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building from plans vs. seat-of-pants designs
By:Paul G. Jacobson
Date: 5/14/2001, 4:04 am
In Response To: Re: Guillemot Expedition (Roger Nuffer)

: I consider such to be guidlines mores than plans. Guess I was aiming at plans
: being more set in stone. Like stating that the beam should be 23.5"
: instead of a cubit or or hip width plus 2 fists. Each person will have a
: slighty different shaped and dimensioned boat with SOF's. Its this dynamic
: that makes SOF's so exciting to build and so easy to change. Think the
: boat should be narrower, build it that way and wrap it in a skin. Try that
: with other building systems. It would be a true challenge.

: But if I'm building strip. I want plans with exacting forms.

Interesting viewpoint.

Actually, the skin on frame technique places certain restraints on you that cedar strip building does not have. that is not to say that these restraints are a terrible burden. Just that they are there and that they are different than the restraints of building with plywood, wood strips, molded plastic, etc.

Even if you use measurements that are based on the length of body parts you are still using a measuring system. What difference if your base unit is the thickness of your thumbnail, or a tiny fraction of the distance from the equator to the north pole? You are still measuring.

Designing a boat based on your personal measurements is a perfectly valid idea, though. The measurements you need though, are not arm length or finger width.
you need to know weight, height, shoe size, width across the hips, and where your center of gravity is when you are seated in a paddling position.

The hip width measurement defines the narrowest size of the boat that you cna squeeze into. Once you know what beam your boat will be, your weight is the determining factor in how long the boat must be to get the necessary displacement to keep you afloat. If you are limited to a certain draft due to use in shallow water then your boat must be longer than if you cna use a boat that sinks deaper in the water. your stability will be determined by these elements, plus the location of your body's center of gravity and your seat height.

If you want to amke a boat that is based on some anthropomorphic or physiological oddity, well, I'd bet you could get it to float and maybe it would paddle OK. But it would probably not be the optimum design for you. Now that we have powerful computers to aid in our designs we can come up with MUCH better boats.

Now, as for the perceived simplicity in changing the design on a skin-on-frame boat versus making the same changes on a strip built boat. I just don't think that is the case. The similarities in the design process are far too many. In fact, any frame you can design for holding a skin can just as easily be covered with woodstrips, which are then covered with glass cloth.

In both cases you can very easily adjust the width and length. with strip construction you can space your frames where you wish to add length, build more (or less) of an entry angle and so on.

Your hip measurement is still going to determine how narrow your boat can be. With a SOF you'll make a rib this size. with a strip built boat you'll make a form this size. If you want the "natural" curves formed by steam bent ribs in your SOF, fine. You can use those very same ribs as forms for a strip covered boat.

I guess what I'm trying to say is that with both styles of building you are essentially making ribs, or rib-shaped forms, and covering them with a material that is either self supporting or one that requires an internal support.

SOF boats generally get bigger in the middle and taper to each end. If, for some reason you wanted a boat that had some asymetric or truly unusual shape then it might be very difficult to get the fabric skin to follow the framework. the fabric would naturally bridge the space between two higher frame elements, negating any narrower formwork in between. Strip built boats, though could be designed to get very narrow in the middle.

If you are looking for real flexibility in design, though, probably the most complex shapes could be made with carved plastic as a mold or plug -- and then fill the mold, or cover the plug with a glass reinforced plastic.

Just a few thoughts

PGJ

Messages In This Thread

Guillemot Expedition
Jason Koldewijn -- 5/11/2001, 9:37 pm
Re: Guillemot Expedition
Roger Nuffer -- 5/12/2001, 12:51 pm
Re: Guillemot Expedition
Geo. Cushing -- 5/13/2001, 9:30 pm
Re: Guillemot Expedition
Roger Nuffer -- 5/14/2001, 2:08 am
building from plans vs. seat-of-pants designs
Paul G. Jacobson -- 5/14/2001, 4:04 am
Re: Guillemot Plans
Mike Hanks -- 5/12/2001, 10:46 am
Re: Guillemot Plans
Nick Schade - Guillemot Kayaks -- 5/14/2001, 10:12 am