A great tutorial on sail shape and trimming from Adam Walsh.
Quick note on the physics of sail shape. The power (pull) and direction of that power generated by the sail is correlated to the max depth of the sails cord length. Meaning drawing a straight line from tack to clew. At the point that has the max distance is known as max draft . Find that point and draw a line perpendicular to the sail That is going to be the most power generated and it’s direction. A full round sail will produce a large amount of power but the boat will have a wide angle of attack. A flat sail will generate a smaller amount of pull but will have a very narrow angle of attack. This is illustrated here.
Literal back of an envelope drawings.
Now with the asymmetrical kite. It is even more pronounced to rotate and move the max draft as far forward as possible. This will put the max effort of the sail closer into the direction of the boat. With an over trimmed kite, the pull is more sideways that induces healing and gives a feeling of power but it’s power in the wrong direction. So the key to the Asym is to constantly be easing the kite and working a robust curl at all times. With a grinder it’s vital to work the sail constantly. The draft of the sail moving forward even for a few seconds gets the pull in line with the direction of the boat This will increase speed dramatically. But you have to stay on top of the trimming and not let the curl break too much.
Bonus point. When you see a huge puff coming, if you can do a massive ease right when it hits it will move the draft way forward and the boat will leap forward. But the grinder Must be ready to quickly grind in the eased sheet and more. As the boat accelerates the apparent wind will move even further forward so the trim will be much greater after the initial ease That’s why it’s helpful to have the kite on a large drum winch in really breezy conditions
Additionally. In big breeze if you can cross sheet to the weather winch it moves weight of grinder to a more optimal place.
Drawings are crude and questions welcomed.
Adam
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A great weekend on Block Island with Kathy, Claire & Bill. Great race results and appetizer contest results. We were fortunate to have the blender and the heater on the boat. After a nice weekend on Block Island we had a fast ride back with everyone taking time on the helm.
A few pictures from our family sail on Grandpa's birthday weekend. Unfortunately hurricane Ophelia changed our plans for a weekend on Block Island. We did a Friday evening sail in Newport, grabbed a mooring for cocktails and dinner, then went back to our slip at the Navy marina. We stayed on the boat Friday night and went to the YMCA for Isla's soccer which was moved to the indoor gym.
Underway on Vento Solare with Grandpa, Kai, Daddy & Isla
Enjoying appetizers in Newport Harbor before sunset.
Family dinner on Vento Solare while on the mooring.
Kai's note to Grandpa for his birthday weekend.
A great weekend of racing with everybody with Vento Solare finishing 2nd place overall. Crew work was fantastic all three days. Starting from the bow with Roland, mast with Will, pit with Andrew, trimming with Sarah & Mary, and main / tactics with Trevor (Jeff Roy for Around the Island on Friday). We saw the full spectrum of wind from 5 to 22 kts over 3 days.
Congrats to Divided Sky who put up all first place finishes. The rest of the class including J/109 URSA, J/99 Upbeat, Sunfast 3300 Avalon and Express 37 COUCOU all provided the challenge as fierce competitors.
A quick note about the finish recorded as 20:45:56 on the JYC website for the Tuesday race on 8 August. Roland noticed that the recorded time did not correspond to the finish order where we were behind Samba and in front of Grimace. I corresponded with the race committee and the finish time recorded on their scoring sheet is 20:24:56. The finish time will be updated on the JYC website and the results updated. I will send the results when the update is made.