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Old 26-03-2015, 10:33   #1
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Replacing Hatch & Port Lights

I intend to replace the port lights and hatch cover this year and from all that I have read, the best product for me to use is tinted acrylic. I am going to install the windows using VHB 4991 3M tape to avoid drilling and screwing the acrylic in place and I am going to use either Dow 795 or Dow 791 sealant. The tech department at Dow said to use Dow 791 rather than Dow 795. Anyone have any experience with these products or can suggest better ones. Thanks
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Old 26-03-2015, 17:05   #2
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Re: Replacing Hatch & Port Lights

You are on the right track. Acrylic is the product of choice, unless you are going to keep it covered all of the time. Polycarbonate loses much of its strength when exposed to UV.

795 is what I used. Unless you are using screws, then butyl tape.

We've done all of our portlight lenses (about $6 each instead of $120 each from Lewmar) and windows. Just pull the old ones out, make new ones with a router table sticking the old one to the new ones with double sided tape. Cut it to approximate size with a saw or a table saw. Then use a trimmer bit, it makes the duplicate perfectly.
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Old 26-03-2015, 17:07   #3
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Re: Replacing Hatch & Port Lights

Thank you for your reply.
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Old 26-03-2015, 17:12   #4
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Re: Replacing Hatch & Port Lights

Posted picture.

By the way, the best way to get the old ones out:

Buy cheap putty knives from HD or Lowes. Also one of those really long razor knives with replaceable blades.

Also, drill a hole near one end of the windows. Put a big piece of line thru it, knot it with a figure 8, and use it to pull the old ones out!
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Old 27-03-2015, 09:13   #5
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Re: Replacing Hatch & Port Lights

Hi on my catamaran I used Dow Corning 791 , and lexan , or , as that is just a trade name , Polycarbonate , not acrylic ,It's has uv protection on both sides ,so when cutting the windows to shape I could turn the left overs up side down if that was a better fit for the next shape . And you'll find that Nemo hatches for instance are Polycarbonate .
Acrylic is the one I was advised NOT , to use after 3 years and 12 thousand miles they are like new .
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Old 27-03-2015, 09:16   #6
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Re: Replacing Hatch & Port Lights

Oh yes , you should try and have a silicon layer of 50 mm wide by 5 mm thick , which allows for expansion and contraction , because it will !!!
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Old 27-03-2015, 10:55   #7
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Re: Replacing Hatch & Port Lights

Quote:
Originally Posted by Duchie View Post
Oh yes , you should try and have a silicon layer of 50 mm wide by 5 mm thick , which allows for expansion and contraction , because it will !!!
What a timely thread.

Instead of leaving today, we removed the lens from the forward bowmar offshore hatch. I can't tell if it's original - seems like it's not, as it's only 1/4", and it's acrylic (nice bunch of cracks which have progressed to leakers, and some concern for taking a wave and collapsing in pieces), the factory telling me that they use 3/8 polycarbonate, and there is what appears to be white caulk, instead of the expected black silicone (795, silpruf, others).

I'm aware of expansion/contraction, but I think my math has 50mm = almost 2" and 5mm about 1/5".

My aft slider used 1/8" spacers per suggestion of Tony, the hatch guru, and about 1/4 gutter/bevel outside. And that was 24x30 inches, no support bars, 3/8" (I forget if poly or acrylic; mostly likely acrylic cuz that's what he likes).

Bomar instructions are to lay a bead on all surfaces and float the lens into place. Once in place, make the outer ring sealant, using an old spoon as a shaping tool (relatively wide radius, slightly concave when finished). Neither case has any suggestions involving that much expansion/contraction.

What surface/dimension do these numbers represent? It's a most timely discussion, as we've been delayed yet again with a gamestopper, on the eve (literally) of our departure after more than 2 years of such experiences (gamestopper just as we anchor, or just before we leave).

Thanks.

L8R

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