Naca Airfoils shape and rocker oft flat bottomed boats

What boats start with a flat rocker at the bow and upward bend at the stern? The Opti is the only I know, and it is a special case because it's a boat for kids.

It is almost universal to have more rocker at the bow, the deepest point a bit forward of mid-length, and a flatter run to the stern. This is more easily seen in older boats (below) because of their extra weight and therefore depth. Note also that the buttock and futtock lines are also critical and generally the futtocks (longitudinal sections at the bow) generally have even more rocker than the buttocks (longitudinal sections in the after half of the hull).

 

"which is expected to be disadvantageous."

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Yes

To (1) reach a high speed (2) on flat terrain with (3) sailboats that hoist an astronomical amount of sail in relation to the displacement e.g. 30-40 square meters per ton.

But

To sail with Waves in relatively slow sailboats with 10-15 square meters of sail per Ton ...

you have to design the hull profile just the opposite of a dinghy designed for planing

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Trapped in a loop

Groundhog Day (film) - Wikipedia https://en.m.wikipedia.org/wiki/Groundhog_Day_(film)

 

R-class destroyer (1916) - Wikipedia https://en.m.wikipedia.org/wiki/R-class_destroyer_(1916)

The four Beasts

The four Beasts that destroyed small sailboat navigation:

1) the impressive Royal Navy destroyers that everyone wanted to imitate

2) the hydrodynamic research in Tanks without waves with the water as an oil lake

3) the light sailing boat Dinghy for planing

4) the summer Regattas of the 70s and 80s of the last century.

 

[1] Planing Dinghy that hoist (Jib+Main) 30-40 (!) (OMFG) squared meter per Ton ... and maybe even 60-80 with Spi

[2] Sailboat that hoist 10-15 squared meter per Ton ....And that it is designed to navigate in the Sea, a place where I assure you that there are Waves, although I know that nobody believes it.

H: HydroDynamic High
L: HydroDynamic Low

 

Let's imagine our worst enemy designing a sailboat, what would the worst possible sailboat for sailing on the ocean look like

The worst possible sailboat (a relatively slow sailboat that hoists 10-15 square meters per ton) ... would have ...



(1) A very deep bow and on top of it very sharp like the bow of a Destroyer, and so the bow will produce a lot of lateral force and no vertical force at all, just the opposite for comfortable and safe navigation.

(2) A flat stern like an old Destroyer, a planing Motor boat or a planing Dinghy

(3) Longitudinal position of Center of Buoyancy (LCB) ahead of Longitudinal position of Center of Flotation (LCF)

(4) And the icing on the cake: the HydroDynamic center of a huge daggerboard/Keel at the bow.

 

And

(5) An enormously wide stern

1+2+3+4+5

 

and between 300 thousand and 600 thousand Dollars-Euros, and does not include the lady in bikini that appears in the catalog.

The owner also gets tired of being the driver, "chofer", who takes the insufferable brother-in-law or the insufferable sister-in-law out for a walk and the brand new boat remains moored in port.

 

Sorry, The correct word was ...

"Chauffeur"

Chauffeur - Wikipedia https://en.m.wikipedia.org/wiki/Chauffeur

 

Apologies in advance for this diversion, but you have NACA in the thread title and that's where I'm coming from. I am trying to use the Airfoil Tools to work with the example of a light aircraft wing, like on a Cessna 172, to see the Cl/Cd ratio, by plugging in the appropriate Reynolds number, of around 5,300,000 which I get from the calculator:

But it only appears to allow for the entry of R up to 5,000,000:
And even with the 5,000,000 value it fails to retrieve the polars.
I wonder if anyone has a suggestion.

 

This might amuse:

https://intcanoe.org.uk/wp-content/uploads/2019/10/Hullform-development.pdf

 

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.

 

Here are 3 examples of the distribution of rocker of classic flat bottomed boats. Source: American small sailing craft. Garvey, sharpie skiff, New Haven Sharpie

 

View attachment 196027 View attachment 196028 View attachment 196029 [/QUOTE]

here’s a pre war German developmental sailboat, which supports your view?

 

"The boat you showed is a one-design class with a sail area of 10 square meters. It was chosen after a 'wild' period of designs with the same sail area in order to identify the best sailors. Today, there are still 40 boats in existence, with 20 available for possible restoration. The boats are very light for wooden construction, at 6.5 meters in length and 230 kg. However, they are round bilge boats with the maximum displacement exactly in the middle."

 

Thanks- I’ve wondered for a long time about the J B line drawings I posted, no body view.