TUNING YOUR FD By the Numbers
by Art Lange

At the Nationals, while waiting for the wind one morning, Bill Hyatt and I were talking about rigging and we decided to measure a few things on all the boats we could. We felt that some things like centerboard stiffness and c. b. position and sail draft are very important. We didn't have the techniques developed to measure these things quickly and easily, but we did measure the distance from the after edge of the jib roller to the forward edge of the mast. (All our measurements and other signifi-cant observations are presented in the accompanying table. ) Since there is some difference in mast size between the Proctor B, Proctor F, and de Havilland, a correction should be made for actual distance to the back of the mast.

We also measured the distance from the jib roller to the side stay along the deck. Our third set of measurements concerned the length and angle of the spreaders. These were figured by holding the trapeze wire close to the stay near deck level and estimating the distance the stay was pushed out and forward. Because of our method, these figures are not exact, but we felt that it was more important to have an idea of who is doing what than no measurement at all.

The position of the mast is important in balancing the helm. Of course, it must be related to the centerboard position, which we could not measure. Most skippers who had the forward edge of their mast more than 67 inches back also had some provision to move their centerboard aft so they could balance the boat. The range of this distance for the boats measured was from 63.75 inches for Roberts and Kerr (999) to 69 inches for Tom Allen (1122). The average for the first five boats in the regatta was approximately 65 inches. (Again, a consideration of mast thickness must be made, since the Proctor F is about an inch bigger than the deHavilland. )

The distance of the stay from the jib tack is related to both the angle of the boom and the compressive load on the mast while on a run. In the lighter winds encountered at Jackson only the boom position was important. This dimension must be related to the mast position to figure accurately how far out a boom can travel. If adjustable shrouds are used, the lee shroud can be let off on a run to let the boom out further. It is felt that the stay position is of lesser importance than the other mea-surements we made, and the table of measurements doesn't seem to show anv trends.

The length and angle of the spreaders has a great effect on mast bend, so we were particularly interested in this set of measurements.    There was a great range in the figures, from Jeff Frayne's 0" out and 0" forward to Tom Allen's 5" out and 3" forward. This was probably the most significant finding of the entire exercise. Another important factor controlling mast bend is deck-level support,that is, how hard you push aft on your mast at deck level. We did not measure this on any boat, since most skippers had easily adjustable deck-level mast bend control.

Only Chatain and Roberts could adjust their spreaders under-way --Chatain the angle and Roberts the length. This may be a new fashion trend. (I'll bet the winning boat at the next U. S. Olympic Trials will sport adjustable spreaders. )

In the top five boats three different mast sections were used, and the sails used by the top seven skippers showed absolutely no trends in sailmakers, with 13 different sailmakers repre-sented. We did not get to measure all the boats and some of the measurements of some of the boats are not valid, since the sailors changed things shortly after the measurements were made. And there are other variables to consider in planning the rigging of any particular boat, such as fullness of sails, crew weight and wind strength.

But for your general guidance and interest, these measurements may be useful. Comments on the subject from other sailors welcome.

TUNING TABLE                      Hull              Mast              Jibtack    Jibtack to    Spreader    Spreader    Mainsail      jib        Spinnaker                                                                to stay    front of mast    out           forward Chatain      Peden double    de Havilland    89        67.5               3               lA*          Miller and    Miller and   Elvstrom                       bottom                                                                                                   Whitworth    Whitworth   Canada S. Allan      1/2 double      Proctor B           88.5       67.5             2.5               0                  Elms    North    Banks                     Plastrend Roberts      1/2 double      de Havilland     87.75     63.75           3A*           .75         Johnson    Pederson    Musto                    Plastrend Lange       Single bottom    Proctor F        87.5       67.25           4                  0             Kenyon    Kenyon    Kenyon                    Plastrend      M. Mouse    North James          Newport        Proctor B         84.5        64.5             3                  1             Musto    Musto    Banks Turner     New Plastrend    Proctor B       85           65.5            3                  1              Musto    Pederson    Musto Saxon        1/2 double       Proctor B         87.5        66            .75                  0             Tasker    Tasker    Tasker                   Plastrend Martinez    1/2 double       Alspar             92           68            1.25               .75           North    North    North                     Hoare Croshere   1/2 double       de Havilland    84.5      66.75           3                    1             North    North    North                    Plastrend Frayne       von Hocht       Proctor F        85           64              0                    0           Johnson    Pederson    Levinson Guedry         Karlish         Proctor B         84.75     64.75          1.5                 1              Musto    Elvstrom    Musto Harris        1/2 double       de Havilland    87         65.5            2.5               1.25              Jotz    Jotz    Jotz                    Plastrend Hall            1/2 double       Proctor B        87          68             3.5                 1.25            Hard    Balken    Hard                    Plastrend Tom Allen  Hoare          de Havilland    91.5        69               5                   3                Tasker    Allen                 double  bottom