Storm Boards for large windows?

[Tim Good]

This is a continuation from this thread which I never got to follow up on and now looking to get them sorted before an Atlantic crossing later this year heading for Patagonia.

I have fairly large windows on my Seastream and I feel the boat is very strong in hull, rig, watertight compartments, encapsulated keel etc... but in a big knock down the windows let her down maybe. I have plywood replacements but I want a transparent semi-permanent solution for putting in place before big passages.

Here are my Qs:

1. Is polycarbonate still the best solution? Is this just what people call Lexan? Does anyone have a decent supplier that can cut to the shape I send?

2. I want to create 4 fixings around each window. I was considering making a new fixing but I think I can just remove just 4 of the screws (of many others) that hold the existing aluminium frame in place at the corners, drill through to the outside of the frame and then replace the screw with a bolt of some kind, secured from the inside. This would also act as extra security for the windows when leaving the boat in dubious places. Thoughts on this? See image of frame below?

 

[Tranona]

Yes, Lexan is a brand name of polycarbonate and it is the right thing for what you propose.

No shortage of firms that will cut and finish to patterns. Some will probably accept CAD files as well as physical patterns or dimensions. Does not have to be a marine supplier and you will find prices vary as do the brands offered, so a bit of googling and discussions with suppliers is the next step.

Just as a start www.sunlightplastics.co.uk and www.projectplastics.co.uk both advertise regularly in PBO and may well have made similar things in the past.

 

[Spirit (of Glenans)]

Consider making a wide, thick gasket/seal from neoprene or similar, that will provide some measure of watertightness all round, given that with only four bolts, compression over all the mating surfaces will not be uniform.
Sealing the bolts when in use will also be a problem, although in the event of storm damage, a rough application of sealant will suffice, using it for security purposes would present difficulties. My thoughts, without any relevant experience would be that thieves would break in through the companionway rather than through cabin windows, and that a determined one, who would smash a side window would just as easily smash through the polycarbonate also.

 

[NormanS]

Mine were made for a previous owner in Polycarbonate. They stand off the windows by about 10mm, so they are not an attempt to achieve a better seal. They are hooked onto a stainless grabrail, which is conveniently pl.aced on the side, just above the windows, and when in place, the lower edges sit in a stainless channel. Rivnuts in the channel, take bolts which pass through holes in the Polycarbonate, securing the bottom edges. They are only fitted to the side windows of my deck-saloon yacht. Apparently the surveyor who insisted on them for serious offshore passages, reckoned that water coming from ahead would be sufficiently broken by the mast etc, but that the side windows were vulnerable to a knockdown.

Polycarbonate is very strong, but is very susceptible to scratching. Mine are 6mm.

At sea, I have never felt the need for them, but I do fit them when laid up ashore in the winter, when they act as extra insulation, and stop condensation on the alloy window frames.

 

[Tim Good]

Hello again. I'm drawing up my CAD files now and wondering how much overlap I should have on the polycarbonate beyond the frame of the existing windows. The existing frame seems like a fairly strong aluminium type and the GRP of the deckhouse is strong. You can see from the photo above how it looks. I'll likely have the polycarb flush to the outer window frame, perhaps will a neoprene seal as suggested elsewhere. But what overlap would be prudent given the worse case scenario knock down?

 

[Tranona]

Don't think you need any overlap past the existing frame if you are going to use some of the frames fixings. You will already have overlap over the existing glazing because of the substantial frames.

 

[Tim Good]

Don't think you need any overlap past the existing frame if you are going to use some of the frames fixings. You will already have overlap over the existing glazing because of the substantial frames.

I suppose I was thinking that 10mm polycarbonate would be so strong that it may end up pushing the frame through in a worst case scenario and then an overlap would be there to catch on the deckhouse structure.

 

[noelex]

The first question is what is the window composition. Rough material thickness and size will give you some idea if there is a need for storm covers.

Our new yacht has a pilothouse so we faced the same issue. Our solution was to specify strong windows that are very unlikely to be compromised, but there is also provision for bolt on security covers as a "belt and braces" solution.

The storm covers can be used in the unlikely event a window becomes broken, or more commonly as security and UV protection if the boat if left unattended for long periods. The factory will be providing 4mm anodised aluminium storm covers for each window, but I also intend to make up a couple of polycarbonate alternatives. Polycarbonate is not very difficult to cut so it is not a difficult DIY project, but you do need suitable fixing points around the windows which is the hard part unless these are part of boats construction. The fixing points can also be used for shade covers.

