from internal if external exhaust is high enough, simply add a blower, perhaps on a timer so it runs intermittently. Alternatively find a way to warm the outlet pipe and thus create the buoyancy needed to drive the stack effect.
Roger

[rslifkin]

Originally Posted by Djarraluda

For volatile fumes such as petrol, duct inlet to low level and extract at high level, for lpg the reverse of course. So for your petrol situation, inlet vent could be from internal if external exhaust is high enough, simply add a blower, perhaps on a timer so it runs intermittently. Alternatively find a way to warm the outlet pipe and thus create the buoyancy needed to drive the stack effect.

Gasoline fumes sink, so you need to extract from the bottom. As an example, a boat with gas inboards is required to have the blowers draw from the lower third of the bilge and generally they have powered exhaust only with passive intake.


For what it's worth, with the vents ducted fairly low in the compartment, my bilges get a pretty good cross-breeze on a windy day, especially if the boat is at some angle to the wind.

[capt.rob]

I don't know if this will work in your situation but I have been quite happy with how my smaller vents for water tanks and fuel were done. I have a 1972 formosa 41. They used the hollow rail stansions for venting by drilling a hole in deck under center of rail stansions then ran the vent tube up inside the stansion several inches above the deck and sealing them at deck level. The holes were safety lines run and cap provde quite a bit of air venting and a couple more holes can always be drilled in the stansion or cap. This keeps all vents well above the water line and the watertight even with the gunnel dipping and make it nearly inpossible to get water in the vents, Larger vents could be run the same way but through a larger stansion or any hollow tubing mounted to deck like a solar arch, davits etc.

[Dogscout]

I'm curious. Where is the fuel smell coming from? That tank should not be permeating FUEL STINK. Your tank should be sealed and not able to spill any liquid or vapor into the compartment. Fill hose, tank vent and engine fuel line should be about it. If it smells like fuel in the compartment then you have other problems and a vent isnt going to fix that. Engine compartments typically have blowers and vents because of vapors escaping from the engine which with the heat cycles and internal pressures often leak a bit.

[Chotu]

Originally Posted by Dogscout

I'm curious. Where is the fuel smell coming from? That tank should not be permeating FUEL STINK. Your tank should be sealed and not able to spill any liquid or vapor into the compartment. Fill hose, tank vent and engine fuel line should be about it. If it smells like fuel in the compartment then you have other problems and a vent isnt going to fix that. Engine compartments typically have blowers and vents because of vapors escaping from the engine which with the heat cycles and internal pressures often leak a bit.

Please reread the first post. PERMEATION

No thread drift. Please Google some things about fuel tanks and USCG regulations.

[Chotu]

Originally Posted by capt.rob

I don't know if this will work in your situation but I have been quite happy with how my smaller vents for water tanks and fuel were done. I have a 1972 formosa 41. They used the hollow rail stansions for venting by drilling a hole in deck under center of rail stansions then ran the vent tube up inside the stansion several inches above the deck and sealing them at deck level. The holes were safety lines run and cap provde quite a bit of air venting and a couple more holes can always be drilled in the stansion or cap. This keeps all vents well above the water line and the watertight even with the gunnel dipping and make it nearly inpossible to get water in the vents, Larger vents could be run the same way but through a larger stansion or any hollow tubing mounted to deck like a solar arch, davits etc.

This is a really cool idea.

I was thinking this was the winner because I have a couple 3” support columns for the roof kind of nearby. However, that would involve me cutting a 3” hole in the main aft structural support beam. I’m not feeling too comfortable with that.

Otherwise , this is brilliant.

Maybe there is another similar way to do this.

[Chotu]

Originally Posted by Tusitala

Chotu, you posted about venting the compart. Doesn't sound like you need the blower itself, but the dorades and vent hose are as you describe and are typical on gas inboards, especially stern drives.

https://www.wholesalemarine.com/boat...ntilation.html

Pat

I have the following items from the link you provided on hand already.

Just not sure where to locate them do they have a good airflow and also won’t allow huge waves to get the bilge wet.



https://www.wholesalemarine.com/sea-...thru-vent.html

https://www.wholesalemarine.com/perk...stic-base.html


Sorry, the pics wouldn’t link. Wholesale marine doesn’t allow it.

[Chotu]

It seems every option I have for installation location is either negative pressure (good for the exhaust opening) or if positive pressure, will be choking on water.

Maybe the inverted snorkel idea would be best. Don’t see those on pleasure boats and don’t see those available to buy either.

[Chotu]

Maybe mushroom type air intake on deck and louvered vent in a negative pressure area like the cockpit, which has a hard top and station wagon effect?

I’m not looking to use any fans. I want it to always work.

[Chotu]

Found something.

Something like this could work nicely.

PVC pipe up through the deck and a “house” on top of it to allow air in, but keep water out.

They make these for trailers.

Something along these lines. It’s upside down in the pic. And the round, louvered part could just be a PVC pipe.

This could sit in the wind and ram air down into the fuel tank compartment while the exit could reside in the cockpit’s station wagon effect area.

Or just a couple of these semi-dorades facing In opposing directions on deck.

[Chotu]

And I’m definitely finding marine versions of these semi-dorade clamshells that look like they will work.

One facing forward on deck, one facing aft.

They can take a wave hit and rain if installed so the pipe through the deck is well above deck level. And they’ll ram the wind through the system.