Friday, August 20, 2010

Moving Backwards and Forward at the Same Time

I've managed to put a lot of time into the project for the past several days, although it may not look like much from the photos.  The list of things to do in order to get the hulls completely closed in with all hatches and portlights installed has been long and seems to be growing.  But I'm looking at having both of them out of shed shortly, it's just a matter of getting all the paint coats on the various parts done and then installing these components and waiting for the sealants to cure.

I took a few steps backwards on the portlights, but I think it will be well worth it in the end.  I regret all the hours I spent messing around with a plan that I've now scrapped, but better to correct it now than have to do it sometime down the line when I'd rather be sailing.  The problem was the ring frames that I made to sandwich the portlights between.  For one, I didn't design them with enough clearance between for a proper thickness of sealant, and two, I made the mistake of glassing the outer frames on first, requiring the ports to be installed from the inside.  Attaching them from the inside is problematic in many ways, first to make this attachment strong enough, and second, to get a good seal.  Another reason for scrapping this idea is that further research and conversations with David Halladay regarding the materials used led me to the conclusion that Lexan is not the preferred lens material and that the ports should be instead made of cast acrylic, which is what all the major hatch manufacturers use.

So to fix all this, I first had to grind off these nice exterior rings that had been so time-consuming to glass and fair into the sides of the cabins:

After a few hours with the belt sander and then the 6-inch random orbital sander with 60-grit, I was back to a flat cabin side surface:

The new portlights will be the overlay style, the perimeters of the lenses overlapping the openings by 1.5 inches all the way around.  There will be no holes drilled and no screws or other mechanical fasteners - the lenses will instead be bonded with sealant the same way that most all modern portlights are attached.  I was skeptical of this at first, until I realized that this is the way large, heavy glass panels are often installed in skyscrapers and other structures, and until I saw first hand how well it has worked on some of the windows David and the Boatsmith crew have installed.  The recommended sealants are either Sikaflex 295UV or DOW 795.  I'm going with the DOW 795 because it is a one-part sealant that doesn't require special primers, as does the Sikaflex. 

My order of cast acrylic to make these from arrived yesterday.  This is great stuff compared to the Lexan I had before. It comes with a heavy paper protective cover on both sides that's easy to mark and stays in place while you're cutting and sanding.  Here you can see my plywood patterns used to mark the outline of the new windows.  The small piece in the foreground is a scrap from which I peeled away the paper.  It is smoked gray in color, a shade darker than the smoked gray Lexan I had.  This cast acrylic is more U.V. resistant and more scratch resistant than Lexan.  It's also stiffer so that it wont flex if a wave hits it, which could break the seal.  That's why hatch manufacturers use it.  If you step on a deck hatch it won't flex under the weight.  The only area where it is not is good as Lexan is in impact resistance, which is why Lexan is used in bulletproof windows.  Hopefully, no one will be shooting at me, so it's not an issue. 

This material cuts and sands well. I cut out the ports with a circular saw, then rounded the corners with the belt sander.

Another job completed yesterday was some major sanding of the stern decks, toe rails and sheer stringers, and then the application of the first coat of primer to those areas. Everything on the hulls and decks is now either painted or primed.  Today is the first sunny day we have had here in over a week.  I will spend the morning putting another coat of paint on the cabin sides, companionway hatches, and other small parts.


briggs said...

Just thought I'd mention that Lexan is 210 times the strength of untempered glass as opposed to acrylic only being 12 times the strength of untempered. just in case you didn't know....

Scott B. Williams said...


I'm aware that Lexan has more impact resistance than the cast acrylic, but despite this the acrylic is plenty strong enough for portlights and is the preferred material used by all hatch and portlight manufacturers and yacht builders for the other reasons stated in the post.

After cutting the new portlights I can see why, as it is much stiffer and has a better clarity. It can also be polished it it gets scratched, and is more U.V. resistant than Lexan.