How does ski race timing work? (part 2)

Part one covered the fine precision required for ski racing timing, and the start gate.  Now that we have a racer on course and the clock is running, let's follow him down the course to the finish.  While the racer is on course, the running time you see on the TV is very, very close to the actual time on course, but it's often not official, because it's based on a computer clock, not the actual timing chronometer.  In some cases, the timing chronometer has an integrated computer processor that runs the race software, so the displayed running time does reflect the official chronometer.  Once the racer passes through the first intermediate timing point and breaks an infrared photocell beam, the timing chronometer stamps the time of that impulse and the computer immediately calculates the time elapsed since he left the start gate and "freezes" this time for the TV display.  The computer software also calculates the difference between the time for the racer on course and that for the leader, usually showing a new leader with a green differential number.

The photocells at the intermediate timing points are set up outside the safety netting, so on a wide "speed" course (downhill or super-G), they might have to "shoot" up to 75 metres.  In between racers, there can be quite a bit of traffic on the course, such as course slippers and course repair workers.  So, the intermediate photocells require an operator, who tells the chief timer when a racer is passing through, and pushes a button to close the circuit and allow the photocell impulse to be registered and attributed to the racer.

At "speed traps", the racer's speed is measured using either a radar "gun" or two sets of photocells set a measured distance apart along a straight section of the course.

The finish uses two pairs of photocells that are vertically stacked.  The snow between the photocells is marked with red dye so that the racers can see exactly where the finish line is.  The finish controller tells the chief timer when a racer crosses the finish and keeps an eye out to warn any non-racers approaching the finish to use a side exit, rather than crossing the finish.

The start and finish are obviously the important timing points, so there are multiple back-up timing systems in place at these locations.  First, there are two or more back-up electric timing systems connected to the start gate and photocells.  Secondly, there is manual timing, which involves hand timers pushing a button when the start gate opens and the finish line is crossed, and writing those times down.  Finally, the very high end races now also use finish line cameras as an additional back-up.  These cameras can scan the finish line at a rate of 1000 line scans per second to build an image record of the finish.

The governing body of ski racing sets strict requirements for timing equipment to be authorized for use in race timing and also requires that chief timer complete timing audit report, which is reviewed by the senior race official at the event.  With all the attention to equipment, procedures and back-up systems, we can ensure accurate and reliable race results.

That's it - all you didn't really need to know about ski race timing. The bottom line is that it really is extremely precise and there are multiple back-ups in case something goes wrong.  Of course the expectation of the timing crew is always that each of the systems will work flawlessly throughout an event!

The photos and text here provide examples and a general description and are not reflective of the systems  in use at the Games at Whistler.

How does ski race timing work? (Part 1)

You've seen displays of ski race timing when watching World Cup or Olympic races on TV.  The running time in the corner of the screen that freezes at the "splits" and shows how the racer on course is doing against the best time posted so far.  The leaderboard that shows that the times of top 5 racers are jammed within a period of 12/100ths of a second.  You may have wondered, "How does this information get  from the race course to my TV screen?"  and "How can the timing be so precise that a winner can be reliably determined by a margin of as little as one hundredth of a second?"

Try starting and stopping a stopwatch as quickly as you can.  Chances are, the watch will show that this action takes you 2 to 3 tenths of a second.  Now consider a time period of 1/100th of a second.  If two racers were to cross the finish line at a speed of 90 km/h (a realistic speed into the finish of a downhill course) and one crossed the line 1/100th of a second before the other, the separation between them would be 25 cm, or a little less than one ski boot length.  That is why you see racers reaching out to break the finish line with their hand.  If done correctly, that can shave one or two 100ths of a second off their time.

So, obviously the timing needs to be very precise throughout a race.  All racers must be timed from exactly the same start point to exactly the same finish point throughout a race, using chronometers that have negligible "drift" over the time period taken for the whole field to complete the course.

Let's start at the top of the course.  The start gate consists of a block with two or more switches in it, and a wand.  The start gate is mounted on a solid post set into the hard snow, so that the wand is below the racers' knees.  When the racers' lower legs push the wand open enough to trip the switches, the switch closures are detected by the electronic chronometers that are connected to the gate via wires.  These wires run out of the start gate and all the way down the mountain to the timing building, where two synchronized timers with precision quartz oscillators receive the signal to indicate that the racer has started.  The chronometers send the time-stamped start data to the race timing software, where the start is attributed to a particular racer that was confirmed to be entering the course.  The race software then starts tracking elapsed time on course and generates the graphics for displaying this running time "downstream" on TV.

In Part 2: moving on down the course to the intermediate timing points, and the "speed trap".