Amidships Chain Storage

Discussion in 'Sailboats' started by Ted Royer, Jul 20, 2018.

  1. gonzo
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    gonzo Senior Member

    By definition, anything that oscillates is vibrating.
     
  2. gonzo
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    gonzo Senior Member

    Are you saying the equation is nonsense? If you tone down your emotional outburst, the posts would be shorter and easier to respond to.
    Do you want a complete and formal definition, including what it takes a semester posted?
     
  3. TANSL
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    TANSL Senior Member

    With the inestimable help of Google translator :D I have managed to write the following:
    This thread seems a discussion between one who does not know what he does not know and another who does not know everything he thinks he knows. And none of them is going to let the other one say the last word. Neither of them cares about the arguments of the other (although there are really few arguments) and both follow post after post clinging to their same sentences. To show that I am acquiring fluency in the use of the language (thanks Google) I will tell you that both are barking at the wrong tree because the tree that they insist on barking does not listen the other.
    I hope that after my comment, as he has done several times, the moderator decides to close this thread that, honestly, does not contribute much to the advancement of humanity. The reaction, I fear, will be that of "furious dogs" :mad: (I keep making progress in mastering the language by assigning animal behaviors to people);)
     
  4. Ted Royer
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    Ted Royer Junior Member

    Don't close the discussion yet! This entire discussion as I have read through it a couple of times has made me worried that some of what I am trying is going to radically change the motion of the boat in a seaway. The motion at the bow is not all that great now. Here is what I am planning:

    1) Addition of a 4 ft. bowsprit + 40 Lbs CG (CoG) about at the bow. (the bow is already a full 4 ft fwd of the waterline).
    2) Addition of anchor/bow roller + 60 Lbs CG right at the bow.
    3) Demolition of the old battery bank under the aft section of the Vee-Berth - 200 Lbs about 3 ft aft of the waterline at the bow or about 7 ft from the bow.
    4) Addition of the new chain locker under the aft section of the Vee-Berth in the same general location as the old battery bank + 275 Lbs.
    5) Demolition of the 70's era diesel and its associated tank, shaft, propeller, and all associated crap. - 470 Lbs just under the companionway.
    6) Addition of a new battery bank in the same location as the old engine +350 Lbs. with a slightly more forward and lower CG than the old engine.
    7) 2KW generator+ fuel tanks in the aft section of the boat in a new bulkhead separated engine room. + 225 Lbs (with full fuel tanks) with a CG about 2 ft fwd of the stern.
    8) Addition of a swim platform and outboard motor +125 Lbs CG 3 ft aft of the stern. This CG is about 7 ft aft of the waterline at the stern.


    I do plan to have a stable and quick way to pull the 60 Lb outboard from the swim platform and get it on the stern rail and that would move it about 3 ft fwd when offshore and obviously I can move the chain to the bilge and the anchor off the bow on a long passage but day to day it looks like I have added 175 Lbs to the front of the boat and 35o Lbs to the stern so my basic question is, 'On a 30 ft. 8,000 Lb boat (with a 23 ft water line) how screwed am I if I do all of this?'

    If you think the motion change is going to be significant, I could move the water tank (now fwd under the vee berth) to under the main salon and that would get 160 Lbs out of the front of the boat, negating most of the issue at the bow. I could also move the fuel tanks (190 Lbs) fwd of their planned location to just ahead of the rudder which would be 5 ft fwd and about 2 ft lower which would help somewhat at the stern. If I am going to make those changes, now is the time to make the decision.

    As always, all thoughts are appreciated.
     
  5. gonzo
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    gonzo Senior Member

    Moving weights to the ends of the boat (assuming the trim does not change) makes the pitching slower. It may make the boat more wet, as the bow takes more time to rise and will plow more into the waves. On the other hand, boats that are too lively (quick motion) tend to make people more seasick.
     
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  6. Ad Hoc
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    Ad Hoc Naval Architect

    There is zero emotional content. That can only be your subjective interpretation of the words I am using. I cannot control how you interep words.

    So, let's get this straight.

    You either can or cannot show me a piece of string - with a T - that has a spring stiffness value and thus a means of calculating its restoring force.

    and

    You either can or cannot show me the free body diagram of the balloon of said...

    And you seem unwilling or unable to describe natural frequency too.
     
    Last edited: Aug 8, 2018
  7. Ad Hoc
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    Ad Hoc Naval Architect

    It is all about changing your radius of gyration.

