Is bulkhead tabbing now redundant?

I wouldn't dispute that the fillet only could be effective. That the laminate might fail before the adhesive is a point, I think the joint design & loading would be a major consideration, say on a hull deck join it might be fine on a "shoe box join" where the structural components overlap & give fiber continuity. I've seen flanged (outwards with a fender mold to external) that have failed on wharf impacts, it dosen't matter if the glueline or the laminate in way of it gave way in peel, a simple generous laminate bandage to the interior would have controlled the joint.... continuity of structure/fiber. With the fillet joins we would be trying to "pick up/join" structural components that include fiber.. that's there for a reason, or we could make the whole boat out of "rubber toughened putty"
Jeff.

 

even a J24 is supposed to have no core at bulkheads and the outer skin is a lot thicker to make up for it.
That sound correct for me.

Many modern boats with laminated bulkheads are L shaped where they meet the hull and glued therefore the repeatability is very high

Of course an aeroplane only has the force of air on the outside, a boat has water..and rocks and other boats

 

The formulae for predicting the minimum ply properties is shown in LR Part 8 Chapter 3 available in this forum (LR rules).

Phenolic is a low modulus resin, Not as good as polyester or epoxy and is heavy (see LR table 3.1.4). However, it does have a very good fire resistance rating. When it burns, it forms an ablative carbon surface that insulates, reducing heat transfer.

 

come on fellas spill the beans how many boats have you built between you ???

The more I read from little red man and groper the more I wonder about how many boats have the pair of them actually built . Now come on enlighten us all !! please tell us !!.
You love taking digs at me now its my turn !! I want to know how good you actually are and what practical things have you actually done !!
like ad hoc said most of it is plain simple poppy cock !!.
Mind you an inflatable boat is part way there !! has a air tight skin and nothing but air pressure inside , because shape gives strength so it is as light as can possibly be .

 

i'd say its not the building its the repairing/seeing failures where you learn

 

I already done a lot of work doing repairs for the reason you just said to learn what works in glassing and what doesn't and why it doesn't !!

I keep wondering why neither of these persistent sons wont tell us how many boats they have actually built them selves ,like hands on and sleeves rolled up or has either supervised the construction leading a gang building a sizable boat . I have my own thoughts on this matter but cant put them on paper !

 

Is bulkhead tabbings redundant? It depends, as there is an engineering solution for all the types discussed in this thread.

Illustration A is a typical single skin plate supported by multiple single skin support. It does not matter if it is a doped cloth supported by ribs in an airplane or a hull plate supported by bulkhead/transverses. It is the load that matters. The load determines the panel stiffness. The critical point is the base under the stiffeners where shear is the greatest. Typical solution to connect the “knife edge” support to the skin is by local reinforcement.

Illustration B is a sandwich panel which is stiffer, reducing the support points. With a single skin support, this presents another problem. The relatively narrow edge of the support will create a localized load cutting through the sandwich, aggravated by a thinner inner skin. Typical solution is again to spread the load by adding a wide reinforcing strip and a tabbing to connect the two elements.

Illustration C is a sandwich bulkhead supporting a sandwich panel. With a wider base area, the span of the panel is reduced (making it stiffer) and the pressure in the local area is reduced. Shear is still greatest under the base of the bulkhead.

Take a typical Class Rule LR Part 8 Chapter 3.18.7- ….to be tied by a suitable weight of reinforcement OR by the use of fillets and wedges of suitable compliant resin (italics mine). The rule states TWO choices. Petereng knew this and proved to the surveyors by test that his second approach is satisfactory (hard to convince the surveyors without tests).

Choice 1 or 2, Ad Hoc is saying that composites are compliance driven. The joint must not be too stiff in relation to the stiffness of the panel. Illustration D shows that when the joint is too stiff or overbuilt, the panel is sheared. Illustration E shows that when a suitable reinforcement (tabbings) is used with just the right amount of flex, shear is eliminated or reduced. For lack of a better illustrative material, I used Euler’s illustration of dissimilar materials to demonstrate my point.

