Seaworthiness

Yes, but not painted! (As per the photos at the DIDI page )

 

Rayk,
In your posting 292 you suggestested the Polynesian voyages were one way trips. That's not completely accurate, as you can discover here.

http://www.pbs.org/wayfinders/polynesian3.html

Ben Finney set out to rediscover the navigational methods of these early voyagers and found some surprising resulta.

http://pvs.kcc.hawaii.edu/finneyfounding.html

Other sites.

http://www.nzetc.org/tm/scholarly/tei-BesPoly-t1-body-d1-d4.html

http://www.nzetc.org/tm/scholarly/tei-BesPoly.html

http://www.strangehorizons.com/2002/20020128/voyagers.shtml

Then, the nautical adventurers of the early Ming period (15th century) upped the ante.

The Mystery of Zheng He and America

A 7-cm diameter plain brass medal with the inscription “Authorized and awarded by XuanDe of Great Ming” was unearthed several hundred miles inland from the American east coast.
In 1430, Ming Emperor Xuan Zong commissioned Zheng He to deliver a message to foreign nations that he was enthroned with a new era named Xuan De. This was the whole purpose of the 7th and the last expedition for Zheng He. “Did Zheng He’s excursion reach east America? Or is there other explanation? The owner of the disk, Dr. Siu-Leung Lee, would like to present some interesting observations and leave the conclusion to the audience.

Ming emperors had a diplomatic protocol to announce enthronement and new era by sending gifts and medals to other nations. Xuan De (1426-1435) is the Nianhao (era) of Emperor Xuan Zong, the 5th emperor of Ming dynasty. In 1430, he dispatched Zheng He to announce his enthronement. The medal represented the highest authority of the emperor and was only delivered by a diplomat like Zheng He or his deputy. After Xuan Zong died, China isolated herself from the rest of the world for more than 400 years. Chinese started to come to America after 1850s as indenture labor mostly through the west coast to mine gold and build the railway. Few Chinese came through this part of the east coast where the railway was built exclusively by slaves and convicts. Today, this little town of 9000 has 4 Chinese by US Census in Year 2000. This brass disk is minimally decorated with little monetary or artistic value to Chinese laborers and European missionaries, who are the other possible carriers of items from China. This kind of medal should be more than one in those days, but they were usually collected, melted down and recycled by the next emperor. Those countries along Zheng He’s route all suffered from multiple wars. Items like this were easily lost in looting.

The brass medal was discovered under 4 inches of soil in a scantly populated area several hundred miles inland from the east coast of America. After almost 600 years, the medal shows no apparent signs of corrosion, other than a tight coating of soil. Preliminary analysis of the metal composition shows that the material is brass, a copper alloy with zinc. Xuan De was the era when brass first became available for making the famous Xuan De brass censers and coins.

The brass medal was unearthed at the center of Cherokee Indians’ homeland that became a major battleground with the first European settlers. Hundreds of Cherokee Indians were massacred in multiple battles. 1776, right after the American Independence, the US government offered land grant to the soldiers in lieu of monetary payment. Cherokee’s homeland was given to the soldiers, resulting in another major conflict and massacre. Could they be the ones who lost the medal in the war? The Cherokee people were later driven more than a thousand miles away to Oklahoma in 1838-39 in a historical event known as the “Trail of Tears” during which thousands of Cherokee Indians died. During the colonial era, 90-95% of the Cherokee perished. But why was the medal found inland? Did they obtain it from other tribes near the coast? This traces to another story.

