Turner Theory

I do a Turner study for my new design but as is the first time that I do this I am a little confusing in take conclusions.

Can someone help me?

The figures annex are from an autolisp program that I do to run in Autocad. After I prove that it is running OK I will make available here.
If somebody has a table of offsets with a Turner's graphic already do and send me, I can test the program more quickly.

 

Never heard of a Turner study, can you provide some background information?

 

PM me with your email and I will send you a copy of my CSYS paper on the method.

Cheers,

Earl

 

I read about in Lester Gilbert site:

http://onemetre.net/Design/Balance/MetaCent.htm

Interesting is also Welch's Line that are lines that represents the distances from the CoG of inclined immersed areas to center line, transversally (plan) and vertically (profile).

The Venetian gondola applies this. To compensate the moment introduced by the oarsman that stay always in the same side, the gondola's frames are placed along the length in a curve, not in a straight line like the usuals boats. When floating this introduces a moment contrary to the moment introduced by the oarsman. If we push a gondola in water the trajectory is a curve.

In inclined sailboats, with the displacement of the CoG from center line, occur the same.

 

Hi Fredschmidt,
I'm enclosing some images I've scanned from a book on classical yachts by Carlo Sciarelli. A beautiful book, written with a very competent and occasionaly pungent style. Maybe there is a Portuguese edition too. If so, run to buy it - you won't regret it.

The first image shows lines of Harrison Butler's Zyklon yacht. At the bottom of the pic you can see the curve of metacentric moments for that boat.

The second image shows qualitative metacentric analysis for various classic yachts (from the times when Turner's theory was still being occasionaly applied) and the names of the yachts. Now, I dont have the linesplans for all of those yachts, but I have included in the following images what I have. I also don't have offsets, but with some effort you can measure them form these linesplans.

In praticular, I think it should be no problem for you to find the offsets for probably the most famous yacht of all times - schooner America. And I also think it shouldn't be a big problem for you to understand the description of Satanita in italian.

I am sure that you are aware of the fact that, strictly speaking, Turner's method is valid for stationary or slowly moving yachts. It doesn't take into account the wave system created around the hull when the yacht is moving at higher speeds, particularily near the so-called "hull speed". Yet, somehow it seems that the method did indeed give some very balanced yachts, like the said Zyklon.

Hope it will help you.

Cheers!

 

By the way, Satanita was given as an example of a yacht with a badly shaped curve of metacentric moments, very unbalanced fore and aft.
In fact, during one of regattas she went out of control, hit against Valkyrie and sank her.

 

Hi Daikiri

Thanks very much. Good help. Is good to see some Turner's graphic with his boats. I will search for America's offsets.

Italian is not a big problem because Portuguese is the last flower of Laccio (?) (nidus of latins languages). I already build a gondole here, with plans from Gilberto Penzo with all texts in Italian. (The work was approved by a gondoliere that came here in tourism and take a shock when view a gondole here.)

http://www.veniceboats.com/it-progetti-piani-barche-gondola.htm

In this site we can view in the first figure the curved center line.

 

Carlo Sciarelli

To those who are familiar with the german language
there is a german translation of the book Lo Yacht

Die Yacht, Delius, Klasing & Co 1973

js

 

The diagrams in Lo Yacht are from Turner's paper "A Law of Hydrostatics and Its Influence on the Shapes of Sailing Yachts," Transactions of Institute of Naval Architects, Vol 79, 1937, pp 207-240, plus plates XIV-XVIII. This is the definitive paper on Turner's work. It is mis-referenced in Chevalier and Taglang's books as being from the SNAME (US) instead of INA (UK). I picked up my copy through an Internet book listing service (Abebooks).

Cheers,

Earl

 

Thanks to Earl that sent to me his paper explaining very clearly Turner's theory.

I understand that cutting heeled sections at each station from sheet material and balancing them on a knife edge we are determining the station heeled immersed CoG and gluing the sections together in a stack and balancing it we are determining the CB position and the metacenter. position.

