Sailing performance
What is VMG in sailing?
Velocity Made Good is the only speed number that tells you whether you are actually winning the leg. Here is what it measures, why the fastest boat is often not the quickest, and how to read it without instruments.
Your speedo tells you how fast the boat is moving. It does not tell you whether you are gaining on the fleet. VMG — Velocity Made Good — is the number that does, because it measures progress in the only direction that scores: toward the next mark.
VMG is progress, not speed
Upwind you cannot sail at the windward mark, so you sail at an angle and accept that part of your speed is wasted sideways. VMG is the part that is not wasted: the component of your boat speed pointing straight up the course.
That cosine is the whole story. Sail closer to the wind and the cosine improves, but boat speed falls. Bear away and boat speed climbs, but the cosine gets worse. Somewhere between the two is a maximum, and it is narrower than most sailors expect.
Why maximum boat speed is the wrong target
Here is the same boat in the same breeze, sailed four ways. The numbers are illustrative rather than from any real polar, but the shape is what every boat shows:
| Angle to true wind | Boat speed | VMG to windward | |
|---|---|---|---|
| 38° | 5.4 kt | 4.26 kt | Pinching — high but stalled |
| 42° | 6.0 kt | 4.46 kt | Best VMG |
| 46° | 6.3 kt | 4.38 kt | Faster, losing ground |
| 50° | 6.4 kt | 4.11 kt | Fastest boat, worst leg |
Read the last row again. The boat doing 6.4 knots is losing to the boat doing 6.0, by a third of a knot of actual progress. Over a ten-minute beat that is a difference of roughly a hundred metres. This is why crews who sail to the speedo tend to foot off and quietly lose the race while feeling fast.
Downwind is where it gets counterintuitive
The same maths applies running, and the result surprises people: sailing straight at the leeward mark is often the slowest way to reach it. Heating up gains enough speed to more than pay for the extra distance.
| True wind angle | Boat speed | Progress downwind | |
|---|---|---|---|
| 180° (dead run) | 4.8 kt | 4.80 kt | Shortest distance, slow |
| 160° | 5.6 kt | 5.26 kt | Better |
| 145° | 6.9 kt | 5.65 kt | Best VMG — gybe downwind |
| 130° | 7.4 kt | 4.76 kt | Very fast, going the wrong way |
How pronounced this is depends entirely on the boat. A planing dinghy or an asymmetric sportsboat gains enormously from heating up, and dead downwind is almost never right. A heavy symmetric-spinnaker keelboat in a strong breeze sits much closer to the run. Your own boat's crossover is worth finding, because it changes with wind strength.
Measuring VMG without instruments
A phone GPS gives you speed over ground and course over ground. VMG needs one more thing: the direction of the wind. You can get a usable answer without a masthead unit.
- Sail upwind on starboard and note your average course over ground.
- Tack and note the average course on port.
- The wind is coming from roughly the midpoint between those two headings.
With that axis established, your VMG is your speed over ground multiplied by the cosine of the angle between your course and the wind axis. Track it over a whole tack rather than instant by instant — instantaneous VMG in waves is far too noisy to steer to.
Strictly, VMG usually means velocity made good relative to the true wind direction. Progress toward a specific waypoint that is not directly upwind is sometimes called VMC, velocity made course. On a normal windward leg they converge; on a skewed course or a long reach they do not, and the one you want is progress toward the mark.
If there is tide, VMG over the ground and VMG through the water are different numbers. The mark does not drift with the tide, so over-ground VMG is what wins the leg — but through-water VMG is what tells you whether your trim and steering are right. Judge the boat by one and the tactics by the other.
Four ways sailors get VMG wrong
- Comparing across conditions. A VMG of 4.4 knots is excellent in eight knots of breeze and poor in eighteen. The number only means something against a target for that wind strength.
- Steering to the instantaneous value. It lags and it jumps. By the time the readout reacts, the puff has gone. Use averages to learn, and telltales and heel to steer.
- Optimising VMG when tactics say otherwise. Sometimes the right move is to foot off to reach new pressure, or pinch to hold a lane. Best VMG is the default, not an instruction.
- Ignoring the sea state. The best angle in flat water is not the best angle in a chop. Footing slightly to keep the bow moving through waves often beats the theoretical optimum.
How to actually improve it
Improvement comes from having a reference to beat. Build target speeds and angles for your boat in each wind band, then check yourself against them every time you sail. Two-boat testing is the fastest method ever devised for this: sail side by side, change one thing, see who gains. Failing that, record your sessions and compare like-for-like conditions week to week — feel is not a reliable memory.
Common questions
As a default, yes - but tactics can override it. Footing off to reach a band of new pressure, pinching to hold a lane on an opponent, or sailing slightly low to arrive at a shift can all beat the boat that simply maximised VMG. Best VMG is the baseline you deviate from on purpose, not a rule.
There is no universal figure. VMG depends on the boat, the wind strength and the sea state, so a number that is outstanding in light air is mediocre in a breeze. The only meaningful comparison is against your own targets for those conditions, or against another boat sailing beside you.
Speed over ground is how fast you are moving in whatever direction you happen to be pointing. VMG is only the part of that speed making progress toward your objective. You can increase speed over ground and reduce VMG at the same time by bearing away, which is exactly the trap.
Yes. A phone GPS gives speed and course over ground, and you can establish the wind axis by averaging your headings on both tacks. That is enough to compute VMG without any onboard instruments, which is the approach Tacktiq uses.
Often more. Downwind the speed gain from heating up is large, so the difference between the best angle and dead downwind can be greater than anything available on the beat - and it is where fleets spread out most.
Because it is computed from instantaneous speed and heading, both of which move constantly in waves and shifts. Averaged over a leg it is a reliable measure of how well you sailed; second by second it is mostly noise.
See your own VMG, every session
Tacktiq records your track over GPS, computes VMG upwind and downwind, grades every tack and gybe, and has Claude AI tell you the one thing worth fixing next. No instruments required.
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