> If your hull is symmetrical ...

Hmmm, drifiting quite a way off-topic here, but what the heck...

The design I'm working on is a baidarka, which is, of course, not remotely symmetrical. The software I use calculates centre of buoyancy based on the waterline as drawn. It also calculates centre of lateral resistance and centre of wind resistance, but simple-mindedly just based on the sectional area. I know not to trust that because a chined hull has more lateral resistance than a rounded hull of the same section, and the aft lateral resistance changes when the kayak is moving forward at speed owing to the increased turbulence of the water further aft and due to the wave-making resistance which causes the stern to sit lower as hull speed is approached. That's all very noticeable in real paddling when a skeg adjusted for perfect wind neutrality when stationary has to be adjusted to maintain similar neutrality once moving... The wind resistance figure (in software which only has boat offsets to work with) doesn't take into account deck load or the paddler, so is not terribly useful (the part of the paddler that sticks up into the wind is typically aft of the centre of lateral resistance, so is contributing to weathercocking). Software works on the basis that the boat is a pure displacement hull in absolutely flat water. That's not the real situation, of course !

The net result is that I know not to take a lot of notice of the numbers the software kicks up in real terms. But the numbers are somewhat useful when comparing different designs (at least some of which I know have been built as real boats). Warning bells will ring if the numbers are saying something very different for my design from what they say about other designs which I think ought to be similar. But that is the crux of the matter - one wants lots of designs to play with to see if one's own experiments are generating something that seems anomalous. Hence the desire to amass lots of free plans, preferably as sets of offsets (rather than, for instance stitch and glue panel shapes) which the software can play with. And hence why I will take any study drawing or half-usable photograph of building plans, or indeed, measurements of actual boats I can lay my hands on and convert them into "free" offsets to play with.

The more free plans that are available the more scope for new designers to "experiment" and build enough confidence to actually commit the time to building a new design. Innovation is squished by designs being jealously guarded as intellectual property just as software development is retarded by all the closed source stuff and software patents. That's not intended to suggest that kayak designers are getting rich off builders' backs - far from it, the market is way too small and those experienced designers do need a way to get a little back for all their effort. To get rich off intellectual property you need a monopoly on a huge market - try selling the world's shoddiest operating system instead of kayak designs ;-)

> Asymmetry can be overdone: a lot of commercial kayaks become difficult to keep in a straight line if you raise the rudder

Ah, British kayaker warning !! We don't do rudders, and try to learn to paddle without skegs as much as possible, though they do make life that bit easier. Boats designed to have rudders do indeed have too much lateral resistance forward, since it is designed to be neutralised by the rudder - which obviously breaks at the most inconvenient time... But far worse is a boat with too little lateral resistance forward, which develops lee helm. No amount of adding rudder or skeg will do anything except make the situation worse. So in my case I am always trying to get a boat with a little weathercocking at all times, which can be corrected with skeg or stern ruddering when running downwind.

Andy