Monday, March 16, 2009
Restoring Thistle #16
The Thistle is a high performance racing dingy, popular in the US for more than sixty years. Fabricated of fiberglass today, the original Thistles were made of molded wood.
A historic Thistle has been in Doryman's shop for the last two years getting a fresh start. Hull #16 was one of the first molded plywood boats ever built, designed by Gordon Douglas in 1946.
The history of hull #16 has been lost, since she was never registered with the national Thistle Class Association as a racing vessel. She may have been one of many boats sold as kits and finished by the owner/skipper. These kits contained a finished hull and all components manufactured to stringent one-design specifications.
Thistle originator, Gordon K. "Sandy" Douglass was a racer, designer, and builder of Thistles who later designed the Highlander. Two of his designs, the Thistle and the Flying Scot, are among the most popular dinghy racing one-design classes in the US.
Their construction originally used heat processed molded plywood. Plywood was the first type of engineered wood to be invented and it's usefulness in building boats was readily apparent.
During the Second World War plywood became a major building material for aircraft. After the war, plywood was adapted for building sailing dinghies. A Thistle is made up of thin strips of wood veneer which are laid diagonally with the direction of each successive layer intersecting at 90 degrees. The Thistle hulls were laid up with five veneers and a total hull thickness of 5/16", at the US Plywood mill, on the same mold, then shipped to professional and amateur builders who completed the detailing of a strict "one design" class boat. The process was known as hot molding, since the hulls were heated in large ovens to set the glue. Modern glues have allowed this process to evolve into a cold molding method ideal for home building.
The Thistle sail plan is large for the boat’s weight, which makes Thistles perform well in light wind. Their hulls have wide flat aft sections, allowing them to plane in winds of 15 to 20 knots.
Gordon Douglas' mentor Uffa Fox introduced racing canoe hull shapes which would plane, and which therefore exceeded the displacement hull speeds for existing sailing canoes. The canoe yawl Beth, featured a few days ago is a modern adaptation of the early sailing canoes.
In effect, a boat which is planing is skimming along the surface, rising up on its own bow wave. This results in less friction due to reduced waterline length, reduced displacement, and reduced wetted area. The power produced by the sails has less resistance to overcome, and therefore speed increases dramatically.
Thistles are typically raced with a three person crew. A skipper at the helm, a middle who controls sheets and centerboard, and a forward person to jibe foresails. The optimal crew weight is 450 lb to 480 lb (US) depending on wind velocity. The crew ballast is not always the deciding factor in determining the outcome of races, however. In all but the strongest winds, an experienced two person crew can handle the boat.
LOA 17' 0"
Beam 6' 0"
Draft, board up: 6"
Draft, board down: 4’6"
Weight 515 lb
Sail Area (main and jib) 191 sq. ft.
Sail Area (spinnaker) 220 sq. ft.
Today was spent putting the finishing touches on new standing rigging wires for the original wood mast. With only the running rigging left to recreate, Doryman expects that the same exceptional sailing characteristics that made an award winning racer will also make a responsive daysailer and camp cruiser. It's been suggested that Hull #16 be named Sweet Sixteen, though she is sixty three this year. She's a spry 'ol gal, that's for sure! Who knows, maybe we'll take a turn around the markers after all!
Weasel the Shop Kitty, on the port rail of Sweet 16
June 10, 2009 Update:
I've been sent a link by a generous soul who has located a reference to hull #16 in Thistle documents from the 1940's. Here is a link to a PDF of Thistle history that identifies #16 as Bonny Boon.