 

[Tranona]

I suppose I was thinking that 10mm polycarbonate would be so strong that it may end up pushing the frame through in a worst case scenario and then an overlap would be there to catch on the deckhouse structure.

Are the frames not bolted through the GRP? 10mm is a bit OTT? They will be very heavy (and expensive!). I would have thought 6 or at most 8mm would be fine.

 

[essexboy]

Are the frames not bolted through the GRP? 10mm is a bit OTT? They will be very heavy (and expensive!). I would have thought 6 or at most 8mm would be fine.

I would think as above 6/8 MM ample. With 10 MM you stand a chance of distorting the frame before the lexan takes up any bend !

 

[William_H]

If the windows are satisfactory now I would leave them as they are. You could improve the strength a huge amount by mounting support bars inside the windows. So dividing a window with a horizontal bar attached through the GRP and with support padding to the actual pane would effectively give you 2 narrow windows. You could do the same from top to bottom giving good support in a knock down and intruder resistance. good luck olewill

 

[Neeves]

I would not assume that because any windows are heavy duty that they will not fail (unless they are armour plated glass). We have 10mm acrylic windows most with a slight bend 2 with an almost 90 degree bend. The windows tend to be trapezoidal and about 1000mm x 700mm, so large. Though the acrylic is large there is a huge overlap of 150mm so the aperture itself is quite small - almost conventional. The slight bend is about 20mm. Upto about 12 months ago they looked perfect but 4 have now developed a crack about 250mm long. I'm guessing the acrylic was cold bent and fitted and the stress from the cold bending and Australian sun has conspired to form the cracks. I'm guessing sun was a major issue as all the cracks have occurred on one side - which I assume has the most sun. The windows have a very dark tint and we never saw the need for sun covers - this was a mistake, we needed covers to protect the windows themselves - not for shade.

The acrylic showed no signs of deterioration, until they cracked at about 16 years of age. no crazing and minimum of scratching.

We are in the process of replacing the cracked windows and have the first one cold bent ready to instal. What I don't know about cold bending, we have bent over a 3 month period, - does the acrylic have memory, will it want to return to flat? 'Hot' bending will not have a memory but a 20mm in, say 700mm is not much - we will find out.

But before they cracked I assume with a heavy sea they may have cracked earlier and may have failed more catastrophically. To put this context - the cabin roof is 3m above the sea level - and we have had seas breaking well over the roof on a beam reach.

Newer versions of our cat have reinforced glass windows - but the roof moulding has changed and they do not now fit our yacht.

 

[Tim Good]

Out of interest... everyone says "polycarbonate is great and strong but it does scratch"

What does Lewmar make its hatches from as all mine are original from 1996 and look as good as new with me standing on them regularly.

 

[noelex]

Out of interest... everyone says "polycarbonate is great and strong but it does scratch"

What does Lewmar make its hatches from as all mine are original from 1996 and look as good as new with me standing on them regularly.

They are likely to be acrylic, which is polymethyl methacrylate. You have done well to keep them in good condition for so long. In my experience they deteriorate reasonably rapidly, but it is not possible for a full time cruising sailor to keep them covered up and over time UV takes its toll, especially on the horizontal hatches.

Polycarbonate is stronger, but flexes a great deal when exposed to significant force. In practice, in many applications, it flexes and pops out of the frame so can be effectively less strong than acrylic. It also scratches easily, as you note.

Glass (treated) is not often used. It is heavy but has a lot to recommend it, especially long term transparancy. It could be used on more marine applications especially widows. Expensive yachts like Oyster tend to use this solution. It is not great deal more expensive especially if you factor in the high costs of replacing hazy or cracked plastics, but potential buyers tend not to notice these sort of details.

 

[Daydream believer]

I would use 8mm polycarbonate & mount it bolted through rubber doorstop spacers through the GRP close to the perimeter of the existing frames. They would have butterfly nuts on the inside & have 6 bolts per window. This will leave a gap of 15mm between polycarbonate & window. This would allow one to hose water between the 2 for cleaning. A couple of times annually the outer skin can be removed for major clean. If a big wave hit the side the polycarbonate would flex a bit but still protect the windows. If a window did break then remove the stops & fit the polycarbonate with some mastic as temporary repair until it could be replaced properly.
Make some 3mm ply patterns. Buy some 8ft * 4ft sheets direct from a wholesaler yourself & take them to any joinery shop to cut them & round of the edges with a router for you.