Choosing a Sail Plan: Balanced Lug Yawl

After choosing a boat to build, I needed to decide on the sail plan.  The Welsford Pathfinder has at least three configurations available: Bermudian sloop, gaff yawl, and lug yawl.  I had considered the gaff yawl plan, and still think of it as the ideal plan for sailing given the flexibility of depowering the boat in heavy winds with either jib and mizzen or main alone.  But the idea of sitting at the boat ramp and setting up shrouds, forestay, and jib with roller furler and associated sheets every time I wanted to sail made me pause.  The lug yawl is a simple plan, unstayed, and the idea of a more relaxed plan without a tensioned, stayed mast was appealing.  Everything in sailing is a compromise, and most advise that the tradeoff here is in upwind performance.

Credit: Watertribe.com “DekesRaceReport”

I was sold after reading about the lug yawl Welsford Pathfinder “First Flight” completing the Everglades Challenge (http://watertribe.com/PDF/Florida2018/DekesRaceReport.pdf ) with decent upwind performance after tuning the main of the lug yawl.  CLC boats also describes advantages of a lug in small boats (https://www.clcboats.com/life-of-boats-blog/lug-nuts-lug-rigs.html  ).

I decided to build the lug yawl version of Pathfinder, and ordered the “Lug Yawl” plans as an add-on to the main plan set from Duckworks.  The Lug Yawl plans consist of  one page, specifying a 145 sq ft main and other details, but it was clear that something was amiss.  There is no mizzen drawn on the plan sheet.  It seemed very unusual for a designer to draw a plan sheet for a sail plan and not include one of the two sails.  Online searching confirmed others had altered the lug yawl plans after raising similar concerns, with the decision made to move the main mast location up to aft of bulkhead #1 (http://forum.woodenboat.com/showthread.php?188315-Pathfinder-Build-In-FL-Keys&p=5006887#post5006887 ).  “Gardens of Fenwick” is the other lug yawl Pathfinder I am aware of that has been completed (https://prep4texas.blogspot.com/2018/03/healing-thinking-and-projects.html#comment-form ), and he also placed his main mast just aft of B#1, specified in what I understand is a different set of lug yawl plans from what I have, drawn by JW specifying a smaller, 105 sq ft main.

Why does it matter where the main mast is placed?  Well, the center of effort describes the central point of force on the sails of a boat, and its location in relation to the center of lateral resistance (determined by the keel and hull size/location) affects the balance of the boat.  If the COE is too far forward of the CLR, there is a tendency to lee helm, and the opposite is true (weather helm) if COE is too far aft of CLR. Most sources suggest that it is ideal to have to COE just aft of the CLR to create a mild weather helm.  I found out as well that the COE tends to move aft as the boat is underway, so the calculated values often place COE farther forward to adjust for this.

Anyway, the COE on the “lug yawl” sail plan-- without any mizzen drawn in -- was exactly where it is located on both the gaff yawl plan and the sloop plan, which suggests that is the ideal place.  But I still wondered - is the COE on my plans accounting for the phantom mizzen, or is there a mistake in the plans and this is actually a lug (non-yawl) plan set?

I contacted a respected authority, who sent a short note recommending sticking with the plans, and using the mizzen location shown on the gaff yawl plan.  It still didn’t feel right, so I went about finding how to calculate a center of effort to double check the plans.  I found an old reddit post linking to a much older article in “The Rudder” circa 1902:

It describes the simple geometry needed to calculate a center of effort.  Scribbled arithmetic decorates the sides.  It’s a reminder that in 1902 you couldn’t simply pull up a calculator for solving math problems.  I found a certain satisfaction in plugging in numbers and getting the answer for the center of effort.  Once I got there, I was able to confirm my doubts.  The sail plan I received was for a balanced lug rig (ie., single lug sail without any mizzen), not a yawl.  That explains why there is no mizzen drawn on the “lug yawl” plan.  So the main mast will need to move forward to just behind B#1 to account for the mizzen and maintain a balanced helm.  The goal is to have the final COE -- including the mizzen -- in the same place as the other Pathfinder sail plans.  Placing the mast in this location is the same conclusion drawn by another builder who has completed his Pathfinder and has youtube videos showing a nicely balanced boat, so I feel comfortable with the decision.