Hatch Cover Rebuilding

[Eggbert]

I’ve had one rather peculiar problem with my boat over the years, and I think I may have figured it out and to some extent, have resolved it. Basically, when my boat was about 20 years old or so, the hatch cover at the cabin entrance became soft with wet rot.

The picture below is not my boat, but the same model, and shows the hatch cover in an open position.



The cover was made of ¾” plywood with a white Formica top and varnished on the bottom. The edges were tapered and teak trim was added. The wood around the mounting plate for the gas strut became too soft and the strut fell away, mounting screws and all.

So I rebuilt it, saving the teak as it was in good shape. I used a new piece of plywood with hardwood veneer, and varnished it with polyurethane varnish. For the top, I used a piece of 14” white plastic; I think is polyethylene.

Much to my dismay, a mere two years later, I noticed the gas strut hanging down again, but this time something different had happened. The plywood was like powder held together by the exterior varnish.

Oh darn! So I rebuilt it again. This time I used 3M 5200 between the teak trim and the plywood. Yet, two years later, the same thing happened. The plywood turned to sort of a dust.

So I rebuilt it again, however this time instead of varnishing the plywood, I gave it a few coats of West System epoxy. Again, I used 3M 5200 to join the trim to the plywood, and even dribbled some epoxy in the screw holes for extra protection.

This time it lasted 3 years until eventually the plywood turned to dust. At this point, I was not only frustrated, but confused. But I did come up with a theory. The original cover had a Formica top, but my rebuilds all used this white plastic. It seemed to me that it was possible that sunlight was passing through the plastic and baking the plywood.

Now I suppose I could have tried to laminate some Formica to the plywood for my next attempt, but seeing I had the plastic, and didn’t know much about purchasing a small piece of Formica, I thought I’d try something different.

I decided to add a piece of Aluminum foil between the plywood and the plastic, shiny side up to reflect the sunlight from getting through.



Two years passed and it was still fine when I covered it last Fall. I fully expect it to OK when I uncover it this Spring. So…. It looks like I have found and rectified the problem. I’ll know for sure if it lasts a few more years or longer.

At the beginning of this post, I stated that I “to some extent, have resolved it”. Maybe I have resolved the plywood disintegration problem, but there’s another issue. The 5200 always seems to crack away. It appears it doesn’t like to stick to teak very well. I suppose sorting that out is as easy as trying another type of sealant. Any suggestions?


ps: I saw a picture of a boat like mine on the net; presumably newer, and it appeared to have a 1-piece fibreglass hatch (no trim either). Probably an upgrade by Carver, but not as pretty either. LOL.

[tomschauer]

I would assume the original hatch was encapsulated in fiberglass. The formica should have a replacement, but who knows.
I would also assumeme the 5200 would stick to the teak. Are you applying the 5200 before the polyurethane? 'Cause it wont stick to the poly. Another issue may be the wood expands and contracts to much for the 5200 to keep up with. Maybe try a modified urethane sealant, much more flexible.

2 cents given.

[PhilH]

AS you know, teak is full of oil, and 5200 does not like oily surfaces. Suggest a trip to marine store or home depot for a 3M4200 sealant or outdoor silicone, but wipe that teak with acetone 3-4 times in the direct area your adding adhesive to remove the teak oil. Also, as Tom said, wipe the teak to remove as much natural teak oil as possible with acetone or MEK

[Viper]

Have you considered doing away with the plastic top and just gelcoat the plywood instead? The ultimate would be to cover the plywood with fiberglass mat, gelcoat the glass, then fasten your teak pieces. Glassing however is labour intensive if you're looking for a smooth finish. A good alternative is to encapsulate the plywood in epoxy then gelcoat it. You can sand the gelcoat to a smooth finish then polish, or an easier route would be to roll it just before it cures to get a non-skid texture. The only maintenance you'll have with a smooth finish is polishing the gelcoat to protect and maintain the shine.

Now, most people will try to tell you that you never gelcoat over epoxy, and while doing so requires extra consideration, it's totally doable if done correctly. It's even doable with West System who's product has been generally considered the least compatible with gelcoat adhesion. Again, you just have to know the process but there is a ton of info on the net on how to do it correctly including West System themselves, and there's several YouTube videos too.

As far as caulking the teak, I'm assuming you're using the caulking to bed the teak as well as a bead on the seams to keep water out of the mating surfaces. If you're having adhesion problems with the caulking bead on the seams, don't use caulking! Apply butyl tape to the side of the plywood top where you're going to fasten the teak trim, you can leave the tape proud of all the edges and after the teak trim is fastened, trim the tape flush. This will prevent water from EVER getting in as long as your fasteners hold.

