Is bulkhead tabbing now redundant?

Discussion in 'Boat Design' started by groper, Jul 8, 2013.

  1. groper
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    groper Senior Member

    Have came across some new information recently that I cannot verify, and so would like to discuss the topic.

    The information I'm referring to is that Australian survey inspectors / marine surveyors, are now allowing non fibreglass taped frame and stiffener joints in fibreglass boats fit for commercial use. The caveat is that the strength of the joint must be as strong as the ISO standards specify for the type of vessel, and this can be accomplished via 3rd party testing to prove the strength is equal or greater.

    Word is, high strength adhesives with sufficient bonded joint design, will pass this strength test.

    I've noticed that most production boats these days, use MMA bonded hat section stiffeners or grid liners...


    I'd like to discuss options with regard to non production built boats, and which methods might be employed in order to reduce building time and reduce fairing work in areas where these joints are visible in a boats interior.

    I'll post some more references when I get some time.
     
  2. TANSL
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    TANSL Senior Member

    Historically there were reinforcements glued directly onto the plate. The problem, apparently, is that this solution requires processes and some glues that make it so expensive, or more, than the solution with overlaps. Mass production allows molds to make a network of reinforcements, fabric that is glued directly to the hull.
    I think, more or less, there is the issue.
     
  3. groper
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    groper Senior Member

    Im being more specific in this reasoning, that is custom boat building, or high performance/racing yacht building - as we already know that production boats generally use liners and bonded hat section stiffeners which are not visible anyway. This also implies a lightweight core sandwich panel type of construction, such as foam and glass, foam and carbon, honeycomb and carbon etc...

    Yes plexus MMA adhesive is expensive. But the cost may be more than worth while if it saves labour in terms of fairing and wet laminating.

    Here is another product which may be suitable for frame and stringer bonding by way of fillet only - no glass tape over the fillet. --> http://www.atlcomposites.com.au/files2/epoxy_products.adhesives/techniglue-hp_r5-eng_data.pdf

    Unfortunately, it also is very expensive...

    Exactly, what is the main load/stress consideration when designing frame and stringer to hull joints?

    What type of testing would be used to determine the strength of the joint, and how would you correlate the result with an ISO standard?

    A seat of the pants method is talked about in the gougeon bros book on boatbuilding, but im not sure of its validity? They talk of determining fillet size when bonding 2 peices of plywood at right angles, such as a frame to hull joint. They simply make a fillet using thickened expoxy w/ silica, then load the frame at right angles to the hull at a distance of 8 times the frame thickness, so basically a cantilever load on the fillet. If the fillet breaks, its no good... if the frame breaks, then the fillet is sufficient.... seems kind of seat of the pants stuff, but is it even testing the correct type of load case?
     
  4. tunnels

    tunnels Previous Member

    Do the job properly and do it once !!

    This topic was discussed a while back and if you stuck bulkheads into a boat by and they show marks outside then there's basically three things wrong
    One is the type and amount of glass used to bond with and second the bulkhead is to close a fit to the hull and thirdly the resin catalyst ratio was to high !!
    As for time save is a totally ridiculous assumption and if you trying to save time by taking short cuts on the really important structural parts of a boat you are a not bright person and Will read about how you were rescued in the news paper after you boat broke up and others risked there lives to save you !! :confused:

    What do you do with all the time you save ?? :eek:
    how do you store it ?
    in a bottle
    ?in a box ?
    or standing leaning on a bar with a drink in your hand ??
     
  5. groper
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    groper Senior Member

    Indeed, and you were told the same thing back then tunnels, "theres no problem doing things the way you already know..."
     
  6. HakimKlunker
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    HakimKlunker Andreas der Juengere

    For a bonding you will need a flange to provide sufficient contact surface. Until now I have seen such parts coming out of moulds. Right now my imagination does not give me a non-mould option. The fibre orientation in these flanges resemble a tape laminate, but naturally only on one side.
    Some years ago I participated in making several 'dk 46's' where hull liner and interiour modules - some of them structural - were built this way. Hull/Deck joint however was additionally laminated inside. The structure was ok as far as I know (one boat went to Cowes Week, one other to Sydney-Hobart, one other survived a gale-race in the Baltic, where numerous other boats had issues)
    This building version requires good fit of the parts, coming out of good moulds. There you loose some of the time advantage from reduced fairing and faster bonding.
    Where such bonding is visible I personally find them looking not the right way, and for the sake of appearance it will be worth taking the extra effort of tape laminates, fairing and finishing.

