flat vs convex surfaces

Bringing this all together in a highly speculative, naive first recipe for the main hull of a proa:

• characteristics inherited from the TH
  • triangle planform 4 to 1
  • relatively deep forefoot
  • bottom sloping up while widening towards the stern
  • low freeboard at the bow with seriously oblique top surface to shed waves washing over the top
• halve the TH double wedge in the middle changing the base plate planform from an isosceles to a right angle triangle
  • the oncoming waves are not split in two but only to one side. that wave can "tuck" under the bottom at that side as easily as in the original symmetric case
  • as there are two hulls, the asymmetry of wave load splits can be picked up by the other hull (conditions apply)
  • the flat vertical lee side extends below the bottom plate horizontally
    • preserve the bottom volume for the wave tuck from windward
    • prevent some leeway as a very low AR minikeel
    • protects the bottom like a shallow ridge that could be especially strengthened
• combine two wedges back to back to produce a bidirectional hull 8 to 1
  • Per TH, the wake from the front going bow will be calmed in the center (the original stern)
  • that flow should not produce much wake around the aft bow flowing off the aft bow in reverse
  • could the inevitable friction from the aft going bow produce better tracking?

This seems to be quite doable. Any glaring issues other than esthetics ;-)

 

I look forward to reading about your prototype

 

I don't believe the claim, but it is a good sales pitch.

 

within the conditions of the tests

 

What do you predict to read?

 

Where is the data from? Usualy it should give a reference to testing protocols, where and when it was done, etc. Also, the vertical axis has no units of measurement, which detracts from its usefulness. I still doubt that the slamming acceleration decreases that much, unless maybe the boat was badly trimmed at low speeds.

 

Slow, wet, uncomfortable.

 

The paper is 29 pages describing theory, layouts, comparison with and summary results of multiple tests using multiple models conducted by the Oceanic Consulting Corporation in the 200 meter tow tank of the Canadian government in calm water and with irregular waves, including pressure measurements. Also a 20 foot manned model was used in seaway. Lots of video material should be available. The only references are:
Calderon, Alberto A., and Hedd, Lee. “Theoretical and
Experimental Investigation on Resistance of Transonic Hulls.”
RINA, High Speed Marine Vessels Symposium (HSMV 2011)

Calderon, Alberto A., and Hedd, Lee. “Theoretical
Considerations and Experimental Investigation of Seakeeping
of Transonic Hulls.” International Conference on Fast Sea
Transportation, 2011.6

found in atlanticyachtandship "Prototype tests of the concept, named the transonic hull, were performed with a 20-foot fiberglass-and-wood model and showed 28-28 percent less drag than even America’s Cup yachts that are already significantly streamlined. "

Alberto Calderon, the Inventor had had a distinguished career in Aeronautical Engineering, being involved in the design of the F1-11B fighter, the Concorde ands with Airbus. He spent two years working as the Chief Designer for Dennis Connors in two successive America’s Cup Challenges. He was tasked with investigating how to mitigate shock loads from wave impact.

 

My previous thinking on negative rocker ended up as a triscarph, which did the job, but had poor weight carrying. Didn't matter because it foiled.
It might be time to revisit it. Easy enough to add triangular ends to one hull of the water taxi or the catamaran fishing canoe the students are currently building. Then tow test it and use the yaw to determine the relative drags. Won't happen before Xmas, but a fun project next year.
Luc, a facetted C50 windward hull which we drew as an exercise. Was more work to build than the channel mould so we didn't pursue it. It looks a lot more angular than it actually is.

 

Wet: I can see this as an issue with pacific proas but less so for harryproas where crew is more to windward.
Slow: the TH was meant to be more efficient compared to even VSV and axe bowed ships, thus, in the higher speed ranges in seaway and defying "hull speed". But it does not look good for ghosting in light air.
Uncomfortable: I would disagree with respect to motion: for the same length, less pitching in seaway; almost no roll because two hulls; less yaw with more "tracking" from the "aftfoot" (the forefoot of the aft bow in reverse flow); less sudden decelerations because more wave piercing.

 

You prove the lure of building with flat surfaces as it lowers construction (and experimentation) efforts. One would think twice about adding a specially curved surface to experiment with. In general.

There is nothing you have not tried yet. I find it hard to see how welding CNCed panels is more effort. I count 15 facets per hull halve.
Even easier is it with the right angled TH bow with only 6 facets per hull halve, using the external side flat on the floor and weld perpendicular bulkheads on that sideways floor plan, finishing off with two large oblique panel (side and bottom) and 3 smaller ones.

 

In summary, considering the application to 40+ foot two hull cruisers

• hydrodynamically, hulls composed of a couple of dozens of median sized facets compete closely enough with their curved surface equivalents
• special hull forms composed of a low number of larger sized facets
  • may even be more efficient within realistic sea operating conditions
  • have a high proportion of right angled straight edges/scantlings to support manufacturing techniques that put less load on skilled manual labor over the life time of the vessel (built, fit, refit, repairs, structural change, maintenance, ...)

Question is: As surfaces gain strength from being curved how much heavier is a flat surface hull built to an equivalent strength? For the higher speed "wave piercing" boats this may not make a large difference, but would it for cruising sailboats?

 

The design pressure varies depending on the bulge of the panel, but this variation is not linear but depends on several factors, which in turn depend on the dimensions of the panel. Therefore, it is difficult, if not impossible, to say how much stronger a curved panel is than a flat one.
Furthermore, if a curved panel is stronger than a flat one (and both comply with the regulatory values), the logical thing would be to reduce the properties of the curved panel so as not to put more material or more thickness than necessary. The panel will always be calculated so that its compliance factor (CF = design sigma/actual sigma supported by the panel) with the applied standard is as close to unity as possible.
In short, and as always happens, "it depends on many things"

 

Yes, it does depend on many things. But maybe NA educated guesses for ball park figures may be more doable in comparisons keeping as many as possible of the parameters the same like when comparing;

• The C50 hull originally curved vs the Denney faceted version vs my naive low facet number version: shallow and relatively uncomplicated curves vs dozens of facets vs half a dozen of facets
• the fast crew boat Sailfish vs transonic hull boat: more classic curves vs radical flat design
• Axe bow boat vs transonic hull boat: more subtle curves vs radical flat design

It still does depend, but on considerably fewer parameters?

 

As I told you in my previous email, my opinion is that your questions do not have a clear or definitive answer.