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Old 30-03-2009, 16:36   #16
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In all of our hatches and hatch repairs we use exclusively cast acrylic. Through our experience building hatches for awhile, we've found this to be the best material on the market. Stronger, easier to work with, more craze resistant. Apparently the extruded polycarbonates secrete an oily residue over time that interferes with seal.

I can also attest to cast acrylic hatches that have been in use for over 30 years. Many times I've repaired hatches that we built in the 1960s that haven't seen service since DOM.
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Old 30-03-2009, 17:50   #17
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In all of our hatches and hatch repairs we use exclusively cast acrylic. Through our experience building hatches for awhile, we've found this to be the best material on the market. Stronger, easier to work with, more craze resistant. Apparently the extruded polycarbonates secrete an oily residue over time that interferes with seal.

I can also attest to cast acrylic hatches that have been in use for over 30 years. Many times I've repaired hatches that we built in the 1960s that haven't seen service since DOM.

Guys this is straight from one of highest quality builders of hatches in the industry, Atkins & Hoyle!
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Old 30-03-2009, 19:30   #18
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"What this means is if you replace your hatch lens with polycarb, seal it and then step on it the ductile material will deflect (bow) in the center. One of two things may happen. 1st you will surely break the watertight seal, 2nd you may end up with a leg in your galley."

Then after you and your broken leg pick yourself up, I will shoot you for stepping on my hatch.

All this is great reading. But then I look up and my hatches are still
crazed.

I'm reading cast acrylic this and cast acrylic that. Are my Lewmars made out of plate acrylic or something? I'm happy to learn that I too can have 30 year hatches if I just replace what I have with CAST ACRYLIC.

"In the meantime, roof panels and solar panels made of Makrolon are being proven to be duarable. I can imagine that thicker materials may be prone to crazing than thinner materials. Makrolon is outlasting other plastics in the sun like crazy. I have no idea what the difference is between one polychickenfat and another. All I know is my hatches are crazed and so are many others", he said as he batteled his cantakerous frustrated inner self for control of the keyboard.
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Old 30-03-2009, 19:42   #19
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Minggat,

It's real simple. When I took my Lewmar portlight into the plastics guy for new material, he took one look at it and said "the crazing and cracks are from cleaning products". That simple. I replaced all 12 of them with Acrylic. I'm planning on doing 6 hatches, and about a dozen windows the same way.
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Old 30-03-2009, 19:54   #20
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I wish it were that simple. No Windex, no natha. My bare hand and flowing water to keep grit from scratching is all that has ever cleaned my hatches. So back to the question. Cast acrylic or what?

Remember, it's only the sun facing hatches that are crazed. So unless sombody is sneaking uo and cleaning my cabin roof hatches with Windex aqnd running off without cleaning the others, I'm stil frustrated.
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Old 30-03-2009, 20:10   #21
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So back to the question. Cast acrylic or what?
Cast acrylic is, in my opinion, the ONLY way to go. Lexan is stronger, at first. But, it degrades with UV exposure AND it scratches easily.
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Old 30-03-2009, 20:16   #22
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Cast acrylic as opposed to _________ acrylic. Please fill in the blank so I can know before my head explodes. Did your Lewmars start out as CAST acrylic or were they originally the mystery acrylic
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Old 30-03-2009, 21:37   #23
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Cast acrylic as opposed to _________ acrylic. Please fill in the blank so I can know before my head explodes. Did your Lewmars start out as CAST acrylic or were they originally the mystery acrylic
"EXTRUDED".

Extruded acrylic does not machine/cut as well, it tends to shrink more, and it reacts less-well to chemicals.
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Old 30-03-2009, 22:52   #24
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Cast acrylic/Lexan/Makrolon

Thanks for that. That might explain quite a bit. All of my hatches and portlights were new in the box, discontinued closeouts, bought at a big discount at a yacht surplus. Suspect.

After all of this, I am the only one with anything to say about Makrolon. I keep hearing that cast acrylic is the only way to go because lexan is not. Fine. But what's that got to do with Makrolon? OK, Makrolon is polycarbonate, but it's being used it in some pretty punishing applications.

I can't say enough about how great it is in my dodger windows. At this point, it's a different purpose material. But we go to the boat shows to check ou the latest & greatest. Why dismiss something without investigation here? It may work out to be simply inappropriate for hatches, but it's not looking like that from what I can gather.

I am in no position to do anything about my crazed hatches here in Mexico. When I am ready, it's good to know that cast acrylic is good for 30 years. By then, maybe acrylic will have been made obsolete by Makrolon and I'll be whining because I can't get cast acrylic.
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Old 31-03-2009, 00:19   #25
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Makrolon / Polycarbonate

Minggat

You are correct Makrolon is a great product. It is sold here in the states by Bayer / Sheffield. It was originally maketed as a twinwall and monolithic polycarbonate sheet sold in Europe by ROHM GMBH, the original plexiglas company in Darmstat Germany. I know as I worked for the US subsidiary, CYRO for 13 years.