    In high performance racing (to respond to 'more specific reasoning') I think that attractive interiour has minor importance. A laminate though may give weight advantages and also provides more stiffness in the joint as it is applied each side. Technically I see nothing wrong with both versions, as long as there is a structural calculation behind.

    One important role not yet mentioned are building conditions: Climatic situation, workshop standard and work force qualification should be considered when material and procedures are specified.

    Tunnels: ... wonders what to do with the time saved.
    I reckon that even in China workers are getting paid (;))and the customer has to come up with the money. If our customer is asked for less payment at the same required quality, he is more likely to place an order. (Please excuse the somewhat absurd combination of the terms 'quality' and 'China'...)
     
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  7. tunnels

    tunnels Previous Member

    So in your opinion its ok ?? wheres your proof ?? wheres the technical data???

    Like was agreed before in the last episode of this subject its the technical details that are not being displayed and is missing and the approval data from a reputable survey company stamped seals and officially approved . also the adhesive company supplying the muck wheres there technical data sheet with there stories of success and benefits etc etcif there really are any !!, Just because some fruit cake charges off and sticks his bulkheads into his boat without explaining in fine detail all the prep and how and why I would keep very quite about it until its made official and some one comes up with the goodies on paper and sticks there head into the noose .:eek:
    I will never become a sheep and just follow blindly and jump off the cliff just because of something I read here with out any solid proven evidence to say how its done !! :confused:
     
  8. HakimKlunker
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    HakimKlunker Andreas der Juengere

    I am mainly a builder and not a fully certified NA. Therefore I believe that others are more qualified to provide the mathematical proof. Which does not mean that the topic is unfamiliar to me. But whenever I see my limits, I make sure to cooperate with producers of material and architects as well. It would certainly be incorrect to simply stick bulkheads into a boat without further consideration.

    The boats I reported about at least prove the following: They were commercially introduced into the Australian and European market and therefore meet the respective standards. The design is from Mark Mills, NA. The producing company was dk Composites, Malacca/Malaysia. All materials we had used then were subjected to on-going quality control, and there have been TDS and material certificates available also for us supervisers. You will understand that I cannot have complete knowledge of everything going on in a 200 people large company.

    Technical details? My intention is not so much to provide a free construction and building manual. All I say is: It is possible, because it was done before.
     
  9. tunnels

    tunnels Previous Member

    Please excuse the somewhat absurd combination of the terms 'quality' and 'China'...)

    You need to spend some of you preciously saved time and board a plane and spend some time in china ,Quality exists on a grand scale , considering the out side world took ,stole ,and grabbed so much from here over the centuries there's a wonder there's anything left . but there is !!,they have the tallest buildings , there bridges stretch on forever and you need to you have plenty of fuel in the tank ,take food and water because they take so much time to cross .
    In the just few years ive been here I have really changed my mind after hearing about china made all my life , what you are probably seeing is the crap your importers get made specially because they and you want cheap stuff !!
    its not what is here and the locals wont touch the stuff . . for a country that has been intentionally deprived for many many life times of technology on all levels and has had there mineral resources' stolen and shipped back at grossly inflated prices in the way of goods etc . Oh you better learn Chinese and put chop stick on your next shopping list because the world is hungry for what china has to offer and the Chinese have markets that are encroaching onto your patch and everyone else's and getting closer and closer every day and you don't even know its happening . !! open your eyes !!! wont be long but the next flight you take could be a Chinese aircraft designed and made solely by Chinese !.
    Oh not to forget the astronauts will have to be bilingual to order there takeaways when they get back to the moon to the Chinese Mc Donald's in a crater close to Ming moon base 2 :eek:
     
  10. groper
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    groper Senior Member

    Makes sense, but lets take a simple bulkhead example. Assuming the bulkhead is made from 15mm cored panel, its bonded onto the hull and the excess adhesive is squeezed out and shaped into a fillet with a 25mm radius.

