Race analysis: how to review starts, marks and legs with GPS replay

Post-race memory is unreliable, especially after a close start. You remember the boat that rolled you; you may not remember entering the final approach too early, arriving with too much distance to burn and giving that boat the chance to take control. A GPS replay shows what memory misses.

Review the start with five questions

Start from the first meaningful decision (the first cross, tack or shift) and work backwards: could you execute the plan you wanted after the gun? Then use the same five questions every race, so you can compare starts across a regatta:

1. Early, late or on time? Use GPS time and your track to see where your bow was at the gun. In a deep, risky fleet, crossing a second or two late with speed and clear air can beat arriving exactly at zero with the fleet stacked above you.
2. Which end was favoured, and did it matter? Line bias is one input, not the whole decision. A pin-favoured line can still reward the committee end if the right has more pressure or a cleaner escape.
3. Did you have speed at the gun? Compare speed over ground in the last 20 seconds with your normal upwind pace later in the race. If it was well below, find out why before blaming the lane.
4. What did the boats around you force you to do? The trace tells part of the story; your recollection of the boat to windward or the overlap to leeward completes it.
5. Could you follow your first-leg plan? Protect the left, reach a pressure line on the right, stay flexible? Did the start let you do it?

Build a personal benchmark from your best starts, and train the last two minutes, not just the gun: the hard part is arriving at the final 30 seconds with options.

Case study: finding time at every mark

Take a club racer in a one-design fleet, 14 to 17 knots, windward-leeward course with two laps, a slight left shift early and uneven pressure on the first beat. They review the race against a rival who finished ahead.

• The start. The approach near the committee boat looks disciplined until the last 25 seconds, when they slow to hold position and end up in dirty air. The rival starts slightly further down the line, with speed and a clean lane. Clean air beats a perfect line.
• The first beat. The sailor’s average speed is lower, and they assume their tuning was wrong. The replay says otherwise: on the long port tack, both boats hit similar peak speeds. The difference is time spent in disturbed air and an extra tack. Speed data needs context.
• The windward mark. This is where the race was really lost. The sailor approaches on starboard, rounds wide to avoid a boat ahead and exits low and slow. The rival rounds tighter, accelerates earlier and gets a cleaner downwind lane.
• The run. The sailor posts the higher top speed, but sails wider angles. Top speed doesn’t equal better VMG toward the next mark; the rival’s lower peak with better angles gains distance.

The outcome isn’t a pile of observations but two actions: a better start-lane plan and more efficient windward-mark exits.

Before you review: check the wind and clean the track

Tack detection, tack angles and VMG all depend on the wind direction saved with the session. Waterspeed takes it from the forecast as one average for the whole session, so on a shifty day tap Edit and correct it, or review each race on its own. Then trim time ashore, the tow out and drifting between races, which can be counted as turns, and fix missed or extra manoeuvres with Manual Adjust (web and Android).

How to run a replay review

1. Watch the whole race at normal speed and notice where the gap opens or closes.
2. Revisit only those moments and ask: was I in clear air? Was I sailing the right mode? Did my manoeuvre cost more than it should?
3. Measure each manoeuvre by its full cost: entry speed, minimum speed, time to recover and distance lost compared with sailing straight.
4. Finish with one or two actions for training.

What a good tack looks like in the numbers

Waterspeed Ultra rates each tack. Use it as a direction of travel and compare your tacks with your own best ones, since boats differ a lot:

Rating	Angle turned	Speed loss	VMG loss
Excellent	90° to 120°	under 10%	under 5%
Good	80° to 130°	under 20%	under 10%
Needs work	outside that	over 20%	over 10%

Then look for the pattern rather than the outlier: port against starboard, early races against late ones, tacks in traffic against tacks in clear water. Tack angles of 140° or more usually mean the wind direction is off.

Preparing for a foil race

• Read the venue before the gear: current, chop, launch, expected wind range and course shape.
• Build a setup you can repeat, one that feels the same on your first tack and your last upwind leg when your legs are loaded.
• Train the start: foiling fleets accelerate fast and crowded lines leave you stuck in disturbed air and water.
• Prepare for high-skill fatigue, because small lapses become expensive late in a race.
• Keep race eve boring: gear packed, weather checked, spares ready. On race morning, confirm the wind and make one clean equipment call; if it’s borderline, pick the setup with the larger control window.

The race-tracking system

Most experienced racers don’t rely on one device:

• A GPS watch for convenience, quick start and wrist alerts.
• A marine instrument for live race awareness on the boat.
• An app for live tracking, countdowns, personal bests and the deeper review afterwards.
• Video, because data shows what happened and video shows why.
• Heart rate, to see whether a gain cost more effort or came from better efficiency.

Live tracking also lets coaches, teammates, organisers and family follow you during the race; at DÉFI, riders shared their live location with spectators on shore. For timers, see Race timers compared; for training before an event, see How to prepare for a race.