Illustration F is to interpret what LR is stating in conjunction with the flexure theory. The beam bending theory is awash with so many solutions for a particular problem.

So is it redundant? No, just the engineering approach.

 

Thanks for that rxcomposite,

Ok I should have clarified this from the start, not sure why I didn't.

This whole line of thought came about when I was considering building another boat, specifically a high performance cruising sailing catamaran no larger than 14m length and 8m beam.

I think some of the main beam to hull connections etc will have no choice but to be tabbed in. The rest of the frames and stiffeners- maybe not, thus the questioning.

So in this discussion, about tabbing redundancy, I should have clarified that I was not referring to large vessels where loads and displacements are higher.

Many of the class rules for composite construction, dictate a minimum scantling for vessels "upto 25m". This leaves you with way overbuilt structures if you only want to build a boat say 10m.

So I think the class rules need addressing for smaller boats, and I'd like to hear more about designing a joint that doesn't require tabbing over which could be used in smaller vessels using sandwich panel building methods.

For those they may not be aware, modern sailing catamarans can utilise the furniture as hull stiffeners to great extent as the layout of the narrow hulls makes it easy to do. In addition, this furniture is often made from structural sandwich panels to keep weight down. The result, is its possible to build very stiff structured hull panel, with tight spacing of internal stiffeners, also made from structural sandwich panels.

When everything is tabbed, there is a hell of lot of labour in all the many joints, plus the fairing of all of the tabbed edges afterwards. My idea was to build pre finished sandwich panels that's finished surface inside and out, that only require some form of bonded joint which then does not create a fairing problem later by adding a raised tabbing edge at every joint. It would seem that many/most of the stiffeners would be lightly loaded at close spacing, especially not those in the forward 1/3 of the boat - which are largely devoid of accommodation spaces anyway and doesnt require fairing.

 

Savings NON !! durability maybe better but fix one problem and create another !!

say what you mean and mean what you say !!

Ok with that sorted yes it is possible to simply stick frames and bulkheads into place BUT you will have to form a Tee section to fit snugly against the mating surface between the hull and the Bulkhead or what ever !! cut and fit nicely then laminate a flange to stick out both sides if the panel remove from the boat and do all your prep and finishing work mark the hull before removing and then mask either side apply you sticky what ever you wish to use then fit and brace the panels in place and clean up unmask and wait for it to cure and there you are !! its one hell of a lot of work involved will look neat !! Maybe !!, but its nothing that cant be achieved simply by tabbing with glass and resin as usual and a layer of peel ply over the top to be rolled out neatly and smoothly .

OK SAVING ??? POSSIBLY NON WHAT SO EVER , in my view would be so expensive it would become prohibitive!!
TIME TAKEN ??? MAYBE 3 to 4 TIMES AS LONG OR EVEN LONGER
PYHSICAL PROPERTIES ?? POSSIBLY BETTER BECAUSE OF THE ELASTICITY OF THE ADHESIVE USED ,SO WOULD TAKE MORE ABUSE BUT REMEMBER ITS STILL ONLY STUCK TO THE INSIDE SKIN AND IF ITS OVER A CORED HULL THE PEELABLILITY OF THE SKIN OFF THE CORE IS OF MAJOR CONCERN !!
LIKE I HAVE REPEATED MANY MANY MANY TIMES ,THE EASE AT WHICH GLASS PEELS OFF A FOAMED CORE IS ABSOLUTLY SCARY !!
YES I KNOW WHAT YOU ARE ABOUT TO SAY THERE ARE THOUSANDS OF BOATS WITH FOAM CORES !! YES I TO HAVE ADDED MY SHARE OF CORED BOATS TO THOSE THOUSANDS AS WELL .

 

question !!

groper ! how many glass boats have you actually made ??

