Archinisis Blog: Mastering Speed Data: From Raw Data to Insights

Imagine having a tool that goes beyond what your eyes can see and your instincts can sense. A tool that gives you a clear, objective window into exactly how your athletes move the boat. Boat speed data does just that. It provides a continuous measure of how fast your crew is traveling through the water, stroke by stroke, and moment by moment. This data doesn't just tell you how fast the boat is going overall; it reveals the subtle variations in speed that occur throughout each part of the stroke cycle. With boat speed analytics, nothing goes unseen.

You've just completed the Basel Head 6 km rowing regatta. Throughout the race, you had Archinisis' sensor, Naos, mounted on your boat, quietly collecting a wealth of data. Thanks to this small and powerful tool, can interpret different metrics that will improve your performance, one of them: speed.

Speed data in rowing is generated by high-frequency sensors (like GNSS or inertial measurement units) that record the boat's position and motion hundreds of times per second. These raw measurements are processed to calculate the boat's instantaneous speed at every moment during the race.

Speed analysis in rowing is essential for athletes and coaches who want to optimize performance. By focusing on speed, you can break down your rowing data into manageable, actionable insights. By the end of this article, you'll be able to interpret three fundamental speed graphs: average stroke speed, speed patterns, and boat speed. Understanding these will allow you to make sense of your data and turn numbers into real improvements on the water.

This 6 km regatta is distinguishable in three parts: an upstream start, a turn, and a downstream finish (more details). As opposed to the analysis of acceleration data, those factors demand a different approach, and the speed data will reflect that. It is necessary to contextualize the effects of current, so that the data accurately reflects crew performance rather than just environmental conditions. Not taking the environment of the race into account would be misleading.

500m Time Stroke Speed

Screenshot of the satellite image with color-coded 500m time overlay

Graph 1a: Satellite image with color-coded 500m time.

This graph provides a visual map of the racecourse. On the right, you'll see a color bar that ranges from dark purple (indicating the highest speeds) to bright yellow (the slowest). As you review the graph, you'll notice that the slowest segment is the turn, while the downstream portion of the race stands out as the fastest. The environment is an influencing factor to keep in mind, as river current and water depth can locally alter the measured speed.

You'll see that when moving upstream, the current can significantly reduce speed. For instance, there's a noticeable speed drop between bridge 1 and bridge 2 after the start, as the boat moves into deeper water with a stronger opposing current. This visual makes it easy to spot exactly where speed fluctuates along the course, giving you a general overview of the data.

Screenshot of the zoomed satellite image with color-coded 500m time overlay

Graph 1b: Zoomed-in satellite image with color-coded 500m time. The location of each stroke is marked with a dot, and the color indicates the 500m time at that point.

Instantaneous Boat Speed

After checking the 500m race time, it's important to look deeper to truly understand performance. There are still aspects of the performance that are yet to be analyzed, such as: which strokes caused speed lose and gain. Instantaneous boat speed is calculated by processing the raw sensor data to show the exact speed at every point in time, 200x per second. By examining it, you can see exactly how the boat's pace changed at every moment, at every stroke. This detailed view gives a much clearer picture of what happened during the race beyond just the finish time.

Graph showing selected strokes during the upstream part at Basel Head

Graph 2: Average speed per stroke for the entire regatta providing a rough overview of what happened.

In this graph, each dot represents a singular stroke. The first part, slower, is upstream. The turn is highlighted in red, where throughout the second half the boat accelerates. Speed peaking is an indicator of the downstream segment.

This is just a small amount of what can be seen with this graph. You can "zoom in" to see each stroke in more detail. Each second of a stroke captures 200 data points, thanks to the high sampling rate of the sensors.

Graph 3: Upstream boat speed during 25 seconds: the stroke starts are marked with the red dots.

In this upstream segment, the maximum instantaneous speed reaches around 5.6 m/s. When you row, each stroke is made up of three main phases: drive, recovery, and check (where the check overlaps with both the recovery and drive phases). Each phase influences the boats speed, and movement.

The catch: Just before the catch, boat speed is usually at its highest as the boat glides forward. As the blade enters the water, speed drops to its lowest point in the cycle. Once the catch occurs and the legs push off, speed increases, marking the start of the drive.
The drive: The legs extend powerfully, producing the steepest increase in boat speed.
The finish: As the stroke finishes and the blade exits the water, boat speed peaks, then begins to taper off.
The recovery: The goal is to maintain as much speed as possible and reduce losses. The boat glides forward, and the rower slides smoothly to avoid abrupt deceleration - a balanced, controlled speed loss before the next stroke begins.

