Is bulkhead tabbing now redundant?

That exactly right like I push the point of working to survey standards . Then you know the boat is built better than most .
You could not believe what guys get away with and the old saying out of sight out of mind and who care no one will ever see it applies more times than you would think . I have a library of pictures of things that would make you hair stand on end !!
most all are surveyed boats but after the inspector guy has gone collision bulkheads got cut and had a hole big enough for a guy to fit through and never recovered over or reglassed just left !! bulk heads glassed nicely one side only the other side no glass at all .Longitudinal stringers all glassed in short length of glass 900mm long x 600mm wide so in a 25 mtr boat takes a lot of 900mm long lengths to cover the stringers with 4 layers x 6 stringers . AND THE unidirectional glass strips 120mm wide that were supposed to be continuous lengths one end to the other with no joins any where and to finish and run out onto the transom and the hull 600 mm each end were also done in short lengths AND get this just BUTTED together and no overlaps any where . These guys are the companies best laminators and there supervisor was the team leader and telling them how to do what they were doing !! with a trained eye and if you know what you looking at all these things are easy to spot even with you hand over one eye .

Timber framing in the bottom of one boat and the guys with battery screwdrivers in hand ready to cover everything with 15mm plywood I told them to take the floor panels out because I had seen all kinds of things!!! places that just had a coat of resin and no glass or a sprinkling of 225 csm
you have no idea what gets covered up when no one cares

 

so where does any of this get tested in a controlled environment so the rules could be made?

 

Groper,

Can you post a drawing or a sjktch of the midship section and profile view? My thinking is guided by Class rules and I do not want to go out on a limb here giving opinions/advice which can be structurally defective.

 

Metal Bonding in Aircraft

BTW Red Dwraf while I was looking for a paper given at the CFA, Composites Fabrication Association, titled "Adhesive Bonding of Large Stringer Installations", I ran across this aircraft study of metal bonding....with adhesives:
http://www.niar.wichita.edu/niarworkshops/Portals/0/Oct27_1330_Alenia.pdf

Didn't have time to read thru it, but some of the photos and illustrations made it look interesting to review. :idea:

 

Dow Chemical Paper on Methacrylates

This is a VERY interesting paper on the development of Methacrylates, along with a history of that development to ever better and wider range of products:

Advances in Structural Acrylic Adhesives

http://msdssearch.dow.com/Published...tive/pdfs/noreg/299-51538.pdf&fromPage=GetDoc

....particularly interesting excerpt,....Bondline Properties

There is also several marine references at
6.4.2 Boat Stringer Bonding
6.4.5 Thick Gap Bonding for Marine and Wind Blade Applications

 

Tabbing verses Adhesion in framing members

Groper I think you have this correct, a lot of the tabbing that was done in old days was a result of polyester resins and their lousy secondary bonding. I used to say that polyester resin loves to stick to everything EXCEPT itself. I witnessed numerous tabbing problems with many of the old British cats that were imported to the USA....and the Gemini's etc.

If the framing structure of a vessel is of a halfway decent design....a real 'grid' , any one particular member should not experience BIG bending loads at the interface of the framing member and the hull skin. At these junctures a bulkhead may try to come unglued from the skin, but not broken by bending. Even with big wide catamarans the major athwartship bulkheads themselves will experience significant bending loads in their 'panel being' , but not at their connection to the hull skins.

Of a bigger concern is the shock loading that might be repetitiously applied to this bulkhead-to-hull skin connection. Many of the fiberglass resins are excessively brittle by nature to accepting this type of loading. So tabbing for safety purposes again enters the picture. One of the real advantages of the more modern adhesives is their ductility. They accept this shock loading a lot better. From my reading the methacrylates are NOT always the answer. Sometimes it appears as thought the newer epoxy formulations may be better.

Bottom line, I would likely go with the tabbing for the major BULKHEADS of a vessel. But for the lesser web frames and stringers I see no sense of tabbing those, considering there loading profiles and the adhesives that are out there today.

 

RX, this is a typical layout for many modern cruising multihulls of around 40ft length here in Australia, the layouts generally only vary in terms of bridgedeck layout, and whether galley up or galley down etc. The benches and lockers down the hulls have shelves in them, and everything is/can be made from structural sandwich panels - even the shelves inside the lockers/cupboards etc. So the panel spans can generally be whatever you need them to be and all stiffeners are generally at least 100mm depth.

I would be interested to know what the largest panel span can be, if bonding only techniques can be used for everything save the main beam bulkheads and mast bulkhead etc...

 

PRISMA Composite Preforms

Wonder what has happened to these guys?....the website doesn't seem to be working....but it is still up?

