The "LIFE DORY" concept

The traditional Grand Banks Dory, as described by John Gardner in The Dory Book evolved over many years into a seaworthy vessel with the ability to carry a huge weight of Cod fish. Generations of fishermen trusted their lives to these boats, and they were rowed and sailed over many miles of the north Atlantic ocean, under all weather conditions. The US Coast Guard uses the seaworthy Dory design as a rough water rescue boat, and many state beaches use the Dory for surf rescue. An added benefit is that the Dory has only 3 main parts, two sides and a bottom, making it very easy to build. If we substitute food, water, and emergency gear for the Cod fish, we have the beginnings of a low cost, effective, self rescue system, or Life Dory.

 

 

The basic Grand Banks Dory has quite a strong shear line, lots of flare, and a sharp entry. The bottom is flat, with a little rocker, ending at a very narrow transom. The beam to length ratio can be as low as two. The beam to bottom width ratio is .514 for the classic rescue dory, and a typical flare angle is around 50 degrees. The boat is initially tender, due to the narrow flat bottom, but it quickly picks ups stiffness as the flared sides submerge. The sharp high ends and flare blunt the effects of large breaking waves, and allow the boat to ride comfortably in heavy seas or on a sea anchor. Keels or skegs are not used, under the theory that the boat should slide along waves with little resistance. They row well, and can easily be fitted with a sail rig. The addition of a fore deck provides dry storage, and the sole can double as sleeping space. This unique combination of seaworthiness, stability, and payload make the Grand Banks style Dory an ideal choice for a dual purpose dinghy and self rescue life boat.

Front View

The design of the Life Dory quickly focused on the conflict between length and weight Vs storage requirements and crew strength. One person should be able to launch every part of the system, quickly, without aid. This limits the weight of any single item to less than 80 pounds. On a large boat, davits can allow one person to launch a fairly large and heavy Dory. Smaller boats will launch their dinghy from the fore deck. It is possible, using light weight core materials and advanced fibers like Kevlar and Carbon, to build a 10 foot long Dory, and still be within the 80 pound limit. If a larger Dory is needed, a two piece, nesting design is an option. Nesting has the advantage of reducing the weight of the individual parts and cutting the deck space required in half. The Dory is ideal for nesting due to its symmetrical lines waterlines and flare.

Side View

The final Life Dory design consists of a family of boats, all sharing a common mid ship section, draft, and freeboard. The selected mid ship section has a wide 64 inch beam, a bottom width of 35 inches, a minimum freeboard of 12 inches, and a full load draft of 7 inches. The length of the Life Dory can be 10, 12, or 14 feet, depending on the owners particular needs. The 10 foot design displaces 600 pounds and can carry 3 people. The 12 foot model is 713 pounds and 4 people, and the big 14 footer displaces 856 pounds and will carry 5 people. All of the boats can be built to split in the middle for storage efficient nesting. With six combinations to choose from, the builder has a good chance for finding a Life Dory that meets their particular requirements.

Top View Showing Wide Side Decks and Fore Deck (used for storage)

Boat weight is critical if you require one person to lift and launch the boat over the lifelines. This means that the one piece dory, and each part of the nesting dory, must weigh less than 80 pounds. These weights can not be achieved with normal plywood and fiberglass construction. The Life Dory’s are constructed out of light weight composite materials (carbon and Kevlar), over a ¾" thick balsa wood or PVC foam core. No solid wood is used, except for a pair of handholds on the bottom. This reduces the weight of the boat to around 40% of the plywood design, or less than 70 pounds.

So what do we do with this "Life Dory" when were not out "self rescuing" ourselves? Easy question, we just remove the emergency gear, call her just plain old "Dory", and enjoy a nice, large, light weight dingy that looks sharp, rows well, and can be sailed or powered. Something for everyone!

 

Additional Options

Nesting Feature: The nested design uses 4 captured ½" screws and two alignment features to join the hulls. The alignment features let you hold the two halves in place with lines, while the bolts are tightened. Large storage areas can be incorporated into the forward hull, as well as a centerboard trunk. The aft hull must be relatively open to receive the forward hull when nested, which limits the storage options.

