# Hydrostatics for a non-planar waterline applied to Rhino Hull

Good afternoon. First time post here. I have a question related to a marine application.

I am looking to apply hydrostatics to a Rhino hull based on measurements taken from a REAL WORLD hull based on our model. As those in the commercial marine industry will attest, there are weld distortions that appear in real life and just general settling of a boat that happens when it is supported by itself in the water. So, as a general practice we take a dozen or so measurements around our finished hulls (Were there no distortions we would theoretically just have to take 3 measurements that would construct a plane… if only it were that easy!!!) and try to manipulate the waterplane in our model to simulate something close to reality for hydro purposes.

In essence, I would like to apply the measured points to the modeled hull and and set those points (taking the hull with it) to the waterplane (like a complicated “setpt” command. The model would be trashed for anything but hydrostatics, but that is ok! Does anyone know how to do this or another method that would yield the same results? By the way, our accuracy is +/- 1/8".

Hi Ben - PlaneThroughPt can get you a best fit plane from the input points- would you then need to reorient the hull to this plane? Or am I missing the problem completely?

-Pascal

Must be a big vessel for the water surface to be non-planar!

That would be an improvement over a 3-point plane; that’s for sure. However, I think it would not take into consideration the distortions with that much precision.

Hi Ben - you do want a plane though, right? I don’t see how to do better than a best fit plane but there’s a good chance I am missing the problem…

-Pascal

Thanks Pascal. You might be right. I’ll give it a try and compare the results.
Best
-Ben

Hi Ben, wouldn’t a fore and aft measurement be enough for a waterline . Then make a plane perpenicular to the hull? Expand it if nessecary to go beyond the hull boundries.

Just in case we are on the right track - To juggle the hull from the best fit plane to world XY:

Cplane Object - choose the plane.
RermapCPlane CPlane; type “Top”

-Pascal

This can be done using CageEdit with a custom control object.

I assume your measured points are from the sheer to the water with the vessel afloat. In the Rhino model create a set of points corresponding to the measured distances of the water surface below the sheer. Then create a curve on each side through these points using CurveThroughPt. I would then rebuild each curve to a degree 3 curve with 4 or 5 control points. Loft a surface between these curves. This will be the control surface.

Start CageEdit. The hull surface will be the captive object. The surface created in the steps above will be the control object. Use SetPt to move the control points of the control surface to the nominal waterplane height. The hull surface will distort to follow the control surface as it is flattened.

From an engineering perspective this procedure only makes sense to do if there is reason to believe the hull overall is distorted to follow the distortion of the sheer; for example the hull is hogging. Unless that is known to be true then using PlaneThroughPt to find the waterplane which best fits the measurements without distorting the hull would be a better solution.

Perfect! This is the best way to do it. Thank you David. There is no doubt a hogging distortion and this accounts for that. Fantastic.