Composite Gasoline Tanks

[fallguy]

100s of alloy tanks we've made over the last 25 or so years...not a single one has ever had a "warranty" issue. You made that up.

He didn't really make it up.

Quite a track record to be proud of, just the same.

 

[IronPrice]

Dear BMcF, you ain't got the point; it is not relevant since they live upside-down in NZ, the gas fumes are pouring out of the bilge......

It's not relevant because US regs don't apply in NZ. Fuel regs and therefore fuel constituents are different. People have been building alu fuel tanks (and boats for that matter) for recreational use in NZ successfully for decades, without the need to rely on regulation. In fact most recreational boatbuilders build to a voluntary standard. Commercial vessels - whole different story and I'm responsible for some of of those in my job. They all run on diesel, thank goodness.

If the boat was upside down, then of course the petrol fumes (being lighter than air) would be unable to escape the bilge

 

[IronPrice]

100s of alloy tanks we've made over the last 25 or so years...not a single one has ever had a "warranty" issue. You made that up.

I made what up? I was specifically referring to HDPE (high density poly-ethylene) welded tanks. HDPE tanks can sometimes split. Your extensive success with alloy tanks is irrelevant to HDPE.

I have no issue with alloy tanks, other than lead time at my location. This is due to availability of plate (alloy plate is not made in NZ) and a shortage of skilled fabricators in the region I live in.

If I could get an alloy tank within 6-months, I would. I got a good run out of the old tank.

 

[Rumars]

Just use painted black iron until someone can make you an Al tank. Nothing will happen to your boat until then, regardless of iron or Al the tank can't touch the hull anyway, just use some plastic spacers for the mounting points.
I trust there is no shortage of steel welders or common steel plate where you live. A steel tank doesn't have to be made from 3mm plate, 1mm and some stiffening ribs in addition to the baffles are enough, there is no weight penalty.

If you still want composite tanks ask your local resin supplier for a gasoline and ethanol resistant vinylester, and use normal fiberglass in whatever form you like.

 

[IronPrice]

Thanks. I hadn't thought of plain old steel as a stop gap. I can MIG weld steel, myself so that would be easy enough. My only issue is that it will likely rust very quickly as the boat lives outside and is used almost exclusively in salt water.

For my boat, the galvanic issue is still there via the mounting bolts. The tank hangs from brackets that are extensions of the side panels of the tank. These are secured by bolts, to a rectangular 'ring' of alloy just under the deck. This is a bit unusual, but it means the tank isn't putting much weight on the structural grid.

 

[Rumars]

Why would it rust very quickly? The outside you paint with primer and topcoat. If you don't trust paint alone additionally spray over it with lanoline grease, but it becomes a sticky mess.
The inside is protected by the fuel. Sure, water will accumulate and eventually the tank will develop pinholes, but it's not quick, we are talking a few years. Just make sure the filler cap has a new gasket and is screwed down properly.

There is no galvanic issue whatsoever if you follow proper procedures. Between steel bracket and Al "ring" you install an electrical insulator. This can be a layer of tape, sealant or as I suggested solid plastic. Get some HDPE plate (cheap cutting boards for example) and cut yourself some nice fitting washers. The bolt itself is stainless steel and gets isolated from the Al by the use of Tef-Gel, Duralac, or Lanocote. This method is industry standard all over the world. Just smear everything with Lanocote before and after installation and you will be fine.

P.S. Was there a previous tank, and if yes what happened to it? Repairing a tank can sometimes be accomplished by other means then welding, it depends on the specific damage.

 

[BlueBell]

I agree with Rumars, nothing wrong with a steel tank if it's done correctly and kept full.
There's a lot more to tank sizing than many realize.
Keeping it near full between outings is essential.

 

[IronPrice]

P.S. Was there a previous tank, and if yes what happened to it? Repairing a tank can sometimes be accomplished by other means then welding, it depends on the specific damage.

The old tank developed several areas of corrosion. I had a bit of a tap around and its quite thin in many places.

 

[IronPrice]

There's a lot more to tank sizing than many realize.
Keeping it near full between outings is essential.

I always keep my tank full. I fill up on the way home. If I can I fill it at the marina pump before the boat goes back on the trailer.

