New Forward Hatch Leaking

[jacksonlord]

I just replaced the trapezoidal Bomar forward hatch on my '87 C34 with a Bomar replacement from Pompanette. See this thread (I think I got the same one): http://c34.org/bbs/index.php?PHPSESSID=bbe89f2fb81fb6d52481f090caaff786&topic=1675.0

I (thought) I did everything right--remove the old carefully, repair/fill any holes, drill new, clean, seal (used 3M 4200), and secure. The new hatch is now in there and seems solid, but leaks readily in each corner on a hose test. I noticed, as did the above post, that the replacement hatch is just a tiny bit smaller than the old, and leaves larger gaps between the deck fiberglass and the hatch flange in the four corners.

Do I just need another go around with the 4200 sealant, especially in the corners? Will this stand up to heavy spray?

[Ted Pounds]

Sounds to me like you just need to re-bed it.  This time use more 4200.  Best to use so much that it squeezes out all around the edges.  To make clean-up easier use masking tape all around the frame.  The best technique for bedding fittings is to tighten until caulk squeezes out around entire edge, but do not fully tighten.  Let caulk dry.  Then tighten down snugly.  This allows the caulk to form a gasket that is then compressed with the final tightening.

[Ken Juul]

At this point that is your only option other than removing and starting over.  You want to ensure everything is dry, I think I would use a hair dryer.  Blow it at one corner at a time, let the frame get warm so it expands a bit.  Then lay a bead of caulk and push it into the gaps with a putty knive.  When you can't squeeze any more in, clean up any excess and move to the next corner (the hair dryer can be drying it while you caulk).  When all 4 corners are done, run a bead all the way around the hatch.  Hopefully as the hatch frame cools, it will squeeze the caulk into any voids that you missed.  Make sure you let it cure for at least 24 hours before you try the water test.

Ted and I were typing at the same time, his is the best course of action, but you can try mine and if that doesn't work start over.

[jacksonlord]

Thanks, guys. I think it's really only leaking in the corners, so the sides may be properly sealed. I'll try Ken's suggestion then start over like Ted says if it doesn't work.
-jackson

[Stephen Butler]

Am curious...which provides a "superior" (easier to work with, longer lasting) seal, marine silicon or 4200 (or similar products)?  The longer we own our boat, the more silicon versus 4200 we seem to use and am wondering if others are doing the same.  Just curious.

[Ron Hill]

Jackson : I installed a new Bomar center hatch this spring.  Here's how I did it:

I used 3M4200 in a tube from a caulking gun.  I squirted a medium bead of caulk on the hull and I also  squirted a bead on the portion of the hatch that would mate with the hull.  After placing the hatch in place I carefully pulled the hatch off and looked to see where the caulk had touched each other and where it didn't.  Then I ran another bead on each surface and places the hatch back into place, using a  slight pressure, I twisted the hatch left to right.  I removed the hatch again and looked at the caulk.  Then I placed another bead using the same procedure.  I set the hatch in place, inserted the screws and tighten them to about 75% tight.  I let the caulk cure for about 6 hours and then tightened the screws all the way down.

Before I installed the hatch with caulk I used a Stanley "centering drill" to drill holes that didn't match.  Also don't try to clean up until the caulk has hardened and then it easy with an Exacto/utility knife.

This fall we had the 500 year rain of 12 inches in 6 hours.  Not a drop came in that hatch !!

A few thoughts

[jacksonlord]

Thanks Ron.

I tried to just add some 4200 sealant to the corners. It help a little, but still leaks. I will try to redo the whole job and let you know how it goes.

Another question: can I use the same holes that I drilled before for the screws? For the old holes, what should I fill them with? I tried MarineTex epoxy for one of the hole before I put the new hatch on this time.

[Ron Hill]

Jackson : You don't have to do anything special with the old holes unless the edge of one is almost but not quite in the right place of a new hole.  In that case fill it with epoxy, let it cure and drill a new hole.
Otherwise I just shot some 4200 in the old holes to fill them.   

I'm sure that your leak stems from a void of caulk.  That's why when installing a new hatch you not only get the cutout hatch dimensions, but just as important are the radius dimensions.  Of course the factory may have left you with a sloppy cut out.  That's why it's so important to to spread the caulk on both  surfaces, mate the two pieces and then pull them apart to see where the caulk isn't touching each other!

Good Luck, now you know why you don't use 5200 (even thought that's what Bomar recommended)!!       

[jacksonlord]

My god, thinking of using 5200 makes me shudder after this!

Ok, thanks for the advice. Last time, as I said, I only put a fairly thin layer of caulk on the deck side. This time I'll try your technique, and let you know how it goes.

And after all this I may replace the hatch yet again next year with something more robust and offshore-capable...