With this latest design, (see here for details in the previous post), I had to produce the basic drawings in a very short space of time (about three days), as we were about to leave on what turned out to be more than four weeks of road travel. Having given thought to such a design in the past, I felt that I could get enough detail out to satisfy the owner/builder, who is an exceptionally capable person with high-level engineering qualifications.
|Stitching-up Flint on which the new design is based|
|Here you can see the complex shapes which can be formed in plywood, as long as the panel shapes are "developable".|
With the availability of complex hull modelling software, it is quite practical these days to engage in the design of developable hulls which were never possible in the past because of the unbelievable volume of calculation required in manual drafting. I am not a computer person, but I love my hull modelling and CAD software!
In my extreme rush to get drawings to the builder before leaving on our trip, I burnt the midnight oil fairing-up the hull shape on the computer, and when all was satisfactory, I hit the button to produce the panel developments.
|Panel developments for one of my other designs|
|Scale model panel developments for Three Brothers, cut from 1/16" plywood|
|Testing panel developments at small scale|
For a long time, I've had a feeling that some hull modelling programs have a hard time doing developments which incorporate large amounts of twist and bend at the same time. When one considers the unbelievable number of calculations required, and the geometrical complication, it is little wonder. In order to test my supposition, I reverse-engineered the offsets of Fleet into Gregg Carlson's "Hull Designer" program, which had proven itself to be very accurate at this sort of job in the past.
I generated a set of developments using the Carlson Hull Designer, and superimposed them over the ones I had generated from the other program. In the illustration below, you can see the Carlson developments in red, overlying the others in a dark colour. The topside panels are virtually identical, but the bottom panels show substantial difference.
|Fleet developments showing the originals in black, and the Carlson Hull Designer developments in red.|
|Bottom panel having failed in tension at the keel-line near the first frame (near the bow)|
|View of the failure from the inside. See how the crack has initiated at the keel line, and extended upwards and outwards from the keel line.|
|Glass tapes dry-fitted, with some extra tapes to reinforce the new cuts|
|A wider view, showing how the repair has restored the boat to a nice, fair shape.|
- I should not assume that drawings for a new design are correct without testing them;
- Never give up, because just about anything can be fixed if you do some careful thinking;
- Don't take what I say too seriously, as I've proved myself to be wrong on frequent occasions!!!