What is the "bulkhead deck"?

[Alik]

Originally Posted by ldigas

1. Of course. It was a pain getting the exact year ...
2. Yup, know that as well :/

Oh, well, to finish this off ... thanks fellas (you too Alik, for the "chat" discussion With this in mind, I'll try to figure something out.

If You post Your calcs, some of us might have a look...

[Perm Stress]

Originally Posted by ldigas

Uhmm, there are steel plates there as well. They are not just wooden floorboards.

Why am I asking this? Because the original design has bulkheads and stiffeners on them, which (even if I take 1980s rules for calculation, when the yacht was built) can in no way satisfy the requirements of the GL.

If your prototype was not classed, the bulkheads well could have been made by "common sense" of builder and/or designer.
There are quite a few boats, made to "common sense" of owner/builder/whoever with weird structural arrangements.

If your prototype was classed to rules of other society, or for inland instead of for offshore use ....

If those bulkheads were not designed as watertight, (i.e. compartments are there only for practical use of boat, not to enable her to survive serious hole in bottom), quite different set of loads and scantlings are applied.

[MikeJohns]

How many watertight bulkheads do you expect? Is this supposed to be unsinkable offshore?

I'd expect a crash bulkhead fwd, and a fore and aft engine compartment bulkhead up to a steel cabin sole and no others actually required for watertight subdivision.

The rest are then stiffening bulkheads for the hull and not for watertight integrity.

[ldigas]

Originally Posted by MikeJohns

How many watertight bulkheads do you expect? Is this supposed to be unsinkable offshore?

I'd expect a crash bulkhead fwd, and a fore and aft engine compartment bulkhead up to a steel cabin sole and no others actually required for watertight subdivision.

The rest are then stiffening bulkheads for the hull and not for watertight integrity.

Yes, that has been my reasoning too (crash blk. + two watertight sealing off the engine room; the others being there for hull stiffening and space separation). However, from what I read in the rules, non-watertight bulkheads are dimensioned according to the same rule

5.3. Non-watertight bulkheads

Components of non-watertight transverse or longitudinal bulkheads, wing bulkheads or such which serve to stiffen the hull are to be dimensioned in accordance with the same formulae.

[Petros]

any horizontal floor diaphragm structurally attached to the bulkhead will be a bracing element, be it the uppermost deck or not. this will reduce the stress on the bulk head so less structure is required. So the free height of the bulkhead between the structural deck levels will determine the stress on the bulkhead elements.

The GL rules have different levels of strength required for different classes and different types of ships or yachts, so the strength depends on the intended use.

[Alik]

It might be treated as accommodation bulkhead attached to side frames, so there is no need to comply with requirements.

[ldigas]

Originally Posted by Alik

It might be treated as accommodation bulkhead attached to side frames, so there is no need to comply with requirements.

So, if I'm to understand correctly ... if the bulkhead is attached to the frame/deck beams etc. etc., i.e. it is not a bulkhead, but more of an accomodation bulkhead then it is not dimensioned according to the same rules, but more according to the common sense of the nav. arch.?

Although some stiffeners are still good to have, even on those.

Am I somewhere close with this?

[Alik]

Accommodation bulkhead does not need to comply if there is enough structural elements. We use accommodation bulkheads in plywood on aluminium craft... Stiffeners -those might be just used to provide stiffness of bulkhead.