Re: Howto lengthen a hull by inserting a parallel midship section in DELFTship?

DELFTship forum Hull modeling Howto lengthen a hull by inserting a parallel midship section in DELFTship? Re: Howto lengthen a hull by inserting a parallel midship section in DELFTship?

#36223
Icare
Participant

Hi Ralph!

Above all, do not cut your ship in halves: Once separated, two parts from a same original net cannot be knitted back together (at least, as far as I know), and this will create leak points. Once the net is broken, you cannot “glue” its parts back together. (You can only replace a missing mesh… this is how to create a window pane B) ). Well, this consideration is valid for FreeShip, and I assume it doesn’t work better with DelftShip…

Second preliminary remark: Are you sure that only the ship’s length was changed? Length was the most obvious change between the two versions of the ship, then the periodical had to comment this change. But, may be, the same scale factor was applied to the width and to the height, and for they are much less remarkable, these changes weren’t mentionned. Furthermore, I guess that changing the length but not the width or the height can have a negative effect on the ship’s stability.

Well, now if you’re sure that only length was changed…

The only way I can suggest you is to move the bow part forward. The result will be not really perfect: the ship’s mid-section will be streched, and this will make a ship with flat flanks, but this can be subdued by moving the neighbouring stations towards the center of this streched part. The model’s meshes are like… errr… rubber-made.

So, select the ship’s fore part’s polygons edges (only half of the edges are required, either longitudinaly, either lateraly… the whole polygon will “follow” its edges) from the bow to the maximum beam (included or not included, it doesn’t matter). Do not forget the stem central line. The more you drew polygons, the longer the time you’ll spend selecting them, and the more you can forget one of them… Too bad for you… :whistle:

Then order a forward move for the selected polygons (The 4-directional arrows button, under the the TOOLS tab).

This will pull the ship’s fore part forward, and strech the mid-section. We’re close to the result you’re expecting, aren’t we? Can you see the ship’s flat flanks? We’re going to subdue this.

Now, move the stations toward the center of the streched part, and make the meshes interval more regular. (Only the stations’ position, not the points coordinates). A larger move for the closest stations, a smaller move for the farthest stations. At this point, do not change anything to the stem or to the transom. You can check the net regularity by comparing the new ship’s Gaussian Curvature (or Zebra shading) colors scheme with the old ship’s.

Finally, the bow has been moved away from the stern, but both parts’ profile (stem & transom) haven’t been modified, neither the height, neither the width.

Note: Instead of moving the neighbouring stations, you can create a series (or many) of new meshes by dividing the “faulty” meshes… and find all the new points’ coordinates… Good luck! :whistle:

Illustrated example using the Ship Demo 7 (forwared with FreeShip):