Wrapping a stainless tank in fiberglass

Ralph Johnstone · Monday at 1:46 PM

Well, as you said at 15:04 "Will it work. Let me know." I've got to let you know, that is the probably the worst idea I have seen for preventing odour leakage, and and most definitely the most impractical idea I have seen in quite some time.

I say probably the worst as far as being a solution to the odour problem, in that it is highly unlikely you have hermetically sealed the tank in FG. It will definitely start to stink once the SS becomes thoroughly perforated and the odours find their way to the leaks in the FG exterior.

For the time and expense you put into this project, it would have been far more beneficial and easier to remove the old tank and have a new tank custom built from polyethylene by a fabricator. At 14:45 you say you expect to get a life extension of 5-10-15+ years. A new polyethylene tank, historically speaking who knows how long it's good for ? I've never heard of one leaking yet. I don't feel 50+ years is an exaggeration.

Problems supplying the specs to a fabricator for a custom tank ? You appear to be somewhere in the Baja. I did this a few times on the job for fancy compartments we were dealing with. Supply the following four photos to your list of three custom fabricators for quotations :

1. Plan view
2. Left end elevation
3. Front end elevation
4. Right end elevation

On those photos, you would have supplied all the necessary dimensions for fabrication. What could be easier with the old tank on the ground ?

One final mention, you didn't mention it but did you inspect your sanitary hoses and vents for odour before getting into the tank.

Peggie Hall HeadMistress · Tuesday at 6:26 AM

I agree with Ralph that it's worst idea I've heard of 'cuz urine is continuing to turn your tank into a colander under the fiberglass. You'd have been better off just sealing the leaks with JB Weld.
Custom tanks are rarely made using polyethylene...Ronco Plastics in Tustin California has more than 400 shapes/sizes in their catalog, makes TOP quality thickwalled (50% thicker than OEM and "off the shelf" tanks) for a very reasonable price, plus they install fittings in the sizes and locations specified by the customer when they make the tank.
Ronco Plastics Water and Waste Holding Tanks catalog
Ronco Plastics marine Tank drawings
As you inspect the drawings, rotate, flip as necessary to find one that fits your space--or perhaps a better location (boat builders rarely put them in the best locations) 'cuz there is no top or bottom till the fittings go in and you decide where they go.

--Peggie

dLj · Tuesday at 7:48 AM

The guy did a huge amount of work. The saddest part, seems to me, is he did not have a leaking tank and he's now made the tank more prone to leaking with what he's done. I guess it's the desire to create YouTube videos that provides the impetus to do these kinds of things. With all the work and all the costs of materials and tools, he could have bought a poly tank as suggested above and achieved a substantially better outcome. I do wish him luck and hope he has a great trip.

dj

Ralph Johnstone · Tuesday at 8:19 AM

Peggie Hall HeadMistress said:
Custom tanks are rarely made using polyethylene...

If one should find oneself backed into such a corner and require a really oddball custom tank, what fabrication material is used ?

Peggie Hall HeadMistress · Tuesday at 10:37 AM

Ralph Johnstone said:
If one should find oneself backed into such a corner and require a really oddball custom tank, what fabrication material is used ?

Typically polypropylene because it's easier to cut than PE and unlke PE, it can be "glued" (PE requires heat welding which includes spinwelding which requires a special tool) that requires injecting enough new melted PE to blend with sufficiently melted edges of the "old" to create an unbroken mass that's strong enough. Female hose fittings are spinwelded into PE tanks, misleading many boat owners to mistake it for some type of sealant.

--Peggie

Peggie Hall HeadMistress · Tuesday at 11:14 AM

baycloud said:
Because of how small the tank is, if I ever have to repair it - then I would look into an integral fiberglass tank to increase capacity.

Fwiw, the first leak in a metal waste tank isn't a pinhole leak in a wall, it's in a weld at a seam or fitting which can be repaired using JB Weld. I once knew houseboat owner with a 50 gallon aluminum tank who'd "JB Welded" so many leaks he came close to having an entire tank made of the stuff..except for the bottom, which urine was gradually turning into a colander.

