Aluminium Construction - ISO vs Gerr

It is OK to change their size gradually (between bulkheads or adding brackets).

I'm very pleased your interest about ISO standard. (All designers and builders here are not) There are unfortunateley too many details to go roud here. All (well, most) your aswers are inside standards ISO 12215-5 and -6. Just need to have time to study them thoruoghly.

 

The way I see it, ISO will surely become the main standard for smaller craft. Yes, there are different standards operating in various regions, but this will surely change over time.

And yes - I'm sure the answers are all there... though I have to say that in some cases they are pretty well disguised! The deep girder type construction that I referred to previously, and transoms being two good examples.
I mean, what good is it to say that transoms and engine beds for sterndrives or larger outboards should be strong enough to cope with those loads...? No procedure for calculating them or the subsequent scantling is given that I can find....

 

I wonder how much added stiffness you would get by making the bottom and topsides slightly concave athwartships, putting the plate under tension when slamming. This shape is not uncommon on fibreglass hulls. Fairing the concave topsides and bottom plates into rounded bows would be a challenge, but experimentation with models may be helpful. It would be difficult , but not impossible.

 

Concave sections tend to slam, are weaker and are much more difficult to build than the convex sections that more closely resemble developable shapes. Why would you want to use them?

 

I'm having trouble figuring out how one should treat bulkheads for Aluminium construction.
In the case of the image below, which I would have thought to be typical of a hard chine planing hull, where the frames become CNC cutout bulkheads. How does one asses this? ISO states that it should be treated as a watertight bulkhead, which is fine.
My understaning is that it would basically be broken down into three sections, divided by the natural stiffeners - deck, seat and deck. Though this ignores the chine and keel...
Would section 1 be classed as a transverse stiffener with the length Lu, the distance between chine and deck? The other two sections, 2 & 3, would be unstiffened panels with heights of a & b respectively?