design displacement question

Discussion in 'Boat Design' started by spaceboy, Aug 20, 2014.

  1. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    True, if the designer is dead you can not talk to him. Well, you can talk but the designer does not answer you. And that's a big problem.
    However, some people, myself for example, draw plans of schooner and we're not dead yet. Therefore, in the absence of a better idea, I think the OP should find out if the designer is not in the phase of wandering spirit to talk to him.
  2. PAR
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    PAR Yacht Designer/Builder

    Previous to CAD assisted design work, many of the more tedious calculations (like full range stability for example) where not performed. They may have used a planimeter and other tricks to shorten other efforts. If the design is fairly dated, you might want to consider another, preferably well documented schooner. We'll just have to wait on the OP's responses.
  3. viking north
    Joined: Dec 2010
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    viking north VINLAND

    The fact that it was described as a cargo schooner might be an "era" clue in this case. Many of these early craft were built from half models or a very basic set of hand me down plans whose displacement was based upon a similar vessel or by the government official in charge of registration at the time of launching using a very basic set of measurements. Generally it involved the completed vessel void of supplies and often prior to installation of fishing or cargo handling gear. In other words "Light Displacement". While I have posted my ancient Grandfathers document on a couple of previous occasions it serves well here as an example of how basic and loose the calculation of a vessels displacement was often determined. This particular vessel was built from a half model based on the popular Heel Tapper Schooner Style of the day. As an after thought I thought I'd throw in this rough sketch I did of the the old Skippers boat also. Bet as he was carving that half model he never in his wildest dreams would have thought his little craft's rendition would been sent all over the world at near the speed of light.:)

    Attached Files:

  4. spaceboy
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    spaceboy Junior Member

    Thanks gents for the replies, the design is from the 80's, coastguard approved to ABS rules. I can contact the designer, but as he is retired I don't like to ask him to many questions. The design has sea water ballast tanks, I assume would be included in the displacement as full. If the design was modified for cruising would the weight of the water volume simply be added to the lead ballast? Or is that to simplistic. Is that something a Naval Architect would need to calculate? Regards

  5. jehardiman
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    jehardiman Senior Member

    Generally a seawater ballast tank would only be used if the ship was unladen to bring her down to her sailing lines. If you are considering a conversion, and you do want to use solid ballast, then you should have a professional do the stability work. Because a refit of a cargo vessel to a cruiser really plays havoc with the CG and it is very easy to change the stability characteristics to make her too stiff (a bad thing) or to tender (also a bad thing).
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