How thick for window glass

[Willallison]

My brother-in-law is thinking about buying a Radford 45 pilothouse yacht (pdf pics attached).
The pilothouse windows he's been told are 8 and 12 mm toughened glass. He wants to know if these would be ok. I suggested that whilst at sea (he's planning to cruise world-wide) he should fit storm shutters.
Any thoughts on this, or the boat in general?

[Willallison]

Oops!......attachment....

[BrettM]

Will,
Depends - Can you get the pane sizes (length x width). then an answer can be given. (also are they toughened or lamianted??)

Brett

[Willallison]

toughened, approx 500 x 500mm

[BrettM]

Checked what you gave against the USL code (the code that applies to commercial vessels in Aust.) 500x500 toughened in the on the front would require 8mm. I assume that 12mm is the front in this case?? or for a larger pane???. Presumeably Radford has based these thickness on some kind of calculation...

No warranty comes with this advice...
Brett

[Willallison]

Thanks Brett. Judging by the interior pics, there's no guarantee that the builder followed Radfords design exactly - hence the question. Thanks for the info - I'll pass it on....

[Willallison]

....In the end, he bought an Adams 40 - and wants to replace the existing perspex raised-cabin "portholes" - possibly with polycarbonate.
I suggested that this wouldn't be very scratch resistant. Any suggestions? The largest pane size is 300mm high x 600 long.

[Dutch Peter]

Toughened safety glass, not less then 6 mm.

Calculate thickness with:

t = .005b*sqrt(B*p) [mm]

b = length of shorter side of window, in mm
p = design pressure (take 70 kN/m^2, highest value from ISO 12216).
B = -.17 + .54*A-.078*A^2 for A<=3
= .75 for A > 3

A = aspect ratio of window, a/b
a = length longer side of window

( no guarantees on this advice)

[mmd]

Dutch Peter, is that fornula from Lloyd's or DNV?

[Willallison]

Thanks Dutch Peter - I don't think he can easily use glass as the panes are not flat. Do you have anything on 'plastic'?

[Dutch Peter]

Originally Posted by mmd

Dutch Peter, is that fornula from Lloyd's or DNV?

That's Lloyd's Special Service Craft P3, Ch 4, sec 7.8

[Dutch Peter]

Originally Posted by Willallison

Thanks Dutch Peter - I don't think he can easily use glass as the panes are not flat. Do you have anything on 'plastic'?

Multiply the calculated thickness by 1.3 for polycarbonate and by 1.5 for acrylic.
In SSC Rules other glazing material then glas is not excepted for the wheelhouse, but for a 40ft yacht it'll do.
When going on long trips it's a good idea to bring storm shutters for all sizes of windows (so, all sizes, not all windows!!) But that can be 12 mm ply that you screw onto the window sills.

Hope this helps!

[Willallison]

Thanks Dutch - it does indeedy

[SuperPiper]

I have considered removing the sliding companionway hatch from my pocket-cruiser. The project would include cutting it away, slides and all and replacing this cabin top area with a solid piece of Lexan. By the calculation above, it would require a piece of polycarbonate 24mm thick! The surrounding cabin trunk is only about 6mm thick.

The construction of this little boat seems to be in the same order of magnitude as Gerr's scantling numbers. We could debate that the boat would not be suitable for offshore cruising and would not survive green water from 20metre seas. But, the calculation seems a little suspect.

Did I miss a decimal point?

[Dutch Peter]

Originally Posted by SuperPiper

I have considered removing the sliding companionway hatch from my pocket-cruiser. The project would include cutting it away, slides and all and replacing this cabin top area with a solid piece of Lexan. By the calculation above, it would require a piece of polycarbonate 24mm thick! The surrounding cabin trunk is only about 6mm thick.

The construction of this little boat seems to be in the same order of magnitude as Gerr's scantling numbers. We could debate that the boat would not be suitable for offshore cruising and would not survive green water from 20metre seas. But, the calculation seems a little suspect.

Did I miss a decimal point?

To be short, NO:

You have to consider the following points:

1. You have to take into account that your cabin trunk is originally made of a different material with different properties.

2. It is also not commen to use a formula for windows for a structural item!

3. The design pressure that I recommended earlier is debatable.'

Originally Posted by SuperPiper

But, the calculation seems a little suspect.

4. This formula comes from Special Service Craft Rules from Lloyd's Register and is used on yachts of 24 mtr and larger. It is correct and workable, and can be used as guidance on a 50ft cruiser, but is NOT intended for a pocket cruiser.

However, taking into account point 1, I think the 24 mm is just right!

Regards,


Peter