Laminated glass in hatches

[bcboomer]

Can anyone tell me if they have replaced the acrylic in a Lewmar Superhatch series 60 hatch with laminated safety glass? The ease of maintenance appeals to me and I suspect the coefficient of expansion is better.

[roverhi]

Laminated/Safety Glass probably doesn't have the strength to support a person standing on it. Probably wouldn't break through but would crack the glass. Also wouldn't handle blunt impact like dropping a bronze winch handle or other heavy object on it. Definitely would look better longer but wouldn't feel safe doing it.

Stick with Plexiglass. It's fairly craze and scratch resistant and won't cost a fortune. Don't use Lexan. It is much more craze prone and has a softer surface so easier to scratch. If you need bullet proof, though!! Whatever plastic you end up with, don't use Windex or other ammonia based cleaner on it. It will cause crazing right quick.

[bcboomer]

10mm is double the thickness of a typical windshield so I'm comfortable with the strength.
Impact is a potential problem but all our lines go to the cockpit so we never have winch handles on deck.
If I do use glass I'll use soft shackles on the sheets.

[model 10]

If you are that confident you won't drop something sharp on it, go tempered. Mighty tuff stuff.

[dwoodall]

Laminated or safety glass only insures that the tiny shards are held more or less together. They do this by sandwiching the glass around a plastic film. If it were my I would us a hard coated polycarbanate. Lexan does have a softsurface, but with proper care does not scratch badly. Proper care means never using paper towels or bath towels to wipe it off and never use a cleaner that is not designed for it. There are relatively new hardcoated polycarbs that seem to hold up very well. The motorcycle industry seems to be slowly heading that way. My experience with polycarbs as motorcycle windshields has been good. With proper care I can get five are more years out of them and still have a windshield I can see through. For a portlight or hatch, I think they would last much longer than that. A quarter inch piece of polycarb is a lot tougher than a piece of saftey glass. I have no idea how they compare cost wise.

Years ago, I was working in the aerospace industry and a standard test was to shoot birds at the cockpit glass of military fighter jets. They used a huge air canon for this and typically supermarket chickens. Some geneous put a frozen chicken in the canon and obliterated the test cockpit. The chicken emerged from the test cockpit and put a hole in the concrete wall behind it. I wish I had kept those pictures. Sorry, off track senior moment.

Doug

[hellosailor]

"10mm is double the thickness of a typical windshield so I'm comfortable with the strength. "
Ever see a standard aviation glass test? There's an old joke, that the Brits ask NASA how to test the glass, and the NASA folks tell them to just fire a chicken at it with an air cannon. The Brits call back and say they can't understand, they bought frozen chickens at the market and the glass shattered every time. "Oh, didn't you defrost them first?"


Or a news report about someone tossing rocks or bowling balls off overpasses and drivers getting injured or killed? My friend's stepfather was killed when a spare tire bounced off a truck on the interstate and took his head off on the way to the back seat of his car. Literally.


Now, a balling ball weighs 16 pounds, a spare truck tire maybe 150? And in comparions, a cubic yard of seawater (perhaps a 20' breaking wave dropping on your hatch) weighs about a TON.


Ignoring all those speed-and-mass calculations...Personally I don't give a damn if Dumbo can tiptoe across it in sneakers. I'd want the glazing and hatch that aren't going to get upset when that breaking wave drops a ton of water on it.


Just one man's opinion.

[bcboomer]

So I guess I should throw out all my NFM stainless portlights with glass glazing and reinstall pvc frames with plastic lenses.
I was hoping to hear from someone with glass hatches.

[hellosailor]

If your portlights are the size of large deck hatches? That certainly might be worth doing.(G)


Especially if there's a chance that anything like a spinnaker pole or wrench being used at the masthead can drop on them.


Otherwise, perhaps not.

[noelex 77]

Polycarbonate is very resistant to breaking, but it flexes a lot in achieving this strength. In practice the limiting factor tends to be when it springs out of the frame/hatch.

10mm laminated or toughened glass should be strong enough. I think Oyster deckhouse windows that are large and subject to potentially a lot wave force are 12mm and they boast that one has never been broken.

It is a mystery to me why so few boat hatches are available in glass.

[noelex 77]

Glass is unusual because the yield and tensile strength are very similar. The tensile strength of tempered glass appears to be about 160 Mpa with a quick Google search.

The tensile strength of a Polyester and Chopped Strand Mat Laminate with 30% E-glass is significantly less at 100 Mpa.

10mm tempered glass should have more tensile strength than a 10mm thick solid fibreglass deck. The yield strength differences would further very significantly favour the glass sample.

Most decks are cored but 10mm tempered glass would seem to be similar or stronger than a typical deck especially the yield strength.

Perhaps I am missing something, I am not an engineer by profession. Any comments would be great. Plastics are a pain in tropical climates and it would be helpful to get some practical information on the strength of glass as an alternative.

Relating the strength of the glass hatch to the fibreglass deck provides a useful guide. A hatch that is "stronger" deck is not a concern.

Tempered/laminated glass is commonly used in even large pilothouse/deck saloon/ dodger windows. It is also used in portholes on the hull sides that may be very close to to the waterline when heeled over, but for some unknown reason (cost, tradition ?) rarely in deck hatches.

[TeddyDiver]

Google "impact resistant glass" in your area. I've installed some. They can take anything what mother nature can throw on them until the frames fail..

[hellosailor]

Glass can be funny about point loads, stress, and fractures. I've seen a Corning Corelle bowl take a bounce and clatter all around a ceramic floor without ay damage. And on another occasion, same floor, same set of bowls, the damned thing exploded like a grenade and sent shards a good 15' out.


But there's no plastic glazing that keeps the clarity and scratch resistance of a good piece of glass, I'll readily give it that.


Finding a shop that deals in extra-thick glass, that tempers glass, or fabrics any type of curve or custom lamination in glass, that may prove to be the bigger challenge.

[sailnow2011]

We replaced our size 70 with laminated glass, I do not walk on them, but I think it would hold me no problem. What a clear picture I can see out of them now. Going to the the second in acrylic because I found a used piece, and the third out of Aluminum because it only goes to the Laz.

[exkma367]

On our last boat we put laminated glass in All the port lights. One window cracked twice on on installation. Third try worked fine. I suspect the glazer may have chipped the edge on those. A year out a shackle hit and cracked the port light in the hanging locker. It remained watertight and was out of sight so it stayed until I sold here. I did keep a few plywood emergency port covers in the lazarette. For me it would depend on what kind of sailing the boat was used for. If I was going offshore regularly I would use lexan or aluminum on a hatch. Day trips between islands glass would be pretty.


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[Snowpetrel]

I've seen a crazed perspex hatch replaced with lexan. The result was terrible, too flexible to stand on without a huge deflection, and the sealant started leaking very quickly. Then again I stuck a spinnaker pole through a toughened glass portlight once, well not right through it, but it had a nice spiderweb crack... So maybe perspex is the best compromise?

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