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

[zstine]

Where did you find this USCG guidance? I've Never heard of any requirement/recommendation to vent a Diesel tank compartments. I know mine is not. But if Lagoon, FP, Outremer, etc. are venting (?) why not copy their methods?

[Chotu]

Originally Posted by zstine

Where did you find this USCG guidance? I've Never heard of any requirement/recommendation to vent a Diesel tank compartments. I know mine is not. But if Lagoon, FP, Outremer, etc. are venting (?) why not copy their methods?

The requirements are for gasoline tanks only. Not diesel. Found freely at

https://uscgboating.org/regulations/...s-handbook.php

[zstine]

Originally Posted by Chotu

The requirements are for gasoline tanks only. Not diesel. Found freely at

https://uscgboating.org/regulations/...s-handbook.php

Roger 10-4.. Gasoline definitely should be in vented compartments. It wasn't clear to me that you were dealing with gas down in the hull. somewhat unusual on larger yachts.

Hope you found a solution. I have nothing to add regarding vents.

[Chotu]

Originally Posted by zstine

Roger 10-4.. Gasoline definitely should be in vented compartments. It wasn't clear to me that you were dealing with gas down in the hull. somewhat unusual on larger yachts.

Hope you found a solution. I have nothing to add regarding vents.

Exactly. Poly gasoline tanks permeate. A not so wonderful feature. they don’t advertise in advance.

So I’ve built them an airtight compartment which will be ventilated as this thread is getting to.

A nuisance, mostly. I really don’t like the stink. Doesn’t really happen in cold weather but above 80F it starts to become noticeable.

Any yes. Everything is unusual (and geared toward performance) on my boat. Outboards. Hence, gasoline.

60HP of propulsion and 5kw of generator power all tips the scales at 460lbs. And no through hulls. No zincs. Everything modular, off the shelf, and easily replaced.

[ggray]

Since you are rightly concerned about water intrusion, you might try starting with smaller openings, and go larger only if you find it to be necessary.

To relate an experience as a comparison, to reduce head odors, I replumbed my heads so that the discharge run from the heads had no sags for effluent to collect. Drained all the way to the holding tanks in the keels.

The tank vents were 3/4" hose attached to plastic thruhulls on side of hulls with what, 1/2 hole? Long story, but wind pressure on side of hull was enough to push holding tank fumes back up through the joker valve, even with the long run and loop in the vent line.

My solution, rather than putting a dip back into the head discharge, was to put a second vent line on the inboard side of each hull (from a second fitting on the holding tank, so to ensure the fresh air that Peggie recommends).

So I would additionally recommend the outlet hose to vent out the opposite side of the hull, or bridge deck if necessary. That would give you a good pressure differential under many conditions.

[Chotu]

Originally Posted by ggray

Since you are rightly concerned about water intrusion, you might try starting with smaller openings, and go larger only if you find it to be necessary.

To relate an experience as a comparison, to reduce head odors, I replumbed my heads so that the discharge run from the heads had no sags for effluent to collect. Drained all the way to the holding tanks in the keels.

The tank vents were 3/4" hose attached to plastic thruhulls on side of hulls with what, 1/2 hole? Long story, but wind pressure on side of hull was enough to push holding tank fumes back up through the joker valve, even with the long run and loop in the vent line.

My solution, rather than putting a dip back into the head discharge, was to put a second vent line on the inboard side of each hull (from a second fitting on the holding tank, so to ensure the fresh air that Peggie recommends).

So I would additionally recommend the outlet hose to vent out the opposite side of the hull, or bridge deck if necessary. That would give you a good pressure differential under many conditions.

Unfortunately, the size of the ventilation hoses is specified in the regulations so as to work adequately.

[Chotu]

So which area has more “pull?” The cockpit under a dodger, or the deck, out in the wind?

I’m thinking the deck, open to the wind, can produce more negative pressure than the cockpit area, under a hard dodger, but I could be wrong.

Would one pull air out harder than the other? I’m hoping so, because I need a pressure differential.
I can’t run a 4” hose 25’ between port and starboard sides of the boat without structural modifications.

[rslifkin]

Originally Posted by Chotu

So which area has more “pull?” The cockpit under a dodger, or the deck, out in the wind?

I’m thinking the deck, open to the wind, can produce more negative pressure than the cockpit area, under a hard dodger, but I could be wrong.

Would one pull air out harder than the other? I’m hoping so, because I need a pressure differential.
I can’t run a 4” hose 25’ between port and starboard sides of the boat without structural modifications.

I wouldn't worry about running a hose to each side of the boat, but one to each side of each hull. Maybe an intake scoop facing forward on the outboard side of the deck and a louvered exhaust vent on the inboard side of the hull just below the bridge deck? That should produce a good bit of airflow with wind on the bow, as you'll get positive pressure at the scoop and negative at the exhaust vent (from air flowing past the louvers as it blows under the boat). In other wind directions, you'll probably still get some pressure differential to produce flow, just not as much.