# Multi-Sensor System for Analysis of Maneuver Performance in Olympic Sailing
## 4 Discussion  
The main aim of this study was to develop and test a sensor system to enable more detailed analysis of maneuver performance for the ILCA Olympic dinghy. We demonstrated a novel, low-cost, multi-sensor system for in situ measurement on the boat, followed by a presentation of the selected upwind tacking data. The discussion on the collected data will serve as a foundation for how detailed in situ data analysis could look when the system is deployed in an athlete-coach collaboration scenario for enhancing technique. We will now discuss the data results and the proposed system, followed by an evaluation of our study relative to previous research. As the ILCA 7 is a single-handed dinghy, the rudder movements directly influence not only the course but also velocity, drag, and interaction with waves. The measured mast rotation provides new insight into how the sail is continuously adjusted, depending on the momentary weather conditions for each tack. As shown in the results, the rudder movement during the initiation of the tacks exhibits a double-peaked trend. This could indicate either an adjustment motion provoked by the sailor, the passing of the filler behind the sailors back, or the fact that the rudder motion induces rotational motion on the boat, delayed by water resistance. Comparing the starboard tacks, we can see that the gradual entry into tack 11 results in a much slower tack and more loss of boat momentum. The mast rotations combined with the change in course could indicate the amount of pressure the sailor puts on the boat and main sheet. Port tacks 6 and 8 show some of the most efficient transitions of all the tacks, with aggressive rudder action to enter the tack, followed by a two-step adjustment of the main sail, seen in the mast rotations. The sailor enables quick acceleration by over-steering slightly lower with respect to the wind for a short period of time to gain SOG, before adjusting course to optimize for VMG. This is supported by the fact that broad reach is overall faster (SOG) than upwind [1]. Note that the tacking course range will be influenced by this compensation if it is maintained for longer periods of time. The nuances of SOG versus VMG are of great importance in sailing competitions, and the EOWD was defined to provide an accurate foundation for the comparison of VMG. The internal shifts in wind around the land formations surrounding the test site are likely the reason behind the offset between MWD and EOWD. For future experiments, onboard wind data collection is desired to expand our analysis with details on the subtle changes from port to starboard. This could indicate if a sailor has a faster side and why that is the case. A potential cause for the offset in MWD and EOWD lies in the natural tidal currents in Trondheim Fjord, which can lead to a sideward shift, influencing the port and starboard course angles. Further, we defined the 80%-SOG time as a performance measurement for the regaining of lost speed in the tack, a metric influenced by variations in entry SOG. The 80%-SOG time should always be considered together with the overall average SOG and VMG of the tack, to ensure that techniques found in overall slower tacks are not preferred simply because of short 80%-SOG timings. A good example is found in tack 8, which has the lowest 80%-SOG time of all the port tacks, but also the second lowest mean SOG of the port tacks. To support objective and replicable analysis, we chose to define the tack ending using a fixed time interval, rather than relying on subjective interpretations. Upwind tacking has served as an example maneuver for analysis. Jibing and steady course wave interactions are suitable for analysis using the same data. We focused on the novel angle measurement systems and on connecting these data points with position-velocity data for performance analysis, not including IMU data at this point. The main advantages of the presented system is its robustness, battery life, and waterproofing.