Bulkheads in ISO 12215

Ahh.. ok... so if you have two flat-bar stiffeners, both supporting the same panel, both with the same thickness, is the taller one any more prone to web sheer?

 

Yes. From point of view of standards, only proportions of stiffener are used to assess web sheer. I would recommend to look at Lloyd's Special Craft rules - they have an album of recommended structural details, both in alloy or FPR. That samples clearly show how to treat high stiffeners.

 

Depends how you arrange the structure. But each stiffener is judged on its own dimensional aspects.

Thus in your example, each will have a shear area. The hydrostatic pressure, on the WTB, is the same. Thus the force being applied to each stiffener is the same. Hence the shorter stiffener has a higher shear stress than the deeper one. But if it passes, so what?

The key thing to consider with all aluminium design is deflection checks. Generally once you have designed the structure to satisfy your design stress allowable, you need to check deflections. Deflections are often too high and therefore you need to make the sections stiffer.

 

Agree with Ad Hoc, same I said - boat designed to ISO12215-5 would not have enough stiffness in some areas. This is matter of experience - to arrange proper stiffening.

 

Thanks gents. As always you've been generous with your time and knowledge.
I'll go and have a little think about all that you've told me... will no doubt be back soon with more questions!

 

And indeed, I am back!
Why does ISO require that metal bulkheads be calculated as watertight bulkheads, regardless of whether they are or not?