Gary, here's my experience:
I removed the hatch from the boat and brought it home. Removal consisted of backing out the 16 screws in the frame and then gently prying the frame loose from the cabintop. I remembered the instructions for removing our Beckson portlights which included: “Do not force it. Apply steady but firm pressure and it should back out.” Although this idea was for sealant, the same proved to be true for the “glue” that held the hatch frame. I gently hammered two large screwdrivers into two of the corners and started lifting. As the hatch started to come out, I moved the screwdrivers to the opposite corners and did the same, leaving wood shims in the first two raised corners. After about ten minutes of lifting the corners the hatch started to come slowly away from the glue, and then it was easy to just wiggle it up and out.
Much of the paint and glue from the lip of the hatch remained embedded on the deck, inside the opening and on the match frame. The good news was that there was no evidence of water damage in the core plywood, between the headliner below and the fiberglass deck above.
What was there? For starters, NO sealant!!! There was a completely uneven application of a light brown substance that, based on previous comments on the Message Board, was reputed to be 3M 5200, also known as “Satan’s Glue.” After 26 years, it wasn’t holding much anymore.
I took the hatch home after placing a 5’ x 7’ tarp over the hole, secured with light line and rolling hitches to the handrails and one around the mast. This size tarp works almost perfectly to fit between the deck handrails.
I purchased some Goof Off, which reputedly is good for removing the 5200. It did work on the hatch, but it was time consuming. For cleaning up the deck and the hole on the boat I used a heat gun and a putty knife. That was much faster than the Goof Off, and it lifted the paint as well as the remaining glue. It took at least three passes over the deck to remove every bit of debris and ready it for the acetone.
[Added]
The Main Message Board and the Pompanette website include this about Bomar hatches:
…Bomar states the following suggestion to deal with 3M 5200 sealant/adhesive that may become a factor:
Removing Hatches and Portlights Bedded in Polyurethane Adhesives.
Many boat manufactures in the past and present use 3M 5200 or a similar polyurethane adhesive to install hatches and portlights. This is great for providing a good water tight seal but it makes removing the hatch or port very difficult without damaging the gelcoat.
There is a product on the market called Anti-Bond 2015 that may help. Anti-Bond 2015 that maybe the solution. Anti-Bond 2015 can be sprayed on 3M 5200 causing it to debond without any delamination of the boat's gelcoat.
We didn’t need to use any Anti-Bond 2015 to remove the glue. The gelcoat was undamaged. If your hatch refuses to move, then it would seem a good material to use.
