Holding tank vent hole

[brianc]

I'm replacing the holding tank vent, but in my effort to get the vent off I also pulled off a little bit of gelcoat (see attached) underneath the fitting.

I was going to use Sikaflex 291 or 3M 4000 UV to install the new vent as-is but now I'm thinking I should repair/seal/reinforce the missing gel coat first.

What would be the best way to go about doing this? Epoxy putty? Should I use a liquid epoxy to penetrate any invisible cracking to reinforce it first? If so, should I brush it on, let it sure, then fill the area with the putty?

Any other ideas, or is it necessary to repair it first at all?

Thanks! Brian

[peghall]

I'm a wee bit confused...are we talking about damage to the hull gelcoat when you removed the vent thru-hull? If so, and if you removed the thru-hull to replace it with larger diameter thru-hull, you may not need to do much to it at all because it'll be covered by the flange on the new thru-hull.

Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein
http://www.amazon.com/New-Get-Rid-Bo...dp/1892399784/

[brianc]

Originally Posted by peghall

I'm a wee bit confused...are we talking about damage to the hull gelcoat when you removed the vent thru-hull? If so, and if you removed the thru-hull to replace it with larger diameter thru-hull, you may not need to do much to it at all because it'll be covered by the flange on the new thru-hull.

Hey! Yes, you are correct, I am talking about hull gel coat that was damaged when I removed the vent.

I planned to replace it with the same "model" so while the flange would cover the damage, and the adhesive sealant would presumably fill the damage, I was wondering if it would be better to repair it with epoxy first to make sure everything is sealed and bonded first.

Brian

[fallingeggs]

Originally Posted by brianc

Hey! Yes, you are correct, I am talking about hull gel coat that was damaged when I removed the vent.

I planned to replace it with the same "model" so while the flange would cover the damage, and the adhesive sealant would presumably fill the damage, I was wondering if it would be better to repair it with epoxy first to make sure everything is sealed and bonded first.

Brian

Brian,

I want to follow the road that Peggy Hall, I think, was trying to get you to explore. In almost all cases, the hose and vents for the holding tank are under sized at 3/8 inch. This undersize ventilation results in a smelly holding tank because not enough oxygen can enter the tank to support the correct (ie, non-smelling) bacteria growth.

If you are replumbing the tank, you should strongly consider bumping up the hose and vent size. I went to a full 1 inch. If you do this, your gel coat issue may solve itself because you'll drill a larger hold AND you'll improve the performance of your holding tank! A win-win.

Don't trust me, trust the experts... like Peggy!

Circulating to your question, search elsewhere on this forum; gel coat repair has been covered a million times. Go to google.com and type in: site:cruisersforum.com gel coat repair

[Cheechako]

Use sealant, don't worry.

[brianc]

Originally Posted by fallingeggs

I want to follow the road that Peggy Hall, I think, was trying to get you to explore. In almost all cases, the hose and vents for the holding tank are under sized at 3/8 inch. This undersize ventilation results in a smelly holding tank because not enough oxygen can enter the tank to support the correct (ie, non-smelling) bacteria growth.

Hey - I'm not re-plumbing the whole thing, just replacing the vent. It's 5/8 (which I think is what you meant when you said 3/8) but I haven't had any issues with the odor, perhaps because the vent line fits the other desired parameters Peggy mentioned (I've read a lot of this forum...) The line is about five feet, doesn't rise steeply until just below the vent hole, and while it's not installed on top of the tank (there wouldn't be room there) it's at the top of the side wall (in front) and pretty close to the center. I also use NoFlex religiously and make sure to flush the tank really well whenever I pump out.

I've just started doing some of this stuff myself so I'm not sure I'm comfortable messing with holes in the hull...regardless of their location...but I'm more worried about creating a bigger gel coat problem than solving this one if I tried to drill the hole bigger! I get what you're saying though, and it may be something I do in the future.

I've seen lots of discussions on the vents themselves as well. I was going to replace mine with the same model which is the round one with two holes (screened)...I'm open to using something else, but not sure what's best. The clam shell ones looked worse because they only had one screen which would seem to make the potential clogging problem worse. If you have any recommendations on that I'm all ears...I didn't find much info about what people actually installed as vents (for those that were upsizing their venting system.)

Brian

[brianc]

Originally Posted by Cheechako

...don't worry.

...hahaha...those are famous last words in my experience.

Any particular reason?

[fallingeggs]

A man with a plan.

I just used a plastic elbow thru-hull (couldn't fit a straight thru-hull, which is why I went 1'' rather than 3/4''). No screens to get clogged up. It's well above the water line at all angle of heel. Perhaps I get some water splashing in during rough weather, but it hasn't become a problem.

[peghall]

I was going to replace mine with the same model which is the round one with two holes (screened)...I'm open to using something else, but not sure what's best.

That type of thru-hull is designed to prevent sea water from contaminating fresh water and fuel, which is not an issue with sewage. But boat builders use the same thru-hull on everything because it costs them less to buy the same thing in bulk than to use the right one for each application.

The ideal thru-hull for a waste tank is a "bulkhead" or "mushroom thru-hull because it allows more air exchange with the gasses in the tank (essential to odor prevention), but also lets you stick a hose nozzle up against it and back flush the vent line to get rid of any waste that spilled into the vent or any spiders or insects. If you do that every time you wash the boat, you'll never have a blocked vent. Any material EXCEPT NYLON is fine for this use.
Seal with a good bedding compound.

Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein
http://www.amazon.com/New-Get-Rid-Bo...dp/1892399784/

[Cadence]

Originally Posted by Cheechako

Use sealant, don't worry.

[Dave Lochner]

In the photo the tan material in hull looks to be balsa coring. If it is balsa core, I'd coat the exposed core with some epoxy to seal it. Doesn't need to be thick just enough to seal the grain of the wood so that water can't get into the core.

As for the chipped gelcoat, put a little extra sealant on it when installing the through hull.

[chris95040]

There is no need to repair the gelcoat before reinstalling your fitting.

[brianc]

Originally Posted by peghall

The ideal thru-hull for a waste tank is a "bulkhead" or "mushroom" thru-hull...Any material EXCEPT NYLON is fine for this use.
Seal with a good bedding compound.

Sounds good. I bought one of these based on your other threads so I think I'll install it instead of the one with the two screens. The flange is significantly wider than the metal one so it will cover the gel coat damage. Thanks!

https://www.westmarine.com/buy/perko...2?recordNum=11

[a64pilot]

I went with SS myself, but why not Nylon?

[brianc]

Originally Posted by Dave Lochner

In the photo the tan material in hull looks to be balsa coring. If it is balsa core, I'd coat the exposed core with some epoxy to seal it. Doesn't need to be thick just enough to seal the grain of the wood so that water can't get into the core.

As for the chipped gelcoat, put a little extra sealant on it when installing the through hull.

I actually can't tell if it's cored there or not...it's definitely not obvious. It seems pretty thin to be cored, probably only 1/3 of an inch thick.

I'll coat it with epoxy either way to make sure.

Brian