Pascoe's method precludes use on many Grady models since it presumes the liner is not in place, as the tanks originally when installed at the factory. When it comes to replacement time, the
only job we ever do, can't remove liner, so the tank(s) may hav eto be slid and lifted up. My 150 gal main tank extends about 2 feet under the bridge deck (liner).
Also, he presumes never having to do the job again. A long time ago I used 5200, never used it again and never will. One finds this out first time they have to undo something. Think of 5200 as concrete, it is permanent.
I prefer the softer Boatlife Lifecaulk and Lifeseal products suitable above/below water line use. They are also permanent but flexible to conform and readily undoable.
Use GEII silicone window and door on the deck seams for economizing.
I also don't like such a hard product between tank and deck, prefer something softer and grippy. If it is softer and grippy it will form itself to the glass pattern on the deck to prevent or at least assist keeping the tank from tending to slide around especially on the beam to beam rock and roll drift thru the rip lines.
Just have to full face seal with Lifeseal the material to tank so it stays put and stays waterproof between the two. Which Grady didn't do originally.
If it is too soft, then 1/4 inch thick is too much. 1/8 inch is fine.
Part of the tank support deck on the Grady actually contacts the hull directly, as Pascoe says this is a no-no.
The deck meets theh V hull rise at it's beam edges, but is also supported along the span with subfloor stringers (2). The diagram he shows is for narrower tanks or a deck of heavy 3/4 inch ply. Grady uses 1/2 inch to economize on height to pack a bigger (taller) tank in there. With more supports undeneath, no problem, and add more glass to top to stiffin it. The 1/8 inch wall tanks are hardly rigid so they will conform to hull (deck)flex.
I recommend a 3-5 year inspection plan after the 10th yr, 1st time pull tanks and arrest any corrosion to save it, apply the above mods, then every 3- 5 inspect below decks, original tanks will last forever.
Inspect for any movement, make sure deck plates have zero leaks, and tank compartment drains are clear and readily drain. You want zero puddles on top of tank.
Wash off all the dirt on tank so as to minimize wetness. At the 20 yr mark, pull again and check below tanks.
This is strickly a DIYer job, you will never get a pro to do the work to the letter, they will be glad to replace the tanks even if not actually leaking.
By the way, the seam crack in the plastic tank is because it's defective, the seam is not supposed to be any weaker than base material. Same goes for welds in alum tanks.
Good luck.
