VMG Lab
About
VMG Lab is an Apple Watch app that connects to an ultrasonic wind sensor to measure VMG and sailing efficiency. It is designed to be a small, sharp tool to improve sailing performance by directly measuring it.
The Vision
May 31st, 2025
The VMG Lab app idea started to form as I transitioned back into sailboat racing in the 470 class, after years of racing hydrofoiling kiteboards in the Formula Kite class. As a teenager, I raced 29ers and trained methodically to improve my boat speed and handling. One of the hardest parts about improving in sailing is determining what actually moves the needle to make you better. In the United States, there aren't regular large regattas for Olympic classes, and most fleets number less than 10 or 15 active teams across the entire country. Testing the changes you have made in training is a costly endeavor that often involves traveling to Europe to compete in regattas with large Olympic fleets. You can become the best at the local level, but national and international excellence is the true end goal.
The common method for improving boat speed is "two boat testing" or "line ups" with one or more teams that are at or above your skill level. One of the obvious problems with that is the top performing boat does not have anyone to push them farther, and it's tricky to determine how much faster they are becoming compared to other boats. Can you tell if you sailed five hundredths of a knot faster on average in the last five minutes? Probably not, unless you're already an Olympic champion. Similarly, if you're a bit off the pace from the others, it's hard to tell if you're really getting closer. That's not the end of the problems. There are many compounding factors in a line up, including wind shifts, unequal starts, bad air, coach boat wake, etc. Any of these could be the reason one boat pulls ahead or falls behind, so it's hard to know what you are really measuring and whether your changes are improving your performance or not.
What if you could directly and accurately measure your sailing efficiency, allowing you to continuously improve on your own? That is the core idea that kicked off the VMG Lab project. VMG is the component of a sailboat's velocity in the upwind direction, so in order to truly measure VMG, you need to know the wind direction and your boat's velocity. Most sailing analytic platforms today compute VMG based on an estimated wind direction, found by bisecting the tacking angles. It's a great approach to get some initial insights, but it is not completely accurate, especially when the wind shifts, or if the sea state causes asymmetries in speed and angle between tacks. There's no good reason to estimate the wind direction when it could be directly measured.
Aspiring Olympic sailors in the US, and likely internationally, usually do not have a direct VMG measurement all. Sailing analytics regularly falls short and is underwhelming. There are two approaches generally in use today. The first one is that sailors will record their session with a GPS tracking device such as a Garmin watch. At the end of their long and tiring day, if spare time is available, they will manually upload that track to a sailing analytics platform. Some platforms provide automatic upload, but the analysis is necessarily manual as the sailor must engage with it in order to learn. Sailors may skim through their track looking at estimated VMG, speed over ground, etc. If they find a section with particularly good VMG, they will want to know, "What did I do to sail well in that segment?" Without a high amount of context, such as video or notes, it's impossible to know. Without accurate measurement of the wind, there may be other variables influencing that improvement, such as a gust of wind or a shift. I know there are high level teams in the America's Cup or SailGP that have all these elements in place, but there's nothing available to the average sailor or widely in use today, that I know of.
The other approach to measuring sailing performance is to have an onboard device like a Vakaros recording data and displaying it live. That's much closer to the right idea, because it gives you an indicator in the moment that allows you to have full context for any performance changes. However, once again, most people are not measuring the wind in any way and so they cannot truly measure their sailing efficiency.
The vision of VMG Lab is to provide a tool for sailors to accurately measure their sailing performance in the moment, enabling iterative, measurable improvement. A sailor will start tracking and set up with a baseline tuning, which is their current best estimate for the optimal set up and technique in those conditions. Then they will sail upwind at full speed, and hit a couple physical buttons on the Apple Watch to start recording a segment. After a minute or so, they can hit those same buttons to end the segment, at which point the app will display a notification with the average efficiency of that segment. Efficiency is defined as the VMG per knot of true wind, and it allows for comparisons across varying conditions. Next, the sailor will stop to make one change, such as moving the jib lead aft one centimeter, and they will start sailing again. They can start another segment, sail for a while with the new setting, get a feel for it, and then end that segment. The app will then show a notification which says whether the average efficiency increased or decreased compared to the last segment and by how much. The sailor is then able to iterate on their sailing, gradually improving efficiency and determining exactly what changes work and do not work. Notes can be taken via speech to text AI, which allows the app to generate a report at the end of the sessions with each segment, whether it was an improvement, and notes about what changed. The app automatically provides a list of lessons learned for the day with the insights based on real measurements. When paired with a camera and the right sensors, it records full context that can be uploaded into a sailing analytics platform, like SailSync.ai, for further detailed review and analysis during a debrief.
