Value of thicker Plexiglas in fixed lights?

[Lou-In-NJ]

I'm going to be replacing the 42 year old Plexiglas fixed lights on my S2. I drilled a hole in the one that was cracked and determined that the acrylic is 3/16" thick. They are larger than most other boat designs of that era, but not as large as some cruising boats I've seen from the 60's and '70s, which I presume also used acrylic. The largest is approximately 11"x 32" but is supported by what appears to be at least a 1" lip, all-around. The lights are actually rebated slightly from the surface of the fiberglass meaning I could probably go 1/16" thicker without them sitting proud of the fiberglass; the question is, should I bother to change the thickness of these to 1/4", which would likely make them perfectly flush with the fiberglass, but may add a bit of difficulty in having the thicker acrylic conform to the very slight longitudinal curve of the opening? Any other benefit or issue I should consider?

[tkeithlu]

The advantage will be slightly greater strength. The time to crazing and becoming opaque will be the same. The curvature can be taken care of by gently heating the acrylic while applying pressure to conform to the frame. You'll have to judge the inconvenience.

Good luck with it. I think you'll be very pleased at being able to see out again.

[Sailing Cyclops]

There are plastic fabrication shops in pretty much every city, and that's where you'll find both the cheapest and fastest way to obtain replacements versus trying to find an OEM part (which would be unlikely at your boat's age). Expect to pay somewhere around $20 to $40 per lens, depending where you are.

I've had replacement hatch lenses made while I waited (about 15 minutes), after bringing in the original item to be copied. It's good that you'll be able to fit a thickness that's a little larger than your existing lenses, because it'll give you some flexibility in having a replacement made from what materials are now available. As long as the new piece isn't any thinner than your existing one, then don't worry.

If the pieces are curved, you're going to want to use a heat gun to soften the acrylic and bend it to the desired shape before mounting it. If you apply too much bending stress while fastening it, you'll increase the chances of it cracking in the future.

[Lou-In-NJ]

Thanks for the advice & comments tkeithlu & Sailing Cyclops! The acrylic in these lights have held up amazingly well; I've seen much more hazy and crazed lights on boats that aren't as old, but nonetheless, it's time to replace them.

[Moontide]

Might want to consider polycarbonate (Lexan) instead of plex. Much stronger and sometimes not that much more expensive. Would guess that 3/16" lexan is stronger than 1/4 plex.

[Lou-In-NJ]

Yes, I thought about Lexan, but everything I read says it's less scratch resistant. I don't know if it would get marred a lot faster or not given the environment. I would welcome comments from anybody with practical experience with that material.

[Sailorman Ed]

Stiffness is the cube of thickness.
Try to get "cast acrylic" as it is more impact resistant.
I would not use polycarbonate (lexan) because it is much more likely to scratch and get hazy. Unless you expect someone to be shooting at your windows, polycarbonate only offers the chance to pay more.

[mark maulden]

I have hull # 40 or 41. Can’t remember..I have had this done three times in the last 5-7 yrs. The first time, they used a sikaflex product that required a primer. Three months later, the windows were laying on the deck. They were reinstalled by another person again with sikaflex. That lasted until fall of 2017. During my repower, with a different contractor, we also knocked out the windows and bought new ones and bedded them in with Dow Corning 795 which I would recommend as it doesn’t have a primer process. As for the thickness, I don’t think 1/4 is much better than 3/16. The very important part here is that plastic expands and contracts differently than the boat. It is very important to have a certain thickness of sealant so the window does not crack due to expansion and contraction. I don’t recall what that value is. If you use a thicker window and stack the thickness of the sealant, the window may be proud to the boat. Also, have the plastics mfgr bevel the edges so the outside is a little smaller than the inside. This gives a little bigger dimension for the fillet seal. The area that contacts the boat should be sanded to give the sealant a rough surface and sealant should be applied to both the boat surface and the plastic surface. This reduces the risk of voids that would be seen from the outside. Feel free to PM me if needed.

[mark maulden]

After installation, a good tape should be all that’s required to hold the window in place

[adjo]

Yes, cast acrylic
No, polycarbonate
Yes, 1/4" vs 3/16"

[djousset]

@Lou-In-NJ: Following. I am also replacing my fixed and crazed lights. They are also 3/16" and I am considering going to 1/4" if I have the clearance. Having replaced the hatch cover with Lexan for strength I can say that YES, it scratches more easily (don't ask me how I know....). Acrylic is the way to go.

[Cheechako]

I used Lexan once, I would not again. It is rippled, while Acrylic Plexi is not.

[mark maulden]

Be sure to get bronze tinting. It enhances the aesthetics a lot. Bronze is also OEM

[wingssail]

Originally Posted by mark maulden

After installation, a good tape should be all that’s required to hold the window in place

Could you explain this please?

[mark maulden]

I could have stated this A LOT better. After the window is stuck to the boat and held in place with spacers, taping the window to the boat applies enough pressure on the window while the sealant sets. Spacers can be used so as not to squish to much sealant out. A couple of very small screws can be set at the bottom for the window to sit on while curing. There a number of ways to do this. I have heard of screwing the window in with VERY small screws until the sealant cures. Then remove screws and fill holes with sealant. You wouldn’t see them unless you are very close. After curing, remove tape and retape as masking and apply the fillet seal. Hope this helps..