Water tank leak

[Bogart]

Hi All

Bogart is a 45CC 2007 model. We have discovered a slight crack in the top of the aft starboard water tank, which is under the galley sink. Photo is attached which shows a very slight white line just near the indentation in the top of the tank. When filling the tanks, this crack produces a small geyser which ultimately makes it to the bilge. Three questions:
1. Why would this happen? and
2. What should we use to try to seal this?
3. Is there anything we can do to try to prevent this happening to the other tanks?
This is a "plastic" (maybe polyurethane?) type tank. I dread having to pull one out to replace it, particularly the aft tanks, as these are under the galley, on starboard and under the inverter/charger on port.

Any suggestions would be greatly appreciated.

Cheers from Australia
Tony

 

[Peggie Hall HeadMistress]

Your tank is polyethylene...and unfortunately there is no "glue" or sealant that will bond to PE permanently. Heat welding is the only way to mend a crack and there's a bit more to doing it than just injecting some melted PE into it...the edges of the crack must also be melted so that the new and old PE become a continuous mass..and it takes a bit of skill to know how much new material and how much of the edges to melt. I suggest you find a plastics fabricator close to you who wouldn't charge you more than the price to replace the tank to make a "house call."

As for what causes this to happen...production boat builders rarely spend the money for top quality thick walled water and waste tanks...OEM tank walls are typically just .25" thick. Over time flexing takes its toll and can result in cracks.

--Peggie

 

[Ralph Johnstone]

If it were mine and given the problems with nothing sticking to poly, I would invest in a poly welding kit and get practicing to the point of getting "good" at poly welding. I'd concentrate on thin sample pieces of poly before taking the plunge. I guarantee this is not anywhere near as difficult as MIG or TIG welding. But that's just me because I enjoy things like this.

Just out of curiosity, what is purpose of the depression in the top of the tank ?

 

[Allan12210]

[QUOTE="Ralph Johnstone, post: 1801396, member: 73635"

Just out of curiosity, what is purpose of the depression in the top of the tank?
[/QUOTE]

It's a design feature to introduce a high stress point at an internal corner. That way the manufacturer can make more money selling replacements. Like Polaroid. They lost money selling cameras but made up for it selling film.

 

[TimFromLI]

I've used west systems gflex 650 + thicker to repair a canoe made of PE. Although epoxy is not recommended for PE, it worked for me for 10 years now. 5200 will work on PE. You may want to drill a hole at each end of the crack to stop it if it is spreading.

 

[Bogart]

Hi All

Many thanks for your advice. I was wondering about using a sealant and note that there is something (product unknown) which is used where the inlet and breather hoses are attached to the top of the tank. Does anyone know what this is?

Cheers, Tony

 

[Ralph Johnstone]

there is something (product unknown) which is used where the inlet and breather hoses are attached to the top of the tank.

This is the remaining material from friction welding connections on to the tank.

This is how nozzles are added to all poly tanks. As has been repeatedly stated, nothing sticks to poly permanently.

 

[Allan12210]

[QUOTE="Ralph Johnstone, post: 1801449, member: 73635"

This is how nozzles are added to all poly tanks. As has been repeatedly stated, nothing sticks to poly permanently.

[/QUOTE]
Or not easily. Back when I was a boy working for a polymer company the three ways we knew to prepare non-crosslinked Polyethylene for bonding was: 1 Flame Spray Ionization, 2 Chromic Acid Etch, and 3 Plasma Etch. Not available to us mortals. Why do I remember that bit of trivia? I can't even remember what I'm supposed to get at the store when I get there half the time.

 

[Ralph Johnstone]

Why do I remember that bit of trivia? I can't even remember what I'm supposed to get at the store when I get there half the time.

I know what you mean. I seem to remember something about flame treating the surface of the poly to encourage attempts at gluing it but that was open to debate.

Any wild theories about what the mechanism of flame treating is ?

I suppose it couldn't hurt unless you applied a little too much flame and the next thing you know :

 

[SabreToothedEngineer]

I successfully repaired a crack in my PE water tank about five years ago using a special type of epoxy (sadly I can't remember the specific brand) designed for this purpose that was recommended by a local plastics supply house. The key was to go over the surface for a few seconds with a propane torch; not enough to melt it, just to oxidize the surface. I used FRP tape with the epoxy for structural strength. The success of the propane torch treatment was obvious later when you could easily pick the drips off the untreated surface with a fingernail, but on the treated surface you couldn't get it off with a wood chisel. I'm sorry I don't remember the specific product, but if you have a plastics supply house nearby maybe they will know what it was. Using it on PE was specifically mentioned in the instructions, along with how to heat the plastic enough but not too much. When people say nothing will stick to PE I know from personal experience that is not completely true.

 

[capta]

I have seen a new system made to repair cracked plastic. There is a new tool that looks and works like a soldering gun, but the hot "tip" is a sine wave shape. It melts its way into the plastic, closing the crack. Then the sine wave shaped metal bit disconnects from the gun, staying there in the plastic. It certainly looks as though it would do the job. Kinda like closing a wound with staples. lol

 

[JamesG161]

The Leak has very little water pressure on that crack.

I have repaired my tank by using a Dremel tool to cut along the crack a "V" notch.

Then I used a Heat Gun to warm the V and filled with 3M 5200.

No leaks for 5 years.

Jim...

 

[SabreToothedEngineer]

I found a reference for how to apply the heat treatment and why: Flame Treatment of Plastic Substrates for Adhesive Bonding - The Epoxy Experts

 

[JamesG161]

I used a Heat Gun to warm the V

Heat Guns can melt PE.
Jim...

 

[dlochner]

Just out of curiosity, what is purpose of the depression in the top of the tank ?

An attempt at a molded in baffle. I have one on a water tank too.