Annotated screenshot explaining different rowing events and phases in the boat's acceleration and speed data

Graph 4: Showing the continuous acceleration (top) and speed (bottom) for 5 strokes with annotated phases and events for one stroke. Please refer to the Understanding Acceleration blog post for an in-depth explanation along with still images taken from a synchronized video.

Each complete wave or cycle in the graph corresponds to one full rowing stroke, in the graph below there are 14. In rowing, the "check" phase refers to a brief but noticeable period of speed loss that occurs just before the catch. This check happens as the rower's momentum shifts. Minimizing check is crucial, as excessive speed loss wastes energy and slows the boat.

The strokes are remarkably consistent: each stroke produces a similar increase in speed, and the intervals between strokes remain steady. This regularity suggests that the crew is able to maintain a controlled, efficient pacing.

Graph showing selected strokes during the downstream part at Basel Head

Graph 5: Downstream boat speed

In the downstream finish, the boat's speed pattern looks almost identical to the upstream one. The main difference is that the maximum speed reaches 7.4 m/s instead of 5.6. The similarity of the stroke patterns indicates that regardless of current conditions, the position and rowing movement of the crew isn't affected.

Speed Pattern

Graph 6: Speed pattern of the two distinct race segments (upstream in blue and downstream in yellow). It is computed by cutting the continuous speed at each check start until the subsequent check stop (i.e., it shows one complete stroke plus an additional check phase) and taking the average acceleration for 11 strokes centered at the distances indicated in the legend. Here at 1300m (upstream) and 4300m (downstream). The shaded area around each thick line marks the standard deviation of the eleven strokes. The time is set at zero at the end of the check which allows to read the stroke duration (time at which the average curve ends, here just under 1.7 seconds) and check duration (the negative time to the very left of the plot when the lines go below zero, here at around -0.45 seconds).

Speed patterns in rowing are created by averaging the instantaneous boat speed data across multiple strokes in a given segment. Please refer to the figure legend for an explanation on how these lines were computed. As the rowers move through the drive, recovery, and check phases, the boat's speed naturally rises and falls, creating a repeating wave-like pattern.

On this graph, the x-axis shows the duration of a single stroke, measured in seconds from 0 to 1.7. You'll notice there's an extra 0.5 seconds at the beginning, this portion actually displays the tail end of the previous stroke giving you a sense of how each stroke flows into the next. The y-axis represents the boat’s speed in meters per second.

When you look at the two main curves on the graph, you’ll see they run almost parallel to each other. This tells you that the rowers' acceleration pattern is remarkably consistent, causing the same thing with speed, whether they're moving upstream or downstream.

The key takeaway from this graph is that a consistent parallel pattern between those two sections is a sign of good technique. If the lines were to diverge or show erratic shapes, that might indicate fatigue or technical issues that need attention. If this is what you notice, in your own data, you would then have to go back to the other graphs, to find which segment was lacking and produced this divergence.

By understanding these patterns, you can start to see how small changes in technique can make a big difference in overall speed.

Conclusion

These graphs collectively illustrate how the crew adapts their technique and power throughout the race, responding to changing conditions with both precision and resilience. This tutorial shows how starting with speed analysis can turn a mountain of rowing data into clear, useful insights. By looking at things like 500m time boat speed, continuous boat speed, and speed patterns in different parts of the race, you can spot exactly where your crew is strong and where there's room to grow.

The 500m time stroke speed graph displays the boat's speed over each 500m section of the race, providing a general overview of where speed varies.

The continuous boat speed graph is a depiction of the continuous boat speed. This graph is a key tool to analyze and interpret specific strokes throughout the race.

The speed pattern graph examines the pattern generated from the data of each individual stroke, highlighting the consistency across the two portions of the race. This graph is valuable for identifying how well the crew maintains a steady rhythm and whether speed changes occurred throughout the race.

Analyzing speed curves helps you understand not just how fast you're moving, but why and when your speed changes, offering insights into the effectiveness of the athletes' technique. In the end, using speed to set clear goals and fine-tune your coaching can lead to real, measurable improvements in both technique and overall race results.

Now you have a good grasp about how to read and interpret boat speed data. If you have not yet done, we recommend to read the article about boat acceleration data.

Blog Post: Understand Acceleration Data