Monday, August 30, 2010

Final Word On Portlight Configuration

Once again, I've made a change to how the fixed portlights in the outboard sides of the cabin will be installed.  My portlight saga is beginning to resemble Neil Hawksford's long-lasting "tumblehome saga" in the building of his Tiki 38, Gleda

This is the final change though, and the modifications have been completed and the window panels will be installed this week.  I decided against the overlay method as described in my last post because with the outer ring frames removed, the openings were of course larger and to have enough bonding surface for the overlay style of installation, the plastic window panels would have to be 1.5 inches wider than the openings all the way around the perimeter, creating disproportionately large windows that would adversely affect the lines of the boat.  Though it took a bit of extra work, I decided to do it the right way and the way that windows are installed in practically all modern boats and yachts - with an inner flange for bonding so that the window will be flush with the surrounding cabin side surface.  This is what David Halladay recommended from the beginning and I should have listened to him then.  It is also the way the windows are fitted in the GRP Tiki 8-Meter, a design David and the Boatsmith crew have now built three examples of, counting the new one under construction in his shop now.

Following David's instructions over the phone, I made new inner flanges from 6mm ply.  The flanges must overlap the inside cabin surface around the hull by 1 1/4 to 1 1/5 inches to have sufficient glue surface.  Then they must overlap the opening by 1 1/4 inches to allow for enough bonding surface for the acrylic window panel, which is cut 1 1/4 inches smaller than the opening all around the perimeter to allow for expansion.   The two adhesives of choice are Sikaflex 295UV or DOW 795.  I'm using the DOW 795 as it does not require a primer and seems simpler to use.  Both are incredibly strong and quite capable of permanently bonding the windows with no fasteners.  The key is to bed the window panels on a sufficient thickness of the sealant to  allow for movement.  To achieve this, I laminated a spacer layer of 6mm ply between the cabin sides and the inner flange rings.  That way, when the windows are installed, there will be a 1/4" bed of sealant and the window itself will be flush with the outside cabin surface.  More explanation of this later when I do the actual installation and take photos.    Here, I am laminating the ring frames with the spacers to the insides of the cabin:



And this is how the inside frames look now that they are glued in with epoxy.  I don't have a shot of the interior side, but on the inside the frames were finished to a nice radius with the router and will be varnished along with everything else inside the cabin. 


The 1/4 inch smoked cast acrylic that I ordered for the companionway drop boards also arrived last week and I cut those to shape using my plywood patterns:  The inboard sides of the cabin are not completely faired or painted and won't be until I move the hulls out and fit the beams.  Because I don't know the exact dimensions of the cockpit and where the seats will land on the cabin sides yet, I will wait until I can mock that up for accuracy before making and installing the rail upon which the seats will rest on the cabin sides. 


The opening Lewmar portlights for the aft cabin bulkheads have also been dry-fitted and will be installed this week.


4 comments:

jimmyboy said...

Scott,been following your change in ports.Ive done the same..wont this make the windows fairly small..Also cant follow what you mean about spacers..My email address is jamesrcarney@yahoo.com If you could describe it alittle more Mahalo Jim

Scott B. Williams said...

jimmyboy, It does reduce the size of the windows by the width of the inner flange, but they are still plenty big enough. They end up being almost the same size as the original windows I cut when I had the outside flanges on. One advantage of this method is that they are easy to replace if one gets damaged.

I plan to begin the installation of these tomorrow and will post photos of the process, which should explain the spacers. I'll send you an email as well.

kgw said...

Scott,

where did you source the small Lewmar ports for the aft cabin bulkheads? Element II is looking quite handsome!!

Kim

Scott B. Williams said...

Kim,

Mauripro Sailing in Texas is the only place I could find them in stock, and at a good price. They are the smallest size (Size 0, I think) in the Lewmar Standard Portlight series. I think they will be well worth the expense and trouble to install. I may put two more in the inboard cabin sides (above the cockpit seats)to get more airflow to the bunks.