Leaking Water Tank

Jan 12, 2017
3
Hunter Legend 40.5 New Orleans, LA
Hi all!

I am new to SBO and also relatively new to sailing so pls bear with me here! ;) My husband and I just purchased a 1994 Hunter Legend 40.5. We've recently noticed a dark spot on the wood flooring that sits above our starboard water tank and when we pulled up the floor piece, found that the starboard water tank was leaking--we can tell this because when we push on the top of it, water spills out (not much but enough that it has partially rotted the wood floor over time). It seems like it's what would be considered a "molded in" tank with screws all around the top of it. And, from what I can tell, the leaking probably has happened to the previous owner, too, as there is silicone sealant applied all around the edges of the tank and some of the screws. Photo attached here.

Any idea how to fix the leak? A friend recommended using a screw driver to pull up all of the surrounding silicone sealant (which I already started to do) and then applying 5200 in its place to seal but I'm not sure if that's the best option for us. Thanks in advance!

Brooke
 

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Jan 7, 2011
4,727
Oday 322 East Chicago, IN
Are you saying it is leaking where the top is screwed to the rest of the tank? If so, I would think removing all of the screws, carefully (so you don't break it) remove the top, scrape off all of the old sealant from top and tank, and reassembling the top with a good (and FDA-compliant) caulk should fix the problem.

I would not use 5200 for several reasons...it is the devils glue, and if you ever wanted to remove the top to clean or inspect your tank, you will destroy it before it comes apart. I see an inspection port...but still, 5200 is permanent. Second, you store drinking water in the tank....is 5200 safe for contact with drinking water?

If the tank itself is cracked, that is a different issue. Not sure if you can chemically or thermally "weld" the crack.

Good luck with your project.

Greg
 
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sailrj

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Jun 16, 2004
43
Beneteau 351 0 Aurora, KY
Your tank looks very similar to the ones on our 1996 Beneteau Oceanis 351. Had a similar problem as you and solved it by taking the top off, cleaned both surfaces and sealed it back with food grade silicone. Make sure all the screws are are secured and replace any that are stripped. I went up one size on several that were stripped. Ours leaked big time when we filled the tank. Good luck.
 
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Jan 12, 2017
3
Hunter Legend 40.5 New Orleans, LA
Thanks so much for the feedback. Yes, I think the leak is only coming from the top of the tank where it's screwed together, not the body of the tank, thankfully. Good point re the 5200 being food-safe--I was worried about it's permanency but your point on whether it's safe has convinced me that's not the best solution.

@sailrj @Tally Ho Sounds like there's a general consensus that I need to take off the screws and clean up both the top and the tank before doing anything else, but do either of you have recommendation for what silicone sealant to use? You both bring up the point of food safe/FDA compliant (so glad you did!) but I haven't found any brands at West Marine that specifically state that on the label.

Thanks again, y'all.
 
Jan 7, 2011
4,727
Oday 322 East Chicago, IN
I looked at some of the spec sheets and SDS for Boatlife sealants, and they don't mention food-safe properties. But I googled "food-safe silicone sealant" and came up with several.

For this application, I think any food-safe silicone would work.

There are some good application notes in this West Marine Advisor" note:
https://www.westmarine.com/WestAdvisor/How-to-Select-Sealants-and-Caulk

Note the section about not tightening the joint too tight until the sealant cures. I tried to use a liquid gasket material to rebed the fill neck on my heat exchanger. I tightened the screws real tight as soon as I applied the liquid gasket, and the joint leaked....read the directions (duh!), and applied a good head of sealant, lightly tightened the screws just tight enough that the two parts were in contact with the sealant, let it set up, and then tightened everything up...no leak.

Good luck, I don't think your prohect will be too difficult to fix.

Greg
 
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Jan 12, 2017
3
Hunter Legend 40.5 New Orleans, LA
@Tally Ho Thanks for all of this info! I'd never heard about not tightening until the sealant had cured. Yikes, I'm feeling like you just saved me a lot of time on that one. (There are about 30 screws in this top (!)) Thank you again. Now off to fix this tank!
 
Sep 8, 2014
2,551
Catalina 22 Swing Keel San Diego
@Brooke B , some great advice given above... Allow the bead of caulk to mostly cure before tightening screws, this how we create a 'form in place gasket'... If at all possible, the screws do not have to go through the bead of silicone, the bead should be continuous and travel inside or 'inboard' of the screws.
Other advice to always remember, thanks @Tally Ho, 3M 5200 is often over used in the wrong applications. They call it the 'Devil's glue' or 'Satan's glue' for a reason... It is so strong that if you ever try to take something apart that has been bonded with 5200 it will rip off gelcoat and fiberglass before the adhesive gives it up. One of very few places on a sailboat it is used is the keel to hull joint. Pretty much don't use 5200 anywhere else on a sailboat.
Silicone... be very careful where you use silicone sealants on a boat! For the most part you should never use silicone, especially anything from Lowe's/Home Depot. There are some special places where you should use silicone sealants, like DOW 795 for sealing windows or port lights, and also as you have pointed out now, using FDA approved silicone for sealing water tanks. Generally speaking, 3M 4200 or the UV stable version 3M 4000 will satisfy the majority of your bonding or bedding needs.
Another tip... Don't buy the majority of your sealants @ West Marine. I shop there too and spend way too much money like everyone here, but the prices for sealants are near double where you can get them other places or online. You can even get 3M 4200 and 4000 at Home Depot now but I usually order mine online.
Here is a link to a pdf of DOW Corning Silicones and their uses/features. You'll notice in the chart that DOW 748 is non-corrosive and FDA approved. You should be able to easily find this locally (industrial suppliers) or online.
https://www.dowcorning.com/content/publishedlit/80-3258.pdf
 
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Jan 7, 2011
4,727
Oday 322 East Chicago, IN
Some good points CloudDiver..
- use of silicone typically creates a layer of silicone that cannot be removed...so it you try to use another sealant, it won't stick. You also can't usually paint over silicone.

For this specific application, I think that is what I would use, due to the fact it will come in contact with your drinking water (or whatever you use your fresh water for).

The Dow 748 seems like a great choice for this. If you can't find it locally to you, you can get a 3 oz. tube on Amazon for about $12 plus shipping.

Greg
 
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