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Thread: plexiglass hatch

  1. #1
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    Default plexiglass hatch

    I made a new hatch. Forward hatch 20'' x 20'' . It's wood and flat on top . Iroko. I'm going to put 1/4 plexi on top with screws and finish washers. I'm debating to use either 3m silicone between the glass and wood or Butyl tape. Either one I'll have to clean up the squeeze out. I haven't used the Butyl tape before and can't decide if I want to give it a try. Any thoughts?
    David Satter www.sattersrestoration.com
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten" Ben Franklin

  2. #2
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    Default Re: plexiglass hatch

    IMO if you use silicone, paint or varnish will never hold no matter how well you clean it.
    “Eventually, all things merge into one, and a river runs through it. The river was cut by the world's great flood and runs over rocks from the basement of time. On some of those rocks are timeless raindrops. Under the rocks are the words, and some of the words are theirs."

  3. #3
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    Default Re: plexiglass hatch

    Butyl
    overbore the holes in the plexi
    oh, don’t use plexi use polycarbonate

  4. #4
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    Default Re: plexiglass hatch

    I think i will try the Butyl. Hatch already has cetol on it. I used lexan on my other boat $$$ , it scratched easy and this is just my little 19 foot daysailer. Yes I'll have to drill and overbore carefully.
    David Satter www.sattersrestoration.com
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten" Ben Franklin

  5. #5
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    Default Re: plexiglass hatch

    Are you sure Butyl won't cause crazing, Wiz? Silicone won't.

  6. #6
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    Default Re: plexiglass hatch

    I've used butyl under plexi with no problems. 10 years thus far (I've long since sold the boat, but I know the current owner who reports no leaks or crazing). Chamfer the holes in the plexi and tighten the screws gradually slowly working your way around the perimeter...bit like tightening head bolts on an aluminum head. I tried grinding a bit flat for drilling the plexi as I'd seen suggested...couldn't tell much difference except for the increased tendency for the bit to wander. I did start with a .06 hole and drill out from there to avoid chipping.

  7. #7
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    Default Re: plexiglass hatch

    Thanks Hugh ,
    David Satter www.sattersrestoration.com
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten" Ben Franklin

  8. #8
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    Default Re: plexiglass hatch

    If you are using and machining (cutting, drilling, sanding, etc.) acrylic sheet material (Plexiglas) then you would be wise to learn how to anneal it. Working this stuff tends to build up stress in it, and these forces are just waiting for an opportunity to spoil your work. The trigger might be flexing it, maybe tightening a screw just a hair too much or even contact with chemicals or solvents in paints, glues, cleaners, etc. The solvent one is pretty crazy as sometimes it can almost instantly make lots of tiny cracks along what was previously a perfectly smooth cut and worked edge. Screw holes are especially vulnerable as spots for cracks to begin.

    The annealing is done after you have finished all cutting, drilling, edge-sanding, etc. and is pretty simple, but it will make your piece of plexi much more durable and less prone to failure. You stick it in the oven at about 200 degrees F for half an hour to 45 minutes then turn off the oven. Leave the door closed and let it slowly cool back down to room temperature. It will not make your plexi unbreakable by any means, but it will be far less prone to cracking at those worked areas than it was when you finished your machine work on it.

    They make special drill bits that are shaped to drill acrylic and not shatter it just as the drill gets through it (which can happen). I don't have them, so I pre-bore all screw holes using the Dremel and a small cone-shaped grinding bit. Once you have bored a small pilot hole through the sheet, the normal drill bit is far less likely to cause a problem.

    Annealing guitar pick guards after cutting, drilling and beveling and polishing the edges.

    pgd.jpg

    Color added to the back side after annealing. Without doing it, the solvents in the paint will attack the edges.

    jg 002.jpg

    another one

    33012-002a.jpg

  9. #9
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    Default Re: plexiglass hatch

    Good idea Todd, that's pretty cool.
    David Satter www.sattersrestoration.com
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten" Ben Franklin

  10. #10
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    Default Re: plexiglass hatch

    Quote Originally Posted by David Satter View Post
    Good idea Todd, that's pretty cool.
    Probably less likely to get you in trouble than using the oven for heating a cylinder head for valve guide installation too.

