Adding Bulkheads 'n stuff to Freeship model

Discussion in 'Software' started by lewisboats, Feb 18, 2008.

  1. lewisboats
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    lewisboats Obsessed Member

    yes...toggling it on and off only gives a minor variation and it doesn't change regardless of the position of the keels longitudinally.

    Steve
     
  2. Guest625101138

    Guest625101138 Previous Member

    Steve
    I checked the keels and they look fine. They displace about 40lbs and take wetted surface from about 25sq.ft tp 67sq ft - that is the killer with these things. They will turn an otherwise nice hull into a dog.

    None of my versions of Freeship or Delftship provide LCR. The give LCB but this is quite different and will not change much by moving keels with small volume about.

    From a performance perspective you should try to use slightly fatter foils that are much shorter in length and the same depth. The higher aspect ratio will improve their efficiency.

    Rick W.
     
  3. lewisboats
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    lewisboats Obsessed Member

    I thought the Longitudinal Center of effort under Lateral Plane was the LCR...but it doesn't seem to work very well if it is. I put a 6 ft deep 2 ft long surface on the bottom of the hull (without any keels or skeg) and suspended it between the aftmost two points on the bottom...it didn't change the center of effort more than a few points. curious.

    Steve
     
  4. LP
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    LP Flying Boatman

    Lcr

    I believe that Freeship only does the LCR computation along the centerline of the hull. I've got a similar problem with a design with twin keels. I've gotten around some of the problem by defining "hydro" appendages on the centerline and manipulate the layer properties to give the desired values.

    You could do a "hydro" keel on centerline that is twice the area of a bilge keel, but you will have to manipulate the shape to maintain the desired LCR and VCR. (Disregard :Keep the thickness at zero, but build the bilge keels as normal. Leave the hydrostatics turned on for both and the displacement will be calculated for the "real" keels while the LCR will be computed from the centerline "keel". As long as the "hydro" keel is on centerline, it will not create a leak, but be sure to leave it as a 2D (all y values=0) shape.)

    I believe this to be the case and I believe there will be some error where there is keel and hull overlap.

    ==================================================================================

    Now I have to correct myself. The 2D hydro appendage doesn't work. I have made a 3D appendage that worked to my purposes. I'm working on a design with an offcenter centerboard (a portboard?) where I had to copy it on the centerline to get a lateral plane area for it. I did take your model and extrude a "hydro" board and did not get a change in lateral area. However, when I started giving it volume, (i.e. taking it off of Y=0) it started modifying lateral area. You might be able to make an appendage of infinitely small volume so you can fool Freeship into giving lateral area. Or, give the "hydro" board the volume and lateral volume of both boards combined turn off the hydro function for the real boards
     
  5. Martijn_vE
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    Martijn_vE Marine software developer

    You're absolutely correct Greg.

    Martijn
     
  6. Guest625101138

    Guest625101138 Previous Member

    Correction

    I have now found the Lateral Plane properties in both Delftship and FreeShip.

    I failed to scroll down the hydrostatics window far enough to find them.

    Rick W.
     
  7. lewisboats
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    lewisboats Obsessed Member

    Well...this gives me something to work with. I expected to have some error with the overlap because the hull would hide some of the fins in the profile view (2 dimensionally) and also things will change as the hull heels and one fin becomes more vertical and the other less so. Also...the angle of attack and leeway will present all of the leeward fin and a portion of the windward fin (making the profile of the two keels appear as a single longer keel...if that description makes sense). Basically the dynamics of the two keels will constantly be changing as conditions change. Thanks much... It would have taken me a bunch more time to work out that I needed to add thickness to a centerline fin before it started to change the LCR. I probably would have been puttering on a different hull shape a few months from now and had it finally dawn on me.

    Steve
     
  8. LP
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    LP Flying Boatman

    Looking at your model, I'd guess each board is canted about 10 deg. Intuitively, your effective lateral plane area will be cos(10) * area. Up to 10 deg of heel this should be constant as the windward board loses effective area, the lee board should pick it up. Your furthur reduction in lateral area with increased heel should not be any different than with a centerline keel yacht, I believe.
     
  9. mizzenman
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    mizzenman Junior Member

    It did not work for me!
    I exstruded a part of the shere upwards, but I was unable to delete the two lines that conects the new pannel to the rest of the hull.

    What did I do wrong?

    thanks in advance!
     
  10. LP
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    LP Flying Boatman

    Deletion

    I suspect you may have hit the collapse icon. And, did you extrude twice? the first extrude gets deleted after you do the second extrude.

    Select one edge of the panel you want to delete and select the trash can. It will ask you if you want to delete one (or more depending on what you have selected) item. Select ok if the number agrees with what you've selected.

    Another way would by to turn on interior edges (the icon to the left of the show both sides icon) and then select the panel that you want to delete. Again, hit the trash can and it will query you on whether to delete or not.

    Good luck.
     
  11. kengrome
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    kengrome Senior Member

    Extruding creates a new face in the previously selected layer, which is probably the layer that's shown in the selection list in the menu bar. If you turned off that layer your new face won't be visible -- it's there, you just cannot see it until you turn that layer on again.

    You must also have the control grid turned on if you want to select the connecting edges so you can delete them.
     
  12. lewisboats
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    lewisboats Obsessed Member

    You actually have to use edit/delete rather than removing the edge by colapsing as LP said. I usually deselect all then select the two small lines on the sides of the first extrusion and hit edit/delete. It asks you if you want to delete these two items (if it is more make sure to deselect all and try again). Kenneth is also correct in that if the layer that is current in the box in the tool bar is deselected in the layer dialog box then your face will disappear but still be there...on that other layer. Best thing to do is create a new layer and then do your extrusions...this should automatically assign it to that new layer.

    Steve

    PS: I did create the center keel and give it some thickness...worked quite well so now I have to play with it to get approximately the same area and move it around until I get what I want. Gonna have to add the sails first then balance the two...I just need the time to do it when I am not too beat.
     
  13. mizzenman
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    mizzenman Junior Member

    Thanks guys, very kind of you!!
    Using the 'thrash can' function instead of the 'collapse edge' was the ticket.

    Thanks again
     

  14. LP
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    LP Flying Boatman

    Here's a trick that I just discovered. Maybe you guys already know it.

    To co-locate two points in the same location, select the point to be moved, hold the ctrl key and select the destination control point. Now, just click on each X, Y and Z coordinate in the destination coordinate box and watch the first control point align itself with the second. Groovey, man.
     
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