A very good place to start learning about this is http://home.ican.net/~735769/shape.htm A clear and understandable page by John Winters on the essential theories of boats, and an example of applying them to create a design. There are also additions pages for further reading.

> So, how do you determine the volume you want for a boat? Obviously
> you know the weight of your paddlers and equipment, but you want more
> displacement than just that number. Do you multiply that times 4 or
> actually figure out the volume in water with a 4" displacement?