    This means the contact area is 15mm directly under the bulkhead + 25mm each side in the fillet - so a total contact area of 65mm! This seems higher or at least equal to the typical bonded flange width of a premolded stiffener.

    So if contact area can be satified through sufficient fillet radius, whats next on the list? What kind of load does the joint need to handle, and is the fillet material upto the loads applied, and is there sufficient contact area on the edge of the stiffener - in this case, 25mm.

    The class rules generally refer to bending moment and shear with respect to hull stiffeners. The loads are also defined by the class rules, however im still at odds on how one can design the joint around the calculated load case?

    Im hoping someone can spell it out for me, how to go from an applied load on the hull plate, to design sufficient strength using an adhesive fillet, and calculating the stress the adhesive fillet needs to handle.
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Perhaps you should re-read this:
    http://www.boatdesign.net/forums/fi...head-joining-question-45735-2.html#post603791

    and here:
    http://www.boatdesign.net/forums/fi...head-joining-question-45735-3.html#post603907
     
  12. tunnels

    tunnels Previous Member

    Ad Hoc; thank you for that !!
    be realistic people ,please ,instead of going off half cocked like all things there's more than first meets the eye .the interpretation of sticking in a bulkhead could mean anything !! so until you actually see with your own eyes how its done ,and what is used, and the actual size and shape of everything just sit and ssssshh!. :eek:
     
  13. groper
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    groper Senior Member

    Adhoc, i read the paper you linked to in the above post - its not really relevant to this discussion topic in a direct sense. The other thread i started was for a simple question regarding discontinuity of the hull panel underneath a bulkhead, or joining a hull plate directly over a bulkhead.

    In this thread, im specifically looking for information on how to design a bulkhead to hull bondline, using modern high performance sandwich panel design. What i mean by "modern high performance" would not be what most commercial Naval architects are familiar with ie. Not single skin polyester resin based FRP hull plate with HAT stiffeners, large quantities of CSM fibre etc. Im talking about much more expensive structures that use thick core materials and thin skins, very high panel stiffness which allows great distance between stiffeners, and generally much lower displacement vessels, such as high performance sailing yachts ie. lightweight. Material properties are of higher strength and flexibility, epoxy resins not polyesters, toughened rubberised epoxy adhesives, 100% directional fibres, no CSM, and including the use of high modulus fibres such as carbon.

    It is not outside the realms of possibility, that a bondline which doesnt include a fibre overlay will not meet the design loads in these applications. The loads are lower, the materials have much better mechanical properties.

    So again, im looking for information on how to design the bondlines of the internal framework of a hull in the above context.
     
  14. tunnels

    tunnels Previous Member

    The ring frame would in actual fact replace what you would take to be a normal bulkhead or a partial ring frame . in racing yachts there is a very strong floor grid that distributes load from the keel and the stepped mast . loads are transferred out onto the skins of the hull that are built in such a way using unidirectional running under and over core that within them self form a frame ,one runs from stem to stern each side of where the keel is fixed to the hull and the mast step and the others run athwart ships crossing and bonding to each other to accept stress and pressures pulling from the side stays . so looking its roughly a huge X frame concept under and over the hull core . Most of the framing are only partial and stop part way up onto the deck a short distance .
    The tabbing for these frames when its done is the glass that is the second skin used to strengthen the sides of the ring frames and also goes out 150mm onto the hull skins, usually a double bias and all corners are coved with 15 mm radius . inside the hulls we were making there was only one complete ring frame forward the supported the back end of the retractable carbon fibre bow sprit !
    These ring frames used a light weight single skin of double bias and the inside edge of the hole had 6 layers of unidirectional glass fabricated to form a tee section 65 mm wide , the second skin of glass for the sides of the frame was what was used for tabbing into the hull . so was serving a duel purpose . The central floor grid was the whole life and sole of the hull and constructed over 2 days with 35 layers of unidirectional running through and each layer cress crossed other layers and formed interlocking with each direction . The schedule for its manufacture and how it was to be made was strictly adhered to with every one that was made . the whole total finished boat was lifted from one single pin through this frame when it was lifted from Its cradle and put into the water .
    The grid had no glass tabbing to the hull what so ever and was 100% totally dependant on the HPR25 semi flexible epoxy adhesive used to bond straight to the inside skins of the cored hull .
    In the construction of racing yachts there is a very sophisticated glassing schedule during the whole of the hulls manufacture layers of uni running in different directions to and from then pads of 0/90 in combination to double bias !! then the foam core is laid and vacuumed in place and the glass skins over the core get yet more layers of uni and even bigger pads of double bias and 0/9 each side of the inside glass skin . a check sheet was made and place on a clip board and as each glass layer was laid it had to be checked off the list and signed but the team leader . this is true glass boat building where each and ever layer of glass used is calculated for and has a specific job to do .
    Back to tabbing to the inside hull ,skin one single layer of a double bias glass 300 mm wide 150 onto the hull and 150 into the bulkhead/ring fame is really all that's needed remember this is both sides of the frame being fitted never one side . resin catalyst ratio is always same as what the hull is laminated with In our case the boats were 100% Vinylester resin so less shrinkage and much better stick-ability of everything done
    So my thoughts on just sticking frames and bulkheads inside a hull , yes it will work but I would never advise anyone unless I had all the facts and done the job myself !!! thrust in another persons workmanship I would have had to have worked with that person for a minimum of 6 months before I would place my life in there hands !!:D
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    Groper

