Whaleback Design Considerations

Small Open-Water Sharpie Sailboat Design


Intended use.

The design concept is based on a desire to create a trailerable, shallow draft sailboat for use on the Great Lakes. The design is intended to be used to sail from harbor to harbor on the Lakes, rather than just daysail around a harbor entrance. This means that it has to be able to take the rough weather that can come up unexpectedly. The design must be capable of handling most conditions that a sailboat can face out on open water. The boat is a singlehander's boat; it is built for one, and although a second person could fit in the berth, there is limited room to move. The intent is that the boat be primarily sailed as a singlehander. The design is intended to allow for sailing long distances, and provide a small but adequate area to sleep inside the boat. Because a number of features of the Whaleback are experimental, no claims are made as to the suitability of the design for its intended purpose. The 2004 Whaleback concept boat will likely be built more lightly than the final version for Great Lakes use. Only after a series of sea trials near shore should this design be considered a vessel capable of open water.

Interior Cockpit.

The Great Lakes are cold for most of the year. The boat must provide shelter and insulation from the chill of the Lakes. Sitting outside in an open cockpit overnight is risking hypothermia, except for a few weeks of the year. The boat is intended to be a small boat, and the solution for this problem is to design the boat so that all lines, steering and ground tackle can be controlled from inside the boat or within reach when standing in a hatchway. The boat has a low profile to reduce windage and promote good close-hauled performance. There is sitting room only inside the cabin, the berth is too low (about 30 inches) to sit up in. There is no traditional cockpit in this design, the position of the pilot while sailing is sitting in the cabin. Standing on the deck in waves would be dangerous in this boat, so all tasks must be able to be performed inside the cabin. The cabin house itself is small, only about four feet in length fore and aft, and about four feet in width. The sides of the cabin extend out at a slight angle to make sitting comfortable. The hatch at the top of the cabin is hinged and folds open forward. The aft wall of the cabin includes a plexiglass washboard which is removable and allows a seated position on the deck with the legs in the cabin.

Full Flotation.

The boat's displacement is intended to be relatively light. This is to improve sailing performance, but also to make sure that the watertight compartments and foam wall linings will have enough flotation to keep the boat floating high on the water, even if filled with water. Fore and aft of the cabin area are watertight bulkheads with entry hatches, which lead to watertight compartments. Forward, the centerboard trunk splits the forward compartment into two separate side by side compartments, each with an access hatch. Aft, there is a compartment with an access hatch from within the cabin, as well as a deck hatch. These compartments can be made more secure during open water passages by loading an inflatable kayak or innertube into the compartment and then inflating it. The berth area is wide (about three feet wide) but does not have much height (about 30 inches). The sides and ceiling of the cabin and berth area are covered with construction foam (blue foam) to provide flotation and to protect the pilot in the case he is thrown against the side or ceiling.

Self-Righting.

The shape of the deck and cabin promotes self-righting. The deck is crowned, a curved plywood deck, with the high point running fore and aft, and the cabin doghouse is bulky to prevent the boat from finding a stable inverted position. The cabin house extends the full width of the deck. The hatches are designed to be weathertight, although probably not watertight, and they should prevent large amounts of water from entering the cabin area. A combination of secured interior ballast and the shape of the crowned deck provide enough instability in an inverted position to guarantee self-righting. This means that there is no heavy keel to provide righting momentum, or to pull the boat down into the water if flooded. These concepts are extremely important to the safety of the pilot: Light displacement with enough flotation to keep the boat riding high in the water, even if holed, and self-righting capabilities due to interior ballast and a deck and cabin shape that force the boat to right itself if overturned.

Shallow Draft.

The Whaleback will not have a centerboard or daggerboard. It will use the chine runner concept to reduce leeway while sailing upwind. Chine runners are wings that extend out from the bottom at the chine. Should these prove unsatisfactory, leeboards may be added.

Ease of Construction.

The purpose of this design is to provide a boat that can be built with a minimum expense and time invested, but still provide a high level of safety on open water. The construction method is plywood/epoxy/composite (also known as stitch and glue). Design features such as compartmentalized storage and watertight bulkheads are intended to be constructed in a simple manner which is still cost effective and most importantly, seaworthy.

Interior Ballast.

The interior ballast is provided by loading gear, provisions and water bottles in floor locker compartments. As an option, a deep discharge marine battery (sealed gel-cell or AGM) may provide ballast just forward of the lowest point of the vessel, to balance the weight of the pilot in the cabin. The boat does not have limber holes to provide drainage to the bilge; if water enters the boat, it will collect in the nearest compartment and must be bailed, sponged or pumped out from that compartment. Sandbags and gear are used to provide ballast, possibly also bottles and jugs of water are used as additional ballast.

Sail Rig.

The sail rig is a cat ketch, with an unstayed, battened lug rig with lazyjacks (junk rig). This rig allows full sail control and reefing by using lines led into the cabin. The gaff, boom and battens are constructed as lightly as possible. Ease of reefing and a wide range of reef points mean that the boat is not likely to be overcanvassed. The mast steps are located at the bulkheads in sealed boxes. All lines are led into the cabin area through a box intended to keep wind and water out, and all adjustments may be made from the interior cockpit.

Ventilation.

Drained ventilation boxes are built adjacent to the forward bulkhead. The shaft has a cowl, and an interior tube inside the ventilation box, made from PVC plumbing fittings. The tube leads down near the bottom of the box, and there is a drain from the ventilation box to the mast box. The vent box openings into the cabin and berth area are roughly halfway between the decktop and hull bottom so that even if inverted, the vents will not leak into the cabin.

Propulsion.

A sculling oar is provided for maneuvering in low winds and in tight quarters. An optional propulsion system while not under sail is by electric trolling motor, using deep discharge marine batteries charged by a solar panel. The solar panel is located on the deck forward of the cabin house. The electric drive is not intended to be used for long distances, only as a way to move the boat at most for two to four hours before requiring recharging over a period of several sunny days. The design is an open water sailing design where seamanship and use of weather are the principle ways of moving the boat. It is not intended for long periods of motoring.

Ground Tackle.

Emergency anchor gear should be secured so it can be released while standing in the cabin hatch, and laid so that it will lead out without fouling, until it grabs and holds the boat in the proper position. An emergency storm drouge should be prepared and in place for open water passages. Because the aft of the boat is more accessible to the pilot, much anchoring will be done over the stern.

Dimensions.

Approximate Dimensions in feet:

Beam: 4 Feet

Design rights.

I am designing this boat for my own personal use. I accept the risks for my own use only. You may use any or all of the concepts, design features, dimensions or construction methods to create your own design. Please understand that any use of this design is at your own responsibility. If you have been out on open water, you know that sailing away from shore can be a dangerous activity, and only you can determine the acceptable level of risk for yourself.

Drawings and Offsets.

See the main page for drawings and offsets.

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