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Old 09-06-2010, 11:35   #1
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Installing Frameless Ports

I have been reading and researching (here and elsewhere) and my head hurts. Sika Flex 295, Dow 795, butyl tape, mechanical fasteners or not. I'd like to run by you what I've tentatively come up with to get your thoughts and suggestions. First, decisions already made and criteria:
  • Using 3/8" polycarbonate (already purchased three years ago after not doing enough research; probably would've gone with acrylic)
  • I won't be reusing the old frames; ports will be installed on the outside of the cabin sides
  • Strength, watertightness, and longevity (of watertightness) is primary concern; aesthetics are secondary
Given these criteria, what do you think of the following? If you think something won't work, please tell me why and explain what you would do differently. Thanks!


Jay White
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Old 09-06-2010, 16:36   #2
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I installed frameless Acrylic portlights about 1 year ago, and after reading the "sexy windows" thread, and related material, I choose 3M adhesive tape, along with Dow 795 to adhere and seal the edges and couldn't be happier. I would not throughbolt. If I were crossing oceans I might reconsider, but mine are on there really strong. Any wave strong enough to knock them out would knock the boat over 1st.

Zero leaks now. I would thinks your way could still leak next to the bolts, as the windows expand and contract.
It was easy to cut mine to shape with a router, and then shape the corners with a belt sander.

Here's a couple of pics.
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Old 13-06-2010, 13:51   #3
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Interesting... did you use VHB tape and did you prime the acryllic with anything?
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Old 13-06-2010, 14:04   #4
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Most if not all plastic windows that are through bolted will crack around the bolt holes. We install our windows with Sika 295 and appropriate primers. This is from small plastic ports to tempered glass windows 18' by 3' on large sport fishers. We allow enough thickness of the Sika to allow for thermal movement. We also usually recess the windows into a ledge. This may be harder on a retrofit. David
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Old 14-06-2010, 06:06   #5
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I did all the reading about primers, and in the end, can't remember if I used any or not. My thought was that the 3M tape may peel the primer off, whereas bonded directly to the fiberglass may be stronger.

Either way, they are not coming off, without kicking them repeatedly from the inside.
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Old 15-06-2010, 06:19   #6
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Looks like you are doing some great pre planning and your drawing is very descriptive. Based on it, a few comments.

1. I used Sika 295 UV and think it is great.
2. I am not sure the Butyl tape is thick enough to allow for thermal expansion. Fiberglass is very stable but the acrylic expands at a rate about equal to aluminum. As I recall, about 0.000006 (6 millionths) of an inch per inch per degree F. Sika wanted 3/16. I molded 3/16 square strips by cutting grooves in a board and lining them with wax paper, then injecting Sika and letting it cure. I then cut into 3/16 lengths and placed the cubes in the adhesive bead before mounting the window. I would cut longer lengths to make them easier to handle next time.
3. I worry about adhesion to the paint you plan to use to hide the bead. If you use Sika, then use the primer which is black and will hide the bead while improving adhesion.
4. Counter sink the oversized holes you are drilling to reduce stress risers at sharp corners.
5. Don’t over torque. Apply only enough to hold the window in place while the adhesive cures. I over torque the first couple I did and ended up with cracks between the holes.
6. I understand the idea of sealing/epoxying the screw into the cabin but, while I can’t put my finger on it, it just seems like it is going to make the installation harder. I put the nut on the inside, using a pan head machine screw. After the adhesive sets up, remove the screws and seal with generous silicon sealant. Gives a neater appearance on the outside. Extra screw length is covered by trim in the cabin. If you put it on the outside, you will end up grinding off excess to get a clean appearance.
7. After the installation, then caulk around the window with appropriate sealant. I started with Sika because I had enough to do it. Now I do occasional touch ups with GE silicon.

I am not saying the way I did it is best, I don’t have that level of experience, but maybe these comments will assist. I can assure you, there is a learning curve. We did 8 dead lights. Our process was much improved after about #4.

Good luck with the project.


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