acrylic window thickness

[Ralph Johnstone]

2x4s, diving weights, ropes, widgets, and Rube Goldberg contraptions. So yes, I can believe the instructions.

I still maintain the easiest way to hold the glass in place until the DC 795 sets is with screws for a month or two, remove the screws and finally fill the holes with 795. That is (was) the factory installation for my fixed ports. Invisible unless you press your nose to the glass.

 

[rgranger]

I still maintain the easiest way to hold the glass in place until the DC 795 sets is with screws for a month or two, remove the screws and finally fill the holes with 795. That is (was) the factory installation for my fixed ports. Invisible unless you press your nose to the glass.

View attachment 175217

Seems legit... curious! Why not counter sink the screws and leave them in?

 

[DArcy]

Why not counter sink the screws and leave them in?

Countersinking screws into plastic adds stress which leads to cracking. A pan head or cap screw compresses the plastic but countersinking adds hoop stresses which can be quite high. Don't countersink screws in plastic for a structural part.
Also, countersinking positively locates the window with respect to the frame which means any lateral position out of tolerance will also add stress. Any thermal mismatch will also add stress. Pan head screws can allow relative movement between the window and the frame if not torqued down completely.

 

[Charlie Jones s/v Tehani]

Seems legit... curious! Why not counter sink the screws and leave them in?

Bad idea. Metal expands and contracts at a different rate than the plastic (acrylic or lexan) he counter sinks act as wedges and can break around the outside edge. Best idea is to slightly over size the hole ..

 

[Ralph Johnstone]

A pan head or cap screw compresses the plastic but countersinking adds hoop stresses

Exactly. I also think Hunter Marine (way back when) figured it looked better with no screws, which it definitely does.

However, the large front fixed hatchlight does retain the screws which are painted black. This was done to assist the glass in maintaining its slight curvature. The screw holes are considerably oversized:

Screws 1, Rube Goldberg contraptions 0 .

 

[Tim22]

My understanding is that the VHB tape holds the port lite in place and provides the bond. The DC795 adds strength to the bond and provides the waterproof seal. Because the VHB provides the bond, and it reaches max strength in 24 hours, there doesn’t seem to be any requirement for screws. I used glass suction cups attached to the interior of the port light to provide pressure for the first 24 hour. The suction cups were tied off to the boat interior using ratchet straps to get good tension.

Tim

 

[Ralph Johnstone]

My understanding is that the VHB tape holds the port lite in place and provides the bond.

Correction:

VHB tape 2, screws 1, Rube Goldberg contraptions 0.

 

[Will Gilmore]

You could try this:

It looks like it might work to clamp a window, doesn't it?

-Will (Dragonfly)

 

[Ralph Johnstone]

It IS the Rube Goldberg contraption referred to in the Catalina instructions, so I don't see why it wouldn't work.

And the corn liquor coming off the bottom spout would be an added bonus .

 

[CYQK]

3/8 is MORE expensive but make sure your sealant is plenty thick to allow for movement
thinner ones cracked on me from heat/cold movement after installing 3/8 no more cracking

 

[CarlN]

Use cast acrylic (plexiglass). Lexan is stronger but plexi is more than strong enough and will look better years longer. UV and scratches make lexan cloudy after a few years. These people do this as a business: Tony's Blog - HatchMasters

Use Dow 795 as the sealant. It’s used to hold windows into skyscrapers. But there’s one trick - leave a 1/8”-1/4” thick beed of the caulk between the metal or fiberglass frame and the plexi. Don’t squeeze it all out. The metal/fiberglass and plexi expand at different rates when they heat and cool. If the caulk is too thin it will eventually tear lose. Big pieces of plexi expand more so need the 1/4” thicker beed.

For small ports 3/16” or 1/4” is fine, For large windows go to 3/8” or even 1/2”. Be sure to get “cast” acrylic.

 

[Robert H. Wood]

I just finished replacing my portlights according to Don Casey’s instructions in Sail magazine. They came out beautifully. Using the 1/4 “ plexiglass was a goof call because they were able flex to match the curve of the boat. Using 3M double sided tape held them in place adequately, while I applied Dow Corning 795 caulking. You do need to masking tape the hull around the window to prevent sealant from going everywhere. Once caulked, I pulled the tape and the protective paper and they just shined! Follow Don Casey and you can’t go wrong.

 

[Dave Groshong]

they will be screwed in place, how do you allow some flex?

If you use Dow 795, screws are not required, screws usually cause cracks or leaks, sooner or later.

 

[fred1diver]

So how do you go about installing them without screws?

 

[SG]

So how do you go about installing them without screws?
My responses
1. Butyl tape --
2. Use the same thickness acrylic that you have currently.
3. I believe your Grampian has framed windows with trim pieces that cover.the window edges -- you don't have a frameless system. Install it the way it went in in the first place. (It's been in there for over two generations...)
4. Be very careful drilling any holes in acrylic -- or you'll get cracking. You have to use a special bit , over drill the holes, etc. Do the screws go through the acrylic now -- or are the holes outside the windows?
5. If the trim pieces have sealant on them (in addition to the butyl tape) then use a LITTLE sealant. (NOT permanent 5200 -- something that can be released later, if needs to be.)

 

[Allan12210]

So how do you go about installing them without screws?

Here is a link to how I replaced my windows, making them frameless.

Hunter 34 Owner Modifications and Upgrades

Hunter 34 Owner Modifications and Upgrades

hunter.sailboatowners.com

I fabricated some clips to hold the window in place until the Dow 795 cured. When I did the other side a couple of years later, I skipped the clip step because the butyl I used was so sticky there was no movement of the acrylic while the Silicone cured. It was even so sticky that the window maintained its curvature to the cabintop. Later I removed the clips and filled the holes.

 

[fred1diver]

So how do you go about installing them without screws?
My responses
1. Butyl tape --
2. Use the same thickness acrylic that you have currently.
3. I believe your Grampian has framed windows with trim pieces that cover.the window edges -- you don't have a frameless system. Install it the way it went in in the first place. (It's been in there for over two generations...)
4. Be very careful drilling any holes in acrylic -- or you'll get cracking. You have to use a special bit , over drill the holes, etc. Do the screws go through the acrylic now -- or are the holes outside the windows?
5. If the trim pieces have sealant on them (in addition to the butyl tape) then use a LITTLE sealant. (NOT permanent 5200 -- something that can be released later, if needs to be.)

The windows are frameless but do have a trim on the outside
they are held in place with screws
so if I understand correctly, I use butyl tape to seal and then screw them back in then use a little sealant to seal the edges
what kind of drill bit do I need?

 

[SG]

The windows are frameless but do have a trim on the outside
they are held in place with screws
so if I understand correctly, I use butyl tape to seal and then screw them back in then use a little sealant to seal the edges
what kind of drill bit do I need?

https://www.hunker.com/12536277/what-kind-of-drill-bit-do-you-need-for-plexiglass

Drill the hole larger than the screw. You want to allow for expansion and contraction -- you don't want to concentrate stresses on the hole.