2021 Spring Speed Testing Summary
During our speed testing session in April, our Evolution Sails team looked at multiple sail designs as well as the modifications to the Evolution Thistle sails in an effort to design and build the fastest Thistle Sails on the water. Greg Griffin shares his experiences from these 4 days in Charleston, SC.
In addition to some tweaks to the designs we came away with a new take on jib trim. Rather than trying to base jib trim off of a measurement off of the mast at the middle diamond, it makes more sense to determine the trim from the flow over the leech of the jib. So, we added 2 more tell tales to the one already on the leech and it made it easy to not only see, but to also easily know if the trim was too tight.
This way we are responding to the air flow as it is affected by changes in wind speed, wave condition and mainsail shape and trim. We found that in flat water, the technique of bending the lower mast to flatten the lower third of the main would let us sheet the main really hard and follow that mainsail trim with the jib trimmed tighter to achieve new levels of height. Of course, we would have to “downshift” out of this “6th gear” or “super tight” mode as soon as the wind lightened, or the wave condition worsened.
As the wind built later in the week, we also were reminded of just how valuable one of the tools for controlling the leech of the main (the traveler) can be. By keeping the traveler car under the boom so that the sheet angle is never more than 30 degrees(see red in photo below), each inch of trim in or out has more impact on the leech of the main.
Think more fine tune than gross tune. We found ourselves making very small, yet impactful changes to the main trim. In doing so, we are able to maintain a fairly tight leech profile in 8-10 knots of breeze and correspondingly we are able to trim the jib tight as well. Notice the foot of the jib inside the rail, yet there is no backwind in the main.
Additionally, by keeping the leech of the main tighter, we keep the headstay tighter. This is important as easing the mainsheet too much and allowing the headstay to sag puts more power into the jib at precisely the wrong time. There were two really big takeaways from this technique. The first was that the boat had a tendency to sail a higher course to the wind than could be achieved with only vang sheeting. The other was that the boat was more balanced and thus steered more easily than with the greater mainsheet adjustments required with a strictly vang-sheeting technique. That is not to say that we were not using the vang. It was important to play the vang very dynamically with the velocity changes. However, the addition of the positioning of the traveler let us fine tune the angle of attack we could sail to the wind while remaining balanced and therefore making the boat even easier to steer. In the photo at right, notice that there is no vang (the boom is not bent), yet we are getting good lower mast bend as indicated by the overbend wrinkles up the luff to the window.
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