Transonic hull

Anything to do with hull shapes in general (i.e. not specific designs)
Robert Biegler
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Transonic hull

Postby Robert Biegler » Wed Jan 25, 2017 8:54 pm

At http://www.din.unina.it/HSMV%202011%20Proceedings/html/Papers/28.pdf there is a description of a hull shape intended not to make waves. One of the postulates which led to the development of the described hull shape, a tetrahedron with rounded edges is:
If such new shape avoids curvature in its waterplane, then there should be no "hull speed" phenomena and therefore minimal wave-making resistance?


Calderon offers no justification for the hypothesis that curvature on the waterplane generates waves. Looking at the shape, I speculate that if the slope of the hull bottom is the same as the angle of the hull side to the longitudinal axis, then the hull sucks as much water under the bottom as is displaced sideways, and that is what leads to the reduction in wave-making, not the straight sides of the waterplane.

Does anyone have an opinion?
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fishwics
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Re: Transonic hull

Postby fishwics » Thu Jan 26, 2017 9:04 pm

Caveat - I've never seen one of these hulls in action ...

BUT

I have doubts that any single hull will operate without making waves*. I suspect that if you work out the curve of cross-sectional areas, and built another hull with the same curve it would have the same wave making characteristics -- or to put it another way - my private theory is that wave-making is a function of that curve, rather like transonic drag is for aircraft.

In aircraft, studies of transonic drag led to "coke-bottle" fuselage shapes, where the "waisted" shape was introduced to compensate for the cross-sectional area of the wings. Swept wings achieve the same thing. I know there are swept keels in boats - do we know if anyone has tried reducing hull cross-section in the way of the keel to compensate for the keel cross-section?

Simon

* I write "single hull" quite deliberately, as if you have two or more hulls you can arrange them so the waves from one are reduced by the waves from others at certain speeds. There is a mathematical curiosity called "Krein's Caravan" which postulates an infinite series of hulls in line astern, where the waves from one hull cancel out most of the waves from the hull in front, the residual error being corrected by the hulls behind. People who have played with Leo Lazauskas' program "Michlet" (a wave-making drag predictor based on Mitchell's equations) may have met it.
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Robert Biegler
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Re: Transonic hull

Postby Robert Biegler » Sat Jan 28, 2017 6:05 pm

Caveat - I've never seen one of these hulls in action ...

The pictures in the paper are reasonably consistent with the claim, but video would be nice.

I suspect that if you work out the curve of cross-sectional areas, and built another hull with the same curve it would have the same wave making characteristics

Assuming the draft at the bow is half the width at the stern (which is what the picture of the allegedly theoretically optimal hole in the water looks like) circumference is constant, and draft decreases as beam increases. The curve of areas is then a parabola because the area of each cross section is draft * beam and draft + beam = constant. Set the constant to 1, and the cross sectional area becomes b*(1-b), with b proportional to the position of each station.

I also realised that my speculation is nonsense. Right at the bow, all the water that is moved goes sideways, and possibly up. When beam approaches 0, the total amount of water being sucked under the hull must also approach 0.

Instead, I suppose what the shape does is that it always sucks a constant amount of water across the chine and under the hull bottom. Why that might reduce surface waves I don't know.

I write "single hull" quite deliberately, as if you have two or more hulls you can arrange them so the waves from one are reduced by the waves from others at certain speeds.

Can, to some extent and for a limited range of speed, also be done with a single hull: http://www.duckworksmagazine.com/04/s/excerpts/yachtreport/01/index.cfm I have been wondering what would happen to drag when the boat heels. Or if you took the lines, and rotated the hull bottoms up by 15 degrees, would it then work well at that angle of heel?

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fishwics
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Re: Transonic hull

Postby fishwics » Sat Jan 28, 2017 6:59 pm

Can, to some extent and for a limited range of speed, also be done with a single hull: http://www.duckworksmagazine.com/04/s/e ... /index.cfm


See also Catalyst No 11 page 9 http://www.ayrs.org/catalyst/Catalyst_N11_Jan_2003.pdf#page=9 et seq

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Re: Transonic hull

Postby mikehoward » Sat Mar 04, 2017 5:14 pm

I am assuming that these comments have been generated by my reference to Transonic Hulls in the report of the December meeting of the North West Local Group, which appeared in the latest edition of CATALYST. There are two members of our Group, one being myself, who have stumbled upon this design. I intend to make a simple large model from a single sheet of CORREX, my favourite material at present, and tow it along my local canal. We shall see if it makes waves!

Ship owners are a very conservative bunch. I know from experience. In 1980 I was part of a consortium trying to promote the use of SWATH hulls for offshore service craft ranging from crew boats to diving and submersible support vessels. We got nowhere. It took another 25 years before the first commercial SWATH ship appeared in the North Sea in the form of a German Pilot Boat. So, I don't expect Mr Calderon will get very far with his radical idea.

Mike Howard

Robert Biegler
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Re: Transonic hull

Postby Robert Biegler » Thu Mar 09, 2017 7:42 pm

I first came across the transonic hull on the proa forum, where someone suggested that two of them joined end-to-end might make a good proa hull. I found that so counterintuitive that I looked it up, and a few days later found your report in the latest Catalyst.

And today, I came across a crowdfunding project for a folding kayak made out of something like Correx, with a hull shaped somewhat like a transonic hull, though without the sharp chines: https://www.hyparkayak.com/ and http://newatlas.com/hypar-folding-kayak/48319/.

mikehoward
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Re: Transonic hull

Postby mikehoward » Sun Mar 19, 2017 1:06 pm

I looked up all the references to Transonic Hulls, including the ones you mentioned, Robert. It seems like Industry has beaten the amateurs of the AYRS to it in terms of coming up with a Correx Transonic Hull! However, I shall continue to invest a small amount of my time, energy and money in experimentation. Who knows where it might lead!


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