    Problem is, without knowing the baseline and its effects of movements it is hard to quantify.

    Thus, if you are able to substitute these items for simple lumped weights you could perform a simple experiment. Move weight(s) to the locations you noted, and take her out and see if you feel any difference.

    Also, you could put her along side, get a video camera trained on the bow. Then get someone who is large and heavy to stand on the bow then get them to jump off the bow onto the jetty, and let the video camera film the bow. Then play it back and obverse the difference in period and amplitude of before and after movement/addition of weights.
     
  8. Ted Royer
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    Ted Royer Junior Member

    The boat is on the hard at the moment so I will have to go on past experience. She is wet at the bow on the wind but so were my other small boats, so it may be normal. That said, I am 220 Lbs and when I would move up there and hang out, I could not say that it was noticeably worse.

    But now with extra weight on both ends...? At least no one is saying I have made catastrophic mistakes, so at this point since I am replacing it anyway I may go ahead and move the water tank and at least that will make up for some of the new weight at the bow. The fuel tanks could be moved later after she is back in the water and I can see the impact.

    Thank you for the feedback.
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    Not sure it gave you the answer you seeked?

    Seakeeping is not a simple one liner. It is a terrible complex behaviour and has some many variables as inputs. Since whilst moving weights about has an influence on the radius of gyration which is an input into the periods of motion, it also affects the GM which also effects the periods of motion. And since we're unsure what the GM currently is, will the change, either increasing or decreasing the GM be more of an influence than the change in radius of gyration? Not easy to say without hard data. Hence just suck it and see...as each boat is different.
     
  10. gonzo
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    gonzo Senior Member

    It is k. What part of the example don't you understand. This is used to make students think about springs that don't stretch or compress. As the string gets longer, the potential energy increases until the weigh of the length of string lifted from the floor equals the buoyancy of the balloon plus the kinetic energy of the balloon (plus a small amount for the string). At that point it reaches the maximum altitude and begins to fall. It releases potential energy (from the weight of the string) as the length of it gets shorter. If there was no damping from the air, it would continue forever.
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Oh dear another one liner now with one symbol, as if that answers the question! o_O
    Which you still cannot or unable to answer.

    Your constant prostrations to the contrary are fine that is your prerogative. But constantly repeating yourself and going around in circles and not addressing the simple question at hand doesn't make you correct. It just highlights your lack of understanding even more to everyone reading this thread.

    So....since you keep deviating and adding endless non-sequiturs to throw up endless smoke screens, lets try this another way.

    That piece of string in that simple balloon...at one point all the string is on the floor. So if i now decided to uncouple the connection to the balloon, it is just a piece of string laid out on the floor, laid out in any way you like, in a circle, a zig-zag shape - whatever shape you like. So now, now i pull it and let go, what happens - does it:-

    1) just move a bit and thus extend its length a bit further than it was before i pulled it
    or
    2) does it return back to the position it was before i pulled it.

    There - that's simple enough for any qualified engineer to answer. You like one liners, so...., is it no 1 or no 2?

    No it doesn't.
    Why... because those are called piezoelectric materials. And as far as I am aware a piece of string is not a piezoelectric material and has nothing to do with it - again another non-sequitur.
     
  12. gonzo
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    gonzo Senior Member

    Both answers are wrong and so is the comment about piezoelectric materials. It is hard to answer your rants. Could you please limit them to technical matters only? Thanks
    A spring is an element in a vibrating system that can store and release potential energy. The object of this example is to show that the material does not need to stretch to act as a spring in the system. When you raise the string, you need to apply a force. It also stores potential energy. When you let it go, it releases potential energy. I can't tell where it falls or how much it moves when you pull it. As an engineer, my answer is that there is insufficient information .
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    aaahh....You have answered the question perfectly. It is now glaringly clear, to anyone, at your lack of comprehension on the subject.
    Thank you.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    By what definition ? Your own ?
     

  15. MikeJohns
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    MikeJohns Senior Member

    These sorts of argument by definitions is misleading .

    We are addressing complex systems that have a response that approaches oscillatory behavior due to resonance with specific excitation. Outside of resonance the response of the system is still complex and bears no resemblance to any model that could be described using mechanical vibration physics.

    I keep saying the vibration model could only be sensibly applied to a very small part of the characteristic response of a complex dynamic system.

    It's unequivocally a completely invalid statement to define any complex system a vibratory system just because parts of the system have an oscillatory response to certain inputs.
     
    Last edited: Aug 9, 2018
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