Weight effect -

written by Stuart Walker  on  November 6  of  2009 and read by 1789

We had an interesting discussion (led by Hans Fogh) at the 2009 Worlds. The major consideration was Roman Koch`s speed - in almost all conditions. And not just to windward (and certainly not on a reach which we never do anymore and where weight has its greatest effect). He is fast downwind - in smooth water and in waves - but (I think) particularly in waves.

We know that weight is fast to windward - twelve men on trapezes in the Garda boats is faster than eleven. The usual explanation is that they can use fuller sails, generate more power and therefore go faster. But to windward keelboats readily reach displacement hull speed and cannot be driven faster - at least not much faster. Weight on the rail means less heeling and therefore a lesser need to feather and reduce heeling force - and that must help. But it certainly doesn`t account for speed downwind - and I wonder if Roman isn`t (relatively) faster downwind. So I think there`s something else.

At Toronto I pointed out that stability matters - that Australia II`s winged keel gave her stability and that she sailed right around Liberty to win the `82 America`s Cup. Spreading the weight across the boat - one crew hiking with the other to leeward - makes for stability and is fast. Robbie Haines always said that one crew`s butt touching the water was fast. Weight alone matters - so long as it is low - heavy power boats are more stable than light ones.

Marchaj says that sail trim is only correct about 15% of the time - mostly because the rig is moving around in the air flow - yawing, rocking and pitching, at least to some degree all of the time. Attaining stability so as to keep the rig steady in the air flow - diminishing its rolling so as to keep the leading edge at the optimal angle of incidence (almost) all of the time, not allowing it to stall intermittently because of yawing or pitching - would certainly improve the percentage of time the sails were trimmed optimally.

And when I discussed stability, John Morgan pointed out that stability increases in proportion to the fifth power of weight. In the old days square-rigged sailing ships required ballast (well, steamships, etc, do too); they would never undertake an ocean voyage without adequate weight/ballast aboard and they thrived on heavy air. Ballast - weight down low - worked. Indeed they would continue to sail (reefed) in 50 knot winds. Their greatest hazard was calm and big seas - when the lack of pressure on their sails caused them to roll - and roll their masts out.

I think high crew weight provides stability and stability keeps the rig steady in the airflow - and steady in the airflow means that the boat is being driven at hull speed a greater percentage ot the time.