Joseph Serio of Brooklyn, New York, asks:
"What is the best way to check that the shrouds and stays are properly adjusted on my Irwin 40 Mk 11?"
Win Fowler replies:
Let's talk about a single-spreader rig. For more spreaders the principles are the same, but the process is a bit trickier. Before you start, make sure the spreader-tip heights bisect the angle of the shroud above and below it. Never let a spreader tip form an obtuse angle with the shroud, either above or below, because it's dangerous. Check the spreader angles from astern.
There are two parts to tuning: static and dynamic. A static tune is done at the dock or mooring and consists of centering the mast athwartships. First, take a centerline halyard and measure the distance to the same spot on each rail, then adjust the upper shrouds until the masthead is entered and the distances are equal. When that is done, use the lower shrouds to align the mast between masthead and deck. Once the mast is centered, tighten both sides evenly. Count the turns until you cannot tighten the shrouds any further by hand. Then take an additional full turn, using the appropriate tools, on both the uppers and lowers.
For a dynamic tune you need to go sailing. Sail upwind in enough wind to fully load your rig, i.e., enough wind to heel the boat about 20 degrees. Sight up the mast and note if it is bending to leeward or to weather. Also note the tension of the leeward shrouds; they should be just snug enough so that they do not move around, but not any tighter. If the mast is bending to leeward, the lower shroud is too tight relative to the upper. If it is bending to windward, the opposite is true. The tightness of the leeward shrouds will tell you whether the looser shroud needs tightening or the tighter shroud needs loosening. Tack and adjust the new leeward upper and lower shrouds in a similar fashion. Then sight along the mast again. Tack again and adjust the new leeward shrouds accordingly.
As you are making these adjustments, always take the same number of turns on each upper and lower shroud. This will ensure the mast remains centered athwartships. Continue tacking back and forth until the mast is straight up and down on each tack and the leeward shrouds are just snug. It may take a number of tacks to get things right.
The headstay and backstay tension should be tight enough so the headstay doesn't sag more than about 1 percent of its length, or about 6in in your case. That may or may not be possible without using so much stay tension that you bend the hull of your boat. Finally, be sure that if your mast has any fore and aft bend it is bending aft at the head, not forward. I think your boat also has a babystay - a short centerline inner forestay - that you can use to control fore and aft bend.
It may take a few hours to get the rig tuned properly, and you may have to give the rig a tweak or two during the sailing season. But taking the time to get things right will pay off in safety, boat performance and the satisfaction of a job well done.