When you're ready for a larger tank, let's talk before you firmly commit to an integral fiberglass tank.
--Peggie

dLj · Tuesday at 12:00 PM

Ralph Johnstone said:
If one should find oneself backed into such a corner and require a really oddball custom tank, what fabrication material is used ?

HDPE (High Density Polyethylene) is an inexpensive and an excellent material choice for this application. There are other polymers but the DIY can become a challenge.

316L is also a good choice but you have to be careful with your welds.

There are other materials but the costs tend to get really high and availability much more difficult. DIY with those becomes a real challenge....

dj

dLj · Tuesday at 12:11 PM

baycloud said:
I think the failure mode would be delamination, and only leakage and smell in the event of massive delamination or other metal deterioration (which would not be caused by my modification).

Time will tell, but the work you did does in fact increase the likelihood of corrosion in areas that previously would not have been a concern. Whether or not that happens is hard to predict. For your sake I hope it doesn't - but I would never have done what you did - no matter how much a genius you feel you are (your words from your video). The reason no one has done this is precisely because it is not a recommended method of repair for your tank material.

With all due respect.

dj

Davidasailor26 · Tuesday at 12:15 PM

For what it’s worth, here’s what Nigel Calder says about fiberglass tanks: “Properly constructed and installed, fiberglass tanks can be expected to last the life of a boat. They would be my preferred option for diesel and water tanks. However, as the UL study notes, ‘the disadvantage of these tanks is that they are very labor-intensive to produce, making this option time- and cost-prohibitive …’”

By doing the work DIY the OP has saved some of the labor costs that seem to be the main downside of a fiberglass holding tank. At first I was skeptical, but the more I think about it the more I think in the worst case he basically has a fiberglass tank with some rusted steel bits floating inside. The only issue would be if the shell he built isn’t thick or continuous enough to be a tank.

dLj · Tuesday at 2:59 PM

Davidasailor26 said:
For what it’s worth, here’s what Nigel Calder says about fiberglass tanks: “Properly constructed and installed, fiberglass tanks can be expected to last the life of a boat. They would be my preferred option for diesel and water tanks. However, as the UL study notes, ‘the disadvantage of these tanks is that they are very labor-intensive to produce, making this option time- and cost-prohibitive …’”

By doing the work DIY the OP has saved some of the labor costs that seem to be the main downside of a fiberglass holding tank. At first I was skeptical, but the more I think about it the more I think in the worst case he basically has a fiberglass tank with some rusted steel bits floating inside. The only issue would be if the shell he built isn’t thick or continuous enough to be a tank.

You need to watch his video more closely. He did not fully encapsulate the tank. Had he done that, I would not have said anything. However, full encapsulation would have to be done either from the inside or from the outside - or both, but only one side would need to be done really.

Fully encapsulating would give a fiberglass structure in addition to the stainless structure. which basically means the stainless structure is being used as a mold to create a fiberglass tank. If the stainless structure goes away - it doesn't matter.

It's not possible to know from the video exactly how the interfaces between the fiberglass and the stainless are intertwined. But to get an understanding of how that "composite structure" will now work. Think about what would happen if all the stainless were to disappear.

My main concerns would lie at the intersections of where the fiberglass was applied, and where it was not. The OP put fiberglass on the inside of the tank at one of the hose outlets. This was done on top of an area with existing corrosion. It is not possible from here to know exactly where the fiberglass stops inside that tank, how well the sandblasting was done in that area - but for sure the OP did not talk about doing any passivation on the stainless prior to applying that fiberglass. All of the aforementioned leads me to be concerned about the long term structural integrity of that region of the tank - a pretty important area to keep trouble free.

After watching that, I did not pay a lot of attention to where the OP said he stopped being concerned about the fiberglass application on the outside, but he did mention how above a certain level, he wasn't concerned...

dj

dLj · Tuesday at 3:56 PM

baycloud said:
Can you expound on this?

