Transverse frame calculation

Discussion in 'Class Societies' started by DUCRUY Jacques, May 1, 2010.

Thread Status:
Not open for further replies.
  1. DUCRUY Jacques
    Joined: Nov 2009
    Posts: 75
    Likes: 1, Points: 0, Legacy Rep: 15
    Location: france

    DUCRUY Jacques Junior Member

    Hello,

    I have a little question about the calculation of a transverse frame for a sailboat.

    I know the equation SM = (83.33 b l² P)/admissible stress. P is the effective pressure calculated at the mid-length at the frame and with a reduction pressure factor of 0.25.

    But, when I compare ABS ORY et ISO rules, I see that ISO take in account a curvature factor ... et ABS no ! Do you know why ?

    Thank you by advance

    Best Regards


    Jacques
     
  2. Brent Swain
    Joined: Mar 2002
    Posts: 951
    Likes: 35, Points: 0, Legacy Rep: -12
    Location: British Columbia

    Brent Swain Member

    Curvature is a huge factor in adding to the strength and stiffeness of a hull, such that I have found transverse frames totally redundant, and useless on boats under 60 feet. The longitudinals are far more relavant in resisting distortion on the highly curved hull panels of a sailing hull, as they are arcs under compression.
    Any rules that dont take this into account are grossly inacurate and irrelevant.
     
  3. dskira

    dskira Previous Member

    Could you please elaborate.
    Transverses frame redondant and useless in less than 60'
    I don't think so.
    How you stop the high vibration when you crash the bow on the sea, how you get your torsional stifness in which the deck by itself will be not enough, how you transmit the stress from the shroud to the hul, then to the other side of the hull, how you take the ballast, ..........and so on?
    Arc under compression, that's need to be explained. This is the kind of bogus explanaisons without any backing, but the fact the plate as a coumpound curve.
    As for the rules, which one are you talking about: The Lloyd's? They impliment frames, but it is just the Lloyd's, of course they are not very well knowne:p
    Brent I realy hope you didn't wrote that in your book, because you are dead wrong.
    Daniel
     
  4. conceptia
    Joined: Nov 2009
    Posts: 203
    Likes: 7, Points: 18, Legacy Rep: 97
    Location: Houston

    conceptia Naval Architect

    the transverse framing is relevant for small vessels only. so I think the point Brent making is obnoxious. The longitudinal stiffening, yes it is relevant for cargo carriers. So, I feel the number of longitudinal members in case of this 60 foot sail boat would be minimal.
    Now coming to the Class rule books - They research, do case studies and come up with a rule only when really satisfied with its relevance. the reputation of the class is unquestionable. Generally the empirical formula given by the class to find the SM or t is derived by taking all the important factors. In this formula they would have considered the curvature and related to any of the variables. the number 83.33 is such an indication. You can rely on the class rules- "In almost 60% cases, the design as per class rules are a bit or more over-designed."
     
  5. LyndonJ
    Joined: May 2008
    Posts: 295
    Likes: 19, Points: 0, Legacy Rep: 233
    Location: Australia

    LyndonJ Senior Member

    Curvature adds a little to a frame or a skin since it effectively adds dimension tio a cross section. Springing a plate adds some pre-tension and makes it effectively stiffer but not stronger. It will still yield at the same extreme fibre proof stress.

    All framing is in tension and compression you are wrong to say it's all in compression, there's always a neutral axis in a beam curved or not.
    One side is in tension the other in compression. Only when you get to an arch is it all in compression.

    The big problem with sheet material with no stiffeners or framing is buckling. Framing limits buckling.
     