The coastal tribe Catawba is well known for making pottery. Every Catawba family has potters. Some of their pottery designs bear great resemblance to bronze censers made in Xuan De era. The Catawba and Cherokee tribes were rivalries but also traded with each other. Could the Catawba tribe be the first to contact with the Ming people? Europeans, especially the English have been trying to reproduce the Chinese porcelain for ages without success. In 1712-22, a Jesuit missionary learned about the secret of Jingdezhen (China’s porcelain capital) and wrote two long letters back home. However, Europe still could not produce true porcelain for the lack of the knowledge to process white clay. The first discovery of white clay was by Andrew Duché in America. Wedgwood, the founder of the first porcelain industry in England dispatched Thomas Griffiths to America to look for china clay. By kidnapping the chief’s wife, he was led to the white clay pit by the Cherokee chief. Tons of the white clay were shipped back to London to set up Wedgwood, the first porcelain factory in England. Even so, England’s porcelain was still not competitive against the Chinese imports during the entire 18th century. Yet, at the same time, pottery in North Carolina was made in Ming style by natives and new European immigrants. What took China close to 10,000 years to perfect was not so easily learned even by the technologically adept Europeans at that time. How could the Neolithic Cherokee and Catawba Indians master this technology so well? The most fascinating fact is the Cherokee term for china clay (kaolin) is “unaker”, similar to what Chinese call it “uk-nake”in southern dialect. Is it a coincidence? All this happened before the arrival of the Europeans. The name uk-nake was used up to Ming dynasty. It was replaced by other terms like china clay. A Jingdezhen porcelain expert said that Zheng He might have brought the clay bricks (petuntse or baidunzi) along with the porcelain gifts.

The Cherokee people have two original flags, viz. one with a white background and the Bigger Dipper constellation in red that they called the peace flag. The war flag is reversed in color. Observation of constellation has been a routine in China since ChunQiu era. A flag with the Bigger Dipper has been used as one of several flags in imperial ceremonial parade from Song dynasty to Qing dynasty. The Ming emperors were especially fond of the Big Dipper in association with their Daoist belief. Zheng He used an instrument Qian Xing Ban (Boards aligning with the stars) to calculate the latitude using the Polaris and the bigger Dipper. On the other hand, lacking a written language to record the celestial observations, the Cherokee people had no knowledge of other constellations on record.

According to the history of Ming dynasty, Zheng He died in India in 1433. But it has never been proven since his body could not be shipped back to China. Ming dynasty had significant advances in brass and porcelain. The brass medal is a specific case and pottery a general case. Could these clues change the history we have been told? More research is necessary.

A chemist by profession, Dr. Lee has been interested in Chinese culture in many aspects. In 1996, Dr. Lee founded the Asiawind.com website which hosts the world’s first Chinese calligraphy website and a Chinese antique website that drew attention to an inquiry about the medal. To many, this medal might be easily discarded as a piece of scrap metal. Perhaps it is the combined knowledge of Chinese history, calligraphy and chemistry that allowed Dr. Lee to recognize the significance of this obscure brass plate. Ironically, Dr. Lee lives in Columbus, Ohio, USA.

For further information, please contact:
Siu-Leung Lee, PhD
SLLEE@ASIAWIND.COM http://www.asiawind.com/zhenghe/



Seaworthiness is such an emotve term it seems The Chinese treasure ships were the best designed and built ships of their time. http://www.1421.tv/pages/maps/voyages.htm
Numbers of them are believed to have circumnavigated the globe 70 years befor Columbus set sail and he was in all probability using a Chinese chart. http://www.1421.tv/news.asp

Zheng He's ships were seaworthy for their intended use because on voyages of exploration demand facing terrible risks. IMO the best vessels for crossing oceans are nuclear powered submarines. They have the very best navigation systems, the most up to date charts and no stormy weather 200 metres down. I wonder when we shall see a "Sunseeker Submariner".

Pericles

 

Humm, about the numbers that you “work” and post, particularly about this STIX number that you have calculated for the RM 1200:

The real STIX of the RM1200 is in MSC(minimum sailing condition) :38.33
And STIX in MxSC : 38.7


To see the hugeness of your “mistake”, let’s take a look at several boats from the same manufacturer (Beneteau), some with a 33 STIX and others with a 39 STIX, to see what kind of boats we are talking about and the differences in seaworthiness.

