Why worry about weight growth?

Discussion in 'Boat Design' started by Ad Hoc, Jun 2, 2013.

  1. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    For those that think...ahh, my boat is a slow chug chug heavy displacement boat and I don't need to worry about weight growth. Well, here is what can happen to such vessels when you don't run the numbers properly and ignore simple checks:

    http://www.telegraph.co.uk/news/wor...avy-submarine-will-sink-to-bottom-of-sea.html

    "A new submarine commissioned by the Spanish navy at a cost of 2.2 billion euros (£1.9billion) has been discovered to contain a serious design flaw – it is too heavy and will sink like a stone."

    Still think weight control is not important?
     
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  2. rwatson
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    rwatson Senior Member

    nah, its not that big a deal.

    They found it before they built it. I bet you a lot of money that the 'extra' weight was caused by the 'client' specifying gear - armament, engine, extra options etc, that wasnt in the original spec

    You know how it works.

    " Navantia admitted the existence of "deviations related to the balance of weight" in the vessel and estimated it would take up to two years more to correct the problem.

    The 233ft vessel may have to be lengthened to compensate for the excess weight, a redesign that comes with an estimated cost of 7.5 million euros per extra metre."

    The designers wont be upset by the extra work.
     
  3. tom28571
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    tom28571 Senior Member

    So right Watson. Happens more than not. Good examples are PT boats, Armored personnel carriers, tanks, F111, F35. The list is endless.
     
  4. baeckmo
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    baeckmo Hydrodynamics

    Oh myohmy.... they do anything to increase their GNP these days........
     
  5. philSweet
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    philSweet Senior Member

    1 person likes this.
  6. dskira

    dskira Previous Member

    philSweet
    That was soo funny :)
     
  7. daiquiri
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    daiquiri Engineering and Design

    LOL!!! Nice one, Phil! :D
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I was asked to inspect a older motorsailor several years ago. They complained of fuel efficiency loses, as well as a slight speed lose. They were looking maybe a new prop or gear ratio or something. I climbed on and it was a live aboard, which clearly showed considerable use and passage making.

    After a check ride and running some numbers, I asked the boat be cleaned of everything that wasn't bolted down. I knew her approximate weight from her last haul out, but when the day was over, she was 40% lighter. They didn't need a new prop or transmission. They'd removed things they'd long forgotten were aboard, including enough spares to completely rebuild their diesel (including a head and manifold!).
     
  9. jehardiman
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    jehardiman Senior Member

    That is one important thing about submarine hydrodynamics that is different than aircraft aerodynamics.

    In aircraft the number of take-offs = number of landings...regardless.

    In submarines the number of dives is not necessarily equal to number of surfaces.
     
  10. baeckmo
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    baeckmo Hydrodynamics

    Well.... number of airborne periods = number of grounded periods minus one....
     
  11. Petros
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    Petros Senior Member

    a number of years ago I read about a government funded study to determine why so many goverment contracts go so wildly over budget. Though the study was focused on civil projects like brigdges, tunnels and dams, I can say from personal experiance that the same forces are at play in military contracts as well.

    They found that the largest sourse of cost over-runs were that both the government sponsors of the project, and the contractor/suppliers colluded to grossly under state the costs from the begining in order to secure the contract. Once the money was spent they would argue that more funds are needed to complete the program. They use a portion of money to hide the lies and blame other factors. But they always end up requesting a larger budget, no matter what the terms of the original contract.

    So, the single largest cause of cost over runs in all government projects is the politicians and the contractor intentionally lying about the total costs from the beginning.
     
  12. daiquiri
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    daiquiri Engineering and Design

    All I can say is - it is definitely a small world we live in. ;)
     
  13. Red Dwarf
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    Red Dwarf Senior Member

    I too have seen and been part of numerous defense contracts that basically function as you describe. One key aspect you failed to mention is in every contract I have seen there are numerous areas in the RFP that are wrong or unrealistic. These are never pointed out or corrected in the original proposal because they are a a key factor in profit. Later once the contract is entered the areas of concern will be slowly brought to light and further funds requested to correct what was clearly the procurers error.
     
  14. maxstaylock
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    maxstaylock Junior Member

    That can't be true: Take offs get canceled all the time, for a number of different reasons, but landings always happen.
     

  15. rwatson
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    rwatson Senior Member

    No just defense projects, but software and legal projects, building etc etc

    Like Mark Twain said "Every Profession is a conspiracy against the public"

    and its been happening forever



    If your favorite lawyer is a 'believer', put this quote on your next remittance advice when you mail in the cheque.

    " And he said, Woe unto you also, ye lawyers! for ye lade men with burdens grievous to be borne, and ye yourselves touch not the burdens with one of your fingers." Luke.11.46
     
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