Watertight Bulkheads?

On metal aircraft structures they have similar issues with pressure bulk heads. what is done is an uninterrupted bulkhead attached continuously to the skin, and the stringers are not continuous but are rather attached to both sides of the bulkhead opposite each other to create a continuous load path, but not a continuous stringer.

 

I have no idea why you think the bkts are misaligned. That is a manufacturing and QA issue not a design issue. If a yard cannot line up bkts either side of a WTB, (assuming it is not one single bkt - as the poster implies), then the yard is lacking in simple shipbuilding skills.

The webs of the stiffeners being aligned or not - for a WTB connection if stopped short of the WTB - makes no difference. Unless you're assuming the flange of the stiffener is not sufficiently stiff enough the transfer the shear load in the web via the flange to the bkt. This does not occur on "normal" stiffeners. Most yards do not allow the bkt to be greater than the thickness of the web/bkt out of plane anyway, as normal shipbuilding practice, i.e. QA.

The placement of the flange on one side also makes no difference. The purpose of the bkt connection is to transfer the shear load, that is achieved via the weld from the flange to the bkt and then the bkt to the WTB. The flange plays no part in that load transfer as it is for tensile loads, not shear. So long as the connection for transferring bending moments is the same stiffness or greater, it matters not which side(s) the flanges are or if they are unequal.

As for section X-X, it is taken from the reference manual issued by Lloyd's Register, I copied it as it was quicker than drawing an example:



However, I do not recommend this type simply because the bkt on the aft side (left hand side) the toe of the bkt is not terminating on another bit of structure (as shown in section Y-Y). If the bkt experiences high shear loads, then a crack with begin at the toe of the bkt as there is nowhere for the bkt to shirk the load and if the welder does not perform a proper weld return just exacerbates the detail. Thus I do not use this method personally.

 

Thanks for the clarification Ad Hoc, the examples I've seen have the bracket lapped & welded to the web of the angle stringer. So only acceptable with the additional control of incorporation of the bulkhead stiffeners to the brackets- with this in mind would the bulkhead stiffener do the job on both sides as the bracket passes through the bulkhead? The system has some attraction as once the slots for the brackets are cut, the set up & spacing is hard to deviate from & easy to clamp off the longitudinal. I understand your reservations, the vessels I've seen it on are low speed work platforms where maybe the simplification is worthwhile. Also typically I see the ends of angles sniped off(usually 45-60deg) although the illustrations you've given don't except in the case of the bulkhead stiffener, this I assume is for easier welding access & "neatness" or is there additional benefit in the tapering of angle flange? Jeff.

 

Technically you only need a WTB stiffener one side (as it is just resisting the hydrostatic pressure).

Ease of access for welding is critical. However, you need to satisfy yourself that the connection, (however it is done) has sufficient shear area in the welded joint, and under a high load there is enough inertia in the welded joint to transmit the bending loads too....since even though the arrangement is to transmit shear loads, when you lap them like this, the long.t stiffener is carrying the bending moments from slamming etc. Thus will the lapped welded joint fail under the slamming loads? One reason why I dont like lapped joints.

 

Ad Hoc, I agree with your solutions. HOWEVER, my objection to "section X-X" continues, because it is not correct, even that is a figure of Lloyd's Register. You can check that does not match with the last figure that you have shown, that is correct.
Again, is a "good" practice to have stiffeners flanges towards the same side. It is desirable that the position of the neutral axis of the profiles that are linked by the console is as close as possible.
On the other hand, one must bear in mind that the slamming does not affect all areas of the ship but only to the bow. Probably the only transversal bulkhead that is affected is the collision bulkhead. It is more correct to speak of the additional pressures induced by the phenomenon of salamming that the bending moments induced by slamming. A load does not always lead to a bending moment.
A watertight bulkhead is never dimensioned by the pressure acting on the hull, or the bottom of the vessel, as is the case of slamming, but by the hydrostatic pressure produced by the existence of liquid in one or both compartments which limits the bulkhead. Long. stiffeners does support slamming pressure, very big in some cases. That's why sometimes it is better not to interrupt the longitudinal stiffener in the bulkhead, making a hole in the latter and seal it with a collar (see my earlier posts)