Acrylic Windows

Boathook

Boathook

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My new to me 'toy' has had the aluminium framed glass windows removed and replaced with acrylic.
It seems that the windows are bedded down on an adhesive / sealant with M3 machine screws every 5" or so. M3 is ok but the nuts are really awkward and there are leaks through the holes that the screws go through. I will eventually bed the new fixings in with a butyl sealant.

I'm wondering whether to go up to M4 machine screws, but how large would I have to drill the acrylic so that the M4 won't crack the acrylic, 4.5mm or even 5mm diameter ?

Another option is that I stay with M3 and get some Big Heads Sighted internally threaded nut | ST38 | bigHead® Bonding Fastener made specially for M3, M4 being the smallest they list. These fittings would allow me to tighten up all the screws without assistance.
I have considered M3 rivet nuts but they are 9mm long and the GRP I'm 'bolting' through is only 6mm.
Unfortunately I don't have any pictures to share, but does any one have other, preferably sensible, ideas / suggestions ? I'm looking at around nearly 250 of the things !
 
How big is the overlap of the acrylic to the fibreglass? If it is narrow you need the screws, if the overlap is significant many windows, on vessels, are simply bonded to the fibreglass, with an adhesive sealant specially designed for the application (3M make one, as does Sika and probably the maker of the commonly mentioned here, CT1.

I've used the Australian, locally made, equivalent, it works - but application needs patience and preferably 2 people, one inside, one out.

One reason you may have leaks is that you need to make an allowance for the windows to expand (and as you are in the UK) and contract in the summer/winter. This movement can be factored into a professional application - possibly missing from your windows (but available from the adhesive/sealant manufacturer, or it is in Oz).

Jonathan
 
Neeves said:
How big is the overlap of the acrylic to the fibreglass? If it is narrow you need the screws, if the overlap is significant many windows, on vessels, are simply bonded to the fibreglass, with an adhesive sealant specially designed for the application (3M make one, as does Sika and probably the maker of the commonly mentioned here, CT1.

I've used the Australian, locally made, equivalent, it works - but application needs patience and preferably 2 people, one inside, one out.

One reason you may have leaks is that you need to make an allowance for the windows to expand (and as you are in the UK) and contract in the summer/winter. This movement can be factored into a professional application - possibly missing from your windows (but available from the adhesive/sealant manufacturer, or it is in Oz).

Jonathan
Click to expand...
Overlap not really big enough and I would still have all the holes, even though the 'adhesive' may well fill them. Also being on a Cat, even though a solid one, there is some flex. New acrylic would be quite an expense, especially as there is nothing wrong with existing.
 
I thought the secret to not cracking the acrylic or the grp was to slightly countersink the hole.
This also allows the butyl to seal better too.
I have found the butyl tape made by scarpa (Hadleigh, Hadley? Marine supply it) to be very easy to use and effective.
I have replaced acrylic overbolted windows on a couple of boats, and have always used M4.
I sourced some black nylon M4 countersunk machine screws to match the existing ones used on a previous Shetland mobo about 15 years ago. They were very easy to use, sealed well with a tiny blob of butyl under the head before tightening, and were easy to trim flush with the nylock nut on the inside.

The internal nuts always made it a 2 person job though
 
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How thick is the acrylic? Our windows are through bolted every 50mm but the acrylic is 10mm. We use countersunk M4 slot heads with dome nuts on the inside. Done thousands of miles and no cracks.
We also would never use butyl. Horrendous stuff to clean off and our experience is that is settles, needing screws to be periodically tightened. This leads to leaks.
We bed everything on Geocel Works. No leaks from windows after a few Atlantic crossings
 
Dellquay13 said:
I thought the secret to not cracking the acrylic or the grp was to slightly countersink the hole.
This also allows the butyl to seal better too.
I have found the butyl tape made by scarpa (Hadleigh, Hadley? Marine supply it) to be very easy to use and effective.
I have replaced acrylic overbolted windows on a couple of boats, and have always used M4.
I sourced some black nylon M4 countersunk machine screws to match the existing ones used on a previous Shetland mobo about 15 years ago. They were very easy to use, sealed well with a tiny blob of butyl under the head before tightening, and were easy to trim flush with the nylock nut on the inside.

