Current Affairs
Current Affairs
The Doc and Racer Rob explore the vagaries of racing in current and get to the bottom of the myth of the lee-bow effect. "Strategy" from our January/February 2012 issue.
Doc: It’s not very often I get to come out on the start boat.
ROB: It’s not very often I get to come out on the start boat, either. In fact, if it comes to a choice, I’d rather be racing. But duty calls.
Doc: So how do you think they all look now with only a minute to go?
ROB: It’s going to be a shambles. A pin-biased line and current running with the wind are going to create a pile of boats that won’t make the pin-end layline. Then someone will panic and tack to port and … What did I tell you? Why is it always Godzilla that creates all the grief?
Doc: You could see that coming, couldn’t you?
ROB: I know a bit about how to sail in current.
Doc: Oh? Do tell.
Rob: I grew up sailing in the upper harbor, so there was always lots of current and often not a lot of wind. You sort of get a knack for it after a while. We’d get these hotshot sailors coming up to our club once a year thinking they could show us a thing or two. But Boris—he must have been in his 80s—was about as cunning as they come, and he really knew how to sail in current. They never beat him.
Doc: So how do you make sense of what he did?
ROB: Boris had a great way of explaining how current worked. You see, racing in current is just … well, there’s no way of making it simple, really. But Boris seemed to be able to explain it to us. He had these little sayings.
Doc: Yes?
ROB: He used to say that there were four things you need to understand if you wanted to sail current well. The first one was about exactly what we saw a moment ago on the start line. “Laylines tell lies when the current flies.” You have to realize—and constantly make allowance for the fact—that current alters the shape of the racetrack.
Doc: How do you mean?
Rob: What you have to remember is you’re sailing around marks that are fixed to the bottom. When there’s current, sailing on the course is like being on a treadmill—and not just walking forward. This treadmill can run in any direction. Let me give you an example. On a start like the one we just watched, because of the current running the same direction as the wind, it seems as though you’re slipping sideways—to leeward—really fast, because you are. It looks as if the mark is moving upwind. It’s not; you’re moving downwind. But that’s what it feels like. If you want to make it past the mark, then you have to set up a lot further to windward. If you use a layline based on where the bow is pointing, there’ no way you’ll make it around the mark.
Doc: Like Godzilla—then they panicked when they couldn’t make it, and tacked on to port. Whammo! There’s carnage at the pin.
Rob: So, any time you have current, it will affect laylines to anything that’s fixed to the bottom, and that means you can’t just point the boat at the mark—the boat will be crabbing one way or the other.
Doc: That’s what happens on downwind legs when boats point straight at the mark, but end up sailing a huge curve.
ROB: Exactly. Sailing downwind, irrespective of where the boat is pointing, you need to work out what course to sail so that the combination of your heading and the current will move you directly toward the mark.
Doc: What is Rule No. 2?
ROB: This one also catches people out all the time. Boris would say, “The less you heel, the more current you feel.” That is, the effects of current change with the speed of the boat.
Doc: [pauses, eyebrows knitted] Go on.
ROB: How often have you seen a boat laying the top mark in adverse current, and then another boat tacks onto its air? The boat slows down and is no longer making the mark. As the boat slows, the current exerts a greater influence on its course.
Doc: I have a great example of that, of how the current effect changes with boatspeed. It was a Snipe race in light wind, and because the breeze was dying, the race committee decided to finish at the wing mark. The current was pushing up the course, against the wind. As the boats came down the final reach, they got slower and slower as the wind dropped, and compensated by pointing lower in order to hold bearing on the finish line. Boats were noticing the effects of the current and sailing lower to get some down-current distance “in the bank.” The problem was, if they squared up too much, the boat slowed down to the point that they stopped stemming the current. In the dying breeze, only one boat realized that they had to stay high enough to maintain speed. They didn’t try to put any “in the bank,” they just went for speed, and managed to sneak across the line before the breeze dropped out.
Rob: I guess that shows how weird it can get. You really need to keep your wits about you, particularly in light winds and current.
