Oh Boy, This Can't Be Good

[Brendanpd28]

You might already know this from other threads but foaming in aluminum tanks is not recommeneded. Results is crevice corrosion from moisture being held against the tank and it's not able to dry out. Especially when open cell foam is used which is not a moisture barrier. I run a residential weatherization and heating department for an energy conservation company in MA. My subcontractors use foam on every project for air sealing measures in attics, basements and crawl spaces and from my experience even closed cell foam isn't completely moisture resistant.

[boatnamesue]

I put 4 - 2" wide 1/4" thick strips of pvc board on the bottom of the tank. Adhered with 5200. Not just a bead...5200 needs to be spread across the entire surface so there aren't any pockets where moisture can develop. I then ran thick beads of 5200 along the bottom of those strips and adhered the tank to the coffin. That's all the Pascoe method calls for. A lot of guys add crush blocks and other methods for additional security....but I'm sticking with just the 5200. it really is a true mechanical bond. I've seen 5200 hold amazing weights. Tank isn't going anywhere. Search "Brendan's 170 tank install" for pictures and additional info.

I read about the Pascoe method, here: http://www.yachtsurvey.com/fueltank.htm   I like the idea of the pvc strips bonded to tank in order to elevate tank from coffin bed.  But what concerns me about bonding the pvc strips to the coffin bed with 5200 is having to remove the tank in the future.  You are absolutely correct, 5200 holds amazing weight.  It's bond is rock solid. 

If you had to remove the tank you'd have no way of accessing the bottom of the tank to chisel away the bond.  And since it's bond is so amazing, if you pry the tank straight up you will take the surface of the coffin bed off thats adhering to the pvc strips.  Kinda concerning, right?!

[boatnamesue]

You might already know this from other threads but foaming in aluminum tanks is not recommeneded. Results is crevice corrosion from moisture being held against the tank and it's not able to dry out. Especially when open cell foam is used which is not a moisture barrier. I run a residential weatherization and heating department for an energy conservation company in MA. My subcontractors use foam on every project for air sealing measures in attics, basements and crawl spaces and from my experience even closed cell foam isn't completely moisture resistant.

I can testify to all of the above as correct.  I just got home from boat yard.  Removed the foam, which was very easy with a narrow curved crowbar.  As I was digging into the foam, there was noticeable pockets (cell?) throughout, widespread.  The foam was dry for the most part, but where there was a pocket it was wet.  Also, whomever poured the foam in did a piss poor job.  There were sections near the bottom of tank where the foam wasn't even touching the tank.  The tank was laying on a thick black rubber mat, about 1/2" thick.  It was soaked in fuel.  Luckily the fuel coffin is in good shape.

[Woodeneye]

I too can testify to 5200 being UNBELIEVABLY strong. In a previous life I had to help change keels on a Americas Cup 12 metre yacht. The keel was bedded to the hull with 5200. Even with the keel bolts undone and the yacht hanging a couple of inches above its cradle the keel would not budge. The keel weighed 17 ton! In the end we had to apply heat with a blow torch to get it to let go...... which it did, eventually, with a THUD.

I put 4 - 2" wide 1/4" thick strips of pvc board on the bottom of the tank. Adhered with 5200. Not just a bead...5200 needs to be spread across the entire surface so there aren't any pockets where moisture can develop. I then ran thick beads of 5200 along the bottom of those strips and adhered the tank to the coffin. That's all the Pascoe method calls for. A lot of guys add crush blocks and other methods for additional security....but I'm sticking with just the 5200. it really is a true mechanical bond. I've seen 5200 hold amazing weights. Tank isn't going anywhere. Search "Brendan's 170 tank install" for pictures and additional info.

I read about the Pascoe method, here: http://www.yachtsurvey.com/fueltank.htm   I like the idea of the pvc strips bonded to tank in order to elevate tank from coffin bed.  But what concerns me about bonding the pvc strips to the coffin bed with 5200 is having to remove the tank in the future.  You are absolutely correct, 5200 holds amazing weight.  It's bond is rock solid. 

If you had to remove the tank you'd have no way of accessing the bottom of the tank to chisel away the bond.  And since it's bond is so amazing, if you pry the tank straight up you will take the surface of the coffin bed off thats adhering to the pvc strips.  Kinda concerning, right?!

[boatnamesue]

Update and Finale:

Time to put this thread to bed.  New tank is installed.  For those interested here are the tank prepping details:

*5200 fast cure bonded 1/4" thick x 1-1/2" width pvc board strips the length of tank, 3 strips, 2 on outer edge and 1 down middle.  Heavy coat of 5200.   

(prior to bonding I etched tank with 80 grit where strips would bond.  Also sand blasted the bonding side of pvc strips.  Cleaned both tank and strips with acetone soaked rag)

*Let cure 24hrs

*Sand blasted strips, acetone clean.  Ran a 1/8" bead of 5200 fast cure down the middle of each of the 3 strips.  Carefully lowered tank down into coffin.  Filled the fuel tank with the 15 gallons I had siphoned out of the old tank (which was brand new fuel).  The fuel in tank provides an even downward weight distribution. 

*As the above cured I worked on the securing tabs.  I cut (4) pieces of 3/4" thick x 3.5" width x 4" length pvc board, (2) pieces of 3/4" thick x 3.5" width x 8" length.

*Opting not to have fabricator weld tabs, the pvc board was 5200 bonded to top of tank and bonded to coffin liner.  Areas of bonding to tank and pvc board was etched prior to bonding, same as previously mentioned.

All in all the install went very well, no hiccups to mention.  The tank is elevated off the coffin by 1/4" strips of pvc and centered in coffin with 2" space between coffin and tank.  No foam, no glassed in locking tabs, or anything on top of tank.

Essentially the tank is hovering inside the coffin, using pvc board to keep it off the bottom and away from the coffin on 5 sides .  If/when water gets in the coffin it drains out via 3 thru holes located most aft that drain into bilge.  Barring some unforeseen accident, this is the one and only tank I'll need to install in this boat.

Wanted to also mention the fabricator I used.  I highly recommend him.  Name is Tony and he owns Sunrise Marine Tanks in Venice, FL.  Tony used .125" AL, 56x20x6, 29 gallons.  Tank price was $355 ($12/gallon) + the WEMA sender for $35.  Same WEMA sender bought at west marine is $75.  Total cost was $390.  He was the lowest quote from the 6 places I called.  But best of all, at least for me, is his turnaround. 

The other 5 tank business I got a quote from told me their turnaround was minimum 12 days.  Tony started fabricating my tank on Wed. May 3rd.  He called me Monday morning, May 8th, to tell me the tank was done.  If he worked on the tank over the weekend it took him 5 days, if not 3 days.  Very impressive.  I recommend him for those of you who ever need a tank.

[boatnamesue]

Forgot to upload pics of the finished project from a few months ago...oops.

[Woodeneye]

Tremendous work. Don't use the leftover 5200 to caulk the lid back in.:)

[boatnamesue]

Tremendous work. Don't use the leftover 5200 to caulk the lid back in.:)

Thanks.  Ha ha nooo, silicon did the job.