Suggestions for sagging floor gas tank access panel - Seafari 20’

[JUST JOHN]

Hello CSC,

So the gas tank access panel had begun sagging noticeably over the last year or so. I was plan on bracing it from underneath, as there's ~2 1/2" of clearance above the tank, with aluminum angle, or other materials based off suggestions offered. I'd like to know if anyone else has had to do this same repair, and if so, how they've remedied it?

I'm undecided whether to just piggy-back the gas tank mounting screws or glue/resin-in new plywood mounting spots in between to screw into...







The tank looks surprisingly ratty for having been replaced in 2010.

[JUST JOHN]

Am I going about this the wrong way? So I guess the cover is made of (now-rotten) plywood sandwiched between the fiberglass. I know this is elementary stuff, but I'm new to this. I saw another thread whereas the cover was grindered clean of the backing and wood to build it back up. Anyone have a tutorial for this type of repair?

[FLexpat]

Originally Posted by JUST JOHN

Am I going about this the wrong way? So I guess the cover is made of (now-rotten) plywood sandwiched between the fiberglass. I know this is elementary stuff, but I'm new to this. I saw another thread whereas the cover was grindered clean of the backing and wood to build it back up. Anyone have a tutorial for this type of repair?

http://www.classicseacraft.com/commu...ad.php?t=26963 Post#23
Since yours already has a significant 'dish' to it you will need either vacuum bag the layup against a rigid flat workpiece (maybe use spacers on hatch edges to bow it the other way) or use weights to flatten it when you put the new core in.

[JUST JOHN]

^Thanks for that...

found this fairly helpful also:
https://www.boatdesign.net/threads/e...t-hatch.42834/

[Bushwacker]

Originally Posted by JUST JOHN

. . .

The tank looks surprisingly ratty for having been replaced in 2010.

The worst thing you can do with a fuel tank is to foam it it! Carl Moesly knew better than to foam in a tank, but Potter evidently started doing it by the mid-70's. Second worst thing is not to coat it with a flexible coating like coal tar epoxy! As the tank expands and contracts, it'll create a small gap between foam and tank which will hold water against the aluminum, causing crevice corrosion in the bare aluminum! While you have the hatch off, I'd break out the pressure washer and blast all that foam away, then pull the tank and inspect it for leaks, or maybe have it pressure tested. Pulling a tank is relatively easy in the Seafari compared to a CC model! Then reinstall the tank per Dave Pasco's recommendations.

As for recoring the hatch, the first challenge will be to get the bow out of it as others have mentioned. One challenge in using foam core material is that resin doesn't penetrate it like it does balsa core, so it's harder to get a good bond all over the bottom side that you can't see, unless you use the vacuum bagging technique. Before you get too deep into the repair, check out Dave Pascoe's article on core materials. Balsa core is actually stronger than foam and bonds much better, so it's a great material provided you don't go drilling holes in it! A 1/2" core will be plenty stiff if you put a layer of 1708 over it, but I'd inspect the top of the hatch closely to see if you can determine how water got into the plywood, which deteriorates quickly if it gets wet because water follows the grain in all directions.

[JUST JOHN]

The worst thing you can do with a fuel tank is to foam it it! Carl Moesly knew better than to foam in a tank, but Potter evidently started doing it by the mid-70's. Second worst thing is not to coat it with a flexible coating like coal tar epoxy! As the tank expands and contracts, it'll create a small gap between foam and tank which will hold water against the aluminum, causing crevice corrosion in the bare aluminum! While you have the hatch off, I'd break out the pressure washer and blast all that foam away, then pull the tank and inspect it for leaks, or maybe have it pressure tested. Pulling a tank is relatively easy in the Seafari compared to a CC model! Then reinstall the tank per Dave Pasco's recommendations.

As for recoring the hatch, the first challenge will be to get the bow out of it as others have mentioned. One challenge in using foam core material is that resin doesn't penetrate it like it does balsa core, so it's harder to get a good bond all over the bottom side that you can't see, unless you use the vacuum bagging technique. Before you get too deep into the repair, check out Dave Pascoe's article on core materials. Balsa core is actually stronger than foam and bonds much better, so it's a great material provided you don't go drilling holes in it! A 1/2" core will be plenty stiff if you put a layer of 1708 over it, but I'd inspect the top of the hatch closely to see if you can determine how water got into the plywood, which deteriorates quickly if it gets wet because water follows the grain in all directions.

