On Friday we were privileged to have an informal seminar at the park pavilion given by Jim Alsop of North Sails, a former crew member in America’s Cup competition, and now working for a company noted in constructing sails for competition yachts, including ones participating in America’s cup challenges.
The
first part of the discussion dealt with sail design, and North Sail’s
computer-augmented design program, which creates a sail designed with
the optimum curvature, and then breaks the shape down into the properly
shaped panels which then can be cut and sewn from the material of choice
to create the optimum sail.
He pointed out that while a sail cut from flat-panel material will perform as a sail, and that the natural stretching of the material will form somewhat of an aerodynamic shape, the sail created from shaped panels will form a more optimum wing shape, enhancing performance across and upwind, and also giving a better wind-catching effect when running downwind. The proper-shaped jib not only has the same effects, but also will accelerate air over the mainsail, increasing its efficiency as well.
There was also discussion on the various sail materials, weight of material, and their properties, including Kevlar, Mylar, and of course, the good ol’ blue (white, green) tarp.
He pointed out that while Kevlar is initially the strongest, it weakens considerably under repeated bending and folding, which Mylar tolerates better. The advantage of the tarp is that it is good for a non-paneled sail, and inexpensive. The chief criterion in material selection is intended use. If you have the dollars, and are into competitive racing where you plan on using the sail once and throwing it away, go Kevlar. If you want a sail that will last a few seasons, go with Mylar. If you are broke, and still want to go sailing (like me), go with the tarp.
A discussion of various sailing and rigging points followed. Several of the topics involved those that have appeared in the forums at various times. (I should add here that we also were doubly lucky to have Peter and Mike Stevenson with us during all of the discussions.)
Boom vangs: Yes, the boats will sail well without them; however, a boom vang will hold the boom down, and keep the gaff from twisting as much, allowing for closer sailing into the wind.
Lashed vs loose footing. Loose-footed sails will work well, and allow for sail shaping, and work well on small boats. However, loose footing puts a strain on the ends of the boom, which in boats with long booms will cause them to bend, and even break under severe loads. Lashing distributes the load along the whole boom.
Important Tips
When we got into talking about actual sailing, several useful tips were given to us to optimize our performance—
- When sailing up-wind, the gaff halyards should be tight. When sailing down-wind, loosing the gaff halyard will allow the sail to billow and hold more air.
- It was also recommended that a streamer be attached toeither side of the sail about ¼ way up and 6 to 9 inches in back of the luff. When sailing up-wind, the lee streamer should be floating back along the sail, indicating good airflow. It was pointed out that on the racing yachts there is a clear window in the sail in the area of the “Cunningham”, so it can be easily seen be the helmsman and crew, who would be on the windward side of the boat.
- Additionally, a telltale should be similarly attached to the jibe. When both of the streamers are flowing straight back along the jib, it is properly trimmed.
- The simplest way to get the sail in trim is still to let out until the leech is starting to flutter (luff), and then bring it in until the luffing stops.
The Sail and Its Parts
The primary guideline to a properly trimmed sail?
“If it looks good, it probably is.”
And if the boat feels sluggish,
tighten the peak halyard.
Would the discussion end any debates permanently? “If you really know all the right answers, you’re the next America’s Cup winner."
Yes, Jim had a full set of Mylar sails with him they had made for a relative of his for our examination. Anyone else wanting to see that set, stop by Commodore Widmier’s house — they’re on his boat.
Back Yard Yacht Builders
A non-commercial association of amateur boat-builder enthusiasts.
All our wooden boats are Stevenson designs.