 

[Rumars]

Measure the metal thickness with an ultrasonic tester, cut out the corroded parts (take proper precautions) and send the tank to be patched by a competent welder. This should be cheaper and quicker then making new ones from scratch.

Regardless of what you decide best practice is to install either a sump with a bottom drain or a separate pickup tube that reaches right down to the bottom. This is so that any water that accumulates at the tank bottom can be regularly removed, thereby reducing the risk of corrosion.

 

[comfisherman]

While audio gauges aren't all that spendy the op has no access to alloy and limited access to alloy welders. Dunno if that means he's in the developed world or right on the edge but an audio gauge probably isn't hanging out in a tool box that can't get basic plate. Shipping out for repair might be viable, but the remaining tank sides need to be in real good shape.

Aluminum that's gone to white dust usually has sucked up enough impurities welding is miserable. My alloy boat repair days are behind me, but I'll never again patch a leak unless it means short term get home. Just not worth the liability for what so often is not a permanent solution.

Steel tanks can be a mess but they do work and if you get the mill slag good and off with some good primer it should be satisfactory. I'd take a well prepped and painted steel tank over a patched alloy tank.

How advanced is your steel welding capacity? If it's entry level your probably gonna end up on the thicker side just to manage heat. Not a bad thing but might end up on the heavier side.

 

[BMcF]

I made what up? I was specifically referring to HDPE (high density poly-ethylene) welded tanks. HDPE tanks can sometimes split. Your extensive success with alloy tanks is irrelevant to HDPE.

I have no issue with alloy tanks, other than lead time at my location. This is due to availability of plate (alloy plate is not made in NZ) and a shortage of skilled fabricators in the region I live in.

If I could get an alloy tank within 6-months, I would. I got a good run out of the old tank.

Are the welded HDPE tanks constructed with anti-sloshing baffles?....pressure tested before delivery? I've got a couple of them lying around that were pulled from boats being scrapped, so I do know what they look like generally, but never gave one a close inspection. I guess you could say we have the "opposite problem" here...an abundance of aluminum and aluminum fabricators and few places that could/would fab up an HDPE gasoline tank that would meet required standards. ;-)

The regulations/standards for building a safe fuel tank are not specific to aluminum, although they do include requirements for alloy and material thicknesses. We deliver equipment certified to ABYC, USCG, ABS, DnV/GL, etc etc. , depending on the client's imposed requirements and/or geographic location.

 

[IronPrice]

Are the welded HDPE tanks constructed with anti-sloshing baffles?....pressure tested before delivery? I've got a couple of them lying around that were pulled from boats being scrapped, so I do know what they look like generally, but never gave one a close inspection. I guess you could say we have the "opposite problem" here...an abundance of aluminum and aluminum fabricators and few places that could/would fab up an HDPE gasoline tank that would meet required standards. ;-)

The regulations/standards for building a safe fuel tank are not specific to aluminum, although they do include requirements for alloy and material thicknesses. We deliver equipment certified to ABYC, USCG, ABS, DnV/GL, etc etc. , depending on the client's imposed requirements and/or geographic location.

The supplier I am referring to does install baffles and pressure tests their product prior to shipping. Because it's welded (not moulded) the structure can be as complex as a metal tank. They can also do a double walled tank if I wish.

I use baffled HDPE tanks in commercial vessels for potable water tanks. I have them in more than a dozen vessels and provided the tanks are baffled they don't leak. If they aren't they will split at one end.

It's a giant PITA if a tank leaks on one of the vessels. The deck has to be cut open to get a tank out and the decks are typically covered in harvesting and grading machinery. We pressure test our water tanks when they arrive, and after installation.

When we buy a water tank for a comparatively large vessel, the fabricator accepts our measurements (which are done by one of our R&M team) they freight the tank to us and we fit the tank. When I want a tank for my small trailer boat, they want to measure it and they want the boat there to fit it. There is too far from here, which is why HDPE isn't an option for me.

 

[IronPrice]

Measure the metal thickness with an ultrasonic tester, cut out the corroded parts (take proper precautions) and send the tank to be patched by a competent welder. This should be cheaper and quicker then making new ones from scratch.

