Update.
This IS the easy way to mount lexan lenses.
And it may not be the best waterproof way - have my doubts because I cheated on the number of fastenngs - but maintenance-wise it IS the only way, because the windows can be removed in a trice, recaulked, replaced without really sweating it. 3/8" p.carbonate is very stiff stuff, it looks impossible to draw fastenings tight enough to bend waves into the sheet. The system does not call for bonding, fastenings are not torked.
Butyl tape comes onsite in a cooler after being unrolled cold from storage in the fridge at home, cut to approximate length with Fiskars and rolled back up into a loose roll.. Still sticky when cold but not sticky sticky.
Place lens on a packing quilt inside up, unroll butyl around the perimeter bearing surface. Use an awl to locate and open holes in the butyl - and from the underside (outside) press thru 1/4" PHMS that each have a 3/32" thick EPDM washer pressed on against the head. The 5/8"D rubber washers seat into a 1/16" deep counterbore in the plastic. EPDM is very squishy under pressure and needs the countersink rim to help keep its shape. Doesn't always work. (PHMS can of course be backed out later and a s,s, washer added on top of the rubber one to get more even pressure.)
The tape is getting warmer the more time it takes to push the screws thru. But the screws get more-or-less stuck to the tape holes and the 1/16" thick clear polycarbonate spacer washer can be dropt over the threads and pressed into the butyl. The piece can be rotated to work on - or break for lunch and left unattended - there's no viscous tube goop to skin over or make a mess! Don't need gloves.
The lens can be picked up, all pieces stuck, and taken to the window opening. Two nylon studs partially screwed in on the bottom row serve as locators to position the lens. Again, NO MESS! Then feel for the T-nut and happily turn each PHMS home.
Miscalculated what the finished length of the screws was to be, so had to changeout longer for shorter, ending up with 3/4". However if hard washers need to be added to cap the rubber washers, the longer ones (7/8") could be back again. We'll see.
Must go without saying that all the time the windows were handled: marked, cut, routed, sanded, drilled and scuffed, the protective plastic films inside and out were carefully left on the pieces. Film got a little ratty and corners came unstuck - but the polycarbonate has to be kept covered during the whole process.
This is especially the case when the plastic is tinted or UV treated (which means it has an inside & outside)
- a scratch on this techy sheet canNOT be buffed out.
As the fourth window was being attached, it happened that the very last screw (really!) did not meet up with its inside partner. It was an empty hole. NO T-nut. WHAT the hell...
Couldn't believe it. Did ALL the holes. So I located the well-used and pretty dull counerbore* and began to drill in the 3/4"D T-nut bore I had somehow missed. Peeked thorugh the hole and saw that it matched the hole in the lens. But immediately hit hard shiney metal and DIDN"T bust a carbide. The T-nut was there alright, but off by a half an inch or so embedded like an aching wisdom tooth. Still shaking my head, that second hole: what happened?
Got it out. Royally screwed up the integrity of the surrounding liner, filler, and ancient cabin polyester - regooped it, rebuilt it, redrilled it, repotted the T-nut - and now the repair awaits primer and the remounting of the fourth lens.
Damn refurbishing gods, how do I get on their wrong side?
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* This counterbore plus one pilot costs about $50. Found at the bottom of pg 2458 in the online MMCarr catalog. Like a champ it drilled more than fifty 3/4" wide holes 1/2" deep in the old cabin liner and new epoxy filler. That would add up to about two feet of solid polyester, glass and epoxy for that HSS bit.
BUT the four flute bit can have the flute bottoms hand honed leaving the sides untouched - as sharpening them would change the counterbore's diameter! For its use on the boat here, its exact diameter bore contributed to the success of the job. It is conceivable that in the future more T'nutz and PHMS may have to be added to make the lenses more waterproof. With a steady hand, extra fastenings can be drilled for IN PLACE. Disassembled, fine tuned, rebedded, maybe TefGelled, and returned to the cabinside. Extra work but do-able.
Might describe counterbores as flat bottom countersinks. The bit leaves a clean flat surface exactly at 90 degrees to the pilot.
[Now have added more pilots and a 5/16" to the 5/8" counterbore (used for the EPDM washer) so that adding fastenings later with the lens in place can in theory be done.[
TEFGEL
[recently Forespar introduced their teflon anti-corrosion product: (not KY for stallions)MareLube TEF45 - 45 refers to their formula having 5% more teflon than Tefgel (making it 5% better obviously!] ,
must be considered to ultimately waterproof this system. PHMS are 316, T-nuts are 304 - in salt they should be isolated. If any screws get backed out they may get TefGelled. But the butyl should perform as hoped: stay forever sticky between the lens and the cabinside, won't let any water under pressure inside (doesn't get displaced), EPDM washers form a seal under each head, and butyl squished in around threads creates the waterproofing.....want to assume the embedded T-nut is far enough removed from exposure not to need any extra protection. Famous last words.
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Bills next post won't make any sense, because there was an idiot's post here, must have been mine - fortunately now erased. Hope this cabin window stuff is credible.
Apologise for exercising Bill's incredible patience!!!!
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