    I didn't know about the annealing - so thanks Todd!
    "If it ain't broke, you're not trying." - Red Green

  11. #11
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    Default Re: plexiglass hatch

    I agree with wiz about butyl being the bedding of choice.I do have reservations about 1/4" thick being up to the job if an adult should stand on the hatch,it could get painful and messy.

  12. #12
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    Default Re: plexiglass hatch

    Dry fit. She's just going on the front of a 1966 O'day Mariner I'm fixing up. She's glass but a classic. I'm giving her lots of wood touches and trim. I could put a couple of stainless rods on the underside for support or strength, might look cool too. IMG_4871.jpgIMG_4473.jpg
    David Satter www.sattersrestoration.com
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten" Ben Franklin

  13. #13
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    Default Re: plexiglass hatch

    You could lay a piece of newspaper on it while its on the bench and see if it feels flexible in static conditions.That might indicate whether a bit more support would help.There would be the risk of needing to source another piece of acrylic though and it is reputed to be in short supply.

  14. #14
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    Default Re: plexiglass hatch

    One might drop in a wood deck beam rather than stainless rods .
    I think that size plexi on that size hatch might be a push .
    or, it may be fine . The stuff expands and shrinks a bit . I put 6 ish inch holes in hatch covers and cover the hole with the plexi with more overlap generally. Not the whole hatch cover

  15. #15
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    Default Re: plexiglass hatch

    + 1 for a bit of reinforcement.

    I know it's unlikely that the boat will cross oceans, but a good, solid, reliable forehatch is a useful thing to have when you most need it, whether to stand/fall on, or simply to keep the water out.

    The chances are that at some point someone will either step on it or sit on it and 1/4" plexiglass, epecially after a year or two in the sunshine soaking in the UV, may lack sufficient strength.

    I have a fixed skylight on my boat that's about 5"x 10". It was replaced last season with 6mm polycarbonate having previously been 8mm (we had a bit of 6mm knocking about so used what we had). It's OK if step on it but it does flex more than I'd like, albeit I do weigh a somewhat elephantine 220 lbs.

    If I may make a separate suggestion before you finally bed it down: paint the underside of the plexiglass around the edge so you have a dark border and won't therefore see the sealant. Same sort of thing as with a car windshield if that explains it better...

  16. #16
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    Default Re: plexiglass hatch

    I've always been a bit suspicious of brand names over replica materials, but in forty years of working with what was once called Perspex, (ICI) Plexiglas (Dow Corning ) in the States, but is still available by name , versus any number of anonymous polycarbonate sheet, from Home Mart, BnQ , Leroy Merlin there is no doubt the imitators are crep. they craze , they shatter , they break out when cutting or drilling, whether by scoring with a straight edge like cutting glass, or using a bench saw or even a hand saw, Plexiglas and Perspex behave well, but you pay for the quality. Fine with me. You could dance on a 6mm Plexi skylight at your dimensions, but the cheaper poly stuff is junk. Also perspex is, and maybe Plexi is, UV resistant. I use it to glaze picture frames where the item is UV sensitive . I had a pair of windscreens on the runabout in 5mm poly, they turned milky and were scored by seaspray, ...replaced them with Perspex, and five years on they are still like glass.

  17. #17
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    Default Re: plexiglass hatch

    If you end up doing it again, I’d make a few suggestions:
    It would ruin your whole day if the plastic failed. I think that 1/4” acrylic will be too light. I’d use polycarbonate rather than acrylic and up the thickness to at least 3/8”.
    These plastics are thermally active and expand and contract with temperature to a surprising degree. Drill fastener holes oversize and use pan head fasteners.
    These materials are slippery especially when wet. There are translucent nonskid tapes that work. They’re also useful over varnish.

  18. #18
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    Default Re: plexiglass hatch

    Thanks guys, for now I think I'll put a support under and see how it goes. I made the large butterfly hatch on my last boat but it had the stainless bars across the top and opened like a regular hatch.100_1033.jpg I do love finally having a boat on a trailer . when things need repairing I can pull it into my shop. I couldn't do that with my old boat.
    David Satter www.sattersrestoration.com
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten" Ben Franklin

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