What is the "bulkhead deck"?

Under GL rules for yachts up to 24m, what exactly is the definition of a "bulkhead deck"?

Quote from rules:
h1 - pressure head in [m] measured from bulkhead bottom edge up to bulkhead deck

and

h2 - pressure head in [m] measured from the center of the stiffener up to the bulkhead deck


Now, my question is - if, for example, you have a pilothouse and an engineroom right below it (see large picture in this post, can't miss it) and the bulkheads to the stern and to the bow, right where the stairs are (at R11 and R22) that go up to the main deck, but are "waterresistant" only up to the pilothouse flooring height (since there is no door the stairs cannot "hold the water"), is the "bulkhead deck" all the way up to the top, or just up to the pilothouse floor?

 

I would guess that is referring to the height on the bulkhead at the level of the deck.

The deck is a bracing element in the design of the bulkhead, so it would make sense to design for pressure from the bottom of the bulkhead to the deck level.

I do this kind of work all of the time as an engineer, and often regulations are worded using a strange form of clipped techno language that is improper grammar and not quite accurate terminology (the committees typically assume everyone in the industry knows what they are referring to-when I get a chance to talk to committee members I always chew them out about poor grammar and vague terminology). There is no such thing as a "bulkhead deck", it is I believe referring to the level of the deck on the bulkhead.

That is the way I would interpret what you posed as a licensed Engineer.

 

Yes it's simply the deck where the bulkhead finishes. On a smaller craft it's usually the weather deck, on larger vessels it can be an intermediate deck, for example; engine room bulkheads.

 

And if the bulkhead does not finish at the deck, but goes "inside the structure" forming a "part of the interior furniture"? For example, in the linked post/picture, would you say, the bulkhead deck is the flooring of the pilothouse, or would you say it is the main (exposed) deck, to which the bulkhead cannot be waterresistant, for it has no means of closure?

That is what confuses me. In case of watertight bulkheads, is the bulkhead deck the uppermost deck to which the bulkhead can be made watertight? (for they are dimensioned to static water pressure).

 

No doubt, but which one?

 

The wheelhouse cabin sole is a 'deck' in this case.

 

Bulkhead deck is a deck, where tops of watertight bulkheads are.
Anything above bulkhead deck is not considered as watertight for damage stability (ability of holed ship to remain afloat and rightside up) calculations.
From here, all the rest -loads, etc. is derived.

So in your case, if pilothouse is not below continuous deck, covering all or most of the bulkheads, it is above bulkhead deck.

 

For small craft, 'bulkhead deck' is equivalent to upper surface of watertight boundary.
Often there are no bulkheads but built-in buoyancy volumes or no buoyancy at all, so the term 'bulkhead deck' makes no sense as it came from big ships.

 

"Upper surface of watertight boundary" - yes, I like that
one. A rather unambiguous one.

Coming back to my example a bit more, however. In its case,
that would mean that the "bulkhead decks" are what is marked
by red lines.

However, if we take a theoretical posibility that the doors
may hold off a column of water, what about the "? marked
volume". It is bounded by front and aft bulkheads, and two
"decks" (the sole floor and the exposed deck).
Does that mean, that in that case, the bulkhead deck
is the exposed deck (the roof)? While in the the other cases
it is the "sole floor"?

Is my understanding correct, that regardless of the name - let's
leave it aside for now, the bulkheads are to be
dimensioned to hold off the hydrostatic pressure of any
volume they enclose, assuming that that volume can
theoretically be filled with water up to full?

So in this case, the bulkheads at R32 and R26 would need to
be calculated to withstand the flooding of "? cabin", while
R22 would only need to withstand the hydrostatic pressure up
to the red line, since there is no way to flood the volume
above that line, and let it "hold the water" (save from
sinking the boat completely)?

 

Ok, for structural design IN YOUR CASE one should take upper deck level for calculations. The floorboards marked in red have no meaning.

 

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.

 

No, this is common sense of ship structural design. The structure should withstand at least hydrostatic pressure in case of full submersion, plus some margin. For this boat reserve buoyancy will be to upper deck level. In other words, the boat should sink before it breaks, not opposite

 

No, no, you misunderstood. The boat (build in the 80s and currently functional) has stiffeners which are much smaller than the ones I calculate it should have by the rules of the GL (according to which it was build), either the edition from the 80s or today's edition (well, 2003).

That is why I suspect I'm calculating something wrong, but am not sure what specifically.

That aside, yes, of course (what you said). I agree wholeheartidly.

 

1. Are You using GL rules for Yachts?
2. Usually, the boat should comply to rules edition valid by year of construction. By grandfathering of class, it is not required to comply with later editions unless it was serious refit or critical safety issues.

 

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.