1927 George Crouch Design, Miss Massacusetts Hydroplane, in 1:3 scale

From this first picture, and the fact this is going to be a large-scale model, I decided I was going to use four 1/8″ thicknesses for the keel and two 1/8″ thicknesses for each of the ten frames I am going to design.

Because I decided to use four thicknesses for the keel, I will use two of them to make a space for the propeller shaft.

Descriptions of these quite positive and encouraging first steps are outlined with the pictures.

It sure would be nice to get this project completed in days instead of weeks!

As I like to work in Solidworks and like to get feedback from builders and designers, I include a few specifics about my design methods.

Figure 1 shows how the splines are created. I use as few spline points as possible. Happily, in this case, I was able to use just start and end points for the curves. With few points you get nice shapes. As soon as you add even one point along a spline, you create a potential inflection point that then becomes a bump in the surface. The “Pierce” function is very nice because it forces the corners onto points in a plane.

Note the 1/8″ offset all the way around the bulkhead. This is to take into account the thickness of the planking.

Figure 2 shows a view of the frames from above. As you can see, the edges of the frames seem to be inside the outline of the boat. This is normal since the frames have been reduced by 1/8″ all around. After faring and planking, the hull should work its way to the outer line.

Figure 3:
I was asked to create just ten frames across the entire length of the boat but I felt the ends would prove difficult to plank with a little over 6″ between the outer frames and the keel, so I decided to add an extra bulkhead in the bow and an extra one in the stern. This picture shows the addition of the frame in the bow.

I sure would like to learn how to use surfaces in Solidworks in order to make it easier to create the perfect frame. In this case, the profile is done by eye.

Figure 4:
One of the keys to making these boats is creating lines that you can use to connect to. I use the Insert->Curve->Projected feature to create a 3D curve from two 2D curves. I suppose one could create the 3D curve right out of thin air but it would be very difficult. Combining two 2D curves is much easier and then one can tweak the curve by fiddling with one 2D sketch at a time.

Using the transparent button allows you to see some of these curves easily when you are working.

Figure 5:
This picture shows the created 3D chine line in blue overlaid over the original 2D lines that I started with. From this angle, the lines match up pretty well.

Figure 6:
This picture shows the new notch I added for the extra frame in the stern. One thing you will notice here is the transparent view of the original lines. When I first started building these models, I used to put those lines right against the modelled parts. One thing that is nice about using CAD is that you can set or remove the depth perception of what you are working on. This means I can put the original pictures at any distance I like and still see the lines at exactly the right position, when I set the model view-on. This means, in views like this one, I can see the model and also get a little idea of how close I am to the original lines at any time. I don’t have to “hide” and “show” the original lines all the time, as compared to if they are in the way.

Figure 7:

Finally, the hull is created and we get to the construction of the T-rail. This was an interesting project because the hull is basically an upside-down half-barrel. Typically, these boats are build upside-down. This means I can stretch the T-rails quite far across underneath the hull, in order to make the structure more stable. I also try and keep the T-rail as close to the frame as possible in order to save on wood at cutting.

In this case, it occurred to me that it would be difficult to reach in-between the T-rail and the hull so I reduced the width of the “ears” on the T-rail and also reduced the width of the tabs. Of course, since each frame is a double-thickness baltic-birch frame, it will still be solid as a rock during assembly. But, hopefully, I’ve given enough space that the builder will get most of the planking done with the boat on the frames.

Figure 8:
This picture shows the model as it will sit on its T-rail during construction. I think there should be enough space above the T-rail to get a good deal of the planking done fairly easily.

Once that is all done, off we go to the creation of the 2D. Always force your 2D to 1:1 scale from the beginning. Do not count on your software to do the conversion for you. It would be a shame to create a nice model and end up with a 3″ boat instead of 72″!