Ups and downs...
Jun. 25th, 2014 06:58 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
khiemtranSo, you're in a sailboat with the tiller in your hand, and your "crew" (in this case just one person) turns around and says urgently "There's a boat below you!"
What's your first thought? If it's "Well, duh!", then read on...
The first big thing to realise is that, for a sailing boat, the world is actually permanently tilted towards the wind. It might help to imagine a giant pinball table, with your boat somewhere in the middle and the wind blowing down from the top. Just as we say "upwind" and "downwind", we can also refer to objects being above or below us; or above and below reference points. To pass "below" an obstacle is to pass downwind of wind. To head "up" is to turn your boat closer to the direction of the wind.
Once you've got that pinball table in your head, a lot of other sailing concepts start making sense. For example, the port and starboard rule for avoiding collisions is often something that confusing to beginners. The rule is that a boat on a port tack (which means your sails will be on the starboard side of the boat) must give way to a boat on a starboard tack (sails on the port). The trick is that when you're starting out, you not only have to work out which tack you are on, but also how to tell at a glance which tack the other boat is on, especially when it's heading towards you. Once you have that pinball table, it's all quite simple. A boat moving towards the right of the table is on a port tack, regardless of whether it's heading up or down, or towards or away from you.
The same mental model is also critical for understanding racing. A race will nearly always start with a windward leg, that is, with the start line at the bottom of the pinball table and a marker buoy somewhere directly "above" you. Since you can't sail into the wind, this means you will need to sail on each tack (port and starboard) at least once to get there.
If nothing else changed, it might not even matter which order you did things. You could start off on a port tack, sail half the distance, then finish off on a starboard tack. Or you could start on a starboard tack, sail halfway, then come back on a port tack. Or you could throw in lots of little tacks and zigzag your way up the centre. Which strategy you choose would largely come down to which part of the course you think the wind will likely to be stronger on and where the currents might be more favourable. But the next trick, of course, is that something *will* change, and that's where all the fun comes in.
Suppose for a moment, that the wind shifts so that it is now blowing from the left of the marker. This has the effect of rotating everything so that the marker is now no longer directly above you on the pinball table. It's slightly to the right and a little lower than it used to be. It's clear now that a tack towards the right side of the table will get you closer to where you want to go than a tack to the left. The port tack (the one with the wind on your port side) is said to be "lifted" because you can now sail a little closer to the mark; and the starboard tack is said to be "knocked" because you've been knocked away from your target.
One of the basic skills when racing is trying to detect when the wind has shifted and register whether it's a knock or a lift. If the tack you're on is knocked, it's often a good idea to tack immediately. Ideally, if you want to be sailing on the "lifted" tack as much as possible, because it will let you cut the corner a bit towards the mark. Of course, to get up that pinball table, you're still going to need to be on both tacks at least once, so you also need to consider what you think the wind is going to do next.
And once you reach the top mark ahead? Well, then it's all downhill from there...
What's your first thought? If it's "Well, duh!", then read on...
The first big thing to realise is that, for a sailing boat, the world is actually permanently tilted towards the wind. It might help to imagine a giant pinball table, with your boat somewhere in the middle and the wind blowing down from the top. Just as we say "upwind" and "downwind", we can also refer to objects being above or below us; or above and below reference points. To pass "below" an obstacle is to pass downwind of wind. To head "up" is to turn your boat closer to the direction of the wind.
Once you've got that pinball table in your head, a lot of other sailing concepts start making sense. For example, the port and starboard rule for avoiding collisions is often something that confusing to beginners. The rule is that a boat on a port tack (which means your sails will be on the starboard side of the boat) must give way to a boat on a starboard tack (sails on the port). The trick is that when you're starting out, you not only have to work out which tack you are on, but also how to tell at a glance which tack the other boat is on, especially when it's heading towards you. Once you have that pinball table, it's all quite simple. A boat moving towards the right of the table is on a port tack, regardless of whether it's heading up or down, or towards or away from you.
The same mental model is also critical for understanding racing. A race will nearly always start with a windward leg, that is, with the start line at the bottom of the pinball table and a marker buoy somewhere directly "above" you. Since you can't sail into the wind, this means you will need to sail on each tack (port and starboard) at least once to get there.
If nothing else changed, it might not even matter which order you did things. You could start off on a port tack, sail half the distance, then finish off on a starboard tack. Or you could start on a starboard tack, sail halfway, then come back on a port tack. Or you could throw in lots of little tacks and zigzag your way up the centre. Which strategy you choose would largely come down to which part of the course you think the wind will likely to be stronger on and where the currents might be more favourable. But the next trick, of course, is that something *will* change, and that's where all the fun comes in.
Suppose for a moment, that the wind shifts so that it is now blowing from the left of the marker. This has the effect of rotating everything so that the marker is now no longer directly above you on the pinball table. It's slightly to the right and a little lower than it used to be. It's clear now that a tack towards the right side of the table will get you closer to where you want to go than a tack to the left. The port tack (the one with the wind on your port side) is said to be "lifted" because you can now sail a little closer to the mark; and the starboard tack is said to be "knocked" because you've been knocked away from your target.
One of the basic skills when racing is trying to detect when the wind has shifted and register whether it's a knock or a lift. If the tack you're on is knocked, it's often a good idea to tack immediately. Ideally, if you want to be sailing on the "lifted" tack as much as possible, because it will let you cut the corner a bit towards the mark. Of course, to get up that pinball table, you're still going to need to be on both tacks at least once, so you also need to consider what you think the wind is going to do next.
And once you reach the top mark ahead? Well, then it's all downhill from there...
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