My first impression of the widely accepted rules for sizing structural members in the construction of sailing yachts was that it was the world of empirical mystery that arrived at structural solutions that would survive most normal events through sheer quantity of structure. Nevin's rules, Herreshoff's rules, Lloyds' rules all offered quick and useful solutions for sizing structural members for the style of yacht and materials available at the time the rules were created. Applied to the current popular style of relatively light displacement, fin keel/spade rudder cruising or racing yacht these rules gave solutions that were often clumsy and quite obviously well outside the range of interpolation intended for the rules.
The approach our office has taken to structures is based on Lloyds, and more recently the ABS Guide, heavily influenced by firsthand experience on boats over a lot of heavy air ocean racing, and colored to some degree by my training as a Civil Engineer.
As a starting point we sought to determine actual loadings that occur on a hull and then organise a structure capable of resisting these loads with whatever factors of safety are appropriate. Other influencing factors such as the nature of the load, resiliance and stiffness of the material, and type of structure should all be accounted for in determining scantlings.
Basing our philosophy on the engineering logic of load x how safe x to last how long = structure we have outlined in the following our approach which we are filling out and refining in the process of conducting our business. We have tailored this approach to sailing yachts in the medium to light displacement range with fin keels, spade rudders, with or without partial skeg. Any application outside this style must be done with care - less witchcraft, more science.