Heeled numbers in Free!ship

[LP]

I was trying to get heeled values in freeship, but ended up cracking the model open! With both hull halves visible, I applied rotation to the model from the transform menu thinking the whole model would rotate in the same direction. The sucker split open!

Pondering issue, I wrote the designer. He has plans for heeled values in later revisions.

In the mean time, here's a trick I devised. I'd like a response as to the validity of the returned numbers.

1) Activate "Interior Edges."

2) Select all surfaces.

3) From the "Transform" menu, select "Mirror."

4) Make sure nothing is selected and from the "Transform" menu, now select "Rotate."

5) Apply your desired rotation along the longitudinal axis.

6) Go into "Project settings" and fiddle with draft until you get back to your original displacement.

Voila! I'd probably create different files for heeled models and keep a master unheeled model.

I was curious though if metacenter and moment of inertia values would be useful in this manipulated state? And then, does that information really tell you anything anyways(the heeled values)?

[Bruce Taylor]

Creative solution, Learpilot. I had the same "split hull" problem, in earlier versions of the program, but hadn't thought of using the new mirror feature.

I tried your method on a couple of designs. It worked well for some, but not others (possibly the heeled model exposed small flaws in hull integrity in some of my test designs).

Offhand, I'd say the heeled hydrostatics should be fine (but maybe I'm missing something?).

[Martijn_vE]

You both overlooked something here. FREE!ship assumes symmetry with respect the the centerplane. This is not the centerplane of the hull under heel, but the XZ plane going through the origin. Because FREE!ship assumes symmetry and only half the hull is normally modeled, the other half is created and calculated automatically. By mirroring the hull yourself and giving it rotation you do not solve this problem, since FREE!ship still calculaes the other half. In this case the entire hull will be mirrored and calculated again, resulting in twice the displacement and again a symmetrical hullform!

[jam007]

Then if you make a catamaran by moving the mirrored hull, then rotate it the heeling angle and move it in vertical direction you could get it to calculate the displacement since the other hull will be above water. But it seems a lot of work.

Anders M

[Bruce Taylor]

In this case the entire hull will be mirrored and calculated again, resulting in twice the displacement and again a symmetrical hullform!

Oops. When I mirrored the model, I noticed that my dinghy's displacement jumped from .128 to .256 tons. But when I rotatated it 15 degrees displacement dropped to .12 (because of the changed waterline), which seemed to be in the right ballpark....

[LP]

The problem with using software in an unintended manner is that you can't depend on the results. With my experiment, you do end up doubling the displacement. Turn on the second half of the boat and look at what you are really measuring.

I am guessing that your dingy is flat bottomed with flaring sides. If you have the waterline visibility turned on, I bet you are showing a long skinny waterline.

I think my trick is useful for visualizing what the waterline does under heeled conditions. And if you adjust the waterline depth to make the displacement read double the unheeled value, you'll get a close aproximation to hull emmersion at that heel angle. Sounds like any numbers derived from it though are useless.

As the software progresses, I'm sure this is all an extraneous exercise anyway.

[Bruce Taylor]

I am guessing that your dingy is flat bottomed with flaring sides.

Planing bottom, round bilge, not much flare...and yeah, a skinny waterplane. That the heeled displacement (with altered waterline) approximates the original displacement is just an accident...as you say, the heeled numbers are of no use.

I'm sure this is all an extraneous exercise anyway.

Given the speed at which Martijn works, this thread might be obsolete already.

[yipster]

ah thought so seeing the numbers go wild, and a bit rotated half hull dont take flowlines eighter, looking now into PDstrip specially developed for sailing yachts, so it can also calculate shiips under heel or assymmetrical hulls http://sourceforge.net/projects/pdstrip but can not get it to start on vista x64, i'll try XP and some more, anybody did try this way?