Thanks for that Bushwacker. I'll look into all those details. Coating the tank is a great idea; I will take heed of your suggestion. My father replaced the tank in 2010. He had it fabricated locally from the original, which leaked out a full tank of gas before realizing the issue. I'm sure he replaced it in the same manor he found it, as you said originally, with the foam. I wish my fuel gauge worked currently to tell me how much fuel I'd need to remove; it works intermittently! Can you guide me on what/how I can check on the tank-end to rule out any possibilities there? The gauge pegs left past E when I turn on AUX. This is another thing I really need to correct before the boating season, in addition to the tach (again works intermittently). Like you say, while the hatch is open give everything there a clean bill of health. The wire connections are badly corroded.

With regards to the source of water, I'm thinking it is the screw holes; although parts of the edges were compromised also. The bottom fiberglass came off in one piece with just a little prying. I got my grinding wheel out, respirator, and ear/eye protection and didn't use any of them... yet. You can see that the original plywood goes right up to the edges, and is not beveled, like is recommended today.

Last night's progress:

Fiberglass bottom removed, along with some plywood...

1/2" plywood originally used:




I still have some scraping/grinding/sanding to do. Doesn't the plywood remnants look like bacon!? Some of the wood scrapes off and looks like pot roast and/or pulled pork. Can't you tell I worked straight past dinner time? LOL

The bow in the fiberglass is one thing. There are also "divots" in it, like heal marks or low spots from use. My wheels are spinning about how I can apply pressure and do so on a FLAT surface. I have a few thousand pounds of weights at home, and although "overboard", granite surface plates at work... I may get quotes from a pro with a vacuum table for the hell of it too.

[FLexpat]

Soak the wood in water for a day or so then go after it with a wire brush on an angle grinder.
Granite slab is perfect for pulling a vac on but you probably want to protect the surface - epoxy sticks real well to it - use poly sheeting as the top side of the vac bag and duct tape to seal it down to the slab if you are doing it with vac instead of weights. Put about 1/8-1/16 thick, ~1/2" wide strip of something (duct tape works) under the edges of the hatch when you do it so you induce a reverse dish - it also keeps resin from running out the old screw holes. Get a cheap vac pump (Harbor Freight or EBay?) - I like rotary vane pumps but piston pumps are ok too - do not use a shop vac; while it will kinda work, you run the risk of igniting the fumes and that is a bad day.

The bottom sheet of glass was never properly attached on any 23 SC tank hatch I have seen - the core should have had the edges beveled and the bottom glass should have been bonded to the underside of the hatch around the edges instead of just laying on the wood and barely touching the hatch edge.

[JUST JOHN]

Originally Posted by Bushwacker

The worst thing you can do with a fuel tank is to foam it it! Carl Moesly knew better than to foam in a tank, but Potter evidently started doing it by the mid-70's...

Spoke to my dad yesterday. That foam you are seeing is the original 40-year old foam. He didn't refoam it, just slipped the new tank back in. Granted that is worse for holding moister, as you can be certain there is a gap to hold moisture. I'll consider removing it mechanically and maybe blast off the remnants, although I don't want all of it just falling into the bilge. We got 33 years out of the original tank. I'm not sure it's worth the headache to pull/coat it for the couple-hundred-bucks it cost to replicate the original ...for a second time some 25 years down the road. It will have an easier life these days on the trailer, as opposed to brackish water frequently sitting in the bilge in years past.

In other news there doesn't appear to be any warping, bows, or divits left in the bare fiberglass hatch shell. They came out; as other point out, it is very thin and forgiving. I tried filling it with H2O to soak, but that didn't go well. It leaked, poured-out, and/or evaporated in no time. Finding time and level ground with my kids running around was also a challenge. Probably won't get back on this project until next week...

I need to purchase plywood and epoxy/fiberglass supplies...
How much resin should I get? I'd like to have some left over for other projects... gal or 1/2 gal of resin?
http://www.uscomposites.com/epoxy.html

For the ply I want to double check the depth/clearance to that fuel bung. I think with the 3/4" of sag, the bottom of the failed cover was making contact (original 1/2" plywood). Adding 1/4" to the plywood thickness from stock should therefore clear with 1/2" to spare. -Need to make sure.

[Bushwacker]

I would seriously consider using end grain balsa instead of plywood. It will save a lot of weight, is cheaper than Corecell, will bond to the fiberglass better, and if you do happen to get a water leak in one spot it won't follow the grain and spread everywhere like it will in plywood. You might also consider using vinyl ester resin, which will be a bit cheaper but with properties almost as good as epoxy.

[JUST JOHN]

where can I source the end grain balsa in 4x8? ... I keep hitting 2x4 sheets, and extrapolating the price is making me nervous. I haven't called lumber yards yet. EDIT: ahhh, end grain balsa, so it's "cubed" or "quilted" like the original plywood was.

Corecell isn't a consideration at $335 a sheet.