Oh Boy...This Smell Ain't Good

[Jason2tpa]

I think no matter how much you try to make the coffin water tight, water will still get in there. Old boat , old deck, condensation, deck plates, I'd say it is inevitable. One reason I went with poly tank and glad I did.

Do you have a drain in the coffin ? Personally I would coal tar the tank and get it higher than a 1/4". Poly tank is a much simpler install as well.

There is no issue with an aluminum tank getting wet, because as you noted, water will still get in. In order to prevent moisture from laying against the tank there must be allowable air flow around the entire tank.

Yes there are 3 drain holes in the coffin aft.

Re: "Poly tank is a much simpler install as well"....

Not in my case. Securing the tank, poly or aluminum, would pose the same issues I'm battling.

[Jason2tpa]

So, not the new tank the Previous Owner said??

No, but now that I've thought about it since having access to tank I think he was speaking of hoses. He probably said he replaced the fuel inlet, pickup, and vent hoses. Because these hoses are in very good shape, compared to the tank.

[Jason2tpa]

Update:

My fabricator started work on the new tank yesterday. Should be finished early next week. Here's what I'm still battling...how to secure the tank. Below is a cross-section sketch of the fuel coffin liner and the adjacent stringers.

I had my mind made up to weld tabs on tank and fixate these to a pvc mounting block, the block either glassed in or bonded. I planned on overdrilling the stringer, fill with epoxy, then drill the tab screws into the hardened epoxy. But the problem I forsee is the liner does not rest against the stringers. The stringers and the liner have completely different angles from their base, as you can see from my sketch. The only contact point the stringer and liner make runs the length of the liner, bottom corner.

Unless I were to cut out large sections of the liner to allow me access to stringers, which I'm not going to do, there is no way for me to have access to the stringers to fill the overdrilled holes with epoxy.

I took a 3/32 drill bit and drilled through the liner, in a location where tabs would line up. Once I drilled through the thin liner I used the drill bit to measure the amount of space between liner and stringer. About an 1" to 1-1/4".






Another option would be to use Moeller's hold down strap, pictured below. I like this method. Actually, it coincides with how Aquasport originally secured tanks, 2 aluminum straps. But if I were to use these straps I'm left with the same problem as described above...no solid structure for the anchor screws to bury in.





I'm open to using foam now that I've read more about methods to keep the foam from creating air pockets. But filling the space between liner and tank with foam will only prevent the tank from moving laterally. I would still be left with figuring out how prevent the tank from elevating. I also don't have the option to glass in a 2x4, the width of tank coffin, because there is only 1/2" between the top of the fuel inlet hose and underside of fuel tank access panel.

Thoughts, suggestions welcomed.

[Jason2tpa]

Update:

My fabricator started work on the new tank yesterday. Should be finished early next week. Here's what I'm still battling...how to secure the tank. Below is a cross-section sketch of the fuel coffin liner and the adjacent stringers.

I had my mind made up to weld tabs on tank and fixate these to a pvc mounting block, the block either glassed in or bonded. I planned on overdrilling the stringer, fill with epoxy, then drill the tab screws into the hardened epoxy. But the problem I forsee is the liner does not rest against the stringers. The stringers and the liner have completely different angles from their base, as you can see from my sketch. The only contact point the stringer and liner make runs the length of the liner, bottom corner.

Unless I were to cut out large sections of the liner to allow me access to stringers, which I'm not going to do, there is no way for me to have access to the stringers to fill the overdrilled holes with epoxy.

I took a 3/32 drill bit and drilled through the liner, in a location where tabs would line up. Once I drilled through the thin liner I used the drill bit to measure the amount of space between liner and stringer. About an 1" to 1-1/4".






Another option would be to use Moeller's hold down strap, pictured below. I like this method. Actually, it coincides with how Aquasport originally secured tanks, 2 aluminum straps. But if I were to use these straps I'm left with the same problem as described above...no solid structure for the anchor screws to bury in.





I'm open to using foam now that I've read more about methods to keep the foam from creating air pockets. But filling the space between liner and tank with foam will only prevent the tank from moving laterally. I would still be left with figuring out how prevent the tank from elevating. I also don't have the option to glass in a 2x4, the width of tank coffin, because there is only 1/2" between the top of the fuel inlet hose and underside of fuel tank access panel.

Thoughts, suggestions welcomed.

[SJCJACKST]

So, not the new tank the Previous Owner said??

[scofflaw]

I think no matter how much you try to make the coffin water tight, water will still get in there. Old boat , old deck, condensation, deck plates, I'd say it is inevitable. One reason I went with poly tank and glad I did.

Do you have a drain in the coffin ? Personally I would coal tar the tank and get it higher than a 1/4". Poly tank is a much simpler install as well.

[Jason2tpa]

Does the tank sit on anything in particular?

Or just sitting on the fiberglass "floor"?

Rubber pads?

