Lug Sails – Four-sided sails derived from the ancient square riggers
Lug sails are four-sided sails derived from the ancient square riggers. These sails are characterized by a yard at the head that is loosely attached to the mast and has a leading end that extends forward beyond the mast. Depending upon how this sail is rigged and handled, the sail can be a balanced lug, a standing lug, or a dipping lug. The balanced lug has a boom which continues forward of the mast to hold the luff of the sail. The yard supports the upper end of the sail luff and is about the same distance forward of the mast as the boom. The standing lug has the tack attached close to the mast and the luff continues at an angle upward to the yard which has its leading end forward of the mast. The dipping lug eliminates the “bad tack” of the other two lug sails by dipping the yard around the mast each time the boat tacks so that the sail does not come into contact with the mast.
The most popular form of lug sail used for small boats is the powerful and usually docile balanced lug. The balanced lug has a section of the sail that is carried forward and to one side of the mast with its throat attached to the forward part of the yard, the tack attached to the forward part of the boom, and the luff stretched taut between the two spars. Luff tension is extremely important to the performance of lug sails and is usually achieved by a combination of a downhaul on the forward part of the boom and a very strong halyard attached to and lifting the forward part of the yard. Where these lines are attached, as well as how the spars are attached to the mast also plays an important part in the performance of a lug sail. For an extensive discussion of these rigging options, I recommend Chapter 6 of David Nichols’ book The Working Guide to Traditional Small-Boat Sails.
Small boat designers seem to have very different attitudes toward the use of balanced lug sails on small, home-built boats. Phil Bolger, in his 103 Sailing Rigs seems to focus on the lug’s disadvantages—a heavy mast and substantial spars, a clew that doesn’t lift in a gust and can sometimes “trip” in the water when the sheet is let out, a yard tip that can behave erratically when the halyard is released and could be dangerous to both boat and crew if not quickly controlled. (Bolger is much more complimentary about the standing lug.) Jim Michalak, on the other hand, finds the low profile of the balanced lug and the more central location of the mast to be features he likes about the rig, so many of his sailboat designs use a short luff version of this rig. Michael Storer is another strong supporter of this rig, especially for his PDRacers. The consensus seems to be that the balanced lug is a great sail if rigged right and a nightmare if it’s not. My recommendation is to buy Nichols’ book or to visit Michael Storer’s web site for a great tutorial on tuning up lugs at http://www.storerboatplans.com/Faq/tradrigperformance.html
Here is a visual guide showing how we construct a balanced rig PolySail.