Mark -'s Library tagged stats →  View Popular

The April 1998 issue of CRUISING WORLD contained an article I wrote
titled Crunching Numbers For A Quality Cruiser. In it I presented a process that
used fuzzy logic and a data base to select boats with characteristics suitable for
offshore cruising. The process sorted out ninety boats that were CLOSE to the fuzzy logic
template, and these were listed in a "Best Cruisers" list. The response from
readers was very positive, and I would like to thank the many people who took the time to
comment, ask questions, and suggest additional boats. Due to this participation, the data
base has doubled in size, and now contains over 1100 monohull sail boats. I have also made
several improvements to the selection process, including more emphasis on dynamic
characteristics and the inclusion of retail prices. With this new price information, it is
possible to identify potential bargains in offshore cruisers. Of course many other factors
are important in selecting a cruising boat, like passing the survey, but looking at boats
that are on the Best Cruisers list and within your price range, is a good place to
start.

The Fuzzy Logic process allows boats to be scored on "how
close" they come to the optimal values applied to a set of evaluation parameters. To
make the Best Cruisers list, a boat must score greater than zero on all the
parameters. Miss one, your out. These parameters (see EQUATIONS)
include the traditional Disp / LWL and Sail Area / Disp ratios, as well as well as less
known ones like Comfort Factor, Capsize Risk,.and Vmax / Vhull. The latest version
includes the LOA / BEAM ratio, and a term called Max Acceleration. The Max Acceleration
term is particularly interesting in that it introduces dynamic factors such as roll period
and the moment of inertia into the evaluation. The acceleration level that the crew
experiences as a boat rolls is especially important for safe offshore cruising. Prolonged
exposure to high levels of acceleration can promote fatigue through sleep deprivation,
which leads to mistakes and accidents. Adding these additional parameters makes the
selection process more discriminating, and increases confidence that the selected boats
are truly unique.

Once the evaluation parameters have been chosen, the optimal values for
these parameters can be selected. In the original article I used my own "best
judgement" for selecting the optimum values for the fuzzy logic variables, which was
a somewhat subjective process. At the suggestion of my internet friend, Jim Manzari, I
modified the way the optimum values are selected, and now calculate them directly from the
work of nine well respected cruising boat designers. Average values for each of the seven
fuzzy variables are calculated for each designers work, covering a total of 131 boats. The
Optimal Value is then calculated by taking the average over all the designers. Figure 1 shows the results of this process