Replacing deadlights (fixed windows)

[Jalepeno]

I’m replacing my fixed saloon deadlights (side windows) with 6mm (1/4”) tinted Plexiglas acrylic and am looking for any thoughts / advice. The existing factory deadlights are about 1/8” thick tinted acrylic held in plastic frames with a pressed-in rubber gasket. The flanged frames are inserted into the opening from the outside and sealed with what looks like white marine silicone. A plastic trim is screwed to the inside of the frame to clamp the assembly and to finish the inside appearance. The cabin wall fibreglass is 0.18” thick with a 1/4 “ air space between it and the headliner fibreglass that is about 0.12” thick. I’ve had new tinted acrylic cut one inch larger than the opening with twenty four ¼” diameter holes drilled ½” from the edge at about 3” spacing. I plan on inserting a ¼” wood shim into the air space between the headliner and the cabin wall and using Butyl tape to seal the Plexiglas to the cabin wall. The assemble will be though-bolted with 10-24 x 1¼” S.S. button head socket cap screws from the outside, fender washers on both sides and Nylock nuts on the inside. I will probably use white marine silicone to finish the outside edges.
What are your thoughts?

 

[Jonrod222]

I have replaced the windows in my boat, twice. The lessons learned, don't use vinyl trim tape as a border to cover up the sealent. The sealent sticks to the tape and the tape doesn't really stick to the window. On the second windows I used a plastic piant for the border. Plexiglass expands and contracts with temperature more than one might think. My first windows cracked on the ends during the first cold weather. The holes need to be at least twice the size of the screws. I have been crack and leak free for 2 years now. The first set of windows cracked and started leaking after 6 months. Rudy at D&R marine sent me a couple of tubes of GE window silicon sealant with the windows and it is working fine. As much as plexiglass moves I am not sure how well the butyl tape will work. I have used it on cars before and I am not sure if it will move with the window or take a set and not seal uniformily. Hope this helps.

 

[Maine Sail]

II’ve had new tinted acrylic cut one inch larger than the opening with twenty four ¼” diameter holes drilled ½” from the edge at about 3” spacing.
What are your thoughts?

First, it is not advised to drill & screw acrylic or polycrbonate. The expansion and contraction will wreak havoc and cause cracking.

I would simply buy new gaskets for the factory aluminum ports and replace the acrylic. Select Plastics can re-build your ports for you or jsut cut the new plastic. Most of the older Catalina's used real glass in those aluminum frames.

If they are leaking it is quite likely the leak is between the frame and hull. They may only need to be re-bedded.

I would not try and replace those ports the way you describe. The newer boats, with dead lights, have a recess in the cabin side to accept the thickness of the glass and they are usually held there with Dow 795..

 

[Jalepeno]

- Maine Sail ,thank you for the feedback:

First, it is not advised to drill & screw acrylic or polycarbonate. The expansion and contraction will wreak havoc and cause cracking.

- I am aware of this, that is why I'm planning on cantering the 10-24 machine screws (0.20" diameter) in the oversize (0.25" diameter) holes.

I would simply buy new gaskets for the factory aluminums ports and replace the acrylic. Select Plastics can re-build your ports for you or just cut the new plastic. Most of the older Catalina's used real glass in those aluminums frames.

- My boat is a 1979 CAL not a Catalina and the plastic frames have weathered to the point where they need replacing. They are beyond repair and I cannot find anything to replace them.

If they are leaking it is quite likely the leak is between the frame and hull. They may only need to be re-bedded.

- The leaking is from both between the frames and the cabin, and between the plastic "glass" and the frame. I re-bedded then two years ago.

I would not try and replace those ports the way you describe. The newer boats, with dead lights, have a recess in the cabin side to accept the thickness of the glass and they are usually held there with Dow 795..

- My previous Hunter sailboat was made like that. Internet research has found that others have made replacements on CAL sailboats as I am proposing but I am not sure if they used only marine silicone or Butyl tape.

ps. I will replace the two small deadlights with two opening Beckson ports later in the winter. Up here in Canada we do not have many suppliers.

 

[Hermit Scott]

First, it is not advised to drill & screw acrylic or polycrbonate. The expansion and contraction will wreak havoc and cause cracking.

I would simply buy new gaskets for the factory aluminum ports and replace the acrylic. Select Plastics can re-build your ports for you or jsut cut the new plastic. Most of the older Catalina's used real glass in those aluminum frames.

If they are leaking it is quite likely the leak is between the frame and hull. They may only need to be re-bedded.

I would not try and replace those ports the way you describe. The newer boats, with dead lights, have a recess in the cabin side to accept the thickness of the glass and they are usually held there with Dow 795..

This project is pressing for me right now. It is starting to rain and my ports are leaking. I read alot of archives from here and else where. Some say to use 3M 995, that it's better than the 795. What do you think of the 995 instead? what is the purpose of the rubber gaskets on the inside? What is the sealing surface? BTW my ports are glass, everyone has a hard time believing that for some reason. How do I know if I need new gaskets?