COMPSYS, Inc
http://www.preforms.com/

 

I think: No.
Only exception is, when the calculation includes a big safety factor; and that is not wanted for weight reasons - especially on a catamaran - and cost reasons.
Not sure, how you approach the calculation, but i.e. in our local case we include fibre ratios: if we would not take samples and check them - we would not be able to see (and prove) that we build what we have planned.
Calculation also involves assumptions that need to be verified, and a practical test does this best.
Whenever we here get stuck with structural decisions, then because of talking too much about it, where a test would show it or at least would provide better information. (Unfortunately, I am not the one here who decides that...)

 

Im still interested to know how many boats you have built !!or is the big cat your first ??

There is some really interesting material finally beginning to surface and have to really spend some time to read and find what's relevant to sticking parts of boats together with .
The use of adhesives is ok but the way its used and how its done is the make of break subject I am concerned with !! bonding and the application process is the key that everyone skips around and avoids wanting to post information about and it really is the most important part .

 

crash test cars,
planes get tested
http://www.cbsnews.com/8301-505123_162-43641624/bend-not-break-boeing-787-passes-wing-load-test/

so for boats its guess work?

 

This weekend has changed my views slightly:
A friend came back from sailing - the boat is lost. I better do not mention names, before the case is clear and complete.
It was a 40 ft sailing catamaran, a few years old; hulls made in South Africa, assembly and fitting out in Thailand by a professional yard. Sandwich construction. It was not ISO certified, neither by other authorities.
I was told that at late night one hull was leaking strongly and the boat heeled a little further than bridge deck level. (I saw photos). Weather then and previously was around 15 knots of wind and no exceptional waves. The boat was at anchor on ca. 20 metrs of water.
The bilge pumps were unable to handle the water, and soon parts of the interiour building (including some that were meant to be permanently fixed) were afloat. Most disturbing to hear was that a large piece of sandwich (presumed to be part of the hull) was floating away during the night. As the boat was grounded on a beach it was soon flooded by sand; unfortunately this (and the excitement of the event) prevented a close look on the damage. But the boat since it was bought here, never had a collision or grounding.

I place this information here, because the story implies a structural failure that correct planning (and building) is meant to prevent.

Generally, I find now that sticking closer to 'traditional' building and generally some overbuilding makes more sense than a possible total loss.
Even if some owner can bear the loss of the boat - there is also safety of human life involved.

What is disturbing, is the fact that many other boats of this style of building appear to do a pretty good job, and at the same time do not comply with building standards.
We presently make a 49 ft catamaran from a modified kit and had it recalculated for ISO compliance; this ended up in roughly doubling the original laminates anywhere above the waterline, and also local reinforcements were altered.
If now both versions seem to be reasonably satisfying, and also both versions here and there fail, I would conclude that design and calculation is not the only factor for success; building method and craftmanship are no less important. The more you test (and doubt) your own work, the safer you feel later.
Unfortunately, legions of self builders with little experience behind meanwhile feel encouraged to believe that they can do as well (or better) than trained (and certified) professionals. That may be the case, or may not.
(Imagine, the same tendency will establish in aircraft building! I better reinforce the roof of my house then...)
Questions such as 'how many boats have you already built' seem to make more sense to me this week than last week.
And to correct a previous statement: Also in China good boats can be made
(if one wants to ...)

As a personal observation I might like to add -speaking of non-professionals- that 'arrogance' in competence, and overestimating oneself's skills and knowledge is more often found in the multihull fraction.

 

I agree with what you are saying. The class rules are based on minimum standards and polyester resins, hence the minimum 2" tab width on each side is mandatory to get a good lap shear, then 1/2" thereafter.

Epoxy does a better job with regards to adhesion. In aerospace fabrication where epoxy is the norm, 1" is the minimum tab witdth and 1/4" thereafter.

Another area of consideration is the joint flexibility. When a tab is made, the best tab is a long tapered tab. When the moment diagram is drawn (of a cantelever beam), the curve is parabolic, with the flex curve starts to go down at approximately 1/4 of the span. So with a beam fixed on its end, there is a correct proportion of this 1/4 rule. This is true even in steel or concrete beams.

With availability of stiffer fabric and resin plus the sandwich technology and the infusion process, the panels are stiffer, the flex lesser, joints are stiffer.

Tabbing the major structure is consistent with the methodology of metal. The guiding rule is major parts that is welded is bracketed or the sectional area is increased.

The problem is if Class rules has to upgrade, composite design will be limited only to select few who (has the math skill) will undestand the technology or the booklet will be so thick with graphs and illustrations of different materials. My first book of BV (1989), half of the book is graphs and tables of possible different materials combination. And they are only talking of GRP, not advanced composite.

 

what does "professional yard" mean, the bill is on letter head?

 

You pays more and the crew struts around with distinctive uniforms color coded with their area of expertise. The engineers/architects wear white coveralls (angels of the gods)