In researching sail plans for my conversion of a 31 foot Searunner Trimaran into a motor sailer I discovered that Lug Sail Plans are few and far between on the Internet. I found a couple of plans for Lug sails of less than 10 square feet for Kayaks, but larger area lugsail plans simply have not been posted on the web.
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Ernest Walter Blockside authored "Ships' Boats: Their Qualities, Construction, Equipment, and Launching Appliances" in London in 1920. He describes the construction and outfitting of lifeboats. My googling lead me to this book, and I purchased a Nabu Public Domain Reprint. The information in the table is a compilation from 3 Tables and 8 Figures on 7 separate pages. I had to convert hundredweights and calculate a couple of dimensions that were missing from the figures. In doing so I discovered that the Working (Standing) Lug drawings in Figures 209 and 210 are transposed. In order to check the dimensions I used this Sail Area Calculator.
Lug sails are rare on multi hulls, but my goal is not speed. I want dispatch. I have planned on a cruising boat that makes 6 knots, with excellent fuel economy, for decades. Providence lead me to my 31 foot Searunner. With apologies to her designer the legendary Jim Brown, I am converting it to power. Jim told me there was not enough room in a 31 foot Searunner for a diesel inboard. He was right. My solution is to build a "box" keel in the last 10 feet of the boat to make room for an 18 HP Saab diesel with the Controllable Pitch Propeller. For safety it seems wise to keep an emergency sail rig on board. Most modern Lug sails are on small boats. Few working lugs are seen, and the fitting of a jib to a lug sail is rare indeed. In John Leather's Spritsails and Lugsails
we see that working lugs with a jib were a popular rig in the days of working sail.
I believe a jib headed working lug rig will function very well as emergency propulsion. It may even save a few gallons of diesel, or make an otherwise unsafe leg across the Pacific into an acceptable route. The price of "Ships' Boats" is trivial in comparison to paying a designer to come up with a sail plan. Reading this article and using the dimensions in the Table is an even better bargain. My budget for the sail and its rig is less than $250.00 out of a $15,000.00 budget for the entire boat. The book is for sale.