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Waterlines on heel

2006-11-07
2013-04-19
  • Heikki Levanto
    Heikki Levanto
    2006-11-07

    I don't know if this is a feature I have not yet found, or if it is really missing. But I would like to be able to see waterlines at various angle of heel (and trim). Both to see how much heel starts to look dangerous (water rushing in), and to look at the shape of the hull in realistic sailing conditions.

    Is this possible? Could it be possible in some future version?

    - Heikki

     
    • This is a good point, it is very important when designing sailing yachts, for checking that the transom does not enter the water when heeled for example. Full hydrostatics, including trim, of the heeled hull are also very useful.
      I am a bit reluctant to switch to FreeShip to design sailing yachts at the moment just for these reasons.

       
    • I'd like this feature too, very important, even Maxsurf doesn't have this feature, could be included in one of the add on modules for FreeShip Pro.

       
    • I've been wanting this too.  It would be so useful.

       
      • Marven
        Marven
        2007-01-10

        I'm currently figuring out how to exactly implement this. The hydrostatics part not that difficult. Just wondering on what waterlines to display other that dwl. I assume you want to specify a displacement and let the program calculate the corresponding draft and trim for a specifeied heeling angle? An then maybe show for example 10 waterlines for that draft?

        If you guys have some other ideas on this I'd very much like to hear.

         
        • Heikki Levanto
          Heikki Levanto
          2007-01-10

          Anything like that would be lovely! I would be satisfied with one waterline, but if I can get a few (say, at discrete steps of displacement) for any given heel, I would be more than happy. Ten lines may be too many, 3-4 would suffice for me. But then again, someone else might want more. So leave it as a parameter.

          Alternatively, it could be nice to see the waterlines for one displacement, but for different angles of heel. That should tell at a glance something about the way the helm balance will go when the boat starts to heel.

          - Heikki

           
          • Marven
            Marven
            2007-01-10

            3 or 4 might be too few if you consider a boat with a keel. Maybe the user can/should specify a distance? For example draw the dwl under heel, and then for every 10cm. down untill the bottom or tip of the keel is reached?

            As heel would be specified by you as a user together with the displacement (see my previous post) you could indeed check the dwl at every angle of heel

             
        • Garibeos
          Garibeos
          2007-01-10

          Hello Marven !
          I'm not sure if we all mean the same thing...
          Personally I'd like to see the following feature:
          (...and I guess that is what the others also mean)

          1. You create or load a ships hull.
          2. You run hydrostatics calculation (or something like that) and FreeShip calculates the displacement, weight and center of gravity for the whole ship (including all layers... and preferable some point loads if set.)
          3. With the results of step 2 FreeShip calculates how deep the ship would lie in the water (depending on our design and the used materials and thicknesses the ships ("real") draft will certainly not meet the value that is set under the project setting as start-value...) Then, knowing the center of gravity and the form of the submerged part of the hull FreeShip would calculate if the lifting force is located in the center of gravity. If NOT, then the ship is not in a stable position and eiter bow or stern need to point more downwards.
          4. Depending on the positions of the lifting force and the center of gravity FreeShip rotates the design a certain angle around the point where the lifting force was situated.
          5. In a loop FreeShip repeats steps 2 to 4 until The center of gravity and the point where the lifting force is acting on the hull are directly above each other (...or until the ship would sink/capsize :) ). Now the actual design has reached one stable position.
          6. While still displaying the "wished" draft set under "project settings" for the rotated hull FreeShip also displays the "real" draft of our design (in a different color) which depends upon the weight of the complete ship and the form of the hull of the rotated ship. (Of course some water would be cool too ...))

          This way the user will immideately see if his design lies stable in the water (horizontally) or if its draft is higher or lower as wished/expected.
          When point loads (motors, tanks,...) could be placed and shifted/moved within the hull this would be a perfect tool to design your "real" ship.

          I think there are more things that could be calculated and displayed in a similar way. (max. sail area,...)

          This is actually the feature that I would like to see next in FreeShip. If this is not what the others meant then they may explain it themself more precisely.
          As far as I guess FreeShip already calculates and displays the center of gravity and the displacement. There also these hydrostatic properties displayed... So it should be "easy" to calculate and graphically display the "real" behaviour and draft of the ship.

