Re: plates tutorial

[otaku]

As for PLATES…

If by plates you mean shell plating, you need to ask yourself whether you want smoothly curving, unbroken hull mesh surfacing or if you want to have the hull “broken” in convenient places where the waterlines and stations intersect.

As for one big half-breadth hull surface, you can turn on the mesh and then export it. Depnding upon the CAD program or hull modeler you’re using outside of Delftship, you may or may not be able do much with the mesh. Since I’ve already mentioned that I am using Punch! ViaCAD Pro, I can tell you how I use the mesh. I export the mesh model to DXF 3D Mesh. Then, in VCP, I import that model. In my early forays into DelftShip, I realized i did NOT want one huge hull, since I am doing detail design and I want to account for weights of EVERYTHING I draw — not just the equipment, ducts, pipes, and so on, but the specific region of the hull and its bulkheads and decks, too.

So, I created waterlines and stations not for (well, not JUST for) hydros reasons, but to “break up” my hull. By creating stations at convenient intervals (matching my paper drawing in general, but adjusted when I found out the 3D model gave me more space than my pencil lead at 1″=20″ did), I found that I could assign mesh areas to specific layers. So, I created layers that were named for the hull compartment. I color-coded each so that in and out of DS, I could more easily see where I was in the model space.

When I imported those into ViaCAD, I realized I could thicken each compartment’s plate more realistically. Instead of going on some “average plate thickness” notion, I could by compartment thicken the plate. But, later, when I CREASED waterlines, I realized that I ended up with individual rectangular plating that I could more gradually thicken or thin in a more refined way to realistically deal with thinning the plate as it got higher or more near an extremity. I could thicken plates in zones needing more protection.

Now, where some may leave that to a hydrodynmics and weight specialist, this is MY model. *I* am all of the departments. So, I am not going to just use a hand-wave and declare or use rules of thumb or wrack my brain trying to calculate weight of x square meters of y type of steel of z thickness. I just tell Delftship the density information so that I can sanity check it against what ViaCAD later will calculate.

In ViaCAD, I assigne the MESH to a sublayer of its compartment, namely MESH. I copy and then transform that mesh into a SURFACE. I assign the surface to a layer in that compartment, and I then create a layer called Plate/Solid/etc as convenient, and then thicken the sideshell and assign it to its appropriate layer. I then go into “properties” and tell VCP to make it 1020 steel and then VCP shows me the CGs and moments of that steel. Later, when I add stiffening, decks, cutouts, ladders, partitions, pipes, and bunks, and so on, I can over time see know with more confidence what my hull region is WEIGHING, not just displacing.

CREASES AT WATERLINES

If you’ve created your points and made the general hull (or if you open one of the demo hulls), create waterlines and stations at convenient intervals just for experimentation.

Crease the waterlines. Note that creasing WILL slightly modify the hydros results. Creasing will likely force you to make more manual adjustments, but the positive side effect is you may end up with more planar plating if you re reasonably careful. Un-creasing can, however, re-introduce multiple problems since DS is not one of those $10,000-per-drafter-seat programs that will automatically re-fair within a tight tolerance close to what you had prior to fairing. DS WILL automatically fair for you, but YOU probably will want a shape of your own, not one of the interated farings.

Now, if you export those creased areas, you can play around and realise the things creasing can do for you besides making single and double chines.

You will probably spend WEEKS interactively iteratign your Delftship to CAD app drawings, looking for excessive sheer, camber, and twists, and reversals that you might not notice in DS if you’re not using the histogram tools correctly. If you’re creating stealthy corvetts or just want to exploit all that buzz around “steath shaping”, then creases can be your friend very quickly.

Remember, though, the manual process can be fun if time is no issue. But, it CAN take a good deal of time if you’re very demanding and perfectionist.