How to analyse a sailing session like a coach

Good analysis isn’t about collecting every metric and staring at charts after sunset. It answers a few practical questions: what happened, why did it happen, and what will you do differently next time?

Start with the session goal, not the graph

What were you trying to do: train endurance, chase speed, work on transitions, test a setup, get comfortable in stronger wind? The goal decides which numbers matter. For racing, decide what the data should answer: were you protecting a lane, gaining on a shift, sailing a mode?

Work from the whole session down

1. Look at the full track. Repeating laps, long reaches, race legs or stop-start drills? Where did the session change?
2. Check the core numbers: speed (top, sustained, average), distance, moving time, VMG where relevant, tack and gybe count.
3. Break it into segments. One long average hides too much. Compare individual reaches, legs and transitions.
4. Find the biggest gains and losses, then zoom into one of them.

Compare like with like

The most valuable comparisons aren’t random: same spot, same point of sail, similar wind range and, ideally, similar gear. Compare a flat-water powered reach with a gusty, underpowered session and it’s easy to draw the wrong conclusion.

Compare runs with the right speed metrics

• Sustained speed beats spikes. If Run A touches 24 knots for one second but spends most of the run at 18, and Run B holds 22 across a long section, Run B is the stronger performance, and more reproducible.
• Speed over ground vs through the water. GPS records speed over ground (SOG). That’s exactly what you want for course performance, but current can change it a lot. A fast run with the tide says something about the tide.
• VMG for upwind and downwind. A lower instantaneous speed can produce better VMG at a more productive angle.

Put the track next to the number

The number says what happened; the track helps explain why. Was the fast run at a different angle, in clearer air, in flatter water? Did you favour one tack? Did a wider line cost distance?

Use manoeuvres as markers

Runs don’t exist in isolation: how you enter and exit them matters. Measure a manoeuvre by its full cost: entry speed, minimum speed, time to recover, heading lost and distance lost compared with sailing straight. For foiling classes, add touchdowns and time off foil.

Use conditions to explain, not to excuse

“The wind was weird” may be true, but it isn’t useful on its own. Note wind strength and stability, current, chop, traffic, crew weight and sail choice, then ask what you could control within those conditions.

Eight training examples

1. Speed consistency block: hold a target pace across repeated runs in similar conditions, instead of chasing one top number.
2. Manoeuvre loss drill: measure speed loss and exit quality in each tack or gybe, rather than “working on manoeuvres” in general.
3. Angle session: sail less distance at better angles upwind and downwind, and check VMG.
4. Starts: rehearse with a countdown, timing your approach and acceleration to the line. Review the last two to five minutes: distance to the line, speed trend, approach angle, time stopped.
5. Endurance and load: combine on-water metrics with heart rate to see when technique starts to break down in long sessions.
6. Foil efficiency instead of raw pace: look at sustained flight and clean transitions, not the top number.
7. Gear comparison: back-to-back runs on a known line, changing one thing at a time.
8. Spot history: use your previous sessions at the same spot to decide what to train before you launch.

Pick one main objective per session, two at most.

Change one variable at a time

Move the mast base, change sail tension, shift foil shims and alter harness lines before the next run, and you won’t be able to explain a speed change. Set a baseline in a known wind range, then change one thing: jib lead, rake, crew movement timing, foil setup, heel target or manoeuvre technique.

Know the limits of GPS

Sampling rate, signal, device placement and smoothing affect short events like quick tacks, mark roundings and fast foiling transitions. A device mounted poorly or hidden under layers gives less reliable data. See How accurate is GPS on the water?.

Finish with a decision

After every review, end with one action, not a vague verdict. “Run 4 was faster because I entered lower, stayed powered and stopped over-sheeting in the gusts” is useful. “Run 4 felt better” isn’t.

Keep the routine short enough to repeat: track, core metrics, one thing that improved, one limiter. Ten minutes. Over weeks, look for whether sustained speed is rising, manoeuvres are getting cheaper and your best sessions happen more often, not by accident. Observe, compare, decide, repeat.