Bedding non-through bolted hatches with Butyl?

[Swift Drift]

Originally Posted by NorthPacific

Talking to me Jedi or Swifty?

I think he's talking to you since he referenced "the lens". All of my recent work and what this thread has been based on has nothing to do with the actual lens itself but rather than frame that houses the lens being bedded to the hull.

I will mention that I did the lens bedding to the aluminum hatch frame portion of the job from the comfort of my shop this winter. I used "GE ssg4000 ultraglaze" in black which I assume is very similar to "3m 4000uv". Both are silicone, both are uv resistant. I went with the ultraglaze because apparently it is what they use to bed windows on skyscrapers.....figured that was convincing enough.

Another point I might mention is that I discarded the original 1/8" acrylic lenses and made new ones out of 1/2". Many advantages to going much thicker, one being reducing flex and therefore reducing the possibility of a seal being compromised by motion.

Good luck with your project!

[Opie91]

Another vote for butyl.

I just pulled a hatch off that had been on the boat for 30 years. Hatch came off with out a big fuss and the balsa core around the hatch was dry as can be.

(Former 5200 addict)

[s/v Jedi]

Originally Posted by NorthPacific

Talking to me Jedi or Swifty?

In general. The sealant that goes around the lens of the hatch is directly exposed to UV. It is therefor good to chose a sealant that stands UV very well so that it lasts longer. 3M 4000UV is specially developed for that plus to make it good looking. I just replaced the first seam done with this sealant and it is 19years old. I also redid marine silicone seams that I put in rather recently but already failed.

[MangoCats]

Originally Posted by s/v Jedi

I had no incentive to take it off, clean up all the butyl, and start over, so I took a lame way and put pieces of bamboo skewers with 5 minute epoxy in there, let it cure for an hour, then drilled the first hole and the screw again didn't grip. These are hefty screws. I then proceeded next hole to put the screw in without any drilling, which went surprisingly well and it was good.

I replaced my Bowmar hatch today, bedded it with butyl, seems good so far. PO had an AC unit in there, he saved the hatch for me but not the screws. When I ordered replacements I got both #12 and #14 against the eventuality of worn out holes (1984 Pearson 303, well built, but still only fiberglass.). Most of the #12 screws bit solid, but the two front corners spun, replaced those with #14s and they bit solid too.

[Stu Jackson]

Originally Posted by Swift Drift

So I've removed and rebuilt the old alluminum framed Bomar hatches on my 1988 Catalina 34 (new acrylic, new hatch dogs, new seals). >>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>

P.S. I have the same scenario/dilemma with plastic framed Beckson ports that mount inside the cock pit and provide light to my aft cabin. I would assume that the same logic would apply in this application with the understanding that there are two main differences: a) Plastic vs. alluminum frames b) vertical mouting orientation vs. horizontal (flat)... any input is appreciated.

I use Maine Sail's butyl on my own saloon hatch a few years ago, worked great. I needed two layers of tape. I wrote it up in a Mainsheet magazine tech note and it's on our C34 website.


Do NOT use butyl on the Beckson ports, use silicone. It is recommended by Beckson and is the ONLY place on my boat I use it. I wrote a recent tech note on this, too.

[roverhi]

Beckson doesn't reccomend using sillycone because it's the best sealant. They reccomend it because the plastic Breckson uses deteriorates with Polysulfide and Polyurethane caulk over time, believe it causes the plastic to crack.

Don't know if Butyl also has the same effect. Would be interesting to hear how the Beckson ports worked with the Butyl after a bit of time.

[CarlF]

I always use Dow 795 to bed glass or plexiglass into metal frames or onto fiberglass. Note 795 is not at all like regular silicone caulk like the old Dow 101. It's a structural adhesive that can hold 10ft tall windows on buildings 30 stories up with no other hardware.

It allows 50% movement due to different expansion rates of the Plexiglas and frame.

The one trick is to have a 1/4" thick bead. If you squeeze it all out then it can't move with the expansion without tearing lose. One trick I've used with a skylight is to run a 1/4"x1/4" foam tape around the perimeter and then fill the rest of the space with the 795 before dropping in the Plexiglas. The tape keeps the 795 from compressing while it hardens.

https://www.dow.com/documents/en-us/...df?iframe=true