A question of Glass?

[Cyruscosmo]

Hey All
I am in need of a little expert advise. I was going over the plans for my steam launch and bouncing a few scenarios around in my head when I had an unsettling thought.

Boats tend to undulate and dance to the waves in much the same way corks do... I do not have motion sickness problems so that is not what the thought was about. The thought was about the "window" I would be looking through in the enclosed part of the boat.

I have never built a boat before but I have been on many and never given this a thought before. What happens when the boat bob's and I weave? The Steam Launch I am building will be something like Annabelle. Steamboat registry http://www.steamboatassociation.co.uk/page-1117882

What kind of glass am I going to need to put in these frames? I am sure at some point in time someone will stand up and the boat will pitch and there will be a connection...

Cyruscosmo

[Lopez Mike]

You have several choices.

For almost complete safety from fracture and giving you the lightest weight, acrylics (Plexiglass) or polycarbonates (Lexan) are the best choices. Lexan is as strong as steel but tends to scratch and is more expensive. You cannot use ammonia based cleaners on it. Plexiglass is certainly strong enough and is less expensive. And both can be cut with ordinary woodworking tools. Lexan is particularly tough in this department. No splitting when drilled. But none of the plastics are very long lived.

Ordinary household glass is dangerous. Laminated glass is much safer but tends to come in rather heavy thicknesses. A good choice would be tempered glass. For custom sizes it must be cut to dimension and then tempered. Any attempt to cut or drill it results in a heap of small bits.

The reason tempered glass is safer is that the resulting bits are surprisingly safe. You can drive a car across a pile of shattered tempered glass without getting a flat.

If I were building it, I would go for tempered glass. A visit with more than one local repair shop would be informative. A place that deals with automotive repairs, especially RV's, would be a good thing.

If the quotes you get are too high, then go for ordinary plexiglass.You can fabricate it yourself and it's not that expensive to replace down the road when the little micro scratches accumulate. Also, it is almost infinitely polishable. Anything short of a bullet hole can be sanded and polished out.

[Mike Rometer]

For a slightly different window that I recently glazed, and subject to similar stresses, I used 6 mm Plexiglass. I was pleasantly surprised that it cut without drama with a standard D.I.Y. jig-saw, and where it was slightly oversize I trimmed it with an electric plane. I also drilled it without trouble. Not a material to be feared, unlike the old Perspex which would split if you looked at it sideways.

[DetroiTug]

The polycarbonates are much less prone to scratching as it is much harder, which also means it will crack under stress. I used Polycarb on all the windows in the tug and they have held up. I think that is what most boat windshields are made from. The front window of the wheel house is flat against the wind and it has held up just fine at high speeds.

-Ron

[Lopez Mike]

My data sheets have it the other way around between polycarbonates and acrylics. The polys less likely to crack but being more subject to scratching.

I used Lexan for my sailboat cabin windows years ago as I was headed out across the ocean and was fearful of a wave breaking them. If I were to do it again I would use acrylic. The waves never came close to threatening the windows and they have all gone to hell. And the expense was alarming.

In the odd chance than someone shoots at me, I will be fairly safe behind those windows. I used 3/8" and I took a shot at a sample with a .22 and only got a small dent. Then blazed away with a .38 and got a crater.

But they are all frosted from the sun and need to be replaced. It has been twenty years though.

[racerfrank]

Does there need to be a concern about weight and center of gravity here ? or would it not be that big of a difference between glass and plexi?

[DetroiTug]

I've been confusing Plexiglas as something else than polycarbonate or Lexan. I've bought plexiglass before that was very poor quality and that's what had me thinking the two were different. Must be different grades of Lexan?

Edit: I figured out my confusion, I've been calling Acrylic polycarbonate or Lexan ( "polycarbonate" sounds harder (carbon) than "acrylic"). When in fact it is Acrylic Lucite, not Lexan. I had some scrap from my tug windows and it says "Acrylic".

-Ron

[Lopez Mike]

The trouble is that I'm easily confused and you had be going there for a minute. Ah, the joys of old age!

[Cyruscosmo]

Thank you for the replies.

As far as regular soda glass goes I can see a potential for severe injuries with that stuff, which is what got me thinking.

I don't have enough experience with using the plastics for windows to know how well it holds up to direct sun and weather over the long haul and I was not sure if there was some special "Marine" material for windows.

I don't believe there will be any balance problems as the same windows are mounted port and starboard. I am not sure about weight or CG problems, I still have to build the boiler and engine to get the final weights then Paul can figure out where they will sit in the hull and balance out the whole thing at once.

So far it is looking good for Acrylic or tempered glass. Can anyone else weigh in on how well Acrylic holds up under those conditions? Frosting/scratches how easy is it to polish?

Thank You

Cyruscosmo

[Lopez Mike]

The glass pretty much lasts forever. You can calculate the weight of either from the densities. 2.6 gm/cc for most common glass and 1.2 gm/cc for acrylic and polycarbonate.

I have a repair kit for acrylic that claims that you can repair anything from a bullet crater to slight fogging. Depends on how much work you want to do. If it is the usual general accumulation of tiny scratches I just use plea polish. No big deal. If it has gone totally to hell, I just replace it. It's fairly cheap.