Bio

Born Edinburgh, Scotland 1962. A decade as a computer network engineer preceded current happy days of long hours and short deadlines in CG animation. 

Designed purpose:

A yawl-trainer - Neither my fiancée or I has sailed a yawl rig. One of us has done almost no sailing at all. What was needed was a boat with high form stability to ease the new sailor’s nervousness about ‘tippy’ boats; one which would be burdensome enough to carry two full-sized folk in the initial stages of learning to take the helm. The prevailing wind at our local launching beach is onshore (when there is any, hence decent sail area). The water at the beach is thin enough to make a normal centreboard or leeboard awkward. Juggling sheet and tiller while raising and lowering the board, trying to claw away from the shore, avoiding the surprise sandbars, led to curiosity about the functionality of the long low-aspect keel. I’d trade some pointing ability to be able to sail off the beach.

• 70lb of additional buoyancy in removable multi-chambered bags.
• Flexible sail plan with split sheeting / gaff vang.
• Emergency oar auxiliary - boom and mizzen mast are same length, plywood blades attach with bolts & wingnuts used to store blades on for’ard face of bulkhead.
• Open inwales allow use of Shetland style thole pins, saving oarlock expenses.
• Dual purpose Sole / Rowing Thwart

Material Usage:

General note: Where the dimensions taken from drawings do not appear to agree with this cutting list, the list can be expected to be the more accurate. 

Plywood sheets, two, 8 foot by 4 foot, ¼” thick.

Hull bottom, sides, bow and stern transoms, rudder sides and bottom plate, keel sides and bulkhead gussets - see separate diagrams for suggested layout. Unallocated areas on ply layouts (aft of hull bottom, adjacent to transoms and between keel sides) will provide mast step plates and jaw reinforcement. Larger triangular areas either side of aft hull bottom are intended to provide material for rudimentary oar blades, shaped to taste.

Two 10 foot long 1x12 boards (calculated as ¾”x11 ½”)

First:

• Main mast, built up ‘birdsmouth’ fashion from 8 strips at 9/16 plus kerf 1/16 total 5 inches from 11 ½" leaves 6 ½" width, 10 feet.
• Two feet of that for partner (main), four feet for bulkhead leaves 4 feet of 6 ½"15/16 for mizzen spritboom leaves 4 feet of 5 ½" 
• which becomes forward half keel core (only 4 ½” width needed)

Second:

• Rip11/16” strip for gaff from 11 ½" leaves 10 ¾" width, 10 feet. (approx 2 feet surplus gaff stock used for sundry cleats).
• Rip11/16” strip for aft keel core top & bottom strips from 10 ¾" leaves 10" width, 10 feet. (approx 2 feet surplus keel core stock used for halyard fairleads and belays).
• Crosscut for 41 15/16”, 10” wide; forms sole/thwart, leaving 6’6”, 10” wide.
• 2” strip ripped from remaining 6’6” (leaving 7 15/16 wide) gives 56” of rudder core,18” of keel core uprights, and scant 6” for boomkin socket.
• 3 strips, 1 7/16“ wide for 16 floatation retaining battens, each 12” long (38” surplus, used for transom stiffener) 
• leaving 3 7/16 wide by 6’6” length used for; gaff, boom and batten jaws, 8” boomkin and 14” mizzen partners.

Two eight foot long 2x4s (calculated as 1 ½” x 3 ½”)

First:

• Gunwales from one 3/4 strip (ripped into two 23/32 by ¾) plus two 1/2 strips plus three kerfs total two inches, leaving 1 9/16”
• Inwales from one 3/4 strip (ripped into two 23/32 by ¾) plus a kerf, leaving ¾”
• Gaff (‘cross bar of T’) ½” leaving 3/16”

Second:

• Rip 7/16” strip for sail batten, leaving 3”
• Top& bottom spacers (82 at ¾” plus kerf, for inwale & flotation retaining cleat) and cleats (16 at 2 ¼” plus kerf), all from 13/16 strip, split into 2 of 23/32”, leaving 2 1/8” wide stock.
• Surplus spacer/cleat stock used for thwart end supports and sole spacing strip on aft face of bulkhead.
• 2 Foot long sternpost and 3’6” sole retaining cross strip on inside hull bottom from 1” strip ripped from remaining 2 1/8 wide stock, leaving 1 1/16” wide. 
• Surplus from sternpost strip makes up mast step spacers, kabes and plugs for hollow mast.
• Half inch strip ripped from remaining 1 1/16” forms optional keel base strip shown in aft section view. 
• Remaining half-inch strip may serve as a spare sail batten, to allow experiment in sail tuning. 

Poles, two, 1 ½” dia., ten feet long.

First:

• boom = 6'9; 3'3" for boomkin.

Second:

• Mizzen mast = 6'9"; remainder unallocated on drawings but could be split to form external transom stiffeners.

Polytarps, two, 8 foot by 10 foot.

• Sails and buoyancy bags - see separate diagrams for suggested layout. 

Notes: Sail expansions are drawn to give approx 10% draft at 25% aft, with the expectation that polytarp will tend to stretch, pulling draft aft. Mizzen is sleeved onto mast to save ties. Hemming has been allowed for but not drawn explicitly on tarp use diagrams. Larger unallocated areas are intended to provide corner reinforcing patches. 

Panel dimensions for sails: All in inches

Two 50 foot lengths of ¼” line.

First:

• Upper sheet span; 11 feet, leaving 39’.

• Upper sheet; 17 ½ feet, leaving 21’6”.

• Main sheet; 12 ½ feet, leaving 9’.

• Mizzen sheet; 9 feet.

Second:

• Peak halyard; 16 feet, leaving 34’.

• Throat halyard; 16 feet, leaving 18’.

• Mizzen Snotter; 2 feet, leaving 16’

• Main Clew lashing; 18 inches, leaving 14 ½’

• Main Peak lashing; 18 inches, leaving 13’

• Mizzen Peak attachment loop; 1 foot, leaving 12’

• Mizzen tack lashing; 18 inches, leaving 10 ½’ used for

• Sail lashings (four each at boom and gaff)

Cordage is calculated for 180 degrees of boom arc. Mainsail halyards (cleated or belayed at partner) are long enough to be reached from a seated position with the sail lowered. To remain within reach they should reeve through a screw eye on the mast, or similar. Where possible, ends are calculated as being seized/sewn eyes to economize on cord. 

Sundry Hardware.

Fasteners:

• Main hull construction in stitch and glue - 50 feet of 3 inch glass tape and resin to taste, including an optional taped fillet at keel / bottom joint not shown on sectional view.

• One pound SI bronze ringnails 1 ¼” (Clip points with pliers if a shorter fastener is needed).

• Using epoxy and a lot of temporary clamps few other fasteres will be required, although a handful of stainless #8 by 1 ½ could be useful for fixing the keel.

Other:

• Ringbolts on gaff at throat and boom at tack to allow attachment of sails with snapshackles.

• Screweyes for parrel on gaff jaws (could be lighter gauge than shown).

• Ringbolts or screweyes also used to turn main topsheet at mizzen top, for snotter, and to turn mizzen sheet at boomkin.

• Additional ringbolt for shackle at under face of batten jaw in lieu of reef lines.

• 16 feet of light shockcord to gather bunt.

• Stainless bolts and locknuts (2” and 4” long, ¼” dia.) for batten jaw attachment.

• 16 feet of ¾ inch nylon webbing and 4 harness rings (or D-rings) one inch diameter, for sail corner reinforcement.

• Four 2” bolts with wingnuts to attach emergency oar blades.

• Galvanized snaps or shackles for sail attachment.

• Ringbolts and brass rod used to form rudder ‘hinge’.

• One or two ‘white plastic’ kitchen chopping boards for keel shoe.

Illustrations:

click to enlarge

Arrangement	Ply Layout	Jaws
Rudder	Sailplan	Spars
	Tarp