“Desirable and Undesirable Characteristics of Offshore Yachts”
Ed. John Rousmaniere, Norton 1987
described in the book was intended to explain why boats capsize
in heavy weather
, but the concepts are likely relevant to stability in general.
To briefly summarize a chapter of the book, stability is a function of various forces, but one that is very significant is the “roll moment of inertia”, or the resistance to rolling movement caused by the weight and placement of the various boat components. Inertia contributed by a given component is related to both its weight and its distance from the fore and aft axis of the boat; in practical terms this means that the keel has less effect than you might guess (it’s heavy but close to the axis) and the mast
and rigging have more (lighter but farther from the axis). A dismasted boat will roll more and is more likely to be capsized by wave action.
It seems reasonable that the same forces affect the way the boat behaves at anchor. To extrapolate (and this is just my speculation based on the above), a long fin keel might actually be better for this - even if it’s not resting on the bottom
- than a shorter full keel.
Interesting anecdote in the book: this was discovered almost by accident
. Researchers were doing tests on a model hull
in a wave tank when someone decided to add a mast
to make it look more like a sailboat. They then found that the model had completely different characteristics than previously observed.