Replacing Ports

[sct5566]

I am refurbishing a San Juan 26 and am trying to make a final decision on replacing 4 dead lights. The existing ports were glass in an aluminium frame and they leaked causing damage to the interior. I am not going to try to repair them as they are worn and were poorly designed and fitted.

I am leaning toward .25 inch acrylic bolted through the cabin sides overlapping the opening by 1.25 inches. I have an understanding of how to install them after reading many of the articles, posts and blogs dedicated to this subject and plan to use butyl tape between the acrylic and the cabin. However, I would like a frame to cover the area where the it is screwed in, a 1.25 inch frame that lays on top of the acrylic that would give it a better finish.

Any thoughts on fabricating a frame from .25 inch thick marine ply, glassed on both sides with 6 ounce cloth for more strength, edge sealed in epoxy, then painted white to match the topsides. The other options would be to fabricate one that is all glass or carbon fiber, or have a flat aluminum frame made. Worth the effort or am I making this too hard.

[mitiempo]

I am in the same position as you and am wondering how to do this. One way is with the acrylic (plexiglas) bonded without fasteners which with Dow 795 or 739 is workable. Except that my cabin side is curved and holding them in place would be an issue.
The other solution is shown below in a picture. Covered with aluminum strips about 1" or so wide to take all point loading off the acrylic. The holes in the acrylic would be larger then the bolt size. In my case the openings are about 19" x 5 1/2" and the ends are rounded unlike the pics with straight edges all around. The strips of aluminum are less expensive than a single piece cut to fit. They could be powder coated or left bare. These might be anodized. It is a neat looking solution I think and the one I like best of what I have seen.

[cghubbell]

Don't use butyl with the acrylic. You want Dow Corning 795. If you do the bonding correctly using Dow 795, the fasteners are only needed to secure the adhesive during curing time. I was advised to actually remove the fasteners after the cure time and fill the holes with 795. I was also advised to use a minimal # of fasteners - just enough to hold it in place for the cure period (four on a 48" port, 2 on a 21" port). This method eliminates the need to fabricate the aluminum frame, and machining acrylic is super easy.

I would go with 3/8 rather than 1/4. Cost difference is minimal, but the thicker stuff is able to withstand probably more than you (or the oceans) can throw at it. From what I've seen, 3/8 is the standard thickness to go with for this kind of frameless replacement.

As for the curved cabin Brian mentioned... (I have the same boat) it may not be as big a deal as you think. In the case of the CS27, it looks pretty curved, but the flexibility of 3/8" acrylic over the span of those windows makes it an easy flex horizontalle which is easily handled by the Dow adhesive. No real flex in the vertical, but still plenty of surface for the adhesive.

I was concerned about it until i dry-fit the new sheets and found the gaps to be really minimal considering the capability of the Dow goop. Should be doing the final install this weekend if all goes well.

[sct5566]

I like the idea of using the Dow 795 - sounds like the way to go. The aluminum frame looked good, but I am now thinking of having a 1.25 inch wide "frame" made out of white acrylic and solvent gluing the frame to the outer edge of the window with acrylic cement. That would give it the finished look I want and cover the sealed attachment holes. Thanks for the responses!

[mitiempo]

My thought would be to use 795 without fasteners of any kind so there are no holes to fill. Without a curve it should be pretty easy but with a curve as on my boat it's a problem I haven't found a solution to. The frames as above look good and will be durable and as leakproof as any method. At the moment it would be my first choice.

[sailingdog]

While a frame is a nice idea... it isn't necessary.

I wouldn't use butyl tape for ports, since Dow Corning 795 is SPECIFICALLY designed for the purpose and a much better choice, especially if you don't want to have the ports mechanically fastened. Every fastener hole you make is one more potential leak point. Every fastener hole you make is also another point you have to pot the cabintop if the deck/cabintop is a cored laminate.

As for thickness... 3/8" is far stronger and will last longer than 1/4". The price difference isn't that big and considering that labor and such is a major part of the project, why go with the lighter glazing material if you don't have a specific requirement for it.

One good option is to fiberglass in a frame around the openings on the interior of the boat and then recess the acrylic by bedding it to the recessed frame. Properly done, this can leave the ports flush with the cabintop.