 

[kenn]

To both Jalapeno and Hermit Scott - if you're replacing these lights because they leak... can you determine where they are leaking? It's going to be either the window itself or at the joint between window frame and cabin wall.

As already mentioned, it would be best to repair/reglaze the existing framed windows, and then properly remount them. probably easiest too.

The Don Casey books cover this task pretty well. Some more info here and here.

* * *

Our boat came from the factory with the drilled & bolted acrylic side windows. They have lasted 28 years, so I guess that means the holes are large enough to avoid problems from expansion and contraction.

One previous owner had remounted the windows, but I think they used house caulk or similar as sealant, and the seal area had become all dirty and mildewy. Looked like hell.

My wife and I removed the windows. The acrylic and the cabin cleaned up nicely. We remounted the windows, this time using clear silicone as the sealant. As each screw was added and fastened, we stuck a toothpick between the cabin and acrylic, to maintain a 1/16" gap, and only lightly snugged the screw to the toothpick.

After 2 days we pulled out the toothpics and lightly tightened each screw a bit more.

This has remained waterproof for two seasons so far.

 

[Jalepeno]

Don Casey has a very good description of how to fix / replace boat windows in his excelent book "Don Casey's Complete Illustrated Sailboat Maintenace Manual". It look like he recommends exactly what my I'm proposing to do.
Which brings me back to my original question. Should I use Butyl tape or sylicone for this application ???????

 

[Maine Sail]

Don Casey has a very good description of how to fix / replace boat windows in his excelent book "Don Casey's Complete Illustrated Sailboat Maintenace Manual". It look like he recommends exactly what my I'm proposing to do.
Which brings me back to my original question. Should I use Butyl tape or sylicone for this application ???????

We should remember that Don Casey is not a plastics expert. He has also been known to give marginal advice on other issues as well including the two step bedding process.

Tony D'Andrea on the other hand, the owner of Select Plastics, is regarded as perhaps the foremost authority on marine plastics in the industry.

I have quoted him below. I did not make the advice up I gave you earlier. You should use Dow 795 or similar in this application to do it right.

Tony on Expansion & Screws
Due to its ductility Polycarbonate it is more challenging to install. I have seen Sika Flex 295UV with primer and Dow 795 both mentioned. I use and recommend both. Don't go over 4 ft continuous length with a fixed portlight. Remember the coefficient of thermal expansion for Acrylic and Polycarbonate is in the neighborhood of .000039 per inch per degree F. That means an 8ft plastic port will expand and contract up to 1/2 of an inch from the coldest day in Feb to the hottest day in summer. WOW!! Compartmentalize the job. It will be easier to install and less prone to leaks.

Never ever bolt a plastic portlight in place. Screws are fine to hold a lens till the adhesive cures. Take them out asap and fill the holes with the aforementioned products. Both of these products are rated at 700 + percent elongation before tear. Strong flexible and UV resistant.

Been to a boat show lately? Seen any screws? Glass is good so long as your boat does not twist or torque. Show me a fiberglass boat that does not twist and I will show you a cocktail barge tied to the dock."

Tony on Sealants:

"I hear the question as to which sealant to use when bonding Acrylic, or Polycarbonate to aluminum, stainless or FRP over and over and over.....
Well here goes... The only three adhesives I would consider using are Sika Flex 295 UV with the primer, GE SG-4000, and Dow 795. Using the correct adhesive is only 1/2 the battle. Do not apply the sealants below 50 degrees F. The temperature must maintain at least 50F during the entire 21 day cure cycle. Cut this corner and your finished before you start. Preparation of the bond area is also very/ very important. DO NOT TOUCH THE BOND AREA WITH YOUR BARE HANDS! Contamination from the dirt and skin oils will make a solid cure impossible. You may clean the FRP and metal with acetone to prep the area but if you touch the Lexan or Plexi with harsh solvents you will ruin the portlight. A 50/50 mix of isopropal alcohol and distilled water will work well to clean the plastic if needed. Remember that clean enough is not clean enough."


You seem to have decided you are going to do it your way, and that's fine, but please understand that Tony's advice is far better than that of Don Casey in this area of expertise.

As I mentioned earlier Select Plastics can likely rebuild your existing ports to like new condition.

 

[Jalepeno]

Thank you Maine Sail, I looked at Select Plastics web site and that would definately be the way to go if I had reusable metal frames and lived a lot closer to them. Thermal expansion is not a big issue here in south-western Canada as our maximum temperature swing is less the 30deg C (50deg F) and this port is about 3 feet long. My previous Hunter sailboat had ports about 4 feet long and the Acrylic came from the factory glued and screwed (oversized holes) to the flat cabin side. I will let you know how the project works out.

 

[Maine Sail]

My previous Hunter sailboat had ports about 4 feet long and the Acrylic came from the factory glued and screwed (oversized holes) to the flat cabin side.

That's the key with screwed lenses, over sized holes that is..