Window Design for Custom Steel Yacht

[pkoken]

I am looking at purchasing a steel motorsailor yacht. All of the windows are badly clouded / crazed from UV exposure and are in dire need of replacement.

My questions are the following:

The current cabinhouse windows are "frameless" with a piece of Lexan or acrylic attached directly to the hull side with screws and sealant over a significant overlap. Is this a bad design? Assuming I keep this design any input on sealant variety that is suitable would be helpful (no 5200! I want to get them OFF someday)

The pilothouse windows do have frames, and are relatively large, I want to replace these with VERY strong replacements- I envision three different routes here:

Option 1 - Tempered Glass
Option 2 - Lexan or Acrylic
Option 3 - Laminated Safety Glass

Obviously Option 1 is the strongest and the most scratch resistant, however it is also heavy and easily broken with a sharp blow.

I thought of using Lexan MarGuard... but I have NO experience here!

Thanks in advance!

[gonzo]

Lexan is very flexible and shatter resistance. The downside is that sometimes it is difficult to seal because it bends too much between fasteners. Also it can't be polished. Plexiglass is more rigid so it stays flat between fasteners. It can be polished. Safety glass, the one with a metal mesh inside, is more scratch resistant but needs a frame. I have used silicone for both lexan and plexiglass with very good success. There are a couple of things to be careful about though. One,use round or pan head screws. Flat heads will crack the plastic. Two, put a thick bead of caulk and set the screws just enough to squeeze it. Torque the screws a bit after the silicone is set.

[pkoken]

Lexan is very flexible and shatter resistance. The downside is that sometimes it is difficult to seal because it bends too much between fasteners. Also it can't be polished. Plexiglass is more rigid so it stays flat between fasteners. It can be polished. Safety glass, the one with a metal mesh inside, is more scratch resistant but needs a frame. I have used silicone for both lexan and plexiglass with very good success. There are a couple of things to be careful about though. One,use round or pan head screws. Flat heads will crack the plastic. Two, put a thick bead of caulk and set the screws just enough to squeeze it. Torque the screws a bit after the silicone is set.

I am assuming you are reffering to continuing with the current "Frameless" design of the windows? I have never had this type of window on a boat before, and while it looks simple enough I wonder about the long term durability of the seal, as well as the physical strength of the window mounting.

Since I have no expereince with "Frameless" windows I am turning you folks to help me determine if it is time to change them out with a another design.

[gonzo]

I have installed windows in many commercial fishing boats with this method. The only problem I ever saw was from overtorqueing the screws.

[pkoken]

OK, I think I've got it then- just don't torque the screws down too much...

• Install new window with sealant.
  
  Lightly tighten screws to hold window against hull whil sealant cures
  
  after sealant has cured finish tightening screws (but not too much as window will crack)

Do you recomend drilling the holes out significantly larger than the screws to allow for expansion? Finally, judging by the fact that Lexan cannot be polished I am considering going with a UV resistant acrylic for the cabin windows.

The pilothouse windows are much larger (of course) and I am considering going with 1/2" Lexan there for safety and weight concerns.

I really appreciate the help!

[gonzo]

I assumed that they are installed with screws and nuts being a metal boat. However, if they are wood or self tapping screws, skip the retorqueing, it would break the caulk around the screw. Sorry if I confused you. The holes should be slightly larger; about 1/16th more or so.

[pkoken]

You are correct, screws and nuts. I was reffering to whether I should replace the windows with a more traditional "Framed" window. This would mean I would either have to make frames or have them made.

Obviously the Frameless route is easiest, and if it is a seaworthy design I won't change it.

[gonzo]

Frameless windows work just fine.

[Zaynab]

The Dashews suggest using neoprene instead of sealant. This way you will always be able to remove the windows. Check out their "Offshore Cruising Encyclopedia" for details. Website: Setsail.com

[gonzo]

Neoprene is great if you have a frame. Frameless Plexiglass or Lexan is to soft to compress the gasket. I suppose you could put fasteners very close together. However, it would weaken the panel and probably crack.

[philwhittaker]

Two things I would sugest,
1. Paint the back of the lexan (sand paint and paint the suface to that will have the bedding on it, this will hide any small air bubbles behind it and give it a much more uniform finnish
2. Use an adhesive caulking, 5200 has worked well over the past (If you need to get the window out or off again it can be taken off, but chances are it is broken and needs replacing.

[Steve Gray]

Frameless lights are safe and very commonly used on tough boats. If the glazing material is thick enough (increasing rigidity as well as tensility) and there are sufficient fasteners (max 4-5cm) then frames shouldn't be needed, but if you're worried then surely it wouldn't be too difficult or costly to make framing 'pads', surrounds that are the same outer profile as the window with an inner profile matching the existing aperture. This could provide extra strength with, maybe, fewer fasteners. And then you could use thin (2mm) single-lined neoprene to make an easy-to-remove-and-maintain gasket...

The manufacturer says that one should not drill holes in Lexan.

Tim Dunn
steelsil@cedarcomm.com

[gonzo]

Which manufacturer? There are several that produce the same product under different names. I am curious to know their reason.

[Tim Dunn]

My information must have been out of date. You can drill lexan.
For more info, see the "seaworthy" thread.