Glazing Thickness

I'm chasing the ISO / DNV / Lloyds (or any others for that matter!!) rules for calculating glazing thickness in pleasure craft...
Can anyone help?

 

Will
The glazing requirements for USL are attached to the end of part 5 construction sub section D watertight sub division for class 2 and 3 vessels (non passenger). You'll find most of the standards similar, USL usually slightly exceeds the thickness of the others .

Free download or I'll email you the pdf if you need it.

cheers
Mike

 

Thanks Mike.
I'll run through it and see how it compares to my current calcs...

 

hmm... interesting....

For the fwd facing wheelhouse windows of the vessel in question (which has toughened glass windows 1170 x 690mm that are 1.8m above the dwl):

ABS Guide for Motor Pleasure Craft gives a calculated figure of 8.4mm
ABS Guide for High Speed Craft gives calculated figures of 8.1 and 13.2mm based on flexural strength and modulus respectively.
USL gives a calculated thickness of 4.6mm, but requires about 13mm to give a deflection of less than 1/100 of the panel width.

A general guide that I have suggests that, depending on service it ought to be between 8 and 13mm

Clearly anything less than 8mm is too thin, anything more than 10 seems somewhat excessive...

I would still like to see what ISO and Lloyds suggest....

 

What service is a boat for that needs such thick windshields? For inshore use where no large wave impacts are encountered, why would laminated safety glass (~ 1/4") as used in trucks not suffice? Do I not understand the question or the problem?

 

Many of the traditional rules (ABS etc) make little or no allowance for service The guidelines that I have do, but they're a little vague for my liking. Hence my desire to see some of the other methods....
For the boat in question, which is likely to do what I would call light coastal work, I would have expected 8mm toughened glass to suffice - the panel spans are quite large, and whilst they are unlikely to see green water, they will probably have to endure the occaisional reclining scantily clad young beauty!!

 

Will
What is your LWL ?

 

I seem to recall reading an article by Steve Dashew a few years ago on this subject. I think he said he used the Lloyd's "All Oceans" rating as a lower limit on thickness, discussing how it allowed for wave impacts but not for the possibility of deck gear or equipment breaking free in a storm. If I'm not mistaken he ended up settling on 19mm (!) tempered glass for windows of about 1 m by 1 m, with one of 3M's magic IR/UV films.

I can't offer up the actual Lloyd's rule for you, unfortunately.... I'm not a boat designer and I very much doubt I'll find it in the university library.

 

Mike, LWL is 7.9m

Matt - there's no doubt that for ocean going service in a vessel that is likely to cop repeated heavy water over the superstructure that a) the panels would need to be much smaller, and b) the glass a great deal thicker. There's some great pics on the net of a large tanker copping a wave that smashed a quite small 1" thick deadlight. She may be elegant, but mother nature sure can be a b#%&ch sometimes!

Tom - I guess you wouldn't expect to take too many waves over the bonnet of your semi too often So whilst the speeds are much higher, I suspect the potential loads would be quite a bit lower

 

Yes you need calculate it on the deflection method. 6mm toughened safety glass is the common thickness on small boats (and the minimum allowed) . But you need to design to this. ( There goes that modern style )

The problem with big glass windows is the weight. You also need to check what thicknesses the glaziers can supply (and the cost).

Cheers

 

All true, of course and I assumed that was the answer. I used the truck safety laminated glass on my boats since they will not ever see water over the bow of such magnitude that it would be any significant problem. It it were, they would be using the boat where I tell them it has no business, ever. Having stood on the bridge of a Navy destroyer in a Pacific typhoon, I have a healthy respect for the power of big water. I once had the bumper of a big truck come through the windshield of my rented Volkswagen and that was no picnic either.

 

I've based all my weight estimates etc on using 10mm toughened glass, which is the result from the ABS method. Weight is really only an issue in terms of providing a suitably sturdy structure to support it - especially as the boat features quite a bit of rake in the screens.
The issue only came up as a result of comparing this thickness with that used by the commercial ferry builder next door, which uses 8mm glass in panels that are apparently larger than those in my boat. I'm not sure of the classification they work too - but suspect it may be DNV....