System Sailing 2.5 - Sail Shape

June 11, 2020

To fully understand how to make your boat go faster, you must photograph and measure sail shape. This information will connect the dots on how your boat performs in different wind speeds. Pictures of sails provoke thought and questions that can be answered by turning the shape of each sail into a number. For this section, please check out the playbook on recording and evaluating data and reach out to Wally to learn more about V Spars. Here is another resource about photographing sails.



  • Sail upwind with sails trimmed properly
    • Top telltale on jib/genoa and mainsail leech telltale flowing
    • Sails trimmed firm
    • Halyard set for conditions
  • Take your smart phone to the mid foot position of each sail
    • Take a picture so you can get three draft stipes in the frame
  • Take a picture of your instruments to capture wind speed
    • If you do not have wind speed, write down your best guess in your wet notes

After sailing, email pictures from your phone to computer and save in a picture file named after your boat. The next step is to send the photos to Quantum Sails and have the sail image digitized.


  • Email picture of the sail to
    • Include picture of instruments
  • You will receive data relative to the shape of your sail
    • Horizontal draft position % at each draft stripe
    • Depth % at each draft stripe
    • Entry angle % at each draft stripe
    • Exit angle % at each draft stripe


Take the numerical information from Quantum Sails and enter it in the Google Doc for your boat. For each sail this should include:

  • Picture of sail and instruments
  • Digitized numbers
  • Sail performance in the race
    • Ease of trim
    • Ability to steer
    • Speed
    • Height
  • Settings for the sail
    • Halyard
    • Sheet
    • Backstay
    • Lead/inhaul
  • Time on each sail
  • Conclusion

The goal with photographing sail shape is to connect performance with numbers. By accumulating enough numbers and experience on the racecourse, a pattern will develop to better understand the proper numerical shape for:

  • Light air, flat water
  • Light air, chop
  • Medium air, flat water
  • Medium air, chop
  • Heavy air, flat water
  • Heavy air, waves

The final benefit for taking pictures of your sails and measuring the shape is longevity. Your race sails will perform at a high level longer by monitoring the shape with Quantum Sails. If the entry angle is changing or the draft is moving aft, and we know the earlier shape was fast, Quantum can make the adjustment early to keep the sail performing well. If you wait until the sail has changed dramatically, the ability to restore the shape becomes impossible.

If you have any questions about photographing and recording sail shape, or are interested in digitizing your sail shape with V Spars, please reach out to Wally Cross.

 Watch our full collection on Youtube

The Discussion