As for the genius comment, I can't tell if my sense of humor is off or yours is. But thats why I added the laugh track on that comment in the video

Can't put a laugh track in written text... (I guess I could put emojis in but not much my style)

"Can you expound on this?"

See my above post that has a lot more detail. Stainless steel likes to maintain a passive layer. It's very hard to do that by covering it. In order to cover stainless, one first should really establish a good passive layer - at least in DIY cases like yours. (In commercial cases there can be other options...) That is of course, if you want the stainless steel to remain part of the system. If it is simply sacrificial, then you don't have to worry about this. From your video it looks like the stainless steel is an integral part of the system.

Encapsulation means that your fiberglass is totally encapsulating that stainless - as I said in the above post, think about removing all the stainless - how well would that fiberglass structure work? If removing all of the stainless, you still have a fully sealed and functioning tank - you have an encapsulated structure. From what I can see in your case - you would have a lot of problems if all the stainless went away. So think about small areas where if the stainless corroded away, how would that affect your boat and this system? And of course, it will always happen where you least want it to....

A black water tank contains highly corrosive material - not just smelly.

You have created several new regions where corrosion can be accelerated - everything under the fiberglass you put on the inside; the interface of where that fiberglass stops on the inside; the surfaces of the stainless under the externally applied fiberglass; and the interfaces where that fiberglass stops on the outside.

Don't know if that makes sense to you....

dj

Peggie Hall HeadMistress · Tuesday at 5:43 PM

There's something that everyone has overlooked: it's only a 5 gallon tank. He doesn't have that much to lose beyond a smelly mess to clean up if his project turns out to be a total failure, which isn't likely to become obvious for at least several months if not a year or longer.

And fwiw, there's a big difference between DYI-ing a fiberglass tank from scratch--something many boat owners have done successfully--and encapsulating a metal tank full of corrosive organic material in a fiberglass shell, something I've never heard of anyone else doing.

That's my $.02 worth...

--Peggie

Davidasailor26 · Tuesday at 5:54 PM

dLj said:
Fully encapsulating would give a fiberglass structure in addition to the stainless structure. which basically means the stainless structure is being used as a mold to create a fiberglass tank. If the stainless structure goes away - it doesn't matter.

Yes, you may be right. I guess I couldn’t tell well enough from the video whether the glass could function as a tank by itself once the stainless corrodes, or if it relies on the stainless still being there. Big difference depending on the execution of the lamination.

Tally Ho · Tuesday at 6:44 PM

Peggie Hall HeadMistress said:
…it's only a 5 gallon tank.

--Peggie

Really?

A Bene 40 with a 5 gallon holding tank?
It looked bigger than the 15 gallon tank on my O’Day 322.

Where was the reference to a 5 gallon tank? I missed it.

Greg

dLj · Tuesday at 6:56 PM

Peggie Hall HeadMistress said:
There's something that everyone has overlooked: it's only a 5 gallon tank. He doesn't have that much to lose beyond a smelly mess to clean up if his project turns out to be a total failure, which isn't likely to become obvious for at least several months if not a year or longer.

And fwiw, there's a big difference between DYI-ing a fiberglass tank from scratch--something many boat owners have done successfully--and encapsulating a metal tank full of corrosive organic material in a fiberglass shell, something I've never heard of anyone else doing.

That's my $.02 worth...

--Peggie

I sure missed that's a 5 gallon tank. It looked bigger than that to me, although I was surprised at how thin it was...

It would be a design/execution nightmare to properly encapsulate a tank like this. The OP will likely get a number of years out of this tank - it wasn't even leaking in the first place. I feel this work actually shortens what would have been it's expected lifespan. But hey, as they say, your boat, your choice....

dj

Peggie Hall HeadMistress · Wednesday at 8:02 AM

Somewhere near the start of this thread, he mentioned 5 gallons and also made several references to its small size. It's entirely possible that Beneteau delivered it to the first owner without a tank (they aren't required everywhere in the world) and a PO installed one for "show instead of go."

--Peggie