    You have just demonstrated that you are unfamiliar with structural design by this statement, when rereading my previous comments.

    Whether a structural joint is made of non-advance extremely low tech materials say like paper Mache, or Switz cheese, or hey even super glue or plan old sellotape, none, repeat, none of these alter the structural load that is being applied. What is does alter is the response.

    If you design a joint with Switz cheese, you need to establish its properties in “x” and “y” and “z” directions, i.e. all 3-planes to understand whether the material is isotropic, orthotropic or anisotropic. Then how the yield stress, strain and shear strengths vary in all 3-planes and of course the Youngs Modulus, not forgetting the importnat fatigue testing too.

    Once you have this data, it is your starting point.

    If you mix Switz cheese with say, Parma ham, how are all the above mechanical properties effected, do they remain the same, if not which change and by how much. Then you test the same ratio in varying environments and so on. Then you repeat with different ratios of Switz cheese and Parma ham to establish a trend. On top of that, when making this mix of Switz cheese and Parma ham, are the properties effected by the quality of the cheese or the ham, if so how, and by how much. When mixing the two together does the temperature when mixed and/or the humidity also have an effect and so on and does the exact measurements become important i.e. can ojne be sloppy or one needs to be exact and the tools for mixing them and so on.

    Thus even with very simple and basic mixture of two materials Switz cheese and Parma ham, there are simply endless variables to consider, endless combination that can be made and endless resulting mechanical properties and endless effects based upon the quality of the material and the method of making and the environment and skill in which it is made. And must shown to be quantitative, i.e. repeatable by others.

    Thus whether one is using extremely low tech materials like Switz cheese and Parma ham or your ultra high tech extremely modern space age beyond light years stuff, the procedure for establishing the technical properties and hence whether a material in a certain combination can resistance and shirk loads, carry shear, not go beyond its “elastic” realm and what deflections are produced under said loads is the same and satisfy any fatigue issues over the standard 10^8 cycles.

    If you wish to use a mix that is not familiar or unknown, you must find out its properties as described above. It must be done by an independent facility and/or witnessed by an independent authority to be used to the satisfaction of a surveyor.

    So, you have designed the boat and in the current configuration the loads being imposed onto the WTB are say 100kN shear and say 50kNm bending moment from other structure and a hydrostatic head of say 75 kN/m^2, how does an ultra high tech space beyond light years material change the values of these loads over that of using Switz cheese and Parma ham? It doesn’t, not one bit. What it does do, is change the response, one will fail and one will pass. But YOU have to demonstrate that with the mechanical properties of the lay up YOU are using, if it is non-standard.

    It is a simple as that.

    If you stray outside accept norms of materials of composites, that is great, you can do that, that is the beauty of composites. BUT and it is a very big BUT, unless you can demonstrate these new properties and their responses and fatigue issues and how quality control influences them , you’re up a creek without a paddle.
     
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