I am thinking of designing several pond boats that will be between three and five feet long on the water line. These are to be square riggers. I was never able to understand my design software that I bought many years ago and the one presently advertised for students of naval architecture (called RHINO) seems much too expensive a way to design these little hobby boats. I have read Chappelle and L.F Herreshoff and a biography of Nat Herreshoff and other similar books so I gather that there are several ways to design boats.
The oldest way seems to have been experimental and the results were recorded as dimensions in notebooks or better yet in molds for the frames (Or every third frame.)
Nat Herreshoff carved half hulls and had a precision machine that took accurate measurements off of the half hull. I gather that these measurements were then expanded by some factor, marked on the mold loft floor and then faired again on the mold floor. I assume that the faired section lines were then converted into light weight molds which were then used to construct the full sized frames (or molds if the boat was to have steamed frames). I also assume that battens were then run around these frames and measurements taken off for the intermediate frames.
A variation of this system was the "hawks nest" or "batten" half hull. Here a profile of the centerline of the ship was drawn on a thin plank. Next a thin wooden section was marked with a proposed shape of the midship section. This was fastened to the profile in "the proper place" and the designer then shaped the remainder of the sections checking each one by springing a thin batten along the imaginary water lines and diagonals. Where the section did not fit properly it was removed and reshaped until the battens curved "properly" according to the designer's eye and concept for the hull.
A variation of this system was a half hull made up of horizontal planks which were temporarily fastened on top of each other and the whole pile carved with planes, gouges etc. until the assembly looked satisfactory to the designer. At that point, I gather that the assembly was taken apart and each plank measured, the measurement multiplied by some scale factor and the measurements put full size on the mold loft floor. Then light wooden frames were created from these measurements and used to build full sized frames for the ship.
Chappelle's and L. F. Herrshoff's system was all done on paper on a drafting table. A profile was established that met the designer's eyeball analysis by drawing pencil lines on the paper using french curves and wooden battens held down by lead weights. Then the midship section was designed using the same tools. Then the waterline was drawn in plan view. Then iteratively, the other sections and waterlines were drawn. Checks were made by measuring the position of points on the three views of the hull until the waterlines, sections and diagonals were "fair" without unwanted bumps. The area of each section was measured and plotted on a curve of areas which was then cut out and the cutout balanced on a pin. That was the center of buoyancy. The displacement was determined by putting the underwater portion of the sections into a table and manipulated by the Simpson rule and the hoped for displacement thus determined.
In another calculation the designer estimated the weight of all major parts of the boat, cargo and crew and the location of each center of gravity and then calculated the expected center of gravity of the complete boat. Hopefully the center of buoyancy coincided with the center of gravity. If not the designer adjusted the section shapes until the centers fell on the same vertical line.
The next task was to generate a sail plan that was properly placed in relation to the estimated center of lateral resistance.
I gather that this took a week or two of concentrated work and that no stability calculations were made because they were so labor intensive. I understand that the computer with the proper software and experience can do the same work together with a complete stability curve in a much shorter period of time.
Thus I am very interested to find out what you do when designing original model sailboats between 1 and say 10 feet long.
George Steele
Author
Topic: Methods for designing pond sailors from 2 to 6 feet long (lwl) (Read 2339 times)