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Discussion Starter #1
The inox water tanks on my 23 year old Gib'Sea 442 have began loosing water due to corrosion. I have taken them out to see if they could be repaired but after getting a negative answer I have decided that its time to replace them with new ones. Unfortunately, building new inox tanks is expensive and I was thinking of putting galvanized steel water tanks instead, which could end up at 1/5 of the price of the inox ones.
Any similar experience anyone?
Besides the issue of adding weight to the boat is there any common problems with GS tanks?
 

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One of None
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Plastic.. so many off the shelf sizes and there are plastic tank welding companies out there making them too.
 

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If you are getting custom tanks the labor is the large part - the material costs vary but there should not be a large difference in the total price.
As Denise posted there are dozens of standard sizes available from Ronco and others.
 

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In the US Inox is just one more stainless steel alloy. I would guess that the problem is coming from pinhole leaks in the welds on the seams, unless there is real extensive corrosion. Any good stainless shop should be able to run new welds over the seams, or you might even consider getting an inexpensive arc welding rig and doing it yourself.

Depends on what new tanks (plastic) would cost, whether they'll fit well, and how extensive your corrosion problem is.
 

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Discussion Starter #5
Thanx everyone for your replies!

Unfortunately the corrosion is so extensive that the tanks cannot be repaired.
I have thought of putting plastic tanks as I think that they will last longer however I have not talked to any manufacturer to see how much they would cost and from conversations I have had so far, they tell me that making custom made plastic tanks could end up to the same price as making inox ones. I will look into it.

I have come to exclude the idea of galvanized steel as this could lead rust coming of the weldings of the water tanks after some years.

I got some prices on inox tanks and the cost is a matter of what type inox you use; 304 or 316. 316 is better but much more pricey. I dont know if the 304 is durable enough or it would lead to corrosion in a small number of years.

Has anyone made inox tanks of 304 inox to tell me if he/she had any problems? (the tanks are places on the hull above the bilges so they are in contact with sea water most of the time)
 

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Bluenoser
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If you go SS, 316 is the alloy you want in salt water. IMO plastic tanks are your best option.

If you cannot find ready-made plastic tanks to suit your boat you might consider cutting access holes in the tops of your old inox tanks and installing flexible bladders inside. This could mean slightly less water capacity depending on the shape of the bladders and your tanks, but it is quick, dependable & relatively inexpensive.
 

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If you cannot keep the tanks dry where they are located plastic tanks are the only logical choice.
 

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Your zones of corrosion are most probably at the tank bottom, especially in the 'heat affected zone' where welded ... edges, and bends, or the welds themselves, etc. It is entirely possible to simply cut off a large section of the bottom and simply replace only that section and into 'healthy' adjacent sections. The welding has to be 'full penetration': perfect - no laps, gas holes, 'inclusions' etc. where corrosion 'starts' in inox-stainless (rostfrei) steel.

On a 442 your tanks are probably in the capacity range of 375 litre (~100 gallons) and such would exclude the use of 'plastic' tanks because of the impact stress needing internal baffles; large plastic (roto-molded polyethylene) tanks cannot have baffles due to the molding process.

Another alternative is to 'build' an epoxy fiberglass tank/liner inside the existing tank, using the current tank as the mold/form. Cut LARGE access holes into the top of the existing tank, lay-up the epoxy fiberglass, use a FOOD GRADE (low amine epoxy certified for contact with POTABLE water) for the final lay-up of internal exposed surface - that which is contact with the water, make 'sister' flanges to close the access hatches, etc. etc.
Also, there is a new composite fiberglass sheeting that is already bonded to polyethylene sheeting ... requires plastic welding of the seams to exclude the harmful leachables that come from 'fiberglass'. This could be built into an entirely new tank or could be used to 'line' the internals of the old tank. This is a new technology ... so it may be difficult to find the material and to find someone who can properly 'weld' it together.
 

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Pol, you got me interested enough to poke around a little. It seems like no one wants to discuss alloys but I did see 316-L mentioned once. And the importance or full-penetration welding, and sufficient plate thickness. And, surprise! Some notes that unless the stainless is pickled (passivated) after fabrication, rust will form and leaks will follow. Not a simple job but one would suppose any of the stainless steel fabricators who work mainly with the food service industry might be aware of how to do the job. I suspect the tanks will cost a bloody fortune, ss workers tend to charge more than brand-name jewelers.
 

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Honestly I can't stand stainless tanks. It's just the wrong material for the job. Stainless by its nature is not really a good material to leave underwater, and even worse when half of it is submerged, and the other half isn't. It leads to selective chromium leaching, which causes electrolysis, rust, then destruction.

Of course some people have them, and the tanks have held up for them, but it's just not a good long term material.

For fresh water I would go with either plastic, composite fiberglass over plywood (food grade epoxy), or titanium. Of the three plastic is probably the cheapest, unless you want to build it yourself, in which case the fiberglass would be. Titanium is likely the most expensive, but also the longest lasting, and has no issues with corrosion on the external side of the tank from poltice corrosion.

What I wouldn't do is spend the money on a custom stainless tank (which is likely very close to the cost of titanium) in 316L or any other super alloy. As the alloys get more exotic the corrosion resistance goes up, but so does the price. And frankly a titanium tank isn't that much more than 316 is, but has better corrosion resistance than even the best super alloys of stainless.

All that being said, for a fresh water tank I would also seriously consider bladders. They are cheap, easy to replace, and in the worst case where they puncture, it isn't the end of the world (this is my objection to bladders for holding tanks).
 

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I cut large access ports in my 4 aluminum water tanks( a total of 1500 liters) and laid down a fiber glass /epoxy tank inside including both sides of existing baffles . One at a time because it was a bear of a project and potable tank 'gelcoat' needs to go on fairly fresh substrate.Welded a 3/16 th by 2 Al inch strip around the cut out lid and tapped threads into tank to take the holddown bolts. Neoprene gasket and Bob's yer uncle .Other than working upside down with a full face mask and extension cord for days, nothing to it. and the finished result was definitely worth it.
 
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