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
Recent Comments
A fun evening sharing a table with Eric, Mary, Chris, Maggie, Francis, Lisa, Bill & Cindy. Mary was recognized with a US Sailing award as a JYC member for her communications role on J/122 Alliance in the Bermuda Race. Maggie accepted the J/122 Leading Edge third place fall series award for Tom and Diana. The picture below shows Bill & Cindy with the 1st place spring series award for J/109 Vento Solare.
In the end it turned out that the Ida Lewis YC awarded the youth trophy to Vento Solare. Pictures from the award ceremony and the trophies are below.
Boat Trophy and Youth Keeper Trophy for Austin, Rory & Henry
Youth Trophy Presentation
Rory & Austin Receiving Keeper Trophies (Missing Henry)
Henry with Keeper Trophy at Home
Bill
Thank you for a great time. That hour penelty seems steep. If you look at yellow brick there were a few other boats in our class that were just inside that south east dot. Not sure how picky they were being.
Either way great work by everyone. Enjoy the party.
Bill went to the protest hearing about our sailing in the exclusion zone to fix the spinnaker. The results of the protest was the RC added 1 hour to our corrected time. This put us in 2nd place for the youth entries. We would have had 1st in youth if not for this. Hope to see you all at the awards ceremony!
Updated boat call time is 10am this morning. Those needing ride on base meet 0945 pass & ID parking lot.