ass bitten


Staff member
A little Saturday morning brain exercise for y'all, courtesy of the way-too-smart-for-us Kevin Hall. We'll drop part two on you Monday morning. And here you thought this class was going to be easy...

Instrument targets are intended to help us get to the bottom mark or waypoint sooner than we would without them. Let’s learn more about how they work and why they bite us in the ass sometimes. When Morgan Larson and I missed out on the silver at the first 49er Worlds on a count back with Jonathan and Charlie McKee, I locked myself in my room for a few days to think about how to over-think while I was racing… considerably less than I usually did.

The 49er was a brand-new class, so nobody in the world had reviewed non-existent videos of the top teams or logged the hundreds of hours modeling the best techniques to develop muscle memory. It was a thrilling time. In my effort to figure out how to flow more while racing, I kept thinking about this: Feel. How can we do more of this just by feel? And, are there cases where my feel is misleading me?

The 49er kites were very full. In previous classes, I had learned that usually side force (tipping-ness) = power = speed. However, in the 49er you could heat to seek more apparent and more speed, put more weight on the wires, trim the kite in to keep it from collapsing, and go higher and much slower. So my feel equation, power=speed, was wrong in that condition. It was worse to over trim, even if you could put more weight on the wires.

Once we figured this out, I designed a way to immediately know this sheet position by feel so that I didn’t even have to look down at a mark: I put the splice precisely at max trim, so that my hand could do the management of the max trim algorithm on its own, entirely by feel. Once my hand felt the splice go through the ratchet, my mouth would say “max trim” to Morgan, and we both knew that the next move if the kite curled was always always always to move weight in and bear away a little, and never never never to trim it past the no-go point.

Now jump with me onto a TP-52 at the top mark. Notice a few things. Number one, there is a little bubble level gauge! Along with the spreadsheet of the targets, along with the scatter plots of data that got sent to Valencia overnight to be analyzed to help refine the targets, there is a Heel-O-Meter. What’s it doing there when there is a fiber-optic gyro compass down below that outputs heel to .01 degrees and displays it in huge digits on the mast? I bet you can guess.

Which representation of the heel of the boat provides more feel? An analogue bubble which is always “straight down”? Or, a digital number which must constantly be compared by the brain to an abstract zero to know how much heel there is (easy) and, simultaneously, compared to the previous number to know rate of change (not only hard, but highly affected by the precise amount of dynamic damping)? To say an important thing another way: the moving bubble conveys rate of change in a way that the human can interpret immediately and intuitively. The digital number does not do that. Instead, once enough hours are logged to build an “internal human app/subroutine” that converts the moving digits to useable rate of change info, the digits approximate the bubble.

We’ll get back onboard after a quick sidebar to understand where a boat’s VPP targets come from. Designers sail their models super well in the VPP – the model gets to hunt for just the right amount of apparent wind (up in the lulls) at just the right heel, with the sails trimmed just right.

Once the computer says the model might have a sustainable built apparent wind speed, it tries taking the virtual puff down to as deep an angle as possible without the virtual kite sheet going soft. The computer then keeps cycling with smaller and smaller moves between “a little too low and slow” and “a little too high and spearing off the course” until the cycles converge and voila: that’s the target! Laminate it to the cockpit as a discreet pair: target BSP, and target TWA. Not included in the 2-D lamination are: wind weight, sea state, sail code, tactical situation, or wind shift.

Photo by Ingrid Abery. 



Super Anarchist
Sask Canada
Thanks ed, and Kevin Hall 

Reminds me of chapter 5 in Martel's Lif of Pi (that other study of numbers and being on the ocean)

And so, in that Greek letter that looks like a shack with a corrugated tin roof, in that elusive, irrational number with which scientists try to understand the universe, I found refuge.
Gad, I love this place.


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