Modified 15 Square Meter Sailboat
|Displacement||1,238 kg||2,730 lb|
|Sail Area||16.05 m^2||173 ft^2|
|Ballast||432 kg||952 lb|
I started this design in the fall of 2009. I wanted to design an affordable pocket cruiser for myself along the lines of the 15 Square Meter class. The boat started out as a full keel design in accordance with the Square Meter Rule. It then morphed into a version having a fin keel and spade rudder with the plans published on this website. While on a backpacking trip in the Sierra Nevada's, I came to realize the design could be further simplified and still be a decent pocket cruiser. So in September 2010 I went about a complete refinement of the design, updating each drawing, adding some details, and getting rid of everything that I didn't need. The result is a nice looking little double ender with absolute minimal accommodations. Less is More.
A lot of engineering and naval architecture went into the design of the K-28. A complete weight estimate, structural calculations, and stability report were done as if this were a large yacht project. I wanted the boat to remain afloat after minor hull damage, so a damage stability analysis was done to verify single compartment subdivision. PDF files of the Weight Estimate, Scantling Calculations, and Stability Report can be downloaded at the Naval Architect's Notebook page. Also, there is now a link to free How-to-Build instructions, Mold Construction drawings, and CNC Pattern DXF files at the bottom of the Free K-28 Plans download page.
The K-28 is a modified 15 square meter Skerry Cruiser, which is the smallest of the Square Meter classes. Because this design has its rudder separate from the keel, it can not be classed under the Square Meter Rule. The hull form and sail plan dimensions are within the parameters of the rule, so the boat will have the general sailing characteristics of a true 15 square meter.
The whole idea behind the square meters is to get as much speed as possible for a given amount of sail area. A basic hydrodynamic principle is that a longer boat has less resistance than a shorter one at a given speed, all else being equal. The Square Meter Rule penalizes length with increased displacement, beam, and freeboard. However, the square meters are generally very long for the amount of sail area they carry.
In addition to the independent rudder, the K-28 differs from the Square Meter Rule requirements for 15 square meters with a self-bailing cockpit, slightly lighter mast, and lighter construction scantlings. This boat is intended to be sailed in the coastal waters of southern California which is why it is designed with a self bailing cockpit and lifelines. I kept the length at 8.5 meters (28 feet) so the boat could have 18" high lifeline stanchions and still meet ISAF Offshore Special Regulations. 28 feet is short for a 15 square meter, but considering the boat has less sail area than a Cal 20 and is equipped with minimal cruising accommodations, 28 feet is about right. To compensate for the extra weight of minimal cruising gear the K-28 has a few inches more beam and a bit less ballast than I would expect from a typical racing 15 square meter. Following the basic hull dimensions of the Square Meter Rule results in a very small boat for 28 feet, and I would say the K-28 qualifies as a minimalist pocket cruiser.