Inclined hull waterline

[Floris Goerlandt]

Hi,

My problem:
I want to model a ship hull, and subsequently detect the waterline coordinates of the hull in an inclined position (inclined in both heel and trim). I don’t really need additional info like hydrostatic curves etc-, just the coordinates.

– Is this possible?
– How?

Thank you!

[Marven]

Have you considered rotating the hull rather than the waterplane?

[Floris Goerlandt]

Yes of course, and that works just fine except for the need to export the data as well, which doesn’t work.

But I’m trying to come up with an alternative solution.

[otaku]

Yes of course, and that works just fine except for the need to export the data as well, which doesn’t work.

But I’m trying to come up with an alternative solution.

This is an ideal off the top of my head:

Export the model as .dxf 3D Mesh and 3D Polylines to 3D CAD software. In my case, i use Punch! ViaCAD Pro v7. Append each name with its contents type, such as “… DXF 3D Mesh.dxf” and “…. DXF 3D pl.dxf”.

Import individually singly each dxf into your CAD app and suitably adjust the layer names if necessary.

Find the sounding pipes or overboard discharges, and so on, that are related to downflooding points. Select them all and turn on their points if that is necessary to select, move, or lock them.

Lock the end points that are above the waterline or at the waterline. If possible, make them further non-selectable after locking them. If you cannot do that, then I have an idea in a few steps past this paragraph.

De-select everything.

Now, select the hull that will be trimmed, rolled, heeled, etc.

Adjust the x, y, and z angles as desired.

If this idea works, then you should see the locked lines “grow” in some direction in accordance with the displaced positions of the model’s movement.

Idea: if that doesn’t/won’t work, then orient the model as desired and then draw rays vertically from the submerged points you’re tracking or exporting to your database. Note the distances and positions.

This obviously is tedious, but it may work. It really will depend on the CAD package you’re using.

Alternatively, to avoid dealing with a massive select/de-select mess or nightmare:

— leave the hull in place and rotate the water (a big square or circle or trapezoidal shape),

— fire out the downflood and discharges positions the rays up to or through the water.

— Segment the lines and one-by-one select the lines that remain, and then get their x2 coordinate points.

It’s a PITA doing it this way, but this is likely how I’m going to do it.

I hope this is useful or helps you arrive at some more workable ideas.

[Floris Goerlandt]

Hi,

Thanks for your answer but I’m afraid it’s too tedious.
The thing is, I need to find this inclined waterline coordinates for a wide range of combinations of angles of roll, heave and pitch. Transferring that to CAD all the time really is too tedious…

Is there no way this can be achieved WITHIN Delftship?
All I need to do is export the waterline coordinates, after the ship hull have been rotated. It’s possible to get the waterlines in a drawing, so why not as export?

-> An alternative, which I’d prefer, is to be able to get the control point information, to construct the NURBS. If I have that, I can use Delftship to come up with the model and then export it to MATLAB, which can handle that sort of computations quite easily.

So next Q: is it possible to export the control points, along with the nodes, to make the NURBS oneself?

Thanks!

[otaku]

Hi.

That unfortunate thought crossed my mind as i hit send.

Maybe this will work: create in Delftship from the box tool one or more planes acting as undisturbed surfaces.

Alternatively, instead of using the box tool, use 4 points and then select each and create a face.

However you create the water surface, turn on the waterlines and turn off the hydros for the surfaces. If you’re experimental, create a number of stations and waterlines that you can use to select points to elevate or displace to simulate waves in a cad pkg, or maybe in Matlab.

I know how you feel. I too would like to have interactive graphing of various displacements in one view rather than export, synchronise, and redo to arive at a manual optimsation. Too bad the baseline version was mired with a modal mindset rather than non-modal .

Cheers.

[Floris Goerlandt]

I found a workaround – at least I think so.
It’s a matter of:

– Modeling the ship hull in DelftShip
– Importing to Rhino3D
– Using the Grasshopper tool for scripting the required calculations.

It’s a bit of a workaround, and I’ll need to learn to use 3 new programs, but it should work. It’ll be for when I find some time for that…

Thanks for the replies anyway!

[Author]

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