Hull portlights

I would like to post a question about replacing the 8 port lights in the hull. Mine are leaking badly and I was hoping to get some feedback from other owners who may have already done the job. Vince S. (#005, Witch of the Waves).

a. I am presently replacing all the acrylic windows and the hatch lens as well. Use ½” cast acrylic, tinted in the shade desired. Make sure it comes with peelable paper on both sides. Use Cast–not extruded, it’s stronger. There is one extruded with a scratch resistant coating, if you want, but Cast is quite scratch resistant. Don’t be tempted to use Lexan (polycarbonate) just because it’s what they use in bulletproof glass. It isn’t as stiff as acrylic – it bends easily – that’s what absorbs a bullet, but you don’t want it to bend and pop out of the window frame. It also yellows quite quickly and scratches easily.

You will need to take out a window and make a template. My center cockpit has radiused edges. I laid out a cutting pattern that accommodated all my windows on the size of sheet I was working and cut them on a table saw. The corners are radiused as well and I did that with the saw and final shaping on my bench sander. I made a router stand and rounded all the edges with a ¼” roundover bit.

Don’t take the paper off until you want to install them.

Making them was easy – cleaning all the silicone out of the boat window frames is an ongoing job. I ground an old kitchen spoon handle to the shape of the cove and sharpened it. It works OK but it takes 2 hours per window and up here it’s usually cold rain while you do it. Silicone Remover doesn’t work very well. Did I tell you I hate silicone!

I did a lot of research on how to get them to seal when they are installed and talked to our 3M rep. They suggest using 3M 730 clear hybrid sealant. It doesn’t react with acrylic and a lot of things like polysulphides do. I am even considering a strip of the bedding Butytl tape, that MaineSail sells, along the inside edges of the frames, and the 730 out from that.

You need to clean the acrylic with acetone before you install it to make the adhesive stick well. Usual caveat – don’t touch the glueing edge after you clean it.

Note: do not use windex to clean your acrylic. We did that at work and watched the spider cracks ruin a lot of good acrylic. Use soap and water. The plastics shops won’t warrantee it if you do.

When I took off out stainless frames the screw holes were in bad shape. I will be Dremelling out the cracked ones and filling with epoxy – then redrilling.

John G. (#181, Spinnaker)

d. Obviously it’s a seal problem. You did not say whether they were existing or new that are giving you problems. When I replaced my own, I used 1/2″ tinted safety glass. Because the new glass was absolutely flat, I had to router out a bit of the curvature that was in the old frame cavity. Because it was glass, I used automotive grade silicone sealant and everything was fine. (Had I used Lexan or any other plastic, I would have heated it to adapt to the shape of the existing window cavity and then used Sika Flex or something that would bind to plastics.) In any event, it’s an easy fix. Good luck with this Vince, Frank B. (#186, Visitant).

e. I replaced all the portlights in the hull and pilothouse; a long job but now, no leaks.

You will need: a scraper, a knife, sander, drill, epoxy, screws, caulking, and the windows

Caulking: I used butyl rubber tape. This stuff is very sticky and a guaranteed seal. It does take time to complete the job because you need to gradually tighten the frame screws, squeezing the excess out. There are many types of this tape; the link ( is the best out there.
What you may find, if your old ports are Lexan, the caulking used did not stick. If you use new plastic portlights and you do not want to spend the money for the butyl tape I suggest you do some research on caulking that works with the plastics. Another caulking to look into is the stuff used on buildings that have glass siding; this is usually two parts sticky tape, to mount and hold the window in place, and then a caulking to seal the edges.

Windows: I used laminated glass in both pilothouse and hull except for the ports in the forward cabin. There, the hull curves, so glass would not work. If you choose glass you can take one of your old windows to the glass shop and they will make a pattern and have the windows made. If you choose laminated glass one tip is talk to the glass shop about how well they will match the two pieces of glass to make laminated glass. What happened to me was the two halves (inside/outside) did not match perfectly.

This was mostly a problem with the pilothouse windows. As with the pilothouse the forward portlight windows need a little grinding to put a slight bevel to the inside edge. For a good match around the edges the place that makes the glass can grind them but I understand that gets expensive, Just be aware. If I did it again I would look into tempered safety glass.

