Replacing pilothouse windows

Asked by Lester Helmus (s/v #010, Insouciance)

a. I used 3/8″ Sheffield Hyzod Polycarbonate with a bronze tint. [Do a Google Search on “Sheffield Hyzod Polycarbonate”] I removed the teak frame on the outsides, removed the old lexan and had all the screw holes and bolt holes re-glassed and the whole PH re-gelcoated. I then used methylacrylate to bond the new poly in place with a bead of Sikka 295 UV around the outside. I then painted a UV shield around the outer edges of the poly with black Awlgrip – much like your car windshield. As soon as the pictures are developed I’ll send some to you. Now I have no holes in the PH for leaks. I did a lot of research before doing this.

A5b: applyingcaulkpart1.jpg by Vincent Salese
A5c: applyingcaulkpart2.jpg by Vincent Salese

Vincent Salese (#005, Witch of the Wave)

b. Thought you may be interested in this approach to replacing the pilot house windows, I designed them using CAD-CAM and then NC milled them from 1/2 inch 6061 T6 aluminum and then had them powder coated. The Glass is 6mm tempered 1/4 bronzed tinted and the windows in the front were bent to fit. They were fastened with 1/4 inch allen head cap screws exposed. and allen head nuts as well ( flush on the inside). It was a bit expensive but I think the price could be improved. The glass was $ 1200 and the material for the frames were $ 1100. I did all the drafting and surfacing on the parts and a friend did the NC milling. I engineered the fastening and that would cost a couple hundred more for the parts. There was some time and labor involved in finishing the parts for powder coating. There was also some time involved in hammer forming the front frames to fit the proper radius of the the glass( which were bent and tempered. ) I have all the radius for the front glass surfaces along with the shapes, surfaces and fasteners for all the windows.
Gene Whitney (#069, Joint Effort)

c. I am in the middle of a fairly major job that I have put off doing for some time, replacing the windows in the wheelhouse. Actually, I am only planning to replace the side windows at this time, the flat ones. I may have told you that I installed my windows by bonding them chemically to the fibreglass. Because of the differential expansion of the Plexiglas and the fibreglass I have had a couple of major cracks. However, the main problem has been the breakdown of the bond at several places on the perimeter flange with resultant leakage. This in spite of caulking all around the groove at the side of the windows. I have now managed to remove the 4 windows (shearing some of the gelcoat on the flanges where the bond was still complete). It was apparent that the polysulphide in the perimeter groove had not bonded well to the Plexiglas. This time I am going to use Sikaflex 295UV as well as the special cleaner, Sika Cleaner 205 (in Canada, Sika 226 in the USA) and Sika Primer 209. This is supposed to give a much better bond to both the Plexiglas and the fibreglass. I don’t believe I used a prime for the original installation. I had attempted to correct the leaks by replacing the polysulphide in the perimeter groove, using a styrofoam bond breaker at the bottom of the groove. However, the lack of a primer obviously negated this effort. I will also use a bond breaker this time, so that the caulk only contacts two sides of the groove and not the bottom. The Sika literature also recommends painting a black band on the outside of the Plexiglas, overlapping the flange bond area, to lessen UV attack. It points out that car windshields have this black band for the same reason. It appears that the black is on the inside of the windshield glass on my Toyota.
David Salter (#050, Opportunity)

Promised summary of wheelhouse window replacement

We have replaced only the 4 side windows in the wheelhouse. These are substantially flat (planar). Our problem was that the Plexiglas windows were originally chemically bonded to the fibreglass flanges. Over time, with the thermal expansion and contraction, we got cracks in the two larger windows and the bonding began to separate. I had 4 new Plexiglas windows made, using my original templates. Where the originals were 1/2″ thick the replacements are 9 mm (about 3/8″). The reason is that the 1/2″ windows are overly strong (I believe) and they did not finish flush with the fibreglass. The technique used for the new installation involved using Sika 295UV urethane caulk and called for a bond film thickness of about 1/8″. This results in the new windows only protruding slightly. We do not have complete stainless frames as used on many boats. Instead, a late modification uses stainless strips along the top and bottom edges of the windows.
Removing the old windows required some leverage at the disbonded section of the window and then a good blow on the inside. The window came out tearing off the surface gelcoat on some parts of the flanges where the bond had remained strong (about 1/8″ thickness removed).

The first repair job was to make a smooth flange surface. I made up dummy patterns for each of the two window shapes (port and starboard were a close match) from 1/2″ thick low density polyethylene. The flanges were sanded and cleaned with acetone. The dummy window had the area contacting the flange coated with mold wax (3 applications). The imperfections in the flange were buttered with thickened epoxy and then the dummy flange placed in position. This was held by means of several small “turnbuttons” of plywood, using the holes that previously held the stainless plates in place. After the epoxy cured the dummy window was removed. The first attempt did not yield good coverage over all the flange imperfections so these were touched up with more thickened epoxy and smoothed with a spatula. Sanding was needed on this. Subsequent windows showed better results the first time with only small areas to be re touched. All flanges were then sanded with wet & dry paper and treated with acetone.

The Sika procedure was well descibed at I couldn’t get the USA site to appear nor could I re-acquire the Technical Data Sheet that was a useful adjunct to the Procedure sheet. The key for a good job is to use:
1. Sika Cleaner 226 to degrease the bonding surfaces (named Sika 205 in Canada!!). Expensive but you need very little.
2. Sika Primer 209 on both the gelcoat and the mating Plexiglas surface (previously roughed up with 80 grit sandpaper)
3. Sikaflex 295UV for the bonding, maintaining the specified minimum film thickness. I used the little rubber crosses intended for spacing ceramic wall tiles on the suggestion of the Sika tech rep (1-888-832-7452).
Quantities of material for the 4 windows: Sika Cleaner 226: 30 mL Sika Primer 209: 250 mL Sikaflex 295UV: 4 @ 310 mL (10.5 fl oz) cartridges
Regards, David (s/v #050, Opportunity)