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I think 1/4 should be plenty thick, 3/8s if you want to play it extra safe. When I lived in the bay are Tap plastics or Salt Lake City or San Diego area. I have never had to buy a whole sheet, they charge me by the square foot, with maybe a $10-15 cut charge.

On my recent plastic needs I screwed it up many times going to close on the size of sheet I wanted and had to go back for a bigger piece to make the two windows I needed. After screwing it up a few times I just had the shop make the piece for me.

Some hints from my lessons learned the hard way. You can cut it out with any saw but faster is better so it does not heat the plastic. If you use an electric jig saw as I have with success in the past but this time i tried to use a fine tooth blade and it melted the plastic as I cut it.

The best way to go is over cut the piece if you can then double side tape the acrylic to the hatch board you are trying to match and use a router bit (in a table preferably) with a straight bit with bearing on top to cut out your board. You could glue some 2 1/4" acrylic strips on the edges to get the thickness you want to fill out the hatch board groove.

I am very much a DIY kind of guy but if you wanted to take your board in and hand it to a guy in the shop, he would make exactly what you want (including the extra strips for thickness) for probably less than $100 and you'd be on the way back to your boat in a half hour with new board in hand.

It was hard lesson to swallow but I realized my time is worth something and the guy that makes plastic things for a living was much better at it than I was.
 

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The hatch lenses I have replaced were 3/8" but they have to withstand being walked on by fat guys.

Mine do anyway. :wink

I just made some plexi drop boards out of a piece of 1/2" I had on hand - that was the best fit in the aluminium track they slide in. Anything thinner would have rattled around unless the edges were framed thicker as described previously.
 

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Do you think 1/4" is strong enough for a dropboard? I sail the Chesapeake Bay so it is extremely unlikely to have a boarding wave but I would still like this to be as strong as the board itself, i.e. 3/4" plywood.
If you are understanding what I am describing, I would say yes. Basically you are creating a double thick Acrylic frame around the outside edge of the Acrylic, not just on the sides, but top and bottom as well. I'd probably make it about 1/2" wide strip all the way around the edge on both sides, making your total 3/4. Plenty of bulk to hold the window section rigid.

It would be best to cut it with a router if you have one. Then you can also chamfer or 1/4 round off the edges, to clean them up and prevent getting cut.

BTY: If you don't like this idea, and choose to go with Teak, I would recommend looking for Brazilian Teak, (technically Cumaru). Its basically the same species, but is much cheaper. The wood is really dense and will dull anything but the most high quality blades pretty quick. I made some grab handles for my previous boat out of the stuff, and it was very hard to cut and sand. The stuff weighed a ton.
 

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Discussion Starter #25
I think 1/4 should be plenty thick, 3/8s if you want to play it extra safe. When I lived in the bay are Tap plastics or Salt Lake City or San Diego area. I have never had to buy a whole sheet, they charge me by the square foot, with maybe a $10-15 cut charge.

On my recent plastic needs I screwed it up many times going to close on the size of sheet I wanted and had to go back for a bigger piece to make the two windows I needed. After screwing it up a few times I just had the shop make the piece for me.

Some hints from my lessons learned the hard way. You can cut it out with any saw but faster is better so it does not heat the plastic. If you use an electric jig saw as I have with success in the past but this time i tried to use a fine tooth blade and it melted the plastic as I cut it.

The best way to go is over cut the piece if you can then double side tape the acrylic to the hatch board you are trying to match and use a router bit (in a table preferably) with a straight bit with bearing on top to cut out your board. You could glue some 2 1/4" acrylic strips on the edges to get the thickness you want to fill out the hatch board groove.

I am very much a DIY kind of guy but if you wanted to take your board in and hand it to a guy in the shop, he would make exactly what you want (including the extra strips for thickness) for probably less than $100 and you'd be on the way back to your boat in a half hour with new board in hand.

It was hard lesson to swallow but I realized my time is worth something and the guy that makes plastic things for a living was much better at it than I was.
Makes perfect sense.

But with the solution I am thinking of now, I won't be cutting any plastics. The board will be constructed AROUND the transparent plastic. So all I will cut is plywood.
 

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Discussion Starter #27
If you are understanding what I am describing, I would say yes. Basically you are creating a double thick Acrylic frame around the outside edge of the Acrylic, not just on the sides, but top and bottom as well. I'd probably make it about 1/2" wide strip all the way around the edge on both sides, making your total 3/4. Plenty of bulk to hold the window section rigid.

It would be best to cut it with a router if you have one. Then you can also chamfer or 1/4 round off the edges, to clean them up and prevent getting cut.

