Re: transom and deck

DELFTship forum Hull modeling transom and deck Re: transom and deck

John R. Coil

I can help you get started as it isn’t hard. Please note: I’m probably going to include a lot of info you already know but that’s because I’m trying to be complete.

First you need a layer to dedicate to the surface you will make to be your transom.

If your tool bar above your model is set up as per the program’s default you will see a bar that contains the following:

  • a small plus sign in a green circle in front of a red dash-line box,
  • a small minus sign in a red circle,
  • a figure that looks like an index card,
  • a grayed out -thing- that is meant to look like a stack of stuff,
  • a selection box with something like “Layer 0” showing,
  • and finally a block of color

This contains some of the same options found in Edit > Layers > Dialog that you presently need.

Click on the green plus sign option to add a new, empty layer.

Select this later and then assign in a color that is (for the moment) different than the rest of your model (I do this to make it easier to judge what it’s doing later when I’m rendering).

Name this layer “transom” — or whatever you want.

With this layer chosen this is now the active layer in your model and any new face you put into it will go here — that way when you later move it around it will be all you are moving around.

Now add 4 control points making sure the surface that they will form will be more than adequate to cover your whole transom.

For my example I’ll just use dimensions similar to those I’d previously mentioned: where the radius of the transom is 4.8333′ and say, just as an example, it’s for a transom that will be 8′ across and 5′ high and which I intend to be swept aftward at a decent rake.

Because I’m going to rotate the critter into place the control points need to be farther apart in the vertical direction than the transom is high: so I’d set 4 new CPs at (0,0,0), (0,4.8333,0),(0.0,10),(0,4.8333,10). It’s better to just make the thing too big in the vertical direction at this stage since adding points later would be a hassle.

Now select all four control points by clicking on them while holding down your control key. Once this is done you will see an option on your tool bar that looks like a yellow dot inside a square light up: click on this to create a new surface from your 4 control points.

Since you’ve done this while your “transom” layer is selected this new layer will be the only thing in that layer (remain in the transom layer).

Now you need to set all 4 control points as “corners” so you are looking at a rectangle rather than a oval.

Select the top and bottom line and create two new control points by splitting the control edges in two (the option looks like a line with a dot in the middle and an arrow points to the dot),

Select these new CPs and connect them with a new control edge (the option looks like a box split by a diagonal line).

Now pull out your own scientific calculator OR go to the Web 2.0 Scientific Calculator I’d given a link to earlier — I’ll proceed as if you’re using the online tool.

The equation I gave you, Yd = Rz(sin(acos(Xd/Rz))), is what we’ll use.

You want Yd so don’t worry about typing anything for it into the calculator.

Rz = 4.8333 and Xd is the changing value of X that you will assume to set the control points for your surface.

It is also important to adjust things to take into account the fact that your surface is to the left of where your radius starts, so “Xd” is really “(4.8333 – Xd)”.

What you will type into the calculator the first time will therefor be:

  • 4.8333 (sin (acos ((4.8333 – 0.1) / 4.8333)))

… I kept spacing in just to make that easier to read.

When you press the equals key you will get a result, rounded to the nearest value, of 0.9781.

This means the two CPs in the middle of your face are to be changed to (0.1, 0.9781, 0) and (0.1, 0.9781, 10) respectively.

Now repeat where you split the edges and inserted a new edge.

In the Web Calculator you will see a selection tool with some numbers in it, use that to pull up the equation you just used BUT change the “0.1” to a “0.2” before you hit the equals key again.

The values for these new, new CPs will be (0.2, 1.376, 0) and (0.2, 1.376, 10) respectively.

Repeat as needed for different Xd values to form the curved surface — using the original outermost CPs of your surface at the last.

In the example above this gives me a curved surface defined by the following CPs connected by vertical edges:

  • 0, 0, 0) and (0, 0, 10)
  • (0.1, 0.9781, 0) and (0.1, 0.9781, 10)
  • (0.2, 1.376, 0) and (0.2, 1.376, 10)
  • (0.4, 1.9253, 0) and (0.4, 1.9253, 10)
  • (0.6, 2.3324, 0) and (0.6, 2.3324,10)
  • (0.8, 2.6633, 0) and (0.8, 2.6633,10)
  • (1, 2.9439, 0) and (1, 2.9439,10)
  • (1.5, 3.5, 0) and (1.5, 3.5, 10)
  • (2, 3.9158, 0) and (2, 3.9158, 10)
  • (3, 4.7609, 0) and (3, 4.7609, 10)

That’s (almost) all the plugging and chugging you need to get your transom.

Next you need to be sure to Selection > Deselect All if anything is still highlighted — this is just a clean up to make sure the only thing you’ll be rotating is your would be transom.

To rotate the transom go to Transform > Rotate.

A pop up will appear showing the different layers you can rotate: make sure that the “transom” layer is the ONLY one still checked before you press okay.

The next pop up will give a place to input rotation around the X, Y, or Z axis. In this instance you will be rotating the transom around the Y axis so input the angle (either forward or backward) that you want your transom to have. I believe, if memory serves right, that a positive angle will result in an aftward slope of the transom and a negative angle a forward slope of the transom.

Once that is done you need to move the transom to the right place.

To have the transom to positioned relative to the sheer line highlight the CP that used to be at (0,0,10) and write down its new values. Next highlight the point on your deck where the transom will end at the middle of the hull and write down those numbers.

  • Alternately, if you want to have the transom positioned relative to the keel use the CP that used to be at (0,0,0) and the one along the keel where you want your transom to start — otherwise the procedure is the same from here on out.

FIgure out how far, and in what direction, you would need to move the CP on the transom to be at the exact same location as the CP on your hull (write that down). This will be the last bit of math you need to perform.

Make sure to Selection > Deselect All at this point so you aren’t moving more than just the transom.

Transform > Move and, as before, make sure that the transom layer is the only layer still checked before you proceed.

Input the values to move your central CP that you came up with earlier.

Now you have a curved surface representing your transom that has the shape you want and is in the position you want.

Next you need to trim the excess so Edit > Point > Intersect Layers and put new CPs in your transom where it intersects with the hull. You may need to repeat this step if you’ve got a deck that’s in a different layer than the hull proper.

Doing this inserts CPs and edges into your transom that has the shape of the hull.

You should also Edit > Point > Insert Layers to put new CPs into your hull (where it intersects with the transom) too. If you do this now be sure to select the proper layer of the hull to make that the active layer before you do so.

After you do this be sure to return again to the transom layer as the active layer before proceeding.

Just to make things easier in the next step I like to move just the transom (or whatever surface I’m working with) a fair distance away from the rest of the model. I do this because I’m deleting stuff and I don’t want to delete part of the model than needs to stay. 10 or 20 feet up usually does the trick.

Once it’s out in clear space with nothing around it to get selected and deleted by accident all you need to do is select everything outside of the final shape of your transom and Edit > Delete it.

If you find that some CPs and / or edges are missing look for the comparable CPs and edges on the hull as these, taking your moving the transom into account, these have the same locations as their twins on the transom,

So if you have to put in any missing points / edges by hand at least you know that they’re in the right place.

Once you’ve got the transom cleaned up do the same with the stern of your model.

FInally move the transom back to where it should be by reversing what you did to get it out in the clear and you’re done — you’ve got a fancy curved transom.

If you look at my “San Jacinto” in show me your ships you can see what all this plugging and chugging can accomplish. A newer version (not shown right now) improves on that one by having the keel line crease starting aft of the water line so that the transom now sweeps down to a fine point rather than be flat along its bottom.