Better Distance to Line Measurements with the Bow Offset on the Velocitek ProStart

Better Distance to Line Measurements with the Bow Offset on the Velocitek ProStart

TLDR: Entering a bow offset enables the ProStart to track the location of your bow and give DtL measurements from the bow to the line.


In the world of competitive sailing, every detail counts. From perfecting sail trim to mastering tactics, sailors are constantly seeking ways to gain an edge over their competition. One often-overlooked aspect of racing is the importance of precise distance to line measurements. In this blog post, we'll explore how utilizing the bow offset feature on the Velocitek ProStart can significantly improve distance to line measurements, leading to better race starts and better finishes.

Understanding Distance to Line Measurements:

Distance to line measurements provide crucial information about how far a boat is from the starting line, helping sailors balance their time and distance on their final approach.

Once you have set (pinged) both ends of the starting line the ProStart connects these two points in a straight line of infinite length. The ProStart calculates distance to line as its perpendicular distance to the infinite start line.

The ends of the line should be set when the bow of your boat is on the line. When you set the ends of the line, approach each ping in the same direction you would if you were approaching the line to start the race.

The Role of Bow Offset:

The ProStart's bow offset allows sailors to account for the distance between the bow of their boat and the position of the ProStart. Once you have entered a bow offset, the ProStart knows where the bow of your boat is at all times using the offset you input and the orientation of the vessel. The ProStart (July 2020 and newer) calculates vessel orientation using the superlative PNI RM3100 3-axis magneto-inductive geomagnetic sensor and a 100 Hz solid-state 6-axis inertial measurement unit (IMU) giving you the accuracy you need for your distance to line measurements.

Benefits of Bow Offset for Distance to Line Measurements:

More Precise Positioning: By setting the bow offset on the ProStart, distance to line measurements are calculated from the bow of the boat rather than the instrument's mounting location. This precision is crucial for accurately gauging the boat's distance from the starting line, especially in crowded race scenarios where every inch counts. Even without the bow offset entered, the ProStart provides useful distance to line data for a timed final approach.

Optimized Start Strategy: With accurate distance to line measurements, sailors can fine-tune their starting strategy. By knowing exactly how far they are from the starting line, sailors can time their final approach and acceleration to cross the line at the gun, at target speed.

Coaches Corner:

To get your timing right you need to establish the ratio between time and distance. This ratio will vary depending on a number of factors including the type of boat you are sailing, the orientation of the start line, wind strength, tide and/or current sweep, etc.

Once you’ve pinged the line, here are a couple starting drills you can run with your ProStart.

Time and distance drill

Sail to a depth below the line like 60 meters (this distance may vary depending on the size of the boat and the size of the fleet). Start roughly paralleling the start line. Start a timer and turn to a close hauled angle or your starting angle. Stop the timer when the ProStart distance to line is 0 meters. Compare your time to distance to get a ratio.

Acceleration drill

Slow the boat to a bottom speed (2.5 knots for example). Once you reach your bottom speed, simultaneously start a timer, note the DtL on the ProStart, and accelerate (trim, weight and steering) to target speed and course. Once you hit targets, stop the timer and observe the distance traveled on the ProStart. Note the time and distance traveled to go from your bottom speed to target.

1:1 pacing

Sail towards the line at 1 meter per second closing speed (perpendicular to the line). Try to maintain 1:1 for the entirety of the drill. This drill is purely about developing feel and technique for approaching the line slowly and in control.


Accurate distance to line is important for good starts and starts are the most important single part of a sailboat race. The ProStart's bow offset feature enhances your distance to line measurements, providing sailors with the perpendicular distance from the bow of your boat to the start line. The ProStart does this using its 44 Hz high-precision magnetic sensor and 100 Hz solid-state IMU along with a 25 Hz Swiss-made GPS module. Inputting a bow offset into your new ProStart is a feature that can improve the accuracy of your distance to line measurement and help you start better.

Bow offset tutorial video:

ProStart firmware v46 manual:

Questions? Comments? Suggestions? Drills you’d like to share? We’d love to hear from you!