Regardless of what you decide best practice is to install either a sump with a bottom drain or a separate pickup tube that reaches right down to the bottom. This is so that any water that accumulates at the tank bottom can be regularly removed, thereby reducing the risk of corrosion.

The tank has been scrapped. There were large areas that were very thin and an inspection cam showed lots more corrosion inside. In several palces despite the alloy looking fine externally, I was able to tap through it with a small hammer. It was FUBAR.

I've seen alloy shaft tunnels and rudder tubes do this too. They look fine on the outside but they have corroded away from the inside. We now use an hexagonal/octagonal tubing and grout in a plastic liner to stop this happening.

 

[huey 2]

Does anyone here have experience making composite gasoline tanks for trailer boats? I'm interested in learning anything/everything about it. Resin types, cloth types, etc etc.

Full background details below.

Why am I even contemplating a composite Gasoline tank?
I found this YT video, How I Made My Kevlar Fuel Tanks - YouTube where a boatbuilder called Dan Lee makes a pair of Kevlar tanks for his trailer boat.

He made them in min-2017 and commented in 2022 that they were still serving their purpose. He says in the comment that he made them using plain old West 105/206 Epoxy Resin. I was surprised by this as I would have thought the gasoline would attack the epoxy. However, Dan's experience suggests it was fine and he seems to be a credible boatbuilder.

Why not just get a metal tank?
I have a 6m aluminium trailer boat powered by a 175 Suzuki. I need to fit a new underfloor tank, ASAP. To avoid galvanic corrosion if it's meatal it needs to be made of aluminium, not stainless steel. The trouble is that aluminium plate is super expensive, these days. Tank fabrication has a long lead time too where I live in a small town in New Zealand. Off the shelf plastic tanks aren't a suitable fit for my boat and the only custom plastic tank place I know of is a full day's travel from where I live. So ... I'm, up the creek without a boat. Literally - I live beside a creek and I can't use my boat at the moment.

Yeah, but can I really make a fuel tank?
I'm comfortable that I could make a tank, like the ones in the video I've linked to above. I've made composite parts before using epoxy and fiberglass as well as epoxy and carbon fibre, including conventional hand lay, vacuum moulding and resin infusion. Mostly this has been things like fish boxes for my fishing kayaks, and storage boxes for my boat. I've never made anything as big as fuel tank (I'm think of a 150L tank) but in some ways bigger is easier than smaller.

I wouldn't use the disappearing foam approach, myself. That's just too scary for my liking (flammables etc). I'm confident that I could successfully fabricate a tank in a slightly different way, that would allow me to remove the EPS plugs physically.

Have built and worked on many composite boats from Mono Sail and Power to Multihulls Sail and Power...the Main Epoxy Resin, that been used has mainly is WEST System Epoxy.
We have made tanks for Water and for Fuel.... If either we have included baffles over twenty liters.
All Components of the Tanks are built with Foam core like H80 divinycell closed cell pvc, laminated inside and out.... the laminates skin are always heavy duty. All corners are coved with filler and laminated in.
We always make an inspection hatch and also install the any pickups off the bottom. We install air breather for fuels external to interior .
Drinking water always vent inside the interior so no contamination from salt.
No one wants a split tank with little reserve Drinking Water on a long trip....
Likewise there is nothing more dangerous than leaking fuel to inside or outside of the boat... To have Diesel leak inside during a cyclone[hurricane] was very, very slippery inside the boat and made most crew nauseous down below , dreadful when trying to have a rested crew for the next watch.
All of the tanks are peel plied for the final cure..... Then sanded and especially corners ...use scotch brite pads stacked for corners....
We have always white epoxy pigment Gel coated the finale layer. .. pre doing when tank open where possible. ...if at all possible tilt tank to let no vertical runs happen.
We do tend to roll with 4" roller[short nap] a thinner layer , followed up once or twice again with roller. ..peel plying if necessary.
Then Final thick coat [longer nap].
Before adding Drinking Water do two washes with alternately Vinegar then warm water ..then clean warm water sluice out.

Ethanol additive can cause problems with some epoxies....