I've used butyl tape for bedding and sealing mating surfaces for years instead of caulking. I've done everything from rail stanchions to transom shower boxes, to radars, etc. I use very little caulking now. No mess to clean up after, no partially used tubes that get thrown in the garbage, the hardware can be removed easily in the future if needed without the pain of having to remove old caulking, no tearing up glass when removing something (5200), and there's no bead around a seal that will peal off.

Consider this; when you fasten something that you are bedding the mating surfaces with caulking for the purposes of keep water out and you have to fasten it tight enough such as a rail stanchion, you squeeze out most if not all the caulking that's there to prevent the water from getting in. If you don't tighten the hardware enough with the intention of preventing everything from squeezing out, you'll have movement which will eventually cause the seal to fail. The practice to overcome that was to not tighten it all the way initially and let a thick caulking layer cure first so it creates a good gasket, then come back later and finish tightening it all the way while squeezing the cured caulk gasket. The problem with this method is that you break the cured seal around the fasteners. All this is eliminated by using the butyl tape. You tighten the fasteners only once and you will never squeeze out all the butyl, its physical properties prevent that from happening. There are a couple of important practices to keep in mind when installing butyl tape but they apply to caulking as well, most people just don't follow the rules. Caulking is an easy product to use and still has a place in my toolbox for areas where tape isn't an option but I reserve it for those jobs only.

[Eggbert]

Thank-you all for your responses. I actually posted this about how sun could be a factor in the quick dry rot of plywood, but I did ask about sealant and I appreciate the replies.

The butyl tape sounds interesting. Is this the type of stuff you mean?

I'm not familiar with this tape, but it seams likely it is the same as stuff I once used to install a car windshield. Never really hardens up, which is good other than I do walk on this hatch-cover. I wonder if it will smear all over? Probably not to any significant extent. I'll no doubt try it next time.

[Viper]

I didn't get anything in the link but yes it's the same type of stuff used to bed windshields. Some rolls are flat, some are a rope type, I only use the rope for very irregular surfaces. I don't know what you mean when you say you'd be walking on it. This would be used to waterproof the joint between the cover and your teak side pieces. In my gelcoat suggestion above, you'd create a non-skid surface on the plywood cover if it's an area you're going to walk on regularly.

Butyl has been used in the industry by OEMs for decades to bed/seal fasteners and hardware on decks and other areas. The only area you wouldn't use it that I'm aware of is for the fuel fill on the deck or the vent in case of overflow as fuel will break it down.

[Eggbert]

That's odd about the link. Let me try again, this time using the URL codes:

https://www.amazon.ca/Butyl-Tape-Black-50ft-Total/dp/B01CUBJ4PS/ref=sr_1_4?ie=UTF8&qid=1524365874&sr=8-4&keywords=butyl+tape

Oh... I sometimes step on the hatch when putting on, or taking off the bridge cover. I was merely wondering if the thin line of tape between the plywood and the teak would smudge over if I stepped on it. Really no matter as I don't generally step on/near the teak and no doubt WD40 would remove any smudge quite easily.

[Viper]

Ya that's the stuff but you can get it in white which suits most applications on a boat.

[Helmsman]

Source of the post I didn't get anything in the link but yes it's the same type of stuff used to bed windshields. Some rolls are flat, some are a rope type, I only use the rope for very irregular surfaces. I don't know what you mean when you say you'd be walking on it. This would be used to waterproof the joint between the cover and your teak side pieces. In my gelcoat suggestion above, you'd create a non-skid surface on the plywood cover if it's an area you're going to walk on regularly.

Butyl has been used in the industry by OEMs for decades to bed/seal fasteners and hardware on decks and other areas. The only area you wouldn't use it that I'm aware of is for the fuel fill on the deck or the vent in case of overflow as fuel will break it down.

I have to re-seal my forward hatch. It is a round hatch above the bed. So, this post is timely for me. I had ordered some of the 3m 4200? (Can’t remember the number off of the top of my head) but would rather use butyl tape. My question is what width of tape should I buy for the hatch. Is 1” sufficient or should I use a wider tape? The reason I ask, is that I would like to do this all in the same day. Thanks for any advice you guys can give.

[Eggbert]

I'm not an expert as I was the one that started this thread, but if it were me, I'd install the tape flush with the inside of the plywood (see picture in 1st post) and trim the excess sticking out the top with a razor blade. (try cutting some first as it may gum up vs. cutting off nicely).

If the tape is narrow enough to fit, I'd install it flush with the top and not worry about the slight gap on the underside.