Installing New Hatch On Curved Deck

[windependent]

I am installing a new hatch on my J/35 cabin top which is curved. I need to build up a "flange" to make it flat. The approach I was going to take is to create a form and build up an epoxy wall that I will then wrap in fiberglass and tab into the deck. Is this a prudent approach? Or, do you have a different approach that I should take? My concern is that the epoxy may not be flexible enough and could crack inside the fiberglass wrapping. Any insights would be most appreciated.

[CaptainForce]

This is a case where I think a frame of soft wood, say pine, that is easily formed and light weight, could be fully encapsulated in the epoxy and then tabbed to the deck

[tommays]

I am sure there are many ways BUT you don't want it leaking or rotting its frame or your CORE as i live next to a sawmill white oak was my material of choice


I scribed the crown and made a jig to sit the router on with a 1/4" carbide bit to reproduce it it did not have to be super perfect


G-Flex was the epoxy i used to hold the pieces toghter







For starting with this mess it came out pretty good

[windependent]

Thank you for you quick reply. I was actually thinking about using some spare teak that i have. But my primary concern is, for an 18" square hatch, whether or not this form of solid epoxy and compound that is about 1"high on the sides and tapers to 0 in the middle might crack under extreme use of the boat or would wrapping a wood core prevent that from happening? I forgot to mention that this is a race boat. So we could have 700lbs of people passing across the cabin top during maneuvers (not necessarily on top of the hatch) and we do contort the boat a bit (e.g. 3000lbs of backstay pressure, frequently maneuvering, etc.). This is where the concern about cracking comes into play. I'm just not sure if I'm dreaming up that this could even be an issue.

[tommays]

I race a good bit on a C&C 35 and we launch and retrive out of the bow hatch so i know of the abuse you speek of

There all the older Bomar cast frames which are still made and IMHP a good bit more rigid then a lot of the newer stuff and i still prefer the cast in braces that support the lens in the Bomars


18" might be on the small side unless that is the inner opening size

[Boatsmith]

I would make a frame of Coosa board and cope that to fit the deck crown.

[turbulicity]

I don't think a pure epoxy wall is a good idea. It will be brittle and it will crack eventually. If you are trying to stay away from plywood or solid wood coring for some reason, you should at least blend in chopped glass with the resin.

[windependent]

Tommy...Thank you for your reply. On the J/35 we launch everything out of the forward hatch which is much larger. This hatch is going over the main cabin and is for ventilation purposes. It is a Lewmar Size 44; the 17 3/8" x 17 3/8" is the cutout size. The hatch itself is around 21" x 21".

[windependent]

Hey Turbulicity...Thanks for weighing in. actually, what we're planning is to use epoxy that is fully thickened with West Systems 410 Filler and then there will be two layers of glass to encase the epoxy "form" and tab it all into the cabin top deck and to the interior cabin top. Does this additional information make sense? Does this change your opinion at all about this approach? I'm definitely open to suggestions.

[turbulicity]

The filler is a product to make epoxy into a fairing compound. Unless you introduce fibers into the mix, the structure will lack tensile strength and flexibility. If you need a load bearing structural member, laminate it with cloth. If you need more stiffness, you will need quite a few layers. If you increase the thickness by using a core material, you can get away with a lot less. Epoxy itself is only an adhesive and filler. The strength comes from the glass fibers.

So, in short, my opinion is that either fully laminate it or use a core.