Carefully remove the stainless frames. Use a thin scraper, flat on one side, pointed on the other. Find a weak area in the caulking, push in the blade, and work around using a wedge to hold the frame away from the hull as you break the caulking seal.

Next step is to remove the caulking from the frame and the hull. I found the caulking was much harder to scrape off from the hull than from the pilothouse. The tool I used was an Exacto knife (the bigger one) with the blade that angles around 45 degrees. After cleaning both frame and fiber glass you can start preparing the hull.

You will likely find that some of the screw threads are stripped out from the fiberglass. For any hole that was slightly poor, I drilled out and ground out (Dermal Tool) the cracked and broken fiberglass, filled with fiberglass epoxy, then drilled new holes. I polished the frames and secured them with all new screws.

The other thing you might find, especially in the pilothouse, is the fiberglass insets vary in thickness and require some sanding to make them level. You will also need to sand flush your epoxy hole repair. Once you have your frames clean and your fiberglass repaired, you can temp mount your frame, mark, and drill the holes you repaired.

Now you are ready to install the windows. First, you might want to check the evenness of the window to the fiberglass surface. Depending on the sealant you may need to build it up thicker in certain places. I had the window held in place, then went inside and marked the fiberglass frame with a pencil for areas I felt I should build up with the butyl tape. Remove the window and add layers of tape as needed. Next stick the window in and recheck if you need more tape in any places.

Next get your frame lined up and gently install the screws so you do not strip them out. If you use tape, snug up the screws and as you work your way around the frame the tape will ooze out. If you are doing this on a cool day the butyl tape will be hard so be careful snugging the screws. The butyl will take weeks to gradually snug up. You can trim off the oozed out excess as often as you like. With tape you should have a good waterproof seal right off. If you still have some gaps you can pack in some putty with a putty knife.

After all the tape was squeezed out I prettied up things with 3M 4200. I masked off the ports inside and caulked the seam with white 4200. On the outside I masked and caulked with white 4200 where I had the stainless next to white fiberglass and black 4200 between the stainless frame and the glass.

Two problems; the butyl tape continued to ooze out in places through the 4200 and in the sun the black 4200 was getting gooey. It continued to ooze for about a year. I have trimmed of some of the 4200 on the outside and I do not see any drawbacks having the butyl rubber seam exposed. I might try something beside 4200 eventually. It sure looks good having the edges finished off with a well beveled edge of 4200. Kind regards, Gene & Patti S. (#158, Swell Dish)

f. Thanks for your responses. I was too broad in my original question. The questions I should have asked are: What have others used to replace their port windows? Has anyone found a manufactured “off the shelf” fixed or opening port light that works? Has anyone had custom manufactured port lights made? Who made them? Cost? etc etc.? What unforeseen problems arose in the installation and how was it handled? If you maintained the original set-up (glazing in the indent and frame on the outside), what materials were used for the glazing? What was used for the exterior frame? What sealants were used?

I know there’s one port area that could be a problem, and that’s the forward ports on the bow. That area doesn’t look flat to me. It actually looks like it twists: ie the rear end may be 10 degrees from vertical while the forward edge looks to be 15 degrees.

Boman [Bomar?] Marine is willing to manufacture the portlights, but the indent in the hull area either has to be removed making the opening larger, or filled in, making the opening smaller. Also the cost is considerable.

I’m leaning right now to just staying with the existing set-up and replacing the glazing with acrylic and having frames made that match the footprint of the original fiberglass ones. I can have them made in polished stainless steel or anodized aluminum. This seems to be rising to the top as the most cost effective and simplest solution.

Again thanks for the response and feel free to comment, advise, chastise etc.
Best Regards, Vince S. (#005, Witch of the Wave)

g. I am replacing mine now and what I understand from the portlight supplier, I must use a special sealer that they use commercially. It is specific to the material that the portlight is made from, either acrylic or Lexan. I replaced the pilothouse portlight and it was successful. Removing the old caulking, sanding and washing with acetone seem to be the secret. Talk to your supplier, he will give you all the tricks. Good luck. It is a tedious work but worth it. Valois N. (#096, Giva).