          I don't know if anybody read my posts, but in the last days I already programmed a little feature for the "layer properties"-window to quickly select standard boatbuilding materials for your layers.
          My idea was to use this to see how different materials (or different thicknesses) for layer of the ship change the ships weight (and later center of gravity). This is already working. I'm only just improving it a little bit more.
          Together with the above explained loop to calculate the stable position of the ship this would be perfect.
          With one click you could switch the hulls material from plywood to steel and then to aluminium and in the background see how your ship lies in the water with these different materials.

          It would be nice to know what I shall do with the source of the feature I'm programming if I think it's ready to be released... - Send it to you Marven ? Or mail it to info@freeship.org ? Or upload it with CVS or similar ? - I'm not sure if this is the latest source as it is dated back to may or something...
          I think if I just release it on my own the project might split up or get out of sync....

          So please someone of the programmers give an answer or pm me.
          Garibeos

           
          • Marven
            Marven
            2007-01-11

            Garibeos,

            The feature you're proposing is already scheduled and implemented for the next release, however for the professional version only. You can specify any number of point loads and fill tanks up to a certain level. Then the program balances the hull in the water and returns the corresponding draft and trim. Also the full stability curve is calculated for this  load case. The hull is drawn on screen in the equilibrium state.

            >With one click you could switch the hulls material from plywood to steel and
            >then to aluminium and in the background see how your ship lies in the water
            >with these different materials.

            I'm afraid there's more to it than that. You should also increase the thickness of the shell if you switch from steel to aluminium since aluminium is not as strong as steel. And you would have to compensate for all the internal structures as well.

             
            • Garibeos
              Garibeos
              2007-01-14

              Thank you for the answer Marven.
              I almost felt being ignored because I never got an answer on my posts.

              I'm glad to hear that such a feature will be implemented. It will be a great improvement.
              I only just noticed that this feature was even in the last release already patitially implemented with the function TFreeHydrostaticCalc.Balance in FreeShipUnit.pas.
              Actually I'm not sure if I will purchase the professional version as this is only some kind of hobby right now. Depends on the price.
              I bet it will also be possible to set different spec. weigths for the liquids in those tanks. (Fuel/fresh Water/sea water/...) - Hey, include a dropdown-list with standard-liquids... :))

              You are right, for a real design you need to consider to use different thicknesses if you change the boatbuilding material in order to maintain the same strength. This was only thought for the amateur boat-builder or new user like me who doesn't know all those parameters by heart. So they can build their design and just choose a material for their  layers from a list. Of course the thicknesses need to be set correctly. This might give them a clue what their design will weight.. or if it might be floating at all :)

              Well, you all seem to be busy programming for the professional version, so I think I will wait with new feature requests until I know it's not already implemented.

              Best regards
              Garibeos

               
    • Hi Martijn,

      Your ideas for the 10 or so waterlines is just what I was thinking.  State the desired displacement (same as upright value by default, but variable) and angle of heel and draw waterlines for the condition, starting at DWL and showing as many as requested at user defined intervals. 

      I'm not sure if it would just be a gimmick, but it could also be nice if the flowlines could be plotted for the hull with this new angle of heel.

      The other idea about just showing the DWL, but at varying heel angles, would also be nice.  But I guess I shouldn't be greedy!

      Regards,

      TP

       
      • Marven
        Marven
        2007-01-15

        Thanks TP, that's very helpful.

         
    • If its possible could we include a stability curve (righting arm), "The Safety of Small Commercial Sailing Vessels" A Code of Practice (UK), which emphasises the point of vanishing stability as THE MAJOR INDICATOR of a yachts ability to resist capsize. The URL below goes into greater detail it also provides the formulas an a table of vessels under 75.5 foot, and the catorgory of vessel Cat 0...unrestricted offshore, Cat 1...Up to 150m from a safe haven, Cat...2 60m from a safe haven etc. I suggest all who are interested in boat design to read this info and save it for later reference.
      http://www.radford-yacht.com/stablty1.html

      Mike Kerr