Adding hull frames

[ChrisH]

Hi everyone:

I'm not sure if this is a virtual modeling question, but it applies to a model I'm building in Sketchup (free version 14.0.04900), and the expertise here is amazing, so here I am.

I'm drawing a ship that is based on a modified TICONDEROGA cruiser hull. I started with a paper model, scanning the hull frames into a 2d drawing application. I used this 2d application to modify the hull (stretched and widened) to get the general shape of the hull. I then used the drawing and modified frames to start building the model in Sketchup, which is my first experience with not only Sketchup but 3d modeling.

Here's what I'm trying to accomplish. The model that I started with had the frames fairly widely spaced (about 25-scale feet), and I'd like to have frames at smaller, even intervals. I am, however, really struggling to draw the additional hull frames with the "correct" shape so the hull retains its current shape. If I had hull plating that would define the shape of the hull and the "missing" frames, of course, but I need the frames to correctly shape the hull and plate it.

Does anyone have anything they can offer? I've been stuck for a week now, so anything that might help would be appreciated.

Thanks, everyone!

[DrPR]

Chris,

This can be tricky. If you want the exact shape of the hull you need hull line drawings or (better still) a Table of Offsets. If you are not too picky you can "guestimate" the intermediate frames. I haven't used Sketchup so I can only give general ideas, not exact steps.

1. Amidships the shape of hulls doesn't change much. Using the frames you do have, stretch a skin on the existing frames and then use whatever tools Sketchup provides to draw intermediate frames.

For example, some programs can find the intersections of surfaces, so draw a transverse vertical plane and find the intersection with the hull surface. Some programs will generate contour lines on surfaces using defined planes.

2. Fore and aft there are more drastic changes in hull shape. Again, you can start with a surface stretched over the frames you have and generate intermediate frame lines as mentioned above. Then edit these lines to correct the hull shape. You will probably have to repeat this over and over until you get the desired hull shape.

3. It is often easier to work only with a half hull - port or starboard - and then mirror image it to get the other half.

4. You can use contour lines or surface intersection lines to inspect the hull curvature. There is a discussion of this technique on the Forum. Here is another discussion of how to get smooth hull lines:

viewtopic.php?f=27&t=150101

Phil

[ChrisH]

Hi Phil:

Thank you so much for the suggestions. Your suggestions have allowed me to make slow but steady progress, which is excellent considering I was about as stuck as I could be when I made my intial post. It's good to know that to some degree the "trial and error" and "draw, correct and re-draw" experience that I have been having isn't necessarily atypical.

Within the last few years I've become interested in air defense warships. I'm especially interested in Talos-equipped warships, Typhon and, more recently, AMDR-cruisers. okieboat.com is largely to blame for my fascination with Talos-equipped warships.

Thanks again for the help. I really appreciate it.

Chris

[DrPR]

Chris,

I am not familiar with Sketchup and how you create complex curved surfaces with it. However, I have done a few hull models with DesignCAD and here is how I solved some problems - maybe these ideas will help you in Sketchup.

In DesignCAD if you try to stretch a surface grid over a sharp transition the grid will be stretched and wrinkled just as if you were stretching thin plastic wrap over a frame. The most common place I see this problem in boat/ship hulls is at the end of the flat keel or skeg, and at the transition from sides to a transom at the stern.

See the attached image. I used seven different grid surfaces to complete this fairly simple boat hull. The sharp transition at the end of the skeg determined where multiple surfaces were joined.

The forward part of the hull was created with a half-hull grid (light blue). It was easier to work with half of the surface than with the whole thing. Once this half surface was smooth I mirror imaged it to get the other side (orange).

The bottom of the keel was a simple rectangular plane (magenta). The front of the keel and bow was a separate surface (red) to get a smooth transition from the flat bottom of the keel to the rounded leading edge of the hull.

The back of the skeg was a separate dark blue planar polygon.

Aft of the skeg I created a single surface (green) for the aft portion of the hull. I did this because it can be difficult to make mirror imaged hull halves join in a curve without a visible crease. It is pretty easy to get the smooth sides to line up without a visible crease.

The transom (red) was the seventh grid surface.

For the initial simple OK City hull I used something like 14 different grid surfaces for the half hull, plus three for the keel, giving a total of 31 separate surfaces. Later I created a plated hull with about 480 individual grid surfaces.

Phil