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Lengthened 1990 Hakvoort LRC; opinions please?

Discussion in 'Hakvoort Yacht' started by hrosetti, Jun 23, 2014.

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  1. Marmot

    Marmot Senior Member

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    You are more than welcome to show where I am wrong or confused.

    It is not rocket science or higher math.
  2. AMG

    AMG YF Moderator

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    You have the answer in post #34.
  3. Marmot

    Marmot Senior Member

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    This is getting really tedious. Either you are trolling or honestly don't have a clue.

    In any event and in the interest of civility, I suggest you find a real naval architect, a hydrodynamicist or a marine engineer, or a stability program for your computer, read a book or find someone with a better sense of humor willing to attempt to explain the subject better than I.

    In the meantime, here is something to play with. http://fas.org/man/dod-101/navy/docs/swos/dca/stg4-01.html

    BTW, post 34 shows just how little the cartoonist understands the concept of stability and trim and how to look at the cartoon. Even it shows the new LCG aft of the initial CG. CG moves toward added weight.

    Adding an aft extension adds weight aft of the initial LCG and moves the new LCG aft, not forward. Unless the laws of physics have changed recently, I am far from confused but you are certainly welcome to document those changes.
  4. YachtForums

    YachtForums Administrator

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    Which is the same sentiment a LOT of folks have expressed about the tyrannical rants of a particularly irritated squirrel.

    At least one of those entities is present and accounted for. I'd like to believe I have a better understanding of hull design and stability principles then the average groundhog, but I bow to your superior intellect.

    That cartoonist has designed the most popular line of boats in Sweden and one of the best riding boats I've ever sea-trialed, not to mention some of the most prolific yacht designs to ever grace our pages.

    Just because someone doesn't write with perfectly descript words or in your native tongue, doesn't mean they lack understanding. What most of us can't understand is WHY you take verbiage out of context and proceed to rip apart every post, effectively moving the CG of YF in the wrong direction?
  5. AMG

    AMG YF Moderator

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    The cartoonist has now shrunk the boat with stern extension to the same length as it was before, so you can see that the LCG has moved forward relative to the original boat. Laws of physics are the same.

    Attached Files:

    • LCG2.jpg
      LCG2.jpg
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  6. Marmot

    Marmot Senior Member

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    You can make and scale all the sketches you like, it will not alter the law of physics that says the center of gravity will move toward added weight.

    Buoyancy is not weight or lack of weight. Changes in buoyancy do not alter the location of CG.

    Why would anyone insist otherwise?
  7. Marmot

    Marmot Senior Member

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    Why is rebuttal of an obviously erroneous claim described as a tryrannical rant?

    Where is the tyranny in writing that "Adding weight aft the the original LCG moves the new LCG aft, not forward." ?

    It's not even a rant, rants are philosophical, my posts have been a carefully measured rebuttal of a profoundly absurd claim with an incontrovertible fact. It also excludes any ad hominem element and I wish it would remain that way.

    Irritated, yeah, probably. I am disturbed at what I have read means about the scientific literacy of our population.
  8. AMG

    AMG YF Moderator

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    This is not what was discussed and you know it.
  9. Marmot

    Marmot Senior Member

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    Thank you.

    Not relative to the original CG which is what this entire discussion has been about since that silly claim that extending the stern moves the CG forward.

    I could just as easily change the point of reference to show that the number representing LCG is anyplace I want to put it. If I measure it from the forward perpendicular or the midpoint, it has moved aft, if I measure it from the aft perpendicular, it is still aft of its original location, even though the measured distance from that new reference location is greater.

    No matter where it is measured from, the LCG is further aft than its initial point due to the addition of weight to the stern. Period.
  10. Old Phart

    Old Phart Senior Member

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    I dunno
    All this back-and-forth reminds of the guy staring at a fish in a tank,

    while the fish is staring at him holding a glass of water.


