Big windows - dangerous in an ocean-going yacht ?

For folks looking for storm shutters the local bus charter shop is the place.

Coach passenger windows are usually made of tinted Lexan .

The Lexan is thick enough to repel a cement block tossed from the street , when driving through more savage areas.

The tour coaches replace the lexan as it becomes scratched , and a good sized hunk,2.5 ft by 5 ft or so5/8 to 3/4 thick costs little , as they usually throw them out.

We use a full sized passenger window with lexan on our boat , and cut down a frame to about 1/2 width to hold laminated auto glass.

The glass is clear , and a wiper is fine (if its wet).

The tinted lexan is much hotter (tinting absorbes heat) but nice on really bright days.

Since heat wouldn't be a bother with storm shutters , the dark color would not matter.



FF

 

A scratched perspex window can be made clear again. Clean the surface properly, then when dry and clean you can gently heat the surface using a heat gun. The scratches will disappear at a certain temperature.

Overheat and water will make bubbles and then you have to replace it.

Curved windows are made the same way, heat it to where it becomes soft and gently bend it to the form required.

 

Nice idea Fred!
Unfortunately not for us Europeans, tempered glass is mandatory on cars and buses.


Fanie
thats true but still does not make them a good choice on a yacht.

 

plain toothpaste can be used to polish out scratches

600 wet or dry also

 

"...I have seen many examples of so called offshore boats with cracked window sections and shattered glass as a result of just twisting forces..

That's the real problem with large windows. The designer has not ascertained the loads that the boat will experience in large seas correctly. And as such has not designed the structure accordingly. On a "global" analysis, the shear paths of the superstructure acting as an I-beam. Where does the load go when there is insufficient shear path....through the glass/laminate.

And in detailing, even if the structure is "stiff enough" to reduce racking to an acceptable level, more often than not they forget the local shear paths and also the local detailing in the corners to reduce the stress concentrations.

 

Don't use lexan. It fogs up so badly you wont see anything thru it after three years..
Brent

 

For that reason...............well, I said it above, YOU can have the name.

Do you think that makes a too big difference Brent?


He was talking storm shutters!

 

Lexan window we used on several boats running around for nearly 15 years now...no problems. Like all things, you get what you pay for!

 

Yup, have got authority acceptance according to DNV 15 m rules (~"Nordisk Båtstandard") for Polycarbonate ("Lexan") in fifi/resque boats for open waters and Lloyds for small survey vessel for bathymetric research, unrestricted operation. In both cases PC panels glued outside to al-structure with "Sikaflex", string thickness 3 mm, overlap 20 mm.

It took some testing evidence though, we had to prove that the completed structure with windows would comply to the specified panel pressures. As for change of transparency; like Ad Hoc said: you get what you pay for!

Our reasons for using PC are weight/strength, better thermal insulation than glass (less condensation), easy to work, thermal expansion versus al easily catered for by flexing glue.

 

What makes a window that is glued to a panel so strong is it can flex a little bit, in order for it to break it has to stretch to the point where it bends enough to break. It takes quite a bit to get it to stretch that far...

I did a little experiment a week or so on clear perspex. You can do the same, sand it to where it becomes dull, then use a heat gun (mine has a heat control) and clear it again, it comes out as new. You won't be able to remove gauges, but even they become clear with heat.

 

An excerpt..........

 

Could be the key to the problems

 

I mentioned that already Fanie. The frames are the issue on first hand.

 

I've yet to see lexan over three years old that wasn't fogged up. Moitessier once told me tha t his ports were 5/16th lexan, and he did several Cape Horn passages with no problems.. The only time they broke was when he ended up on a Baja beach. I suspect the problem with plexi in Florida was 3/16th thick or less pelxi. I use half inch plexi and couldn't get it to break with a sledgehammer ,last fall.
I've seen quick cracking around bolt holes on lexan.
A friend in the plasics buisiness told me that plexi has ten times the impact resitance of common glass.
Don't use lexan. Maybe OK for occasional use storm covers, but useles for full time ports, unless you want privacy full time with no curtains.
Brent

 

Brent
the refractive index of plexi is 1,49- mineral glass is 1,45 up to 1,9- so, in the very best case it has 1/10 better properties! The impact strength is significantly lower than that of polycarbonate! But a bit higher than untreated mineral glass. Bernard Moitessiers dome was plexi, it was almost blind and finally it broke.