Perspex window thickness?

[JumbleDuck]

You better start with a degree in structural engineering then buy the most comprehensive text book you can find on yacht and boat design.

Don't forget the extensive studies in fluid dynamics and oceanography needed to predict the loading.

 

[rszemeti]

Because I don't want the answer, I want the method of calculating it.

I would suggest you start with the Kirchoff-Love equations, which can be simplified for rotation angles of less than 15 dergees and are trivial to solve. Perspex can be considered as an isotropic and homegenous material, so the equations for finding the stresses are very simple.

The basics are of course listed on Wikipedia: https://en.wikipedia.org/wiki/Kirch...y#Isotropic_quasistatic_Kirchhoff-Love_plates

Wolfram Alpha has some tools for visualising the von Mises stresses in a simple Kirchoff plate, but I completely understand that you would prefer to do the calculations yourself rather than have some automated tool do it for you.

Incidentally, Kirchoff is of course the same Gustav Kirchoff that gave use Kirchoff's laws of electrical circuits, (which are essentially the low frequency limit of Maxwell's equations) and no doubt familiar to every GCSE level physics student.

 

[Yara]

There are many things in engineering which do not lend themselves to calculation, particularly when the loadings are extremely variable. So in this case you have to work on experience.
Hard to accept for some in modern times, when the media would have you believe that risk can be absolutely eliminated, and that computers are the key to calculating everything exactly.

 

[fredrussell]

deleted.

 

[rotrax]

Hi,

Looking at buying new perspex windows and struggling to find any recommendations about desired thickness.

I'm assuming that some clever person has worked out the minimum thickness of perspex required per maximum height or width of the window span???

Cheers,
Ian

Not sure about your 'eye roll' bit earlier, but for someone asking for technical info the OP was very vague.

I feel sure that the thickness of the ones you intend to change would have been your best clue as to what is required. Eye roll..............

If in doubt, go up a couple of mm.

My two pennyworth anyway.

As to supply, I recently used a sign maker in Petone, near Wellington NZ for my new windows.

Half the price of the marine specialist and very good quality.

Perhaps the same price advantage will exist in the UK.

 

[Motor_Sailor]

. . . people have gone to the trouble of producing an agreed international standard for such things (ISO 12216), but it'll cost £146 to buy a copy.

This was the answer to your question and contains everything that you need. Depending where you are, you might be allowed to access a copy in the University Library (Southampton, Newcastle, Glasgow, etc) or your local reference library will get a copy for you given time (and opportunity at the moment)

Interestingly it was the first standard that was developed and from where the whole RCD grew. (Who knew back then that a simple request from American speedboat manufacturers for a common window standard for Italy and Spain would lead where it did.) A new version is pending.

 

[Graham376]

I expect that I'm going to get a lot of similar responses, I'm hoping for something more scientific...

Window thickness and aluminium frames often need to match, not much point in buying new acrylic if it won't fit the frame profile. If definitely replacing, just drill a small hole in one and measure thickness, then temporarily plug the hole. If you say what boat you have, maybe someone knows what's needed.

 

[rotrax]

Window thickness and aluminium frames often need to match, not much point in buying new acrylic if it won't fit the frame profile. If definitely replacing, just drill a small hole in one and measure thickness, then temporarily plug the hole. If you say what boat you have, maybe someone knows what's needed.

If that IS the case with the OP's windows he must change like for like surely, so no need to ask.

I suspect - but cant possibly know because of the lack of info in the OP - that they are fitted overlapping the apertures.

Changing thickness just a matter of suitable length fastners............................

 

[PaulRainbow]

I suspect that sometime in the year that has passed since he asked the question, he's found an answer and changed the windows

 

[Big John]

Uses of Perspex® Acrylic Sheet vs Polycarbonate Sheet - Industrial Plastics

Useful app for thickness.

 

[Halo]

Are you sure its perspex ?
I would use polycarbonate.

 

[[70521]]

Looking at buying new perspex windows and struggling to find any recommendations about desired thickness.

I'm assuming that some clever person has worked out the minimum thickness of perspex required per maximum height or width of the window span???

Hello Ian

As a retired engineer you are asking how long is a piece of string without giving any of the design parameters. Nobody can answer your question given the information supplied.

1. Where are you wanting to sail? Lake Solent in a F4 max or the Southern Ocean in a F12?
2. What are the size of your windows?
3. How are your windows going to be attached to the boat, this might be your weakest link?
4. What material are you intending to use?
5. What speed is the vessel intended to be used?
6. Finally, what colour would you like it?

There are a couple of places that might be able to assist, the RNLI [www.RNLI.org] and Safe Haven Marine [www.safehavenmarine.com].

Slainte

Sandy

 

[PaulRainbow]

I know we're all a little bit bored, with the lockdown and all, but this thread is a year old and the OP hasn't been seen on the forum since May 2019

 

[DownWest]

I know we're all a little bit bored, with the lockdown and all, but this thread is a year old and the OP hasn't been seen on the forum since May 2019

Quite
In general, the maxime is "If you can't come up with a good idea, borrow/steal the next best one you can see out there'. Which seems to apply in this case and prob what he did in the end.