Is bulkhead tabbing now redundant?

...this was posted on another subject thread, but applicable here

 

Is BULKHEAD tabbing now redundant?

Groper, I just wanted to restate your initial posting, and re-affirm that we are NOT talking about just Bulkheads (the title of subject thread) here, but internal framing,....frames. ribs, stringers etc.

I assume you wish to look at all of this internal structure, and how it might have some alternative construction??

 

Yes Brian, that's correct. I figured if bulkheads can be done without it, perhaps everything can also be done. Question is, how and who will prove it? I like to know more about how some of the high performance yachts are built, how do they install structural stiffeners? I'm sure some people have already omitted the taping, just need to find a few examples of such to see how they fare...

 

Where Is All This Going ??

boats are boats and travel over the surface if the water , planes are planes and fly though the air !!
stresses and strains that apply to each are totally and completely different so how the hell can you try to compare the two ?? it doesn't make any sense at all .

GROPER how many boats have you actually built with you own two hand and are still sailing or motoring ???
How many boats have you supervised the construction of and had the pleasure of watching being launched ???
what size is the biggest boat you had anything to do with ??

 

Why a 'flange' , .....not for an I-beam member

In many cases where one is bonding the 'edge of a plate' style bulkhead or frame to the inner skin of a hull, then yes a flange area does really need to be included.

But what if the reinforcing member is of an I-beam form....somewhat akin to the T-bar reinfocements in many metal boats. Lets say the frame, or rib, or stringer was built in an I-beam form, and one end face (flange) was bonded to the inner hull skin, and the other end face (flange) acted to resist compression loading the hull skin might experience.

This actually could be a better use of a sandwich-cored reinforcement than placing the edge of the sandwich against the face of the skin. One could then build the skin of the sandwich that mates with the skin of the hull in a lighter fashion, and of type of glass that would most readily bond to the hull skin. Then the opposite skin of this sandwich reinforcement could be faced with a much tougher glass lay-up. In fact it might utilize a lay-up of material which is much stronger in compression than tension as that is likely the only force it will receive, Taken a step further this I-beam reinforcement might even be pre-constructed over a curved surface such that it have some pre-stressed attributes to it.

One thing that always concerned me was placing the edge of a sandwich cored 'panel' in perpendicular to the hull's skin. One better have a very well constructed sandwich cored panel least the compression force of the hull might tried to buckel the skins off of the sandwich-cored reinforcement 'panel'...bulkhead, frame, etc.

The face width of that I-beam should provide plenty of 'flange width' to bond to the hull skin without any other tabbing.

 

Like these.. I beam from CST http://www.cstcomposites.com/industrial/
Last month I went to a presentation from Clive Watts founder of CST, great & interesting story starting with the beginnings of his garage built filament winding machine complete with blue tarps outside to protect the tubes from weather. Very cluey bloke & employs similar talent, also spends a big percentage on research/testing etc.

Jeff.

 

Well this is already done in some respects Brian, the edge of the sandwich frame is sometimes decored and filled with a UD reinforcement. The same is done for the opening of the frame inside the boat, eg a doorway etc. so the frame is of an I-beam configuration, the web has Dbias reinforcements each side. It produces a very strong frame, question is the join or bond to the hull... What is adequate? I was hoping just the high strength adhesive alone could handle it in a typical cruising yacht load scenario but I'm no engineer so don't know better...and as I said earlier, with a 20mm frame, and 20mm fillets either side, you do have 60mm of hull contact area...

 

Groper, I'm sure others have omitted the taping also, quite common on some splodged hull/deck joints(& also commonly repaired after wharf impacts).
How do you prove it.... maybe make an as drawn & approved joint from plans in a test piece or ten & on the opposite bulkhead leg of the piece a purely coved joint & test them by whatever means in various loadings... Joint against joint , may the tougher joint win!
I've seen structural stiffener installation on high end carbon race yachts(McConagy) & usually involves labour intensive bagged in tabbing, adds up to hundreds of meters with both sides of stringers & bulkheads/divisions. The use of stitched glass fabrics goes back a couple of decades+ now especially in sailing cat builds, so it's hardly bleeding edge stuff, your looking for labour saving rather than material/weight savings here, I'm sure your going to need more "goop" in the corners.
I've also inspected a Buizen yacht under fitout, here the infused hull & structure including chain plates, floors etc was complete & the whole ply fitout installed with a sika? style compound(probably to eliminate movement squeak also) to it's perimeter, the deck was dropped on & the fitout "sealed" to it also, sorry didn't pay attention to hull/deck flange.
One of the catch cries of my composites training was "continuity of fiber!" not to say that a coved joint won't work, the material from the Gougeon brothers supports that, tempered with they obviously wanted to sell more goop too.
Jeff.