 

Groper,

If you are building a cat, the bulkheads are small and the use of compliant resin MIGHT work (depending on the frame spacing). If you are building a monohull where the bulkheads are large and often stiffened, then tabbings should be the primary consideration. If the bulkhead is connected to the crossbeam of a cat, then it must be tabbed and special attention must be looked into the area of the inner haunch (a bracket actually)

You need at least 3 watertight bulkheads for a pleasure yachts/boats. The steering bhd, engine room bhd, and the collision bhd. In case of breach, these are designed to contain water and pressure will be greatest at the bottom part. In cats, there is a centerline bulkheads to prevent crossflow of water. Bulkheads are primary structures and needs to be fixed correctly. If the bulkheads are far apart, intermidiates such as web frames can be installed but are still considered primary structure.

Longitudinals are secondary stiffeners/structures. Joineries and divisions can form part of the substructures to add stiffness to the panel/boat. Such structures are considered secondaries with infinite depths. Spacings are much closer together and pliant tabbings can be considered.

 

As has just been raised water tight bulkheads !! now thats going be a test of your imagination ! how will you first make them amd secondly how will you fix them to the hull and deck and what ever . Now points to remember are they need to have vertually no bend in any direction !!if theres bend the panel will simply pull away from the hull or where ever and gets back to glass peeling off the foam core !! and with a few hundred kilos of H2o the push being exserted on one side will just that sticky stuff hold up and not let go !! what about the tabbing would it be a better choice ??
which one will hold the best thats the million dollar question there is a third option no one has even made any mention of for fitting Bulkheads such as collision and or water tight bulkheads .remember bending is your biggest worry if it bend it will collaps completely so you dont even have to thing to hard about that !!

Next question is should stringer simply be butted and finished at bulkheads or should the stringer become the primary concern for laminating and holding panels stiff and straight and bulkhead be seconday to them and be cut around and over stringers then glassed in place ?? for me this is a non issue and does not even warrent a second thought !! but whats you veiws ???? who do you believe ?? strength wise whaich is best ?? not easyest but best !!

Lets take a step back to the collision and water tight bulkhead !! what is its primary finction ?? what are all the possible things that could happen to it how much water pressure would it have to withstand and where is the place that reallt will get the most amount of water pressure pushing against it ??
Ever thought about how tanks are built ?? what part of any water tank takes the biggest loads ??
GET this wrong and in a life and death situation it could cost you everything as in totall even your life and that of others !
.

 

Gawd.....anyone would have to think twice about stepping aboard any water-borne conveyance after reading this thread, fearing the boat break up like a biscuit from dodgy construction practices !

 

Thanks again RX,

In a typical sailing catamaran currently built here in australia, the first 3 bulkheads are in front of the crossdeck structure, there is generally no accomodation spaces in there, only anchor or sail lockers typically accessed from the foredeck of each hull. Fairing is not a problem is these areas as noone goes in there, so tabbing doesnt both me in these areas - which also occur in the front 1/3 of the boat - which needs to be stronger. Behind this is where the problem begins;

The first part of the cross deck structure and the accomodation spaces begin, so fairing inside these spaces is best avoided - especially if you build an already fair hull. Tabbing is no doubt required for the main beam and mast beam is these areas, ok so we have a little fairing to do. But what about all the stiffeners in the form of cupboards, chart tables, frames for doorways, steps, and other furniture... all structural PVC foam or balsa or polycore sandwich panels with sufficient stitched fibre laminates. These can be made with additional unidirectional reinforcement already incorporated inside the panel, and would be best to simply bond them in, and save massive amounts of wet laminating and subsequent fairing.

Behind that, we still have accommodation spaces and the main structural bulkheads are the aft cabin bulkhead and rear beam bulkheads - one of these will no doubt carry a shroud or 2 for the mast rigging. Again we must probably tape and fair. The rear beam is usually far enough back to also not have any accommodation spaces inside, so the taping is not an issue.

Id be happy if i only had to fair out 2 or 3 of the main bulkheads tabbing, a small amount of work in comparison to every little horizontal and vertical stiffener / frame.

Can we determine if it can be done, via calculation alone - so no destructive testing?

 

So all this is about cosmetics, in not having to fair tabbing ? Now you understand the time and money women spend on cosmetics and beauty treatments ! I think you will need to make up some test pieces and see how the various ideas you have perform under different stresses, and satisfy your curiosity that way.