While Makrolon has its fit and is useful in the construction and re-fit of blue water vessels it is no way shape or form the prefered material of any builder.

Makrolon, Lexan or the genaric Polycarbonate just dont stand up in the marine environment. The Largest Hatch manufactures in the world will not use it. It is not approved by CE or ABYC in hatch applications. Companies like Select Plastics and Atkins and HOYLE rebuild lots of hatches they will not use it either.

Sealing Lexan while possible presents unique challenges due to its ductility. Polycarbonate has significantly different surface properties and moisture absorbsion characteristics which make the bond strength of the adhesive difficult to maintain.

Lewmar, Goiot, Moonlite, Gebo, Hood, Man Ship, and Bomar offshore all use cast acrylic not because its cheap but because its the correct, tested and approved product for the application.

Back to the question: How do I seal a lexan Hatch? CAREFULLY AND WITH DOW 795.

Make sumbrella covers for your Lexan / Polycarbonate / Makrolon ports and dont use windex and you will be OK... Dont sweat the small stuff.

On your next boat use cast acrylic.


sage advice from an old salt....


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Old 31-03-2009, 07:51   #26
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Quote:
Originally Posted by bstreep View Post
"EXTRUDED".

Extruded acrylic does not machine/cut as well, it tends to shrink more, and it reacts less-well to chemicals.
That's all true. We've found that seal does not last nearly as long either. My father says its because the extruded products eventually breakdown and an oily residue forms between the lens and the sealant.

One of the easiest ways to tell if your getting cast or extruded acrylic (sometimes its not always clear) is price. Through our experience, cast acrylic is about 2-4x the price of the inferior stuff. It really does make a big difference though. No clouding, much cleaner looking because of scratch resistance, and most importantly the seal is much better.

Always we use cast acrylic, whether its a new hatch or a repair, otherwise our warranties wouldn't hold up.
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Old 31-03-2009, 08:35   #27
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cheap hatches

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That's all true. We've found that seal does not last nearly as long either. My father says its because the extruded products eventually breakdown and an oily residue forms between the lens and the sealant.

One of the easiest ways to tell if your getting cast or extruded acrylic (sometimes its not always clear) is price. Through our experience, cast acrylic is about 2-4x the price of the inferior stuff. It really does make a big difference though. No clouding, much cleaner looking because of scratch resistance, and most importantly the seal is much better.

Always we use cast acrylic, whether its a new hatch or a repair, otherwise our warranties wouldn't hold up.
This is the one most convincing point of why my sun facing, closeout sale hatches are not my friends. Now I'm wondering if I should get these repaired or if the same size is available in CAST acrylic. That would make it more doable here in Mexico.

One thing I do which really helps cool the boat down is to use a "space blanket" coverings for the big hatch. For less than a dollar each I bought 3 of these blankets. I cut one up and tape it to the forward hatch so I can open it to let air thru. To my surprise, it is not opaque. I can see thru it and still reflect most of the heat. So my next question is, would reflective window tinting be a negative for the cast acrylic? I would think it would only help protect it.

It makes such a huge difference to the inside cabin temp that I can imagine what I will do when the space blanket police come and take it away from me.
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Old 31-03-2009, 08:57   #28
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I have to second the use of 3m VHB tape. We use it at work for bonding aluminum panels to aluminum structure and it is an incredibly strong bond. One strip of tape between two pieces of 2"x2" square tubing and you CANNOT separate the two. One of our suppliers has been using it for over 20 years without a failure. It's what I plan to use when I build my own boat soon.
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Old 31-03-2009, 11:29   #29
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I did this research years ago and found that GE "Sil-Pruf" is one of the only recommended sealants for Lexan (Polycarbonate). The Polycarb/Acrylic debate has come up before. Polycarbonate is much tougher and I like to use it but I'm sure all the self made scientist will come out of the wood work on that statement.
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Old 31-03-2009, 13:20   #30
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Wow..

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The Polycarb/Acrylic debate has come up before. Polycarbonate is much tougher and I like to use it but I'm sure all the self made scientist will come out of the wood work on that statement.

Did you even read the thread? We have one manufacturer of hatches and a guy who worked for Cyro for 13 years and who owns the worlds largest hatch repair facility giving advice here. These are not back yard scientists these are experienced folks with years and years in the industry.

The backyard scientist is the one who will use polycarb because he incorrectly thinks it is right product for the wrong application.

I'm guessing your science background trumps the experience of port and hatch makers/manufacturers, who actually have to warranty this stuff, and folks who have worked or been in the industry for many, many years and who have recommended the proper sealants and the proper product. I don't think I'd call Adkins & Hoyle or Tony D'andria of Select Plastics a "backyard scientist".

Go for it, use Lexan.
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