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Old 13-07-2006, 20:06   #1
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Plastic Pilothouse Windows?

I have a 1973 hardin force 50 that is being brought back to its natural beauty. I am not a big fan of large pilot houses and the large windows that go with them. The windows of the pilot house are glass, cracked, and are waitting to be replaced. I want to replace them with plastic. What is the best plastic (lexan?) and how thick? I want to match the strength of the plastic windows to the strength of the fiberglass and wood pilot house as much as possible-no weak link- in the event the boat ever gets slapped with a wave. Anyone with information or experience with this subject, your knowledge would be much appreciated.
Thanks Duane.
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Old 13-07-2006, 21:09   #2
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ALoha Duane,
I understand that lexan scratches but is tougher than plexiglass. I use 1/4 inch lexan for large portlights that are verticle fore and aft and for hatch covers I use 3/8 inch plexiglass.
Your windows probably will be much larger and require thicker material. I hope others who are more experienced in this will reply.
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Old 13-07-2006, 21:20   #3
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Lexan does indeed scratch and scratch easily. As soon as you wipe it, it will scratch. Plexi is more resiliant to scratching, but does not take as well to sunlight. So eventually, it's surface goes hazy anyway. Lexan is the stronger for given thickness of the two. But it also tends to be more flexi and tends to warp and distort more. If also tears along itself easily. So any bolt holes or shuch, must be made slightly bigger than the bolt/screw and must be countersunk. Same must be done with Plexi, but it isn't quite as delicate. Both expand and contract with heat and all attachment holes need to be such that the movement doesn't place strain on the panel.
Niether is going to withstand wipers.
The best for clarity and hard waring scratch resistance is still glass. But you don't use ordinary glass. You need special toughend glass. 10mm(3/8") toughend glass has the same strength as 100mm(4") thick normal glass. As for how thick you need to go, depends on the square area of window size. A supplier should be able to give you advice in regards to that.
The real biggy does not matter what material you use. You need to be able to support the material in a frame and not have the frame give way or allow the material to bend enough that it pops out.
In off shore boats, it is good policy to have storm shutters, which are ply panels that you fit over the windows to add additional strength.
Personaly, I would go glass.
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Old 13-07-2006, 21:39   #4
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Lexan or it's equivalent is what's recommended. I don't know how big your windows are but Lexan has a rating of 9000 psi for 1/8" thickness.

I think I would contact your local plastic vendor. They may have some spec's on size vs thickness for boats.

And lexan is not cheap either, so you may want to get quotes on lexan vs tempered glass. If your old windows are cracked then they had the wrong stuff to start with. Tempered glass should always be used where there is impact possiblities. Maybe even laminated glass (plastic in the middle-car windshields) depending on the risk factor of bodily injury. e.i. If your helm is right next to the glass.

The problem with lexan is the cleaning. If this is a window that you have to see out of to navigate. Glass would be a better choice. A couple years of cleaning will cause Lexan to get hazy even if you take care. Just wiping you hand across the Lexan causes micro scraches.

Polishes are available but it's much like ones car. How many times does the average person wax their car????

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Old 13-07-2006, 22:28   #5
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I would go with plastic of some sort, not glass. A portlight of mine (safety glass) was stove in by a massive wave and there wasn't much left.

Lexan is really strong, but besides already mentioned here, also very susceptible to anything like acetone, mineral spirits that you might use cleaning up after installing. I learned that the hard way and had to redo a hatch cover I installed!
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Old 14-07-2006, 00:41   #6
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Scott, what part stoved in. Did the glass break or did the frame fail or ????
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Old 14-07-2006, 01:16   #7
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both. the safety glass left a shattered, though not dangerous, mess. i think plexi or lexan would have stayed in one piece
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Old 14-07-2006, 02:11   #8
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There are two types of plastic to use here

Acrylic (e.g. perspex)
Polycarbonate (e.g. Lexan)

The acrylic has a harder on the outside and is thus more resistant to scratches (and scratches can be polished out).

Polycarbonate is a much softer material, thus gives to the hard point impacts and absorbs them, but this softness means it will scratch more easily. However it is much stronger and in the right thickness is bullet proof!

