Page 193 - The Complete Rigger’s Apprentice

below) pretty much hamper virtue. But even here, there’s one big monkey wrench deeply lodged in the
responsible designers and rule-making bodies can design works.
prevent the worst excesses of unseaworthiness.
Rating Rules
Fore-and-Aft Stability The noble, sensible, sporting idea behind most rat-
The transverse righting moment curve is only the ing rules, which address hull and rig designs, is to
simplest, most accessible of many seaworthiness-in- provide a basis for comparison among vessels, so
dicating factors, and it is by no means definitive. that they might be assigned appropriate handicaps
C. sA. Marchaj addresses these other factors in his for even competition. In yacht racing, handicaps
book Seaworthiness: The Forgotten Factor. Many take the form of time allowances; a favorably rated
of those factors are outside the scope of rigging per (ostensibly “slow”) yacht can finish a race well
se. I’ll touch briefly on just one, an item of grati- behind its competitors and still win if its handicap
fyingly far-reaching significance, and one we can allowance is great enough. This seems fair enough,
study without having to decode any of Mr. Marchaj’s but rules have historically had unfortunate effects
graphs and formulas. on the integrity of the vessels built to suit those
A hull also describes a curve of fore-and-aft rules. Designers and sailors naturally want to see
stability, again dependent on hull form and ballast their boats finish first, and creative exploitation of
amount and location. A heavy vessel, fat at bow and rules can give them ways to do this without neces-
stern on the waterline, will be very stiff fore-and-aft, sarily making the boats go any faster, let alone be
but with so much hull dragging through the water it more comfortable, stable, or stout.
will also be very slow. By making the hull—and par- So, for example, rules often “tax” the water-
ticularly the bow—relatively skinny at the waterline, line length, since in theory a vessel’s maximum
but flaring above it, you get minimum resistance to non-planing speed is approximately 1.1 times the
forward motion in light conditions, but “reserve square root of the waterline length. An easy way to
buoyancy” in heavier conditions, when the hull will exploit such a rule is to design a vessel very short on
tend to dip at the ends. The amount and degree of the waterline, but with great long overhangs at bow
flare is crucial. Too little too high will not keep the and stern. When the vessel heels under sail, more
bow from diving, or might result in a “hobbyhorse” hull length is submerged. As a result, the boat will
motion. Too much down low, and the hull will slap sail faster than the rule predicts.
and pound in a sea. The history of sailing rule-making is essentially
Ultimate fore-and-aft stability must be suffi- an endless exercise in loophole-plugging. So rules
ciently high to discourage the somersaulting action have grown ever more Byzantine, and hull shapes
known as “pitchpoling.” As with transverse loads, have grown ever more bizarre in attempts to exploit
sometimes wind and waves can gang up on the most the endlessly generated loopholes.
stable vessel, but good design can minimize a flip in The International Offshore Rule (IOR), which
either direction. predominated from the 1970s into the late 1980s,
To sum up, we’ve worked out stability in two was originally intended to be an all-time loop-
planes, and seen that this stability must be played hole-plugger. But its creators underestimated the
off against sailing performance. Different hull types resourcefulness of—and perhaps overestimated the
and sailing styles, of course, demand different sta- principles of—yacht designers. In a nutshell, boats
bility compromises. And if this were all there were that most successfully exploited the rule were very
to the question of stability, rigging sailboats would fine forward, very beamy aft, high-sided, lightly
be a much simpler subject. But aside from matters built (rig weights in the 1980s were typically a
of preference like rig configuration and materials, third lighter than in the 1960s), and relied heavily

172