Beneteau F310 ~ APOTHIC
Join Date: May 2009
Location: Ontario, NY (PYC)
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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.
Beneteau F310 ~ Apothic
PYC, Lake Ontario