  6. Brent Swain
    Joined: Mar 2002
    Posts: 951
    Likes: 35, Points: 0, Legacy Rep: -12
    Location: British Columbia

    Brent Swain Member

    When you put pressure on a transverse frame, you are putting as simple bending load on a straight frame, in a hard chine hull. When you put pressure on a longitudinal ,on a fore and aft curved section of hull, you are putting it and the hull skin both under compression. It is an arc, under compression. It's far easier to bend a flatbar on edge than to compress an angle on end ,especially if it is stitch welded to the hull skin , preventing it from moving sideways.
    This is not the case with flat sided hulls, like power boats and freighters nor with completely round bilged hulls. It is the case with radiused chine hulls.
    When you weld the longitudinal seams , the shrinkage of the plate edges are longitudinal ,which transverse frames alone do nothing to control . It simply bulges in and out between the frames. Put more frames in and it bulges in and out in shorter lengths between them.Longitudinals eliminate this starved dog look. Ditto for side decks. I've seen some horrendous distortion ,when people naively assume they can control longitudinal shrinkage with transverse support alone.
    Thus, any small steel hull should favour longitudinals over tranverse frames. The more longitudinals, the fairier and stronger the hull will be. Obsessions with transverse framing is a throwback to wooden boat building , with a material which only had strength in one direction. Different materials require different design priorities. Steel aint wood!
    I recently read an article where Lloyds insited a cold molded hull have stainless keel boats. Most stainless in wet wood corrodes like hell, from oxygen starvation, an abysmally bad choice for keel bolts, and were structurally unecessary on the type of hull in question. Passive stainless is rare. So the owner epoxied the tops of stainless bolts in, just to please the Lloyds surveyor. Keel boats had no structural relevance in the type of boat it was.
    Lloyds approves wood and fibreglass boats . I wonder how many of them would have survived the 16 days of pounding on a Baja Lee shore in 8 ft surf, pounding across 300 meters of Fijian coral reef, collision with a freighter in Gibralter, single season passage thru the NW passage ,etc. etc. that my unapproved frameless designs have survived.
    So go buy yourself a Lloyds approved wood or fibreglass boat ,and we'll have a demolition derby ,with my unapproved frameless steel boat.
    Stating the truth is obnoxious? Only to those trying to hide the truth.
    So much for LLoyds!
     
  7. DUCRUY Jacques
    Joined: Nov 2009
    Posts: 75
    Likes: 1, Points: 0, Legacy Rep: 15
    Location: france

    DUCRUY Jacques Junior Member

    Very insteresting discussion ...

    When you read the ABS or ISO rules, you can think that the plating is supported by longitudinals ... and the longitudinals are supported by the transverse frames or bulkheads. But maybe this approach is too simplified ?

    You can also to have bulkhead only, but it seems to me that few frames between bulkhead are better in the slamming zone or in the ballast/mast zone.

    And my question concern the necessity (or not) to use a curvature factor for calculating the SM of a frame (this is IMHO a big difference between ABS ORY and ISO).

    Thank you agin

    Regards


    Jacques
     
  8. Brent Swain
    Joined: Mar 2002
    Posts: 951
    Likes: 35, Points: 0, Legacy Rep: -12
    Location: British Columbia

    Brent Swain Member

    With my origami hulls and their conic ends, the conic shape gives them huge compression strength. We once had to use a 12 ton hydralic jack to force one out ,when it bent the wrong way. It is easy to design a lot of conic curve in the ends of any sailing hull, eliminating structural compression worries there, as well as eliminating distortion there.
     
  9. dskira

    dskira Previous Member

    Brent you should know that passivated ss do not pit (not corroded).
    Read and learn, you have hard time with this word: LEARN
    Caught your pants down you just sink deeper.
    So much for Lloyds you said. Are you just insane or you are just fooling around to see the reaction. I realy hope, for your sanity, it is the latter.
    Daniel
     
  10. Brent Swain
    Joined: Mar 2002
    Posts: 951
    Likes: 35, Points: 0, Legacy Rep: -12
    Location: British Columbia