 

Indeed Jeff, one line of investigation on my part was to figure out the legacy...

So what are the mechanical properties of a polyester / e-glass fibre matrix? The only reference i have is for a woven roving glass with phenolic resin and from hexcel design guide its quoted as;

Phenolic WOVEN GLASS
(7781-8HS) 400 / 360Mpa tensile/compressive strength and 20 / 17Gpa modulus elasticity tension/compression

Compared to a toughened epoxy adhesive, no fibres, the mechanically properties are only marginally better in the above regard. But i dont think these properties are relevant, i think the shear strength and adhesion/peel/cleavage is the most important, and the toughened epoxy wins hands down. Same goes for the MMA plexus adhesives, the shear strength has proven to be higher than the interlaminate properties. The testing for this adhesive, always pulls apart the laminate its bonded to, before the bondline fails... So is continuity of fibre that important? What if the adhesive is stronger than the laminate?

What sparked this thread, was this post from a forum member here, and a professional engineer;

And then;

And then;

Not saying i beleive 1 guys opinion, but it did spark my interest and figured it was worth further investigation...

 

What you saying is using ring frames that are made with unidirectional glass wrapped continuously for form a T shape in the inside the layers of uni can be varied as to the amount of stiffness required . its what gets done inside of race boats normally !! trying to fix and bonding dis-similar materials is getting easier these days .Aluminium frames have been used buts expansion and contraction is a issue to contend with, so solve one problem and end up with 3 more . best to stick to what's already been used for ever !!

 

If I am following this thread correctly I think you guys may be looking for a magic solution that doesn't exist.

If you are talking about a solid hull, no core, ignore the rest of this post. The image on post 20 shows what I am referring to.

Any structure that bonds a bulkhead or stiffener to the inside skin of a cored structure is crap. I don't care if you have adhesive that is stronger than titanium, all the loads will be carried by the inside skin which is bonded to foam. The loads will be transferred to the outer skin by foam. Just to be sure you understand it doesn't matter if the bulkheads are steel and the adhesive is magic, stronger than titanium, adhesive all the loads must be transferred through foam core to the outside skin.

Normally in a sandwich panel the outer skin of the hull is much thicker than the inner skin and is the primary load structure. If you want to bond to the inner skin it will have to be beefed up considerably and you end up building a boat within a boat.

Look at aircraft construction to see how proper sandwich structures are made. Many textbooks are available on the subject.

 

Very interested to learn more about aircraft construction RD, do you have any references or links in particular?

 

I recommend you find a college bookstore so you can browse through the books. No point in buying an expensive book for just some specific information.

This is an excellent book, many similar books on the page. http://books.google.com/books?id=z39Y6CGu7OsC&source=gbs_similarbooks

Here is a pic from that book. Look at the one the arrow is pointing. That is a simple excellent way of joining panels without all the edge corefill pain. For a bulkhead you would have that as an interrupted joint with the bulkhead penetrating the inner skin and core of the hull for a few inches every few inches. I have used that many times. Of course it is a lot easier with a huge 5 axis router to make all the pockets for you.

 

tell us !!

GROPER how many boats have you actually built with you own two hand and are still sailing or motoring ???
How many boats have you supervised the construction of and had the pleasure of watching being launched ???
what size is the biggest boat you had anything to do with ??

 

Is this an oops ??

Normally in a sandwich panel the outer skin of the hull is much thicker than the inner skin and is the primary load structure.
If you want to bond to the inner skin it will have to be beefed up considerably and you end up building a boat within a boat.


little red person how many boats have you built in you life time ?????
I never heard of such a thing before in all my life , what books did you get that information from ????.

So your thinking the inner skin is not doing much if anything at all its just there to cover the core and keep the water out !!.
So in you view its the outer skin that does all the work !! why even have a core at all ??

Why are so many people quoiting aircraft construction when its boats we should be talking about ??? there is very little relation between the two .
Boats are boats and planes are planes they don't even look alike or haven you ever noticed !!!!