Hull Section Shapes

[PI Design]

Too true! However, drawing them is only the final part of the design. It would be nice to make this visualisation part easier.

[Wayne Grabow]

Admittedly I am a rank amateur, but the idea of using mathematical curves to create a completely mathematically-defined perfectly-fair hull form first interested me 30+ years ago. I settled on a form of the parabolic equation (easy to integrate, differentiate, and calculate) to define chines and other longitudinal curves to build up the entire hull form. Thus far I have home-built six modest-sized boats (first one in 1976) of various types using this design method. I have some pictures on a website listed below. The designs may be crude, but the method works.

http://developable-surface-boat-designs.blogspot.com

[Tim B]

They look good. I agree it would simplify the maths, but by the time you get to more complex shapes, numerical integration is common, and it can be pretty accurate on modern computers. particularly if you're considering stability at very large angles, you need something that works for all cases.

Tim B.

[PI Design]

Hi Wayne - any chance of posting the pictures on the forum? I can't get access to your website, but would love to see your designs.

[Wayne Grabow]

Having never posted an image on this board, I'll try a photo of my most recent boat as an experiment.

[marshmat]

I would hardly call that "crude", Wayne... she's quite an attractive little boat IMHO

[PI Design]

Thanks for posting that. It looks great. Just to clarify - are they parabolas in the sections or the waterlines? Can you expand on your method?

[Wayne Grabow]

I use parabolas (piecing together sections of such curves to achieve the overall shape I am seeking) to define mainly longitudinal basic curves. Then I use multiple mathematical conic projections, linked by ruling lines, to create surfaces. On the design I am working on now, the sheer is defined by the intersection of the hull surface with a defined curve for the deck surface and also camber. I once investigated using curves, such as an ellipse, for sectional shapes, but I am committed to curvaceous conic projection designs which are amenable to fairly simple mathematical techniques, and you can't have such projections curved in two directions simultaneously. Diagonal projections can mimic such a situation and, if not, I resort to multi-chine design to approximate such sections. Not as difficult as it may seem when you break it down to steps.

I realize that modern computer programs have superceded the need for such skills, but by putting together the pieces myself, I maintain complete control. It's only a hobby for me. When I started, 1975, all I had was a slide rule. I'll include a couple of photos of my early boats which were surface-defined. More complex shapes are defined by their internal framework.

Thanks for your kind comments. I mainly lurk on this board to learn from those who really know what they are doing.