Hydrostatics Explaination

[Grant]

Hi, I am lost on how to use your hydrostatics.  I finally figured out that the radio buttons are for initial conditions and not for what you want calculated.  But most of my attempts to get results give a 0 displacement.  I took the paddle boat design as a simple text (see file about 6 entries down in this entry: http://www.boatdesign.net/forums/showthread.php?t=11932).  The Rhino xy plane is even with the top of the design (totally submerged).  When I then run the hydrostatics with a model sinkage of 0 (which I assume would be equal to totally submerged in this case, I get an error that one or more computations failed, and nothing there after.  If I go for 1 inch submerged, then I get a displacement of a few hundred kilos.  If when I do that and ask for the waterplane to be inserted, its 1 inch above the design!  There are no naked edges that I saw, and it has a top and bottom, etc.

I note that next to the override initial plane height there is a -4 (but I assume this should not affect the calcuations is its disabled for this kind of calculation).

As an asside, I generated the water planes for this, and when I asked for the bounding box, it gave something like -3 to -8.5 inches... which gets me to thinking that somewhere there is a setting about the 0 plane that I need to change...


(PS another oddity: I have an external hard drive, G: at this moment, and when I run the hydrostatics it seems to, the first time, stop the HD from spinning, and then the following times I have to wait for the drive to spin up before the hydrostatics start - if I shut the drive down there after, I still have to wait about 30 seconds for the hydrostatics to start the next time I run it, but there after is OK ...)

[Admin]

Grant:
Thanks for your questions. I was able to download and run the paddle boat file that you have been using, and here are my comments:

1. Perhaps we need to add a label to the dialog, such as "Define the condition by:" (either weight/cg or model sinkage)
2. With a sinkage of 0, it successfully ran for me (with a displacement of 576 pounds). Running a model that is just barely submerged like this one (or right at the water's surface) is a little tricky, because the software iterates the sinkage and computes the change in displacement per change in sinkage to find equilibrium. Normally the change is gradual, but in a case like this, a small change in sinkage could go from a large change in displacement when the deck is still slightly above the water, to zero change in displacement once the hulls become fully submerged. In other words, it goes from a large waterplane area to zero waterplane area. We have made the iteration engine more robust, so I think that is why I am able to run it using the current software (which is not yet released) and it failed with WIP3, which you are using.
3. When you enter a sinkage of 1", you are calling for a waterplane that is 1" above the Z=0 plane, which is why the inserted plane is where it is.
4. The bounding box that you are seeing for the waterlines is actually -8 inches to -3.50003331070738E-16 (effectively 0).
5. The external drive issue is perplexing. I'd have to know more about your particular set up (operating system, whether the external drive is used for swap files, whether Orca3D or Rhino is installed on it (I assume not), etc.). When the ReportViewer starts, it seems to create a temporary file, but I'm not sure why it would do it on G: rather than C:.