Replacing an Overhead Hatch Lens
by Gary Ivey, C34 #580
I removed the rubber gasket and cleaned all remaining silicone remnants from the gasket and the frame, using rubbing alcohol as a final cleaning agent on all surfaces. This would be the time to replace the gasket if desired. I wasn't advised of this when I purchased the lens and didn't want to wait an additional 10+ days for the new gasket, so I used the old one. Incidentally, removing the old silicone isn't easy, so expect painstaking effort to do do. But remove it ALL!
Be absolutely sure to follow the instructions that come with the replacement lens regarding the use of masking tape on the hatch frame. Also, leave the protective paper on the top side of the lens, removing it from the side that you place into the frame. The black silicone used in this installation makes a helluva mess, but is minimized by these steps. DO NOT peel your masking tape OR the protective paper from the lens until the silicone has cured at least 48 hours! But I would NOT recommend leaving it until the silicone is fully cured (seven days).
Depending on which type of frame you have, placement of the lens can be critical as the dogs (handles) used for closing it tight may need to mate with a flange. Mine was such a replacement, and required approximately 1/8 inch gap from the front of the lens to the frame, on the side that the handles are located on. The handles are obviously not put back onto the lens until it is mounted and at least semi-cured. It takes about two days for initial curing, and seven days to fully cure. The lens literally sits on top of the rubber gasket inside the frame and is held in place by this extremely strong silicone.
Things you need to know: Frame measurements should include hatch opening size (which should be square) and the height it extends from the deck (mine was 1-1/8 inches). Have a quantity of disposable, heavy duty paper towels around for wiping and cleaning. I bought a silicone application "gun" for this installation. Usually, when inserted into the gun and "tightened up", a seal breaks on the silicone tube and allows flow of silicone for your application. This didn't happen with mine. I tightened and the seal didn't burst. Instead the tube burst. I created a new and unprintable conglomeration of randomly chosen words, strung together in a unique and expressive way, arranged for this particular situation. Particularly after I had paid $20 for this stuff! However, I was lucky in that the tube held together enough to allow me to use it anyway. I had to find a long, thin, sharp instrument to slide down the throat of the applicator cone, and puncture the inner seal on the top end of the tube. Having competed this, and perfecting my new vocabulary, I completed the installation without further "incident" It works just fine!
I ordered the replacement lens, gasket, GE UltraGlaze sealant, and hatch dog from Bomar (http://www.pompanette.com/bomar). I had the charter maintenance crew remove the complete hatch, then took it home to remove the old sealant, a tedious job best done with a distraction, like TV. I followed the instructions that came with the replacement lens, masking the lens from excessive sealant. After it cured, I rebedded the hatch to the cabintop with, I believe, 3M 101.
GE UltraGlaze is an industrial grade sealant/adhesive used in commercial window applications. It can be found on Amazon for about $14/tube. I've also used it around my fixed portlights. I expect it will hold up better to UV than just regular silicone.
Craig Illman, Espresso #1150, Seattle