What I understand is that the Tuner's moment is a statical moment of immersed area in reference to the CB/M line. Each of these moments represents the station contribution for the CB position and by the verification from boat plans with good and bad balance, hulls that have good balance have the Turner's Moments Curve in one way and bad balanced hulls have it in the other way.

And about Welch's line what we can learn?

 

Frank Welch designed a fast cruising yacht named "Fidelis" in 1930 to Turner's principles. She won races well into the 1970s, and was documented in a very rare and delightful privately printed book called "Faithful Fidelis." I've attached a scan of her lines.

Anyhow, Welch had an article in Yachting Monthly for November 1933 entitled "The Secret of 'Balance' in Yacht Design," in which he describes Turner's ideas. For some reason, this led people to call the Metacentric Shelf the "Welch Axis." As far as I have been able to determine, they are one and the same.

Cheers,

Earl

 

What I have noticed is that being Turner's moments a station statical moment about CB/M necessarily the areas above and under the axis need be identical in order that the total Volume Moment (sum of the areas) be zero because CB is resultant from each station CoG position and therefore the ratio Volume Moment / Volume need be zero. Each amount of A area and C area is something that intrigue me.

Being Welch's Line the positions of station CoG several afirm that if the Welch's line beeing right the boat has stability direction.

However my exercices show me that I can have good Turner's Moment Curve and bad Welch's line and vice versa.

Unhappy it seems me that the Turner's Theory was aborted untimely.

Still accepting Daikiri arguments:

" Turner's method is valid for stationary or slowly moving yachts. It doesn't take into account the wave system created around the hull when the yacht is moving at higher speeds, particularily near the so-called "hull speed"

I understand that if is valid for slow motion is valid for the boat in other conditions like in waves and in a limit velocity and in this case what we can do is study accordingly.

 

By saying "slowly moving yachts", I was referring to a velocity where waves created by the hull are small enough (in amplitude and in wavelength) to not create humps and hollows which would void the assumptions behind the calculation method... I didn't refer to weather waves.

See the 2 pics I have enclosed here. The first one shows an upright hull and it's static water line. The second one shows the dynamic waterline, near the "hull speed". Btw, it is easy to modify the drawing in order to obtain a heeled hull, drawing it upright is just a matter of commodity for me.

Turner's method considers only the first (static) case. As you can see (and as you know) a dynamic waterline at the midship section (Section A-A in the pic) is lower then a static one, because the midship section floats in the wave trough. So it is obvious that any stability analysis (Turner's included) done for a static waterline is not valid in this condition. All the submerged areas and volumes are completely different than the static ones.

But then, when does a yacht heel so much that Turner's analysis would make sense? Answer: when the sail force is so big to push it near the hull speed. But in that case you will also have large waves travelling with the boat, so you can't use a method based on static waterlines...

Summing it up, Turner's method wants to analyse a hull balance at high speeds by considering static-case waterlines and sections. That is the single biggest contradiction which has led the sailing community to abandon the method.

 

Hi Daikiri

Exactly this I say with " is study accordingly ", my lasts words in the post above.

The problem is: Why abandon the method study?

I only say, if the environment of the phenomenon change we need change the approach.

If we need calculate the immersed areas using the real station form in the wave, with the real dynamic waterline, why do not do this?

If we have a approach that seems reasonably to explain a phenomenon why not extend the study of the case to go further?

 

I agree, but then it becomes a guesswork. We do not really know the shape of the dynamic waterline. Actually, of dynamic waterlines, because they will be different for different speeds.
Maybe you could use a trochoidal waveform to approximate a wave around the hull, but it still remains a guesswork.

And then, there is another point: Turner's theory only considers the hullform in order to determine whether it will be balanced at speed or not. It completely neglects the effect of sails, keel and rudder, which are equally (if not more) important.