Keels and Keels Again!

Discussion in 'Boat Design' started by D'ARTOIS, Feb 9, 2006.

  1. Guillermo
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    Guillermo Ingeniero Naval

    I was not aware of Remmlinger's work. Most interesting.
    Thanks for telling, Mike.
     
  2. Paul B

    Paul B Previous Member

    It has gone largely unnoticed because it is GIGO.

    With the assumptions made in this paper it is a wonder the oceans are not littered with boats that have had the keels broken off due to these 10m free falls.

    Hell, I don't think you could run this experiment in full size if you tried it at Mavericks.
     
  3. powerabout
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    powerabout Senior Member

  4. Roly
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    Roly Senior Member

    +1

    I did not read the article as it smacked of the extreme.
    If everything was built to a 500k year flood/earthquake/wind, remote occurence, we would not build much. Life is a compromise.
     
  5. MikeJohns
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    MikeJohns Senior Member


    So post on that thread why you think the inputs are garbage.



    The poster is looking for input and he can either correct his assumptions or you can modify yours after some meaningful dialogue.
     
  6. MikeJohns
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    MikeJohns Senior Member

    There's a fair amount of irony in this statement.

    So for you too, go and give him some dialogue .......Maybe after reading his effort!
    Anything else is grandstanding on a platform of hot air.
     
  7. Paul B

    Paul B Previous Member

    The whole premise is garbage.

    Boats do not free fall 10m to a flat splat in the real world.

    I'd like to see his statistics of all the boats worldwide that have lost keels in this manner.

    It is a solution in search of a problem.

    The danger is he might find some politician in the EU who will embrace his idea as reasonable, and the next thing we know this sort of nonsense will be mandated.
     
  8. Roly
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    Roly Senior Member

    "Anything else is grandstanding on a platform of hot air."


    Fair comment. At least I disqualified it as having no substance (my comment) by "having not read it".
    I have the inclination, just not the time.
    Hopefully the irony doesn't become reality.

    BTW, Just how many freefall episodes have been recorded?
     
  9. MikeJohns
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    MikeJohns Senior Member


    Common enough for the damage from such occurrences to be well described.

    Common damage to the lee side of the vessel, stove in portlights structural damage deck hull delamination and breaking of the weather side shrouds chainplates. Smashing off lee side Bulwarks. And the engine breaking it's mounts. And that's only the vessel not it's occupants.

    It's termed "Falling off a wave" design for such an event is not part of commercial class requirements and as Ulrich actually points out it's probably of more interest to people wanting to design robust intrinsically seaworthy type boats that are being designed to withstand all the possible depredations of a severe storm at sea.

    Of more interest is the dynamic 'mechanism' of failure. The maths is there, Work out your own estimation and design to your S-N curves.
     
  10. BATAAN
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    BATAAN Senior Member

    It is amazing the length of this thread, and all seemingly premised on boats that are light displacement, canoe-form, mostly over-rigged and depending on their ballast fin for all stability while being always being driven as hard as possible at sea, the most inhospitable habitat on earth that thinks nothing of swallowing the random supertanker.
    There are more than a few (130,000 years of seagoing) examples of other approaches that work well to solve the practical problems of falling off waves and surviving storms at sea. Only the ever going quest for faster, lighter, more 'stable', faster and faster yet in the service of competition drives this present design development, most other sail boat uses like cargo or fishing seemingly lost in the dim past as long as the cheap fuel holds out.
    The present form, with its inherent problems, will be developed further and further by well-paid design staffs with new alloys and better engineering analysis for those who can afford these huge racing toys.
    All we seem to know these days is how to compete with each other, and sailboat design is a good example.
     
  11. BATAAN
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    BATAAN Senior Member

  12. Guillermo
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    Guillermo Ingeniero Naval

    Good point.
    Cheers.
     
  13. philSweet
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    philSweet Senior Member

    There seems to be widespread confusion about what a backing plate is and why it is used. A backing plate is not intended to distribute a bolt's load to the skin in some nice manner for the benefit of the surface being attached to. Rather, it is used to collect the load from the skin and transfer it to the bolts in a way that is kind to the bolts. It is a part of the keel, it is not part of the boat. It is there because the guy drilling the holes to receive the bolts can't be trusted not to walk the bit around and make oversized, egg shaped holes. So you send a backing plate with holes that you drilled and that has a nice flat surface. The business of distributing the loads imposed is a job for boat parts, not keel parts. Backing plates should rarely exceed the profile of the flange, but they are occasionally used to accurately locate a part, such as centering a part bolted to a channel section. The backing plate is determined entirely by the requirements of the bolt and is sufficiently standardized that it is usually sufficient just to say "comes with backing plate". This business about using wide plates to distribute loads doesn't make sense to me. Why would you put a floating keelson in a boat? If you bonded it to the boat it would be much stronger. But remember to use backing plates.;)
     
  14. MikeJohns
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    MikeJohns Senior Member

    Phil
    There's not much in your post that I'd agree with except that the backing plate does provide an accurate temple !

    You cannot sensibly attach a narrow ended bolted cantilevered structure to a GRP laminate without substantial washers but it's better to use a plate.

    A backing plate is part of the mechanism by which the bending moment and shear forces are more evenly distributed into the hull structure. The bolts are tension elements only if you think about it.

    Plates gives a lot of redundancy over individual washers. The laminate is considerably weaker in shear than in bending. Shear stress is directly related to the washer or backing plate edge length. Also importantly partial shear from one bolt/washer or differences in bolt stress tension through a bolted connection are evened out by the backing plate. The more bolts go through the plate the more robust it is because of shared and distributed load paths.

    The plates importantly provide a clamping friction connection and stop the individual bolts chewing out laminate.

    If the backing plate has room to be wider than the keel top flange then there are advantages in designing it so since it will assist in reducing the moment arm , shear and fatigue . Ideal design and the edges of the backing plate should really taper out or curve away from the laminate to reduce edge stiffness, catastrophic shear action and give the fibers some chance of acting in tension and also reduce local fatigue.
     

  15. philSweet
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    philSweet Senior Member

    I think we agree a lot more than we disagree-

    The plate pictured in the torn out keel are ordinary backing plates. I never mentioned washers in my post. That's another can of worms. If the hull guy wants to reinforce the keel area and decides to do it with a wide plate and the bolt pattern and surface are equal the task from the NUT and BOLT's perspective, the you don't need a backing plate, just the reinforcing plate that's part of the boat. My argument is more than just semantics. A supplier will provide a plate so that there may be some reality associated with the S-N curve he designed to. Kittywampus nut loadings and egged holes make a mockery of engineering load studies. The backing plate is the ONLY thing the supplier can do to ameliorate the situation. He's working his end of the problem, providing a joint that stands up on his end. That is the crux of the matter as far as I'm concerned. If the hull laminate has issues bearing the load, address it any way you want, but it is not a backing plate. We're taking about a design here of modest ambitions. It's not a gate on a fence post but it's not an F-22 either. Assuming that the keel installer will craft their own plate is not too smart. If they do and want to toss the one provided onto the scrap pile, they are free to do so.

    I will give in a little bit. A backing plate does play a role distributing load during assembly and disassembly when the bolts aren't properly torqued. That is an important consideration in many designs where point loads can be higher then than at any time under actual use.

    I'm sticking to my guns in that if a box says "comes with a backing plate" everyone ought to have a pretty good idea what its going to look like, and it will have a footprint no bigger than the opposing flange.
     
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