BTY: If you don't like this idea, and choose to go with Teak, I would recommend looking for Brazilian Teak, (technically Cumaru). Its basically the same species, but is much cheaper. The wood is really dense and will dull anything but the most high quality blades pretty quick. I made some grab handles for my previous boat out of the stuff, and it was very hard to cut and sand. The stuff weighed a ton.
Yes, I understand what you are saying. But I think I will go with something simpler, just a piece of 3/4" plywood shaped to fit the companionway, with a transparent plexiglass window where the chartplotter is. Simple, cheap, sturdy.
 

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"What would be considered to have strength comparable to 3/4" plywood "
I'd look up the strength of 3/4" solid core marine plywood online, and then check the the specific type of acrylic you are using, to match it. Bear in mind that a highly UV-resistant scratch-resistant acrylic may be 5x weaker or stronger than a "generic" grade. Both polycarbonates and acrylics vary widely in impact resistance--which is presumably the "strength" you are looking for.

Also, you should be able to find some mounting instructions online. The plastic MUST be abel to move as it expands and contracts, or there will be damage to the frame, leaking, and crazing. But you don't want the plastic to slip around. So two ways to mount it are by placing tubing (i.e. surgical silicone tubing) all around the plastic, in the channel of the frame, to act as a very compressible gasket. Or, by screwing the plastic down, with the screws going through oversized slots and using large washers, not simply making holes for the screws. Either way requires extra time and work--but every manufacturer will tell you this is not optional if you want long-term performance.
Personally I'd go with the surgical tubing, out of sight in the channel of the frame. Silicone, not rubber, for long-term performance.
 

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Discussion Starter #29
"What would be considered to have strength comparable to 3/4" plywood "
I'd look up the strength of 3/4" solid core marine plywood online, and then check the the specific type of acrylic you are using, to match it. Bear in mind that a highly UV-resistant scratch-resistant acrylic may be 5x weaker or stronger than a "generic" grade. Both polycarbonates and acrylics vary widely in impact resistance--which is presumably the "strength" you are looking for.

Also, you should be able to find some mounting instructions online. The plastic MUST be abel to move as it expands and contracts, or there will be damage to the frame, leaking, and crazing. But you don't want the plastic to slip around. So two ways to mount it are by placing tubing (i.e. surgical silicone tubing) all around the plastic, in the channel of the frame, to act as a very compressible gasket. Or, by screwing the plastic down, with the screws going through oversized slots and using large washers, not simply making holes for the screws. Either way requires extra time and work--but every manufacturer will tell you this is not optional if you want long-term performance.
Personally I'd go with the surgical tubing, out of sight in the channel of the frame. Silicone, not rubber, for long-term performance.
Very timely posting! I actually started thinking about how to mount the plexiglass window. I had considered embedding it in epoxy (and of course with a wooden frame overlaid for strength), thinking that this might provide enough flexibility. But the surgical tubing is a much better solution.

Thank you!
 

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Easiest way is to set it in goo like Dow 795 and screw it through slightly oversize holes - 1 drill size larger than the shank is usually plenty. It doesn't grow & shrink enough to require all the effort of slots.

Actually the Dow 795 is plenty adhesive enough to stick it down and seal it both - it's used for glazing curtain walls in highrises so it should have no problem with a scrap of plexi.

Most hatch lenses are held into their frames this way.
 

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Makes perfect sense.

But with the solution I am thinking of now, I won't be cutting any plastics. The board will be constructed AROUND the transparent plastic. So all I will cut is plywood.
By the time you cut the plywood, buy the acrylic, buy the parts and glue to mount a frame to fit the acrylic. You still might be easier having the plastic shop make you a board. I'd do a 3/8" acrylic sheet and double up the edges where it fits into the hatches groove to make 3/4" thick in that part.

If you want to save money use a router with a pattening bit to trace your current hatch board to make it yourself.
 

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Here is a pic of the plexi drop boards I made recently. Dead simple to make, especially if you have an existing one to use as a router template (I didn't). Just stick the old one to the plexi with double sided tape and trim the plexi with a bearing guided flush trim bit in a router.

After they are cut, sand the edges to 240 or so and then play a propane torch over the edges to make them nice & smooth & shiny.
 

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Epoxy, fwiw, as a rule does not bond to acrylics and WILL let go at the least opportune time. Some special epoxies are supposed to be compounded to bond to them--but unless the package guarantees that it will, expect that it won't for very long.
 

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I have my chart plotter mounted on a swivel arm inside the cabin so I can see it both inside and out. Except, when the dropboards (teak) are in, I am flying blind. So I had the idea of replacing one of the boards with plexiglass.
This is slightly off topic, but I also installed a chart plotter at the nav station. The chart plotter is set up to use WiFi to display on an iPad that is in the cockpit. I can control the chart plotter remotely using an app on the cell phone. Works really well. No need to see the chart plotter on the nav station while in the cockpit.
 
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