How to finish edges at portlights?

[SeaHusky]

My port lights will be polycarbonate bolted onto the outside of deck house which is about 4mm fibreglass. On the inside I will insulate with 10mm foam and on top of that a vinyl(?) liner with 5mm foam. How do you suggest I finish the edges so that it is functional as well as not unsightly?

[Owly055]

Personally my biggest concern would be for them to be water tight and stay water tight.   The method used for automotive glass for many years would be the best as far as I'm concerned.   The best are one piece that fit the opening and the glass very tightly.  I've installed windshields and non-opening side windows using these rubber gaskets.   The installation can be difficult at times, but the results are incredibly tough and rugged.  Modern auto windshields are glued in and I don't consider it as good.   Soap helps the installation, and a string is placed in the groove, which when pulled out, brings the rubber out around the edge of the window easily if done correctly.   Hamilton Marine shows a rubber one piece gasket for a 7x14 portlight and one for a 5x12 portlight.   These look to be something like what I was talking about above, but without handling them, it's hard to tell.   This material is also available by the foot..... but the material sold that way will leave a tiny gap at the ends unless you to a wonderful job of fitting it, and will lack the molded corners, but if located correctly the gap if there is one, will not present a leakage problem, except for a tiny one when your keel is pointed skyward, and you are walking on the cabin top.   

                                                    H.W.

[SeaHusky]

Thanks but you misunderstood my question.
The oversized polycarbonate is bolted onto the outside of deck house.
It is the edge of the insulation/liner on the inside that I need to finish in a way so that it is sealed from condensation running on the inside of the glass and also looks ok. 

[Jim_ME]

One option might be to frame the port openings with trim that matched the thickness of the insulation. Initially, I assumed that the trim frame would be round [cornered both inside and out] to follow the shape of the port light, but maybe you could have a rectangular board/panel that covered the port lights with holes cut in it in the shape of the portlights, but the outside faces were straight. You might even cut a rabbet in it that would allow you to attach the out sheet/liner to the edge, and then cover that insulation-to-wood joint [and any insulation fasteners/tacks/etc] with a trim batten.

I've attached a photo from the cabin of a Cape Dory cabin, showing how they apply a wood boards/panels over the interior of a fiberglass cabin trunk. You may be able to do a more limited version of this around your portlights?

[Owly055]

     I've been mulling this over, and there really isn't an easy way to accomplish what you want unless you can find something specifically designed for the job on exactly the size hole you have.  The logical solution is to laminate two or more pieces of a suitable material.   The first piece would have a hole that matched the opening for your portlight, and perhaps a 3/4" to 1.5" margin outside that.  It would be less than the combined thickness of the two layers....foam and foam backed vinyl so that when the outer piece was installed, it would compress the foam some.   This piece might be several built up layers.    The second piece would be a bit larger cross section so it would extend over the two layers of foam by at least 1/2".  I would want this layer fairly thick for strength, and to be able to round the outer edge nicely so it looked good.  The entire piece would be attached to the inside of the cabin around the portlight and shaped along with the opening so the surface was fair, and the corner toward you was nicely rounded.   
     The problem here is that ideally the entire piece would be bonded to the inside of the cabin with a good water proof glue.  This means that final attachment would have to be after you install the insulating layers.   It also means that replacement of those layers would be a challenge.  I would look for a glue that can be released with a heat gun for this bond.  It might be worth using a lower adhesion sealer on this joint and putting a series of countersunk screws from the outside through the cabin side into it so it can be removed later when the insulation needs to be replaced.    The actual trim pieces could be made from wood, or some composite.   Any way you do it, it's going to be a time consuming job to make it work well and look good. 
      I'm not all that good at drawing pictures with text........... and some people are not good at reading them either.   I can visualize the process and the end result clearly, but describing it clearly is a different challenge.

                                                                                         H.W.

[CapnK]

I'm having to do this as the old, original plastic portlight frames leaked, resulting in rotting of the interior teak ceilings of the cabin trunk.
My plan is to use pre-made fiberglass panel cut into a 'frame' shape of maybe 1.5-2" width, bonded to the deckhouse on the inside like the wood used to be. I think doing it so that it stands just a bit proud of the wood next to it will result in a decent enough finish. It should also serve to strengthen the openings, as well as clean up the appearance of the rather rough and asymmetrical cutouts from original manufacture.