There is a version in UK called marelon which has a harder skin and thus much better for windows.

Neither will work with windscreen wipers - they will just scratch.

Glass will last much longer, whereas the UV will degrade the plastic and reduce its strength.

I have polycarbonate on my big windows, and glass on my smaller ones.
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Old 14-07-2006, 06:34   #9
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I replaced 10 windows in my boat last year. there are some pictures in the photo section on this site. I used 1/2" acrylic with the Sika flex system for bonding. The 5'x8' sheet of plastic that I bought was $500. I used a carbide blade on my table saw to cut the basic shape then used a sanding disk to make the shapes, and a router to finish off. I am very happy with the job. It would be hard to beat tempered glass and the Dow corning bonding system so think about what you are going to do carefully.
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Old 14-07-2006, 09:23   #10
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A word of warning about using sikaflex on the windows. Make sure that you get the one designed for this purpose, cause the others dont have the same UV stability.

A proper sikkaflexed window doesnt need screws or bolts.

If you are going to use screws or bolts, make sure that the hole you drill has enough space for expansion when it gets hot, otherwise it can actually fracture the plastic (particularly acrylic).
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Old 14-07-2006, 09:51   #11
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Sika Flex has a web page and 800 number. I used both allot. Not needing screws made for a very clean leak free job. Jametown distributors was the best place that I found to buy from.
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Old 14-07-2006, 10:23   #12
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Just curious - if you use Lexan for its strength, couldn't you then apply that window tint film that also is a shatterproof barrier for glass windows? Seems like the combination of the 2 would resist scratching and provide maximum breaking resistance.

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Old 14-07-2006, 18:05   #13
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Also consider laminated glass as an alternate to Lexan. Sika Flex is the best bedding for sure. You need to consider the area of each port to really know the strength. The strength issue gets more important as the size of the port increases.

With lexan you can only use the proper cleaner. Ammonia is a killer on lexan (any palstic). Any strong detergent is also bad for all plastic. Only use a plastic cleaner.
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Old 14-07-2006, 21:28   #14
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There are many grades of acrylic (i.e. Plexiglass or Perspex) and polycarbonate (i.e. Lexan) and your best bet is to contact some of the distributors in your area, or look at the manufacturer web sites (i.e. GE and Rohm & Haus) to see the properties of the grades and materials. You can get Lexan MR10, which is a commercial glazing grade that is extremely strong and has an anti-scratch coating on it. But, you won't find it at the local plastic bathroom accessory shop. And you may want to figure out first, how much strength you want or need, and then whether you can afford to buy it. An alternative may be to use heavy glazing in one or two key panels, and have plywood or metal storm panels made up to cover the other ones.

Generally polycarbonate will be 10x-100x stronger than acrylic for the same thickness. The softness can be a problem, and in commercial applications it is often solved by using a laminate. In the south US you can now buy "hurricane windows" for homes, which typically are a laminate of thin glass on both sides of a polycarbonate sheet. That way there's no scratching--although there will be a repair if the window gets hit by something, as the glass layers crack up but the structural polycarbonate core holds up.

And then of course, you've got to spec an installation design that is as strong as the glazing.<G> In the US you can get outstanding tech advice from the folks at GE, who make Lexan(R). There's a toll free number for their "structured plastics division", meaning plastic that is already cast into a structured shape, rather than raw resins used in manufacturing.
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Old 14-07-2006, 22:47   #15
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Hi Irwinsailor,
I did my perspex windows with the silkaflex system in the summer. Everyone in our marina told me to keep away from it. They are all using a urethane "bostik".
I used a 7mm dam rubber to contain the silkaflex and give a good gap of product between the window and boat and degreased, sanded and prepared both surfaces real good. I used their expensive primer and then the acrylic uv sikaflex.
So far no leaks and it looks real good. No screw holes either which makes it look great.
I have a few samples at home (sitting on the dog kennel) that I have left in the sun and every now and then I go past & give them the treatment to see if I can seperate the two perspex samples. So far, holding tight.
I think that when peoples windows fail using silkaflex, they may not have cleaned or primed the two surfaces correctly or done something wrong.
cheers
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