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Rebedding Water Tank Lid

6K views 19 replies 13 participants last post by  fefrich 
#1 ·
Hi Sailnet -

I have a forward water tank on our '96 Crealock 34 that has numerous leaks around the perimeter. It is currently bedded with silicone (only 3 years ago), which after researching, seems like an ineffective bedding compound considering the extensive upward pressure of 40 gallons of water when in a seaway.

Can anyone walk me through the process of removing the lid (it has an inspection port)?

And why silicone is typically used? If you can recommend a different bedding compound, that would be great. What are the pros and cons?

See photo for reference. Many thanks, Celia
 

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#2 ·
Are you actually contemplating re-bedding the cover, removing all of the screws? It's hard to tell from your photo what type of screws those are, philips head?

As close as all of the screws are together, I wouldn't think there would be that much pressure from just sloshing water. You would probably want to use some type of sealant that wouldn't taint the water or impart some taste to it. Do you know what was under there originally? Was it some type of sealant or a gasket?

I would think that you would want something that becomes inert once it is cured. This is one of the few places on a boat where kitchen&bath grade silicon might be appropriate. You are not rebedding a deck fitting.

You might also be able to find a large sheet of plastic closed cell foam you could use to cut a gasket using the lid as a template.

I'm just brainstorming.
 
#3 ·
Use PTFE gasket on a roll, which provides soft, highly compressible gasketing. You'll find it at McMaster-Carr or plumbing suppliers who deal in flange to flange piping. Select tape approx 1/3 the width of the flange. When compressed the two sealing surfaces are torqued down it provides a very wide, thin ribbon-like joint sealant and it fills the irregularities on rough or uneven surfaced flanges. PTFE gasketing does not support bacterial growth and is FDA compliant for water and food service.
 
#4 ·
Sounds like the Butyl I use on deck, no question this is the right stuff, I might suggest tightening a little let it settle and snug a bit more, these types of sealants take a while to re-form when tightening no need to squeeze it all out. You should see it even out as you go.
 
#9 ·
Silicone was probably used because it is on every shelf and folks think it is the greatest stuff on earth. Of course if it is "bathtub caulk" grade, it contains arsenic to prevent mildew, not the best thing for a water tank.

Food grade silicone, neoprene, teflon...many ways to skin a cat. You might check with PermaTex or LocTite to see if they make a "Form-A-Gasket" sealant for water tanks. That's a product that is similar to silicone seal (to the casual user) but you apply it to a surface, like the edges of an oil pan, and then bolt it up and let it cure. At which point it becomes basically a custom made gasket, designed to be compatible with the fluid it has been used with.

I would think that tightening all the screws to a *very* similar torque would be more important, in the long run, than the specific gasket material. If you pick up a cheap "foot inch" 1/4" torque wrench, even the $10 ones from Horror Fright, that can give you a fast way to match them all up. Or use an electric drill/driver that has adjustable light torque settings, and use that.
 
#11 ·
All? Probably not, these days. Maybe the "Number One Best Top Quality Export Grade" stuff from Shenzhen. [Slap! Bad monkey!] I really don't know, I haven't read the contents on silicone sealant in a long time, but I'd bet whatever has a "mildecide" in it, isn't good to use around drinking water.

These days, someone out there is making and selling anything you might need. Or not.
 
#12 · (Edited)
Our Ontario 32 has a very similar tank. When I bought the boat, there was just a plywood lid and the bin was used for storage. However, it was intended to be the holding tank and since boat did not have one, I converted it.

I made a new cover out of a product similar to Starboard. It looks just like the one in Toddoh72s first post, except white.

Not much sticks to the plastic I used, so I did some experimenting. In the end, I used Marine Goop! However, I have at least twice as many screws as Toddoh and each one has a large fender washer. The span between washers is quite small. (I learned to do this when trying to seal external bolt-on Plexiglass windows on an earlier boat. They always leaked until I added more bolts. Bolt or screw holes need to be slightly oversize so as to allow for some movement.

My holding tank has been in service now for about 10 years. No leaks and no smells (well ventilated tank!)

ADDED: Our water tanks are under the settee berths. They may have originally had covers, but are now glassed over (problem solved!) There are clean out ports.
 
#13 ·
We replaced our plywood tank lids with the gray PVC ones from PSC about 20 years ago. Robin, Thumper's predecessor, sold us the 3M sealant along with the lids. I don't recall the 3M product number but there was a primer/accelerator that Robin said was essential to use for a good bond. We have had no leaks since the installation even after a Baja Bash back north from Mexico.

s/v Pelagic
1980 C37 Yawl
 
#14 ·
toddoh72: Sorry for dragging up an old thread but I'm going through the very same project on a PSC37 and wondering which path you took. I have the same gray plastic lid that was put on with a silicone of unknown type. After taking all the screws out the lid lifted off as if the silicone was not even attached. I have a hard time believing that a fresh application of silicone will do the trick.

Looked at the PTFE tape and am intrigued. But how does it do around the tight corners?
 
#15 ·
I found a copy of the instructions from Robin (Thumper's predecessor in Fullerton) regarding installing the PVC tank lids. I have attached it here but the important point is that he stresses using Dow Corning 1205 Primer and Dow Corning 999A Clear Silicone. As mentioned in my previous post our tank lids have been on for many years without any leaks.

Note, this doc is a fax dated 2007 to another owner but is identical to the instructions Robin gave me in 1998.

John
s/v Pelagic
 

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#16 ·
I rebedded my aft PVC tank lid last season with the 999A silicone and following the instructions posted by John. So far, it is holding well. I had one screw that had ever so slight a leak. I eventually had to remove the screw and I filled the hole with 5200 and that seems to have solved the problem.

Bill
Belle Voile
PSC 34
 
#17 ·
I saw your post on sealing PSC 34 water tank. I was just scoping out this project myself for my 1992 PSC 34. How did you wind up doing this project? What sealant did you wind up using??? Any help would be appreciated...

Thanks

Rich Feffer
Green Ayes PSC 34
Key Biscayne
 
#18 · (Edited)
The most painful part of the job was carefully removing the PVC without damaging it. I cut all around with a utility knife and cut away as much of the sealant as possible. Then, beginning at the forward edge, I used large flat blade screw drivers to gingerly pry up a corner of the lid. I also used wooden wedges (door shims from HD work well) to hold up the corner that I got loose. I worked around the forward edge gently prying up and also cutting the sealant with the utility knife (I used one with the snap-off blades so I could extend it out and reach as far under the lip as possible) as I went. Eventually I got enough of it up (about a foot and a half back) that I could easily reach under the lid and cut away the remaining sealant and easily got the rest of the lid off.

Then clean up and follow the instructions that John posted above to rebed it. So far it's been holding.

I guess the other pain about this job is working back in the limited space of the quarter berth, but that's just typical on a boat the size of the PSC 34.

-- Bill
Belle Voile
PSC 34
 
#19 ·
I used clear Lifeseal and added about 8 extra screws (total) in between the existing ones where the tank lid attachment was narrow and previously leaked. Let it sit for about a month to cure before adding water just yesterday. Only able to test with the pressure of water coming down the fill tube but so far so good. In the water next week and will start sloshing things around.
 
#20 ·
Thanks to all for the help on this. I spoke with PSC and they recommended replacing the lid(s) on the tank, then quoted me $2100 for just the quarter-berth tank. Seems high so I am going to try and re-seal existing lid as per the notes and comments above... I'll let y'all know how it turns out...
 
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