Rod Davis- Rethinking the Current Tactics
by Rod Davis on 26 Aug 2012
Professional sailing coach, Olympic Gold and Silver medalist and long time America's Cup crew and skipper, Rod Davis gives his insights on the effect of current on catamarans, and the new tactics, in San Francisco.
Ben Ainslie Racing heads for the shore - out of the current, maybe - but not the place to be. © Jon Nash / J.P.Morgan BAR
We are always learning in this new Cat world.
You have to think a bit more laterally when comes to racing high-speed boats like cats, particularly in current. Be it San Francisco’s America’s Cup course, or anywhere else that you try to play the current.
A few quick facts: In your 50 foot mono hull, you sail up wind at say 8 knots. If the current is 2 knots that means current is about 25% of total speed. The new Cats will sail up wind at, about 18 knots, a 2 knot the current is about 10% of the boat speed.
That is two and half times different, and is a very big deal.
When you play the shore short by tacking into the shallow water where the current is weaker, you can make big gains in your monohull. The wind shifts are a secondary consideration to getting that 25% boost in performance.
With the cat it is only 10%, so balance between current and shifts enters a different equation. On top of that, a monohull loses about a boat length in a tack.
A good tack in the cat costs you four boat lengths in smooth water, and more in waves. That's a big part of the new cat equation too. You can’t afford to short tack up shore.
The easy conclusion - no short tacking up a shore for current.
Ahhhhh, not so fast. You don’t abandon the current all together; just the current has a factor, given the new situation we are in at San Francisco sailing catamarans.
There is a mind twister: Downwind in some conditions at cat will go two knots faster with just a knot more wind speed. So, in those conditions, you would sail out into adverse current of a knot, increasing the winds speed by a knot, and boat speed by two knots, to get to the finish faster........
That's something you never purposely do in a normal boat.
Strange but true. Still learning.