Back home in Munich, I read all the new responses and immersed myself in:
"This might amuse:
https://intcanoe.org.uk/wp-content/uploads/2019/10/Hullform-development.pdf"
Interesting stuff, really. Marchaj was a fan of this type of boat, and he was adept at explaining things using this type of boat or verifying their potential validity in practice. The above document complements his comments in his book very well.
However, beneath these investigations, despite the encouraging results, lies the question of the best hull shape for an easy-to-build hull: a flat-bottom boat that sails reasonably well. Bolger once condemned the Dory with its flat bottom hull (almost) without rocker as unsuitable for sailing and presented the Featherwind as the alternative he considered optimal at the time:
A slim, flat-bottomed boat with a lot of rocker and a 16-degree flare in the typical distribution for flat-bottomed boats - i.e., flat at the bow up to the middle and then volume towards the stern (with an upward curve) that lifts the transom above the water level even when heeled. If you wanted to achieve this differently, you would have to give the boat a lot of width in the middle (!), which can lift the stern without causing bad trim when heeled. I trust Bolger because the rocker he showed in variations can also be found on those old Sharpies that were proven to be fast and successful and capable of planing despite this distribution of the submerged volume.
The question for me now is whether this distribution of static supporting volume, the spatial distribution of the potential energy of such a boat when immersed in a medium, is a matter of chance or a deliberate intention shaped by experience. One argument for chance could be that such a boat shape results when you bend two almost right-angled planks and a trapezoidal frame, connecting them at the front to a bow and at the back to a transom. If you nail on a bottom, you get the typical shape of flat-bottom boats. The bow naturally ends up above the waterline, and the transom does as well. If you place the trapezoidal frame closer to the transom than to the bow, the larger volume at the stern results in a boat that trims well under a good load and hardly gets out of trim when heeled. All this can be achieved by the random placement of a fixed or temporary frame in traditional simple construction methods.
However, I doubt that the successful volume distributions in flat-bottom boats are the result of a recognized advantageous chance. This distribution has been retained, even though it could also have disadvantages, because it might create a "sucking stern" due to the curvature of the bottom. In aviation, such a profile of an airflowed surface would not be tolerated. It would lead to flow separation and additional drag. I now want to understand why this is not the case with successful flat-bottom boats, but with other simple dinghies, it results in a "boiling" stern water instead of the desired smooth wake.
Good, I posed this question at the beginning, so I should now explain why I am asking it. I believe that using lightweight Paulownia wood offers the opportunity to build a classic solid wood flat-bottom boat in a traditional manner—in the garage. I have already done this, constructing a 4.4-meter-long sailboat from 18 mm thick planks with a bottom width of 1.02 meters. This was done without stitch and glue, but rather through classic joinery and adhesive bonding. The finish requires no extensive treatment, as it is sufficient to wet, sand, impregnate, and oil the surfaces once, followed by two additional coats of oil. This process, excluding drying times, can be completed in a day using a roller. This method brings us back to flat-bottom boats as they were 200-100 years ago, but at a fraction of the weight. My prototype boat, made from 18 mm thick solid wood, weighs less than 50 kg.
For this boat, I chose the typical rocker profile of a flat-bottom boat, as described above, but with the ends slightly hollowed out. This results in a very small wetted surface area. However, for a new design, I do not want to rely on this being a good choice. Especially since I lack comparison opportunities, as there are almost no flat-bottom boats here (in Germany). The few that exist are 6 meters long and belong to a very old class derived from fishing boats—Plätten or Flatties. Therefore, it would be nice to know exactly what makes a flat-bottom boat perform well and why that is the case. Hence my question, and I apologize for the repetition.