The internal nuts always made it a 2 person job though
Click to expand...

Minor niggle

Scapa not Scarpa

They specialise in....tape.
 
geem said:
We also would never use butyl. Horrendous stuff to clean off and our experience is that is settles, needing screws to be periodically tightened.
Click to expand...
I agree about butyl putty or such being awful, always slowly leaking out. I used it once and would never use again.
The Scapa butyl tape (thank you Neeves) was wonderful though, lightly self adhesive to hold itself in place while assembling, and super quick. I cut it to length with sharp scissors and trimmed the excess inside with a craft knife once tightened. You don’t need to mess about with washers as spacers either.
 
Dellquay13 said:
I agree about butyl putty or such being awful, always slowly leaking out. I used it once and would never use again.
The Scapa butyl tape was wonderful though, lightly self adhesive to hold itself in place while assembling, and super quick. I cut it to length with sharp scissors and trimmed the excess inside with a craft knife once tightened. You don’t need to mess about with washers as spacers either.
Click to expand...
The difference for us maybe that we sail a lot in the tropics. The higher temperatures mean the butyl tape is more fluid. It's softer so compression is achieved more easily over time. It just doesn't work here.
We have found Geocel Works far better. We also found cleaning up with Wonder Wipes a great solution. They will even take the sealant of clothing.
I actually glued my hardtop windows in with Geocel Works rather than screwing it because the acrylic is only 3mm thick. I don't think I would have been able to screw it without cracking the acrylic. We have done 5,600nm with the hardtop since the summer, experiencing some rough weather, and they are still nicely fixed with no leaks
 
geem said:
The difference for us maybe that we sail a lot in the tropics. The higher temperatures mean the butyl tape is more fluid. It's softer so compression is achieved more easily over time. It just doesn't work here.
We have found Geocel Works far better. We also found cleaning up with Wonder Wipes a great solution. They will even take the sealant of clothing.
I actually glued my hardtop windows in with Geocel Works rather than screwing it because the acrylic is only 3mm thick. I don't think I would have been able to screw it without cracking the acrylic. We have done 5,600nm with the hardtop since the summer, experiencing some rough weather, and they are still nicely fixed with no leaks
Click to expand...
The butyl tape I buy is this from Hadlow marine windows

‘Scapa 3507 bedding tapes

High density closed cell UV resistant PVC foam sealing tape, self adhesive on one side. Available in grey. Ideal for bedding perspex windows, aluminium frames, etc. Easier and cleaner to apply and just as effective as mastic but with the advantage that if you need to take things apart again they come apart easily. Watertight when compressed by 30%.’
 
Dellquay13 said:
The butyl tape I buy is this from Hadlow marine windows

‘Scapa 3507 bedding tapes

High density closed cell UV resistant PVC foam sealing tape, self adhesive on one side. Available in grey. Ideal for bedding perspex windows, aluminium frames, etc. Easier and cleaner to apply and just as effective as mastic but with the advantage that if you need to take things apart again they come apart easily. Watertight when compressed by 30%.’
Click to expand...
That isnt a butyl tape from what i can see.
We have about 20 years experience using modified polymer silicon sealants (as used to fix and seal glazing panels in skyscrapers) on our boat. They work incredibly well and are far better than the widely used and over priced Sika products.
 
When the acrylic windows on ours got too tired/crazed we discovered that several fixing holes were also tired. We resolved the issue by cleaning out and epoxy filling all of the existing holes and then drilling both the new windows and the fibreglass in locations offset by a tad from those original holes; windows were then bedded in good quality butyl tape - crossed the Pacific leak free.
 
Boathook said:
Overlap not really big enough and I would still have all the holes, even though the 'adhesive' may well fill them. Also being on a Cat, even though a solid one, there is some flex. New acrylic would be quite an expense, especially as there is nothing wrong with existing.
Click to expand...
I had not realised yours was a cat. Our windows were big, on a cat, and we used 10mm acrylic - big overlap - 100mm.

Being large demanded 2 people to instal and one window at a time (or you end up with the interior being open to the elements). The 2 of you need to talk through how you are going to instal as black sealant/adhesives gets everywhere.

Jonathan
 
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