how to connect a sent fin keel to the hull.

DELFTship forum Hull modeling how to connect a sent fin keel to the hull.

Viewing 8 reply threads
  • Author
    • #33935
      enrico fontanesi

      Hi everyone,
      I’ve some questions:
      after sent the keel from the “keel and rudder wizard” and moved it to my designed location, should I connect it to the Hull?
      and How?


    • #33939


      Have you so far used the translate/move tools to get it very close to the hull and position and alignment?

      I haven’t tried it (other than to import and mirror a rudder to be twin rudders) and have not put too much into it. I am thinking, however, you may need to use the imported part as a guide, and then add points to the hull and move those edges to match the imported part.

      But, if the angles/pitch/chord etc. are not ideal, you may have to do this over and over until you like what you have.


      I’m wondering whether it would be useful if DS Pro would have (or, does it have) a capability to interactively modify chord/length of fins (fixed and/or active) to change hydros in a narrow band of interest of a designer.

      I find that when i modify my hull i get improvements in various speed bands depending on the draft settings. I was thinking it would be really nice if DS could “hint at predictable improvements” by displaying a color line along non-ideal regions based on speed/displacement targets. The Free! version would still be manual, but the user might have fun being distracted by a new feature. An enhancement in the Pro version might allow for dealing with four fins but maybe automatically and independently adjust the fins separate from the hull geometry.

      Just some finning ideas.

    • #33940
      enrico fontanesi


      and thanks for your ideas!

      Yes I used the translate/move tools to get close to the hull, but because my hull is not flat at the point I had to moved the fin keel above in order to don t have part of the fin keel not attached to the hull.

      I will try to add some points to the hull and see if they can match with the imported part.

      I wonder also if i have to move everything to the baseline, or if I have to leave the canoe body at the baseline and the fin keel below;
      because I get really different value in the resistance calculation if i move keel and hull above the baseline or not.

      Is this normal? does DS recognized negative part of the hull in the resistance calculation, because it does in the hydrostatic…

      thanks again

    • #33941

      You’re welcome.

      I noticed that too, that moving the hull up or down makes some difference. In my case, since i’m designing cruiser/destroyer hulls (my hobby), and i have a sonar dome in a semi-bulbous bow, they hydros are automatically impacted. A bad shape really detracts. Depending on your model, if you really move the hull too far down or too far above the baseline in the interface, you may get the Design Hydros, but you will get an error message and no appearance of the plain Hydros (resistance/speed) report. I got that with a Carderock 5415 model someone put on the Internet. For maybe a year i had not a clue as to what was going on, and in frustration i cursed the model maker and set it aside. Only a few weeks ago i serendipitiously noticed and changed the model position and could then make comparisons of that hull compared to mine. The perils of not knowing…. hehehe…

      Don’t forget that you can use the Add Flow Lines tool to visualize what happens when you modify the hull shape. You have to press (IIRC…see the manual… if you have pdf, search on just flow or flow line) ctrl+ click on a waterline or submerged featured. The flows will, according to Marven, pretty much pattern CFD, even tho he has not intended nor asserted that this IS CFD. So, if you intentionally detract from your hull to see bad flow lines, they should appear. Optimize (manually or automatically) and the flows should restore or reimprove/improve.

    • #33944

      Connection Keel to Hull,
      1 create keel, make it a slightly deeper draft then necessary.
      2 move keel to required location with the keel protruding through the hull.
      3 go to Edit –> Point –> Intersect layers…. a box will appear, there are 2 lines one above the other, hull in one and keel in the other, cant remember where each one goes (trial and error)
      4 An intersection line will appear between the keel and hull. The line should be on the keel surface, it will turn red or make it red, and delete everything above the red intersection line, and there you have it. You can permanently join them to gether but dont as you will change your keel several times during the design cycle.


    • #33951
      enrico fontanesi

      HI guys,
      I have followed Mike’s points (1,2,3) , but after having created the intersection i can not cut the surface above.
      how can i cut surfaces?
      i realized that moving the finkeel up or down, the surfaces of the hull changes without being selected… why is that?
      the gaussian curvature turned negative close to the keel.
      and i have not modified the hull during the sending/moving of the keel.


    • #33953

      Hi enricofontanesi,

      Do you remember that little box after you did Edit…
      Point…Intersect Layers its called Intersect Two Layers box. Well you have to put the keel layer up the top and the hull down the bottom, to me it sounds like you did it the other way round, you want the intersection points on the keel not the hull.
      Once your corrected that and your keel has a yellow intersection curve around it, make sure the yellow line goes all the way along the keel ( usually in my experience it doesnt join up to all the control points on the intersection line, just check to be sure ) now turn the yellow intersection line to a red crease.
      Highlight all the red lines above the intersection line and Edit…Delete OR turn the control net above the new intersection line from red creases to normans and just leave it there, you might want to raise or lower the keel at a later date.


    • #33959

      Hi Mike,

      Do you know whether the Professional version will do this automatically? It would great if the user could say:

      – Based on my hull’s hydros without a fin, having these resistance values at these speeds and drafts, show me:

      — 2, 3, or 4 realistic/acceptable, fin sizes, angles and positions/lengths/chords

      — 3 or 4 optimal, and 3 or 4 ideal or better than ideal sizes, angles, and positions/lengths/chords

      and such to either improve stability:

      — at any or at all speeds

      — at this narrow range of speeds

      — outside (below and above) this speed band/range

      — Or, for active fins, at zero speed

      — and prioritize either stability at various speeds, or speed regardless of stability,

      — and then plot or animate it

      — show me the human factors limits as impacted by accelerations/motion/moments (assume the user is more interested in affects/effects upon humans and has no knowledge of equipment limitations….)

      Yes, realize this is a lot to ask…. hehehehe

    • #33960

      Hi otaku,
      in reply to your questions ‘NO’ but the program does give you a certain amount of feed back but you have to interpretate that feed back yourself.
      The program is not HAL in 2001 A Space Odyssey,
      Yes Dave, No Dave. For the answers you have to use,
      heaven forbid, your BRAIN.
      “Dammit, I know I had one of them, now if only I can remember where it put it ?”


Viewing 8 reply threads
  • You must be logged in to reply to this topic.