Self Bailing Cockpit: Raising the sole 7" makes the cockpit self bailing and creates a large storage volume suitable for water ballast. This is also a good feature for catching rain water, since the cockpit will rinse itself until you plug the drains. The raised sole is not practical in the nested version since it increases stack height by 9".

Outboard Power: Dories are not planning hulls and get along fine with motors under 5 HP. The transom can be slotted for a steering oar, and a bracket fitted with tracks for a removable outboard mount.

Climbing aboard or righting a dory is easier if rope hand holds are laced around the gunwales. Wooden hand holds, about 6 feet long can also be installed in the bottom panel, near the chine.

Because the Dory has so much flare, wide side decks, or gunwales, can be boxed in to provide a large amount of storage. The upper 4 inches of this volume should be foamed in order to have good floatation even if the storage compartment access hatch is left open (Murphy again). The nesting version can only box in the forward half, but this is still a considerable volume.

A 2" coaming can be fitted to the inside edge of the side decks. This will add another few degrees of heel before flooding starts. Most effective on the one piece design, but helps the nested version also.

A clear plastic port in the bottom is useful for checking your anchor’s set or looking for fish.

Heavy "U" bolts should be fitted to the bow and stern for towing or lifting. They are also good points for the crew to clip onto during rough weather.

A wide variety of side decks, fore decks, seats, rowing positions, and storage options are possible. You can keep it simple and just tie loose gear to the gunwales, or you can fabricate storage fancy compartments with watertight access ports. Your choice.

At the expense of an ounce or two, consider building the fore deck out of wood strips. If you want to really get fancy, join them into a notched "king plank". Its worth the extra time.

 

Building Details

The Life Dory is designed without compound curves. Assembly is a modified stitch and tape technique. The following discussion details the low weight version. If weight is not critical, the foam core may be replaced with plywood and the high tech reinforcements replaced with fiber glass. The first step is to glue together 4 x 8 panels of 1/2" Klegecell core material, per the plans, using hot melt adhesive. The foam is then cut to shape and the inside surface covered with one layer of 1.8 oz. Kevlar cloth ("K", 1/3 the weight of glass for same tensile strength) and one layer of 5.6 oz Carbon fiber cloth ("C", twice the stiffness of Kevlar). The laminate lay up can be abreviated with "KC", meaning that Kevlar is the first layer, followed by a layer of Carbon. The center bulkheads for the nesting versions are cut out of two layers of Klegecell, bonded together, and glassed with a CKC lay up, both sides.

The sides are bent around the center bulkhead until they touch at the transom and stem, then glued in place. The bottom is then fitted and glued in place. The boat is next turned right-side up and all inside seams finished with epoxy fillets and two layers of 4" wide bi-axial tape. The boat can now be turned upside down, the chine rounded and the outside surface covered with a CK lay up. These materials are difficult to lay up by hand, and are normally vacuum bagged. Since the dory shape is so simple, a piece of a plastic tarp can be substituted for the vacuum bag.

Do one panel at a time. Cut a piece of plastic tarp (like a cheap painters drop cloth) big enough to cover the surface being covered plus 12" of overhang. Set it aside, mix up a batch of epoxy, and quickly roll it on the panel. Spread the Carbon over the panel and roll it with resin. Repeat for the Kevlar. The edges of the cloth should extend an inch or two past the chines. When the surface looks uniformly "wetted out", place the plastic over the panel, and stretch it in place with tape. Pull hard, stretch the plastic, and tape it down. Then take a squeegee and work the excess resin to an edge where it can be wiped up. Practice on some scrap first, and avoid removing to much resin. When all panels are covered, the joints are smoothed and covered with a CG lay up of bi-axial tape.

All storage compartments are formed with ¼" Klegecell, covered with one layer of Kevlar, both sides. Do a complete 4x8 sheet all at once, and cut out panels as needed. Sharp saw blades are need to cut Kevlar, it is extremely tough. Hold the panels together with hot melt adhesive and glass in place with one layer of 2" wide bi axial cloth. Reinforce all hull joints with 3" bi axial Carbon covered with 4" bi axial Glass. Form "breast hooks and knees with 6 layers of 4" wide bi axial GCGCGC lay up. Reinforce the center bulkheads at the gunnels with 6 layer knees, extending 6" past the joint.