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Old 23-11-2009, 13:37   #1
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What Hatch Material?

We are replacing the inadequate 1/4" plexiglas in our forward hatch and salon hatch, preparing for some blue-water cruising. What would be the best material for this application? The material will be set in a wood frame using the proper sealant of course.
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Old 23-11-2009, 13:55   #2
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Putting my foot in it...

My worry about the (old) glazing in in my hatches is the danger that if I step on them with my feather weight foot it might go through, an event that would likely be unpleasant, messy and have long term consequences.

6.5mm does seem a little thin for a hatch, depending on the size.

Have you considered putting protective/reinforcing strips either under or over the glazing?
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Old 23-11-2009, 14:03   #3
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use 1/2" cast acrylic, several brands are available and you can get it from any quality hatch manufacturer. They would be able to cut it out for you easily. keep in mind its at least 3x the price of extruded product.
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Old 23-11-2009, 21:15   #4
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We used these. They've worked very well.

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Old 24-11-2009, 09:19   #5
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Our primary concern is taking a wave that would punch-out the hatch. I've already removed the old plexiglas and am shopping for new, thicker material. We've used Manship hatches here at the yard, unfortunately our own boat has a hatch combing integral with the fiberglass deck, raised 4". I'll check on the cast acrylic.
Some people have suggested tempered glass over "plastics", saying heat expansion can cause cracking in the plexiglas and lexan type materials.
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Old 24-11-2009, 09:35   #6
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We're splitting the difference in our portlights, using 2 pcs of cast acrylic; 1 tinted (inner layer) and 1 non-tinted (outer) layer for "sacrificial" purposes (crazing, UV, etc.). Got the idea from an earlier thread here.
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Old 24-11-2009, 10:55   #7
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Boat manufacturers normally use Lexan for horizontal hatches. It is much stronger than plexiglass and resistant to breakage. Thickness has lot to do with the size of the piece. About 3/8" is nominal with thicker pieces if the hatch gets rather large.
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Old 24-11-2009, 13:18   #8
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Quote:
Originally Posted by Benjamaphone View Post
use 1/2" cast acrylic, several brands are available and you can get it from any quality hatch manufacturer. They would be able to cut it out for you easily. keep in mind its at least 3x the price of extruded product.
This man knows of what he is speaking. UNLESS the hatch is covered ALL OF THE TIME, don't use Lexan. It is softer than cast acrylic, and it is WAY less UV resistant. Left in the sun, it may quickly become weaker than acrylic.
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Old 01-12-2009, 13:22   #9
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Thanks all! I found a supplier for cast acrylic online (Delvies Plastics). $38.00 for a 2' x 2' piece of 1/2". The 3/4" stuff is $68.00. Not bad really.
Bob
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Old 01-12-2009, 13:30   #10
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Quote:
Originally Posted by osirissail View Post
Boat manufacturers normally use Lexan for horizontal hatches. It is much stronger than plexiglass and resistant to breakage. Thickness has lot to do with the size of the piece. About 3/8" is nominal with thicker pieces if the hatch gets rather large.
Actually most manufacturers such as Adkins & Hoyle, Lewmar, Goiot, Manship and others use cast acrylic just as Benjamaphone suggested.

BTW Banjamaphone is from Adkins & Hoyle, the hatch manufacturer, and knows exactly what he is talking about..

Why do I care? Because a good friend was given bad advice about Lexan as hatch material on a boating forum, which will remain name less.

The long and short is he installed it and the first time someone stepped on it during a race they totally broke the seal because it flexed so much. He had replaced the same thickness cast acrylic with the same thickness Lexan and it just would not work because it flexed to much.

After this disaster he went back to cast acrylic and never had a failure of the seal again. Of course his v-berth cushions will never be the same as he only noticed the broken seal after a week of rain..
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Old 03-12-2009, 07:05   #11
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Quote:
Originally Posted by Benjamaphone View Post
use 1/2" cast acrylic, several brands are available and you can get it from any quality hatch manufacturer. They would be able to cut it out for you easily. keep in mind its at least 3x the price of extruded product.

Ordered some hatch gaskets from you last night. In our phone conversation you said you used silicone to bed your cast acrylic to the hatch. Is that truly the best way to bed these? Since I had one fail, I am not to keen on using silicone again. Seems that it just doesn 't have the adhesive properties that this hatch requires. Maybe when applied new, or when the hatch is completly reconditioned... but I can't afford that now.

So what about 2 part products from 3m like Scotch weld ? Although more expensive than silicone, It looks like it would do a much better job when the prep is not as good...

3M Scotch-Weld Low Odor Acrylic Adhesive DP810NS

McMaster-Carr

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Old 03-12-2009, 16:26   #12
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If you hatch frame is metal then try Sika 295UV with Sika 209 Primer and Sika 226 Cleaner. I have used this adhesive to bed my plexiglass window into an aluminum frame. The seal lasted for 10 years before UV finally degraded the plexiglass and the adhesive. It is basically the same stuff that is used to hold automobile windshields in place.
- - You must use fine sandpaper to abrade the surface of the plexiglass that is going to be buried in the adhesive. Then the Sika226 Cleaner to remove all dirt and oil from the plexiglass and frame. Then use the Sika 209 Primer on the cleaned edge/surfaces that are to be bonded. You must be very careful to not get any of the processes on the plexiglass portion that will be the "window". I used boat painting quality masking tape to protect the plexiglass.
Then use the Sika 295UV - a black thick stuff that you place a bead in the frame then lay in the plexiglass and I overlaid the adhesive onto the edge of the plexiglass which was recessed into the frame about 3/16 inch. The adhesive forms a rubber like bed gasket that captures both the underside and topside of the plexiglass. I used a glazing trowel to smooth the adhesive beveling it from top of the plexiglass to the top of the frame.
- - If your hatch is wood, this adhesive might also work but you would need to be absolutely sure the wood was clean, dry and all oils were removed from the portion where the adhesive and plexiglass are to be mated.
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Old 03-12-2009, 21:06   #13
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Here is a link to a company that repairs Lewmar Hatches about sealants:
Which Sealants To Use
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Old 06-12-2009, 09:38   #14
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Quote:
Originally Posted by bobfnbw View Post
In our phone conversation you said you used silicone to bed your cast acrylic to the hatch. Is that truly the best way to bed these? Since I had one fail, I am not to keen on using silicone again. Seems that it just doesn 't have the adhesive properties that this hatch requires.
Might Benjamaphone have been talking about this?

http://www.meiglobalsolutions.com/im...corning795.pdf

Dow 795 is not your father's silicone and is used to keep windows in skyscapers.

Mike
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Old 06-12-2009, 10:16   #15
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No actualy it was GE1200 with a primer. Not sure if it was benjamaphone I talked to or alex maybe...

anyway Osirssail thanks for the info on the sikaflex. That is what I ordered with the primer and cleaner. Expensive stuff, but if it works, thats OK by me.

Couple of other thoughts.

Why is the cast acrylic from hatch manufactors so darn expensive. Online you can get a 4x8 sheet of 1/2 inch cast acrylic for what they want for a 2x2 sheet.
Same goes for the gaskets.. ouch.. very pricy for a small strip of neoprene rubber...
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