Holding/Water Tank Thru - Hull Vents

[Blitz]

Over the past few years, the thru hull vent fitting on my holding tank corrodes to a point I need to replace it. I have noticed in walking around the boat yard that most boats seem to have the same issue. These vents are ususally some chrome plated junk which doesn't seem to last (the same is true for fuel tank vents - Diesel).

I have read here some suggestions so as to avoid clogging to put a regular thru hull mushroom type fitting instead of the ones that are readily available. Does anyone have any suggestions on the materials and ones that last more than a few years before looking all pitted and corroded? Is chrome plated bronze mushroom better, or marelon, or?

I hope to open this discussion to someone who might have found the solution to this.

thanks

 

[sailingdog]

Go with a marelon mushroom through-hull. They won't rust and are far easier to clean than the screened ones. Besides, if insect enter the holding tank, where are they going to go???

Over the past few years, the thru hull vent fitting on my holding tank corrodes to a point I need to replace it. I have noticed in walking around the boat yard that most boats seem to have the same issue. These vents are ususally some chrome plated junk which doesn't seem to last (the same is true for fuel tank vents - Diesel).

I have read here some suggestions so as to avoid clogging to put a regular thru hull mushroom type fitting instead of the ones that are readily available. Does anyone have any suggestions on the materials and ones that last more than a few years before looking all pitted and corroded? Is chrome plated bronze mushroom better, or marelon, or?

I hope to open this discussion to someone who might have found the solution to this.

thanks

 

[Don S/V ILLusion]

This may be one of those "be careful what you wish for" solutions. The clam shell metal vent cap will corrode over time but it does serve to limit the odor compared with a wide open thruhull which, arguably will allow more ventilation with less corrosion at the "expense" of causing the odor to waft throughout the cockpit more easily than the clamshell.

I don't know how much it would add to the smell but replacing the clamshell periodically seems preferable (to me) than a constant odor.
If you do choose to replace the vent cap with a thruhull, please let us know if the odor becomes more noticeable.

 

[Stu Jackson]

My understanding from all of Peggie's posts and

her book is that with proper ventilation through the increased vent size and clear opening that odors should not occur. That's the (w)hole idea!

 

[Peggie Hall HeadMistress]

Yep...

Go with Sailingdog's advice... A claimshell is only needed if the thru-hull is likely to be under water when the boat is heeled...to prevent water from being forced up the vent line. It doesn't do a thing to inhibit any odor...in facr, just the opposite...it interferes with a free exchange of fresh air into the tank, actually contributing to odor.

 

[Blitz]

Location of Vent matters

This may be one of those "be careful what you wish for" solutions. The clam shell metal vent cap will corrode over time but it does serve to limit the odor compared with a wide open thruhull which, arguably will allow more ventilation with less corrosion at the "expense" of causing the odor to waft throughout the cockpit more easily than the clamshell.

I don't know how much it would add to the smell but replacing the clamshell periodically seems preferable (to me) than a constant odor.
If you do choose to replace the vent cap with a thruhull, please let us know if the odor becomes more noticeable.

I'm not really worried too much about the odoe reaching the cockpit, since the vent is toward the front of the boat. It might however create an issue if odors were to realease and I had the front hatch open. I'm going to go with the marlon and I'll report back if any issues.

Now the only question is what type of vent should I use for the diesel and fresh water tanks - since they also corrode very easily and we don't want bugs in either of these tanks.

 

[sailingdog]

The fuel and water tank vent lines can use the screend vent fitting, since they don't generally need to be cleared, and aren't likely to be fouled or clogged by the contents of their respective tanks...

I'd also add that adding an air filter to the water tank vent line can help keep the contamination of the water tank down quite a bit...

I'm not really worried too much about the odoe reaching the cockpit, since the vent is toward the front of the boat. It might however create an issue if odors were to realease and I had the front hatch open. I'm going to go with the marlon and I'll report back if any issues.

Now the only question is what type of vent should I use for the diesel and fresh water tanks - since they also corrode very easily and we don't want bugs in either of these tanks.

 

[Peggie Hall HeadMistress]

Fuel and water tank vent lines

A loop (an arch, not a sag!) in the vent line that goes well above the thru-hull is recommended on fuel water tank vents if the vent thru-hulls are likely to be under water when the boat is heeled.

You don't want a loop in the holding tank vent line though.

 

[sailingdog]

water contamination is a problem in the Fuel or Potable water tanks... hence the need for a high loop... ventilation is the primary purpose for the holding tank vent line and contamination with saltwater isn't an issue...so no loop is required or wanted...

A loop (an arch, not a sag!) in the vent line that goes well above the thru-hull is recommended on fuel water tank vents if the vent thru-hulls are likely to be under water when the boat is heeled.

You don't want a loop in the holding tank vent line though.

 

[Guest]

Through hull vents

Our 1991 model boat has the original chrome clam shell type vents for fuel, potable water, waste tank, anchor locker, etc. We keep the boat in sea water all the time and have never had a problem with corrosion. I do make it a practice of rinsing the boat with fresh water from time to time, but none need replacing.

Terry Cox