THE MYTH OF BEAMY HULL​​

The Song dynasty wreck presented a significant challenge—her bow, deck, and portions of the transoms were missing. To reconstruct the hull lines, I had to make educated assumptions about the sheer line. The resulting design revealed an exceptionally beamy hull with a length-to-beam (LOA/BEAM) ratio of 2.85—a proportion rarely seen in modern vessels. However, historical records suggest that Admiral Zheng He's fleet featured even wider hulls, with ratios ranging from 2.45 to 2.66. This discrepancy forced me to confront a dilemma: should I adhere to archaeological evidence or conform to contemporary naval design norms?

Modern sailboats occasionally exhibit LOA/BEAM ratios below 3, but their widest sections typically lie toward the stern, lifting out of the water when heeling upwind. Experienced sailors recognize that asymmetric underwater hull of a heeling boat generates weather helm—a hydrodynamic force that increases with beam. A wider hull thus produces stronger weather helm, demanding more CE adjustments on the sail to maintain balance.

Ultimately, I chose to honor the archaeological findings, trusting in the ingenuity of ancient Chinese shipwrights. Historical literature suggests that fore-and-aft rig were developed by Chinese as early as the Han dynasty, allowed for center-of-effort (CE) adjustments to counteract weather helm. They should have solved the weather helm issues of the beamy hull,  I believe.

Sailing this medieval vessel for the first time felt like resurrecting a Jurassic Park dinosaur. The beamy hull proved remarkably stable and stiff, enhancing the junk sail's driving power—a phenomenon consistent with Annie Hill's observations that flat-bottomed hulls pair exceptionally well with junk rigs. As anticipated, weather helm emerged, but the single junk sail's extensive fore-and-aft travel—far exceeding that of Bermudan rigs—enabled good balancing by simply shifting the CE relative to the heeling angle. The same principle as surf board sailors maneuver their rudderless board. 

The experiment proved that the wine glass shaped beamy section in combination with junk rigs provide an exceptional synthesis of stability, power, and adaptability that conventional Bermudan rig keel boats typically fail to achieve.

The beamy hull's shallow draft grants access to shoal waters—allowing vessels to seek storm refuge in protected shallows, estuaries, and lagoons. This minimal draft also permits intentional beaching for emergency repairs using tidal ranges. Unlike protruding-keeled designs, a beamy hull with internal ballast sail faster off the wind with less drag. Windward performance is maintained through retractable daggerboards or centerboards—features now adopted by modern expeditionary cruisers for their versatility in coastal and bluewater sailing.

(To be continued ...)

Congratulations John! She's going really fast in that video! Please keep us up to date on the progress of the project.

Thank you all for your kind support and interest in this project. The full story behind the LeFang 23.8 one-design class racing junkboat is quite extensive, and I'll be publishing a detailed article in the JRA magazine for our members. For non-members who are curious about this unique vessel, allow me to share a brief introduction.

My journey with junkboat design began a decade ago when I observed several distinctive features of traditional junks being successfully incorporated into modern sailboat designs. These included the evolution from triangular sails to trapezoidal square-top sails, full batten sail configurations, the replacement of protruding keels with centerboards in adventure sailboats, and length-to-beam ratios decreasing below 3. Notably, experienced ocean voyagers were increasingly favoring junk-rig designs for short handed long-distance trips.

These observations inspired me to delve deeper into the ancient design principles of Chinese junks that once dominated the oceans for centuries in pre-colonial times. My research led me to a particularly fascinating subject - a Song dynasty wreck discovered in 1974 at Quanzhou (the ancient Zayton Port). Unlike modern fishing junks, this vessel featured a distinctive "wine-glass" hull section similar to Viking drakkar (they shouldn't have met). The archaeological discovery of frankincense in the wreck provided concrete evidence that this ship had completed the Maritime Silk Route journey from Arabia.

Using computer modeling to analyze the hull lines, I discovered that this ancient design offered superior stability and low resistance characteristics compared to modern fishing junks. To test these findings, I constructed a 10-meter FRP prototype in 2019 - the LeFang 33.8. As predicted, the vessel performed exceptionally well in most conditions, though we did encounter some challenges with tacking maneuvers. The stiff hull provided by the wide beam benefits to the stability and sail power.

(To be continued...)

Congratulations John, your boat carries all our hopes for the glory of the junk rigs !

Very nice indeed.
Could be developped into a small trailer sailer as well if one were so inclined.
I think.