A Photo & Discussion Forum for Wharram Design Enthusiasts
Acrylic seems to be the best material. On the hulls (Tangaroa MK IV) my windows are mounted on top of the skin and so I use bolts (6 mm stainles) in addition to the silicon. The area covering the silicon should be painted, not as a primer, but as a shield against UV, which is harming the silicon. It also looks better.
On the cabin tops and deck salon, the windows are mounted flush, so no bolts are needed. However, the acrylic should still be painted to protect the silicon.
Sikaflex give very good advice.
Thanks so much for all of the advice everyone- one question- is it possible to glue the material (acrylic or lexan) to the outside of the skin without rebating or fixing a frame inside the hull material? Would this be strong enough without bolts/screws? Might not look as nice but would be much easier!
Dave, that's my blog that Boatsmith referred you to. I considered simply bonding the windows to the outside of the skin as you are suggesting, and yes, it would be strong enough as long as you have sufficient overlap of the plastic over the edge of the opening. In the end I went with the rebated lips to reduce the overall size of the windows, which would look far out of proportion to the rest of the cabin sides if they were big enough to overlap properly. It would be easier and faster, but as it turned out, making the interior lips was not too much trouble, and I like the fact that the windows are now flush with the outside of the cabin sides. I would never use screws again to fasten windows after discovering this technique.
We are now at the heart of the question. All seem to agree that there are no problems as long as the windows are in a suitable recess. Now to the hull port holes. I was thinking of gluing in an internal 'lip', but that makes the window smaller. I also did not want to add an external frame. So I thought I would use the bolts. Sure enough, I would put in 5 mm shims until the silicon has settled. The question: Would you rely on a simply 'glued on top of the skin' acrylic sheet, one foot above the water line? What if another boat scrapes along your hull? Would it be strong enough even if it hooked up somehow?
So I will still add the bolts, but, as pointed out, not to tighten the acrylic close to the hull, just as added strength. Shims of 3 - 5 mm must be used until the silicon has settled.
Any other fire-sure, space technology?
Well, I admit that all the arguments supplied have made me think of a compromise solution. Let us cut the acrylic glass at an angle of about 45º so that it cannot be hooked by an object scraping along the hull. Glue only (silicon). Will it pass our marine inspection, surveyors, South African Marine Safety Agency (people who don' t know the difference between a belay pin and a nail)?
It means that we (I) will bevel the protruding windows in a way that an object scraping along the hull will simply be deflected, but will not hook onto the window, and hence will not exert an undue force onto it. Thank you very much for saving me all this work!
Thanks Scott- do you bond the adhesive direct to cured epoxy on the lip and then paint over, or paint the surface first then apply the adhesive to glue the sheeting?