    The man says to the fish,

    "It's called thirst;

    but I'm not sure how to explain it to you."
  11. Capt J

    Capt J Senior Member

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    You're wrong. You are adding length to the stern and less weight to the stern extension per linear foot than what is forward, so the center of gravity, if you would put a log underneath one point of the boat to rest on would move foward from it's overall length and slightly foward from it's previous COG. You are also increasing the overall length of the hull, so there is no way to not change the center of gravity when the overall length changes unless you are really good at adding a precise amount of weight in the build of the extension.

    Much like if you take a 30' see-saw with the fulcrum point in the middle.....You put a 200lb kid on one side and add 3' to the other side with a 150lb kid.....the fat kid will win everytime. So you will now have to move the fulcrum point further foward than 16'6 towards the fat kid to balance out the 175lbs of the 150lb kid and 25lbs of wood you added......
  12. PacBlue

    PacBlue Senior Member

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    I'll chime in and say I am onboard with you Marmot, with the minor revision that the Red position looks to be the original LCG position, for illustration purposes only. :)
  13. AMG

    AMG YF Moderator

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    OK, here is a drawing with a substantial extension where the new LCG is aft of the original hull. But it is forward of the old position when you scale the drawing down for comparison. So in my world, the Longitudinal Center of Gravity have moved forward in the extended boat, not aft. Capt J is right.

    Attached Files:

  14. K1W1

    K1W1 Senior Member

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    Hi,

    I have just been told that by removing 40 tons from the aft end of a yacht we are looking at will move the COG fwd and up.

    If taking weight out moves it fwd how can adding weight do the same?
  15. AMG

    AMG YF Moderator

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    This is about adding length. If you not only removed 40 tons of weight, but also took away some length, the LCG may move aft...
  16. Yachtjocky

    Yachtjocky Senior Member

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    Kids

    I would suggest that those two fat kids go on a diet or you could get a bunch of them to move around the boat using them as ballast to keep everything as it was.
  17. Marmot

    Marmot Senior Member

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    "I am disturbed at what I have read means about the scientific literacy of our population."

    And I might add, the knowledge of some "captains" of vessel stability and trim. The only time a ship has a "fulcrum" is when it is aground.

    Moving aft means it moves from an initial point of reference. That point is the original location of the LCG. If you add a single gram aft of the original LCG, the new LCG is aft, no matter how you care to measure it. If you remove a single gram aft of the original LCG it will move forward.

    Arguing otherwise is like saying mid winter is summer and believing the snow will go away.

    This should be about reality. If you removed 40 tons of weight and any amount of length (from the stern) the CG will move forward and depending on the CG of the removed portion, either up or down.

    Again, I suggest a few members do some reading of ship stability and perhaps find a stability computer or calculator. Pay careful attention to the terms "moment" and "arm."
  18. AMG

    AMG YF Moderator

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    Do you really believe in what you are saying, or are you trying to play with words instead of facts..? Show me a book where a ships length is not part of the LCG calculations...
  19. PacBlue

    PacBlue Senior Member

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    I would be less focused on length and offer this approach:

    If you are measuring from the Aft Perpendicular (Station '0'), keep this station in the same location for both cases - Hull-Original and Hull-Extended. You will observe that for Hull-Extended, you will now have additional stations aft of Station '0' in the sequence of Minus 1, Minus 2, etc.

    When you do your revised weight study and summing of moments for LCG / VCG / TCG, those weights associated with the cockpit addition are calculated negative (minus) as they fall aft of the Station '0' datum line, which you are holding constant. Fwd of Station '0' are positive values.

    You will then observe that the LCG has in fact moved aft, closer to Station '0', NOT fwd and I believe the math will hold-up, confirming Marmot's dissertation, scale or no scale.
  20. AMG

    AMG YF Moderator

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    OK, but your station '0' does not exist in the extended boat, it is a new hull and a new position of the LCG, further from the transom than in the old hull, also in percentage. But this discussion is really on a pre-school level, so I give up.
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