New Portlights

[itsme6582]

On our long list of items to be repaired before our May 26th launch date is to replace these awful portlights on a 23' cruiser for Lake Erie. The rough measurements are 40x10.





One option is to cut new plexiglass (I'm not sure if you can tell from the pic but these are cracked), find a gasket and install.

What we are seriously considering is cutting larger portlights and using an adhesive to hold them in place. Here come the questions...

1. Can we use a router to cut plexiglass or will there be issues? If this is not a problem we can just use the old windows as a jig. This seems too easy to actually work.

2. What sort of adhesive would be good for this. I've read about a few Dow products on this site. IIRC they were 791, 795, and 739. Well, I can't find any Dow products in town. Where could I find them? There are a few products I found at Cleveland Lumber and Home Depot that looked promising. Are any of these acceptable or am I looking in the wrong place? My gut is the PL Ultimate and the Lexel will work.

DAP Titanium - This is my least favorite choice. Silicone - High flexibility - Strong Adhesion - Nothing stated about UV resistance

PL Ultimate - Claims strong adhesion to most plastics, flexible, UV resistant, doesn't crack or shrink

All Purpose Lexel - This is an interesting product that seems like it will do the job as well. Co-polymer rubber based sealant, sticks to everything even wet things, ok to use in the sun

[mdbee]

When you get to a certain length, you have to contend with issues of expansion (screw holes cracking / adhesive issues) and compensate.
(if you weren't going back with a gasket installation)

I don't remember the length that this becomes an issue.

[sailingdog]

Originally Posted by itsme6582

On our long list of items to be repaired before our May 26th launch date is to replace these awful portlights on a 23' cruiser for Lake Erie. The rough measurements are 40x10.

...

One option is to cut new plexiglass (I'm not sure if you can tell from the pic but these are cracked), find a gasket and install.

What we are seriously considering is cutting larger portlights and using an adhesive to hold them in place. Here come the questions...

1. Can we use a router to cut plexiglass or will there be issues? If this is not a problem we can just use the old windows as a jig. This seems too easy to actually work.

Yes, this should work. However, it might be a better idea to get the acrylic cut to size by the vendor. Many vendors will do this for a small fee.

2. What sort of adhesive would be good for this. I've read about a few Dow products on this site. IIRC they were 791, 795, and 739. Well, I can't find any Dow products in town. Where could I find them?

I would recommend using Dow 795 Silicone Structural Adhesive. You can order it from McMaster.com pretty easily.

There are a few products I found at Cleveland Lumber and Home Depot that looked promising. Are any of these acceptable or am I looking in the wrong place? My gut is the PL Ultimate and the Lexel will work.

DAP Titanium - This is my least favorite choice. Silicone - High flexibility - Strong Adhesion - Nothing stated about UV resistance

PL Ultimate - Claims strong adhesion to most plastics, flexible, UV resistant, doesn't crack or shrink

All Purpose Lexel - This is an interesting product that seems like it will do the job as well. Co-polymer rubber based sealant, sticks to everything even wet things, ok to use in the sun

No, don't use any of these, unless you like re-bedding ports and dealing with leaks...

[maccauley123]

For what it is worth I just did this and so far I am very happy with the results. Removed the very old metal frame windows from my 1971 Ericson 29 and replaced with Acrylic bonded to the outside. I have not launched the boat yet so can not comment on the long term results.

I bought the acrylic from estreetplastics both cut very close to the size I needed and then a larger sheet I cut what I needed out of. I found cutting with a saber saw with a good metal blade worked well. Then sanding the edges with a palm sander. I did not put a bevel.

Old windows removed and then scraped and sanded to remove all the old caulk and gunk and cleaned with acetone. I sanded the inside edge of the acrylic to give the adhesive a better surface to bond to.

Dry fit the windows and then taped around the perimeter giving about a quarter inch extra. This allowed me to smooth out the adhesive and create a fillet around the windows since I did not bevel. I applied the adhesive and used the Dow 739. I was able to find a local distributer from the Dow Corning web site. Advertised as a plastic adhesive and seen another recommendation here for it. The data sheet on the Dow site reinforced my choice.

It was very easy to work with and dried to the touch within an hour. I didn't need to clamp as it stuck pretty well on its own. My hull has an extremely slight curve to it so did not have to flex the acrylic much. Smoothed out the edges of the adhesive around new window and removed tape.

[itsme6582]

And of course Dog finds time in his day to post on yet another thread.

Thanks for the follow up on the products I found. Indeed, I won't be using any of these. I've looked at Dow's site and read about both the 739 and the 795. Any reason why one is better than the other? The 739 specifically states boat windows as a typical use. I'm going to send Dow an email and see if I can get an explanation on which to choose. I'll post their response. The good news is there is a supplier about 15 minutes away.

[maccauley123]

Do a search in the forums for Dow Corning 739 and you will find a few discussions. What convinced me was discussions in there about how Dow recommended 739 for this use. Plus the data sheet like you found specifically says bonding boat windows.

[Northeaster]

I had long strips of Acrylic cut to the proper height for the windows, with about a 2 - 2 1/2" overhang past the edge of the opening. Then I rough cut the vertical sections (Used a router). then used a belt sander with rough paper to scult the corners to get the shape I wanted.

I used 3M adhesive tape (3/4" I believe) primarily to hold the new oversized acrylic windows in. Then I left a 1/4" - 1/2" gap outside the tape, and then ran a large bead of Dow 795 to further adhere and seal the edge. I ran a finger around the edge to bevel it off to a clean (approx 45 degree) edge.

I am extremely happy with the job. It has been a year now, ad no leaks.
Made the boat look much better and newer than the old, cheap, white plastic frames.

On the strength or the 3M tape. I had lightly set one into place, and hadn't even pressed it hard to the tape. Of course the Dow 795 was still wet (not adhering). I realized it was the wrong tint, so it had to come out. I had to put my shoulder into it wit halot of force, from inside the boat, in order to break it free. I would imagine that once the Dow was dry as well, with well over an inch of pressed sealant, it is in there good.

By using the 3M tape, I did not have to use spacers to allow the correct thickness of D795. If you had not read about this, to get the Dow to be able to flex and expand with the acrylic, during temperature changes, you need it to have some thickness. You do NOT want to press the window tight against the fiberglass, squeezing out virtually all of the Dow sealant.

Tried to upload a couple of pics, but they failed.

[itsme6582]

I can't find a way to email Dow Corning. I may or may not call them. It seems like we could either go with 795 or 739 and be happy with the results. I'm leaning towards 795 because Skynet/Dog suggested it. I want to be on Skynet's good side once it takes over. There is also a very informative writeup about 795 on this thread. Scroll down a little on the link. You can't miss the info.

I'm also aware there needs to be some space between the boat and window to allow the sealant to stretch as the window expands (like Northeaster said). Any suggestions on what to use. I don't think we'll be using tape.

[sailingdog]

LOL.... Skynet/Dog???

Originally Posted by itsme6582

I can't find a way to email Dow Corning. I may or may not call them. It seems like we could either go with 795 or 739 and be happy with the results. I'm leaning towards 795 because Skynet/Dog suggested it. I want to be on Skynet's good side once it takes over. There is also a very informative writeup about 795 on this thread. Scroll down a little on the link. You can't miss the info.