Suggestions to rebuild floor hatch over gas tank 24 offshore

[Sparkdog118]

I am in the process of rebuilding my floor hatch. It is approximately 5 ft by 2 ft. Not sure what the best core material would be. Was thinking 3/8 or 1/2 in ply covered with ounce n a half mat? Biaxal? Woven riven? I know enough about fiberglassing to get myself in trouble. Lol.

 

[SkunkBoat]

I need to do my tank hatch this summer. its wet and coming apart at the underside edge.

Simplest way is 1/2" exterior douglas fir AB plywood. Doesn't have to be one piece but you don't need to go crazy making squares either.
I will leave a 1 inch edge with no core and fill that with glass and filler. (so screws don't go thru wood anymore)
remove old, grind clean, coat inside with glass strand matt, fully wet out core with resin, press it in place wet and cover with a layer of chopped strand matt.
Chopped strand conforms to shapes and doesn't pop up and leave air gaps. Its best to use at least one layer of mat before using woven roving or other heavy cloth.
When thats set, cover with heavy glass cloth.
This can be done with Epoxy or cheaper polyester resin

I'm thinking about getting fancy and using 1/2" pink foam and epoxy, with wood reinforcing strips.
My hatch is giant and heavy.

never tried using foam before but there is first time for everything.

Maybe I will do a test project first....

 

[Sparkdog118]

That sounds great. Thank you. Heard about the foam divinicil option. How much later would that be?

 

[SkunkBoat]

That sounds great. Thank you. Heard about the foam divinicil option. How much later would that be?

Lighter by the weight of the plywood. In my case a 4'x6' sheet.
foam weighs nothing.

 

[DennisG01]

Divinycel, Coosa... nice products but expensive. Weight savings is negligible, given the square footage of the hatch compared to weight of the boat.

3/8" might be fine... but go with 1/2" - you're only talking a couple bucks here - not the place to cheap out. And, again, weight is inconsequential.

When I rebuilt my entire floor (and hatches), I used marine plywood (all layers have waterproof glue and there are NO voids anywhere in it, unlike regular or even exterior plywood) for the floor (first, FULLY encapsulated with resin). But knowing it would be really easy to redo the hatch, I decided to try something different. I used that purple-ish foamboard insulation from Home Depot. I experimented with it first, but it's now been about 5 or 6 years and it's still rock solid.

FYI, there's a number of threads on here about this process (including my write-ups about the foamboard) - with lot's of information in them. Just use the search and you'll find them. BUT... lightweight mat between the core and the hatch, then a single layer of 1708 over the new core.

 

[ScottyCee]

I used 5/8" foam with confidence that it would never, ever, be subject to rot or water damage again. Worked like a charm.

 

[Summertop511]

I recored my overnighter deck last year. Definitely do what skunk was saying leaving the wood back from the edges so it doesn’t get water in it from the screws. PITA job but glad I did it afterwards. Just checked my 2005 seafarer. Even in 2005 they used a bunch of small pieces of wood to the very edge. I just rebedded the screws with caulk today actually to keep the decks hard.

 

[Sparkdog118]

Excellent advise from everyone! Thank you so much for the info. There is a marine store here in town that I am able to get a 4x8 sheet of 1/2 divinicyl for around 78 bucks. This will do both of my hatches over the gas tanks. I will be getting into this project this week and I will report back n let you know how it goes. Thank you again.

 

[Sparkdog118]

Finally got the hatch torn apart and rebuilt. I tore out the rotten wood squares and ground down the underside. I put 1 layer of ounce n a half mat and extra resin as a base and laid 1/2 in divinicyl on top while it was still wet. Put weights on top until dry. I cut the foam 1 inch from all edges of the shell. Then I razor knifed the square edge all the way around at a 45deg so the mat will lay over easily without bubbles. I used biaxel over top of the divinicyl for extra strength insurance. I used about 2/3 gallon of resin for the under side of the foam and almost a 1/2 gallon for the biaxel. The hatch came out amazing. It is extremely lighter than the original. I am very glad I went with the divinicyl. Wanted to thank everyone again for all your advise.

 

[Summertop511]

Finally got the hatch torn apart and rebuilt. I tore out the rotten wood squares and ground down the underside. I put 1 layer of ounce n a half mat and extra resin as a base and laid 1/2 in divinicyl on top while it was still wet. Put weights on top until dry. I cut the foam 1 inch from all edges of the shell. Then I razor knifed the square edge all the way around at a 45deg so the mat will lay over easily without bubbles. I used biaxel over top of the divinicyl for extra strength insurance. I used about 2/3 gallon of resin for the under side of the foam and almost a 1/2 gallon for the biaxel. The hatch came out amazing. It is extremely lighter than the original. I am very glad I went with the divinicyl. Wanted to thank everyone again for all your advise.

Pictures or it didn’t happen

 

[Sparkdog118]

here is a pic of the finished product just before I bolted it down. I will take more pics when I do the other hatch.

 

[ScottyCee]

Nice work.

 

[Summertop511]

Looks really good. If I ever have to do another floor I’m going this route with the lighter foam

 

[Sparkdog118]

Thank you. It’s my ocd. Lol. I can’t help paying attention to detail. I had the tanks covered with my buddy’s hatch since he had his gas tanks out of his Caribbean 24. I really noticed the difference in weight when I lifted the factory built hatch out and dropped mine in place of it. 1/2 inch divinicyl was the ticket. This is the finished product.

 

[DennisG01]

Has anyone ever compared/looked up the weight of up a GOOD hatch with a wood core compared to foam? Meaning, comparing the weight of a hatch that is in need of repair is not fair as it would be water logged. I always the difference was only about 5 pounds, or so?

 

[Sparkdog118]

I know my buddy‘a hatch is hard as a rock. I’m not thinking there is any water in it. I would guess it to be about 10 pounds difference. Maybe 15 lbs foam to 25 pounds wood. Wood may also soak up more resin. Percentage wise, the difference was huge when I picked them up.

 

[Fishtales]

I like the 1/2" wood core option best.

 

[seasick]

I don't think I would have used foam. Coosa board would be my choice.
If you want to view some really good videos on fiberglass work, take a look at Boatworks Today website, videos. Great info and very detailed. Be careful, you may get hooked for hours!

Videos | Boatworks Today

www.boatworkstoday.com

 

[DennisG01]

I don't think I would have used foam. Coosa board would be my choice.

Generally speaking, I would agree. And it's really not something I would highly recommend, either. But I looked at this as a "fun experiment". It's quick and easy enough to redo, should it fail. But so far, after 5 or so years, it's still rock solid. The reality is that the core's main job is NOT about strength, itself. It's simply there to create separation in the two glass layers. The core does, however, have enough shear strength (might be a more appropriate word) to keep the resin/glass from breaking free of it's grip on the core... otherwise we're basically back to the same situation as rotten wood.

 

[Sparkdog118]

Mine was waterlogged and had the rotten squares of wood from the factory in 1988. It was getting soft. My buddy’s hatch that I borrowed so I could use the boat is also original but still hard as a rock. I was curious so I put his hatch on a scale. Lol. It weighed 34 pounds. I’m thinking mine is around 22 to 25 pounds when I was done. The hatch seems just as strong as the deck of the hull above the stringers.