Also, that 2" space is plenty. As you saw on my pic's, that angle aluminum mounts are about 1" tall and my space might be 3"..

Tank was resting on a rubber mat...which is worse than if the tank was resting directly on the coffin floor bc rubber absorbs water.

I'll elevate the new tank off the coffin bed by bonding 3 pvc/frp strips to the bottom of tank, each running the length of tank. Strips are 2" wide and 1/4" thick. A 1/4" elevates tank enough to allow air flow around tank.

[TownsendsFJR1300]

Does the tank sit on anything in particular?

Or just sitting on the fiberglass "floor"?

Rubber pads?

Also, that 2" space is plenty. As you saw on my pic's, that angle aluminum mounts are about 1" tall and my space might be 3"..

[panasonic]

For those of you interested in the properties of precision board in marine applications.

HDU Marine Board - Coastal Enterprises - Precision Board Plus HDU

According to the manufacturer it does not absorb or hold water. Most solvents wont damage it and it can glased over with epoxy or polyester resin. Check out the spec sheet.

For Jason's fuel tank, blocks of it bonded on to the tank sides with 5200 for spacers to keep the tank from shifting around would work good. Aluminum tabs around the top perimeter secured to the boats framework to keep the tank down tight to the bottom.

Jason if you decide to try and use it get the highest density possible.It comes in
probably 10 different densities,the higher the number the denser it is.

[Jason2tpa]

I dropped the tank i'm replacing back into the fuel coffin to gauge the amount of space. I'm still undecided as to how i'll anchor the tank on the sides...foam, glassed blocks/precision board as a wedge, glass in 4 mounting blocks above level of tank secured to welded tank tabs using screws. As you can see from the pictures, space is limited. 2" at top and bottom, 1/2" on sides.

[TownsendsFJR1300]

EDIT: I tried to just respond with just the smilie face thingy, but the forum said I had to use at least 10 characters. So I edited by adding these two statements... which is now much longer than 10 characters...

Just type in a bunch of periods. That works as well..

Back to the thread.

[Jason2tpa]

Are you saying that Pascoe says to bond the PVC strips to the coffin bed? If so, that wouldn't affect pulling the tank later as the PVC is only bonded to the bed, not the tank. It also would allow moisture to possibly collect between the strip and the tank.

Or, are you saying that Pascoe says to bond the PVC strips to BOTH the bed and the tank? If so, that's wrong. As I wrote above, the PVC strips HAVE TO BE BONDED to the tank ONLY. But they need to be bonded completely (ideally with a faired edge) to avoid moisture staying in contact with the tank for extended periods of time.

I'm not sure if you're reading Pascoe incorrectly or if he is actually wrong, but... do as I mentioned - bond the PVC strips to the tank bottom.

How to Install an Aluminum Fuel Tank : Boats, Yachts - Maintenance Repair and Troubleshooting

There is actually a term used to describe the method you're speaking of...bonding only the pvc to tank...it's called the modified pascoe method. The standard pascoe method bonds both pvc to tank and pvc to coffin bed with 5200.

[DennisG01]

You know, if it wasn't for my good conscience I'd be 100% with using the complete pascoe method (5200/4200 bonding pvc strips to coffin bed).

Are you saying that Pascoe says to bond the PVC strips to the coffin bed? If so, that wouldn't affect pulling the tank later as the PVC is only bonded to the bed, not the tank. It also would allow moisture to possibly collect between the strip and the tank.

Or, are you saying that Pascoe says to bond the PVC strips to BOTH the bed and the tank? If so, that's wrong. As I wrote above, the PVC strips HAVE TO BE BONDED to the tank ONLY. But they need to be bonded completely (ideally with a faired edge) to avoid moisture staying in contact with the tank for extended periods of time.

I'm not sure if you're reading Pascoe incorrectly or if he is actually wrong, but... do as I mentioned - bond the PVC strips to the tank bottom.

[Jason2tpa]

You know, if it wasn't for my good conscience I'd be 100% with using the complete pascoe method (5200/4200 bonding pvc strips to coffin bed). It's simple and the least amount of tank prep time. I'll have this boat for maybe 5 more years, 7 at most. I'll sell it off and buy a bigger boat.

My point is, I won't be the owner of this boat when it needs another fuel tank. Bonding the pvc strips to the coffin bed with 5200/4200...extracting the tank will be an absolute nightmare. It would have to be lifted straight up to break the bond, and along with it would come the coffin or pieces of it. It won't be my problem....but then my conscience kicks in

[99yam40]

anyone ever wonder how they make connections between aluminum and copper for buss bar electrical connections?
The SS to aluminum statement made me think of this.

they use explosions to force the 2 metals together, and then press the parts back flat and machine them down to the final size and shape
aluminum and copper do not get along well together, but the explosion makes them bond together well and the copper surface on one side makes a better bolted connection that holds up well