replacing plastic windows

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discoduck

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The windows on my tommahawk 25 have are now terminal.I went to our local plastic provider for a quote on perspex,but he recomended polycarboate. To prove his point he took an offcut and beat up his bench with it,very strong stuff.Any reason why not to use P/carboate.Thanks for your help.
Discoduck
 
Polycarbonate : soft on the outside, thus able to take blows from objects without shattering, but will also scratch very easily and will flex a lot so could cause a leak unless bedded on the correct stuff - note that there is a special sikaflex product designed for this task that is UV resistant.

Acrylic (=perspex) much harder skin so much more resistant to scratching, and less flex, but also more brittle

Both of these are subject to UV degradation, so need replacement - probably around the 10 year point depending on exposure to the sun.
 
Polycarbonate is the way to go, IMHO. The reason most windows start to leak after a while is that they are "just glued in". Put in 1 mm washers ( cheapo nylon ones will do) between the windows and the coachroof proper. Use a good sealant like Sikaflex UV transparent ( NOT SILOCONE BATHROOM STUFF) . Don't be amazed by the amount required. The GRP and the perspex or polycarbionate have wildky different temerature expansion characteristics. The idea is to "float" the window panel on the coachroof body, by means of the sealant.
Cheers, an good weather...
 
Any body know of a good plastic company in surrey/south London area, that could cut out some 6mm grey tinted polycarbonate from sheet to a template (burnishing the edges)?
Regards and thanks
Rob
 
I've been told that bycycle inner tube makes a great gasket for window
bedding. Going to try it in the spring.
 
This is how we do it
1 Offer up perspex and mask ALL of it that you can see on the inside

2Sand up the glue area and the frame

3 PRIME both surfaces with the approproate primer.Sika make them to go with their sealants

4 Cut a hotglue stick into 2mm slises and stick them with a littlesika onto the primed frame. You wont see them as the primer is black

5 Use a power sealent gun to save your fingers, put in a large bead of sealant and put the perspex in place

6 Leave to cure for a couple of hours then backfill and leave it alone for a week to cure Sika cures at 3mm per 24 hrs
7 With a sharp knife cut back the excess wich will come off with the masking

We allways guarantee our windows but to do it right isnot cheap or fast
 
Thank you all very much for your help,like all things you only know the half of it when you are an amateur.I am intrigued with the hot glue 2 mm spacers.I would never have thought of it 'ever'.Exspansion rates were interesting,would again not thought they were so widly different.I shall install a small plaque thanking the forum,below the plaque already there,that says 'no drinking without the captain'.
 
HI
A question for' Boatbuilder'. My windows on Tommahawk have a curvature.How do I hold the window before the Silka takes over. Is it clamping. The present windows have holes and screws,which have caused problmns and are the problmns. How long do I have to hold the window on the sika before it holds the curvature.
Thanks
Bryan 01582 597755 I pay for the call as it is diverted.
 
When dealing with gently curved windows, which I believe yours are, we use a series of clamps and I will try to explain how.

Get some bits of wood say 1"x1" and lots of small wedges
after you have placed the perspex in place , screw the bits of wood into the GRP so that they stick out over the perspex.
Use the wedges between the wood and the perspex.
Backfill and leave for a week. It is very important that you mask up as much as you can, and being outside use longlife tape not the standard stuff, or tou will find it harder to remove than cured sika.
We all make that mistake,once.
 
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