    Brent Swain Member

    My first boat was a" Pipe Dream" , tested at the Davidson Lab, where they tested all the America's cup boats, designed by Francis Kinny and featured in the book "Skenes Elements of Yacht Design."
    You'd think a boat with all that world reknowned expertise going for it would be an excellent boast. It was an abortion , with zero directional stabilty , and was hard pressed to make 90 miles a day downwind.
    That completely blew my blind faith in world reknown gurus. The change I had envisioned in the construction phase , which I didn't have confidence to do, having no sailing experience, proved in the end to be to the solution to the world reknown guru's major screwup.
    I no longer believe in the infalibility of sacred cows , be their name LLoyds or anyone else. If you wish to bow down to them , go ahead. I did during my greenhorn years. Now I value my freedom of religion more, so I don't worship anyone elses gurus, not even yours. ******** by anyone , including LLoyds is still ********.
    A freind built a Lloyds approved ,custom designed Laurent Giles 50 footer. The framing called for was the structural equivalent of 12 inc by 24 inch douglass fir framing , closely spaced with no longitudinals ,drastically reducing the interior space of the boat. The fact that such total ******** came from Laurent Giles ,didn't mean that a wooden boat with such framing would be inadequate. It wouild still be ******** regardless of who drew it.
    No one is guru enough to turn ******** into truth by decree.
    Your suggestion that they are seriously undermines your credibility as does your suggestion that many boats that have survived extreme torture tests are not strong enough. So tell us , how many steel boats of your design have you built with your own hands? Whats your experience in keeping distortion out of steel hulls? Maintaining the same steel hull over decades? Crossing oceans in steel hulls that you have designed and built with your own hands and maintained over decades?
    What I have designed and built , have gone thru enough torture testing to prove their structrural strength beyond all reasonable doubt.
    Again, bring your Lloyds approved wood or fibreglass boat over and we'll have out demiolition derby. No? Then you clearly don't believe your own ********.
     
    1 person likes this.
  11. LyndonJ
    Joined: May 2008
    Posts: 295
    Likes: 19, Points: 0, Legacy Rep: 233
    Location: Australia

    LyndonJ Senior Member

    Whoaa


    When you pre tension a beam then load it , the pre-load has the beam in tension on the outside (of the hull) and compression inside in the longitudinal.

    This pre-tension-compression has to be overcome before you are back in to normal beam theory.
    But a massive pre-load would be required to add massive strength.

    What pre-load do you manage to add flexing skin and longtnl frames? Then that is divided by the length of the structure.

    A large vessel such as the 60 feet you suggestet would be lacking in global strength without transverses, the hull would be very flexy I think.

    Have there actually been any even 50 footers built this way that you can show? All your boats look to be 36 footers.
     
  12. conceptia
    Joined: Nov 2009
    Posts: 203
    Likes: 7, Points: 18, Legacy Rep: 97
    Location: Houston

    conceptia Naval Architect

    Brent, i was pointing out your reaction over the classification societies. You cannot just simply blame the class for any design errors. Also, as there has been CSR(Common structural Rules) by IACS popped up all the rules are same. They made it so to felicitate the class conversions.

    You are correct- blind faith wont help anyone, maybe its religion or science. You gotta understand wat it is on your own.
     
  13. fcfc
    Joined: Feb 2005
    Posts: 779
    Likes: 29, Points: 28, Legacy Rep: 399
    Location: france,europe

    fcfc Senior Member

    Yes.

    History.

    ABS was the first rule for general public boats under 100 ft (30m) in 1986 . Then the second edition was 1994. Then in 1997, ABS dropped support for boats below 80 ft (24m) to leave place to ISO that will support up to 80 ft. Then the first version of ISO in 2002, starting with ABS work and experience. and now, ISO 2008.

    As time goes, industry is getting more experience, and is using more refined rules.
     
  14. conceptia
    Joined: Nov 2009
    Posts: 203
    Likes: 7, Points: 18, Legacy Rep: 97
    Location: Houston

    conceptia Naval Architect

    thank you fcfc for your info.. i never knew dis...
     

  15. fcfc
    Joined: Feb 2005
    Posts: 779
    Likes: 29, Points: 28, Legacy Rep: 399
    Location: france,europe

    fcfc Senior Member

    Just a side note on ISO

    In Europe, all cars sold pass all legal safety requirements. Drivers associations ranks safety of cars on the market from 0 star to five stars.

    Meeting ISO boating requirements just means that you have the legal right to sell your boat on the EU market. It does not imply at all that boaters associations will rank you boat safety 5 stars.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.
Thread Status:
Not open for further replies.