With a STIX around 33 we have:

OCEANIS 321, STIX 33; OCEANIS 343 STIX 34; FIRST 33.7, STIX 32

With a STIX around 38 we have:

OCEANIS 42cc, STIX 38, OCEANIS 423, STIX 38, OCEANIS 461 STIX 37


The difference in size and seaworthiness of boats (same manufacturer), between a STIX of 33 and a STIX of 38 is the difference between a 33ft and a 42 ft. It’s HUGE.


At the Paris boat show I have talked with a factory technician from RM boats and asked him stability data about the RM1200. He provided me with the information (he was a nice guy and a sailor). I thought that it would be interesting if he, or any other from the technical staff of RM boats joined this discussion, since the RM is considered in France a seaworthy boat.

But when I told him that a Naval Engineer had said that the RM 1200 had a STIX of 32. 9 and an AVS of 115º and that it was a boat “not safe in open ocean”, the only thing he wanted to know was if that was a reputable forum and what was that forum, because RM would like to advance with a lawsuit for Slandering.

And you know, he his right. You can express your personal opinion on anything but you can not support your opinion on grossly inaccurate data “worked by you”.

You have no right to post grossly inaccurate data and then base opinions on it. That is SLANDER.

That ended a perfectly enjoyable talk because I didn’t want to bring any lawsuit problems to this forum.

The AVS is not 115º, but 119º and only if we don’t consider in the calculations the upper structure that in this case (deck-saloon configuration) contributes a lot for a higher AVS (more than 130º).

[/QUOTE]

Yes Guillermo, work on that, BUT DON’T POST INACCURATE DATA, nor base your assumptions on Data calculated by you and that are grossly inaccurate.

As you know each boat in the EU is certified and the accurate data are the ones that have been checked and that provided that certification.

If you persist, with time, someone is going to feel sufficiently annoyed to see his boats SLANDERED, based on false data, to carry out a Lawsuit to you (or this forum?).

 

Whatever you say, Paulo, thanks
I will review RM 1200 calculations and if there's any mistake, I'll gladly correct it at the STIX thread. As there are no data available for the Dfl angle, I'll work out numbers from 100 to 180 in 5º intervals.
But maybe I'm not so wrong. We'll find out.

 

Some interesting considerations from the Wolfson Unit for large yachts:

"Some designers who have experienced difficulty (to comply) with the (Large Commercial Yacht Code stability) criteria have identified particular characteristics that have an influence on the compliance:
- Performance orientated design. Owners seek performance and are attracted to forms that resemble those of modern racing yachts.
- Low displacement/length ratio. Light displacement is good for performance but may result in low ballast ratio and a relatively high KG. Weight growth during the design or building phases may result in reduction of ballast to maintain the design draft, accentuating the problem.
- High beam/draft ratio. Wide beam provides good initial stability and sailing performance, and a spacious interior.
- Low freeboard/beam ratio. The popular style for sailing yachts is for a single deck of accommodation below the main deck. The depth of this accommodation remains roughly constant regardless of the size of the yacht, because it is dependent on headroom requirements.
- Low superstructure height and volume. For reasons of styling and performance, superstructures tend to comprise a single deck, and large areas of open main deck facilitate sail handling.
- High performance, high aspect ratio rig, with mast height greater than yacht length.
- Lifting ballasted keel or unballasted centreboard. Shallow hull draft enables access to a wide range of ports with the keel raised.

Most of these characteristics are recognisable as being desirable in terms of performance, and contribute to good stability at low angles of heel. Unfortunately they are detrimental to stability at large heel angles."



Some papers for the ones interested:
(Maybe some of them have already been posted)

Directional Stability and Control of Sailing Yachts
Walter H. Scott, Irwin Yacht and Marine Corp., St. Petersburg, Florida
Modern ocean racing yachts often encounter considerable difficulty in steering and directional stability. In order to understand and correct these difficulties, it is necessary to identify these separate force and moment components of the hull, keel, rudder/skeg combination and the sail plan. This paper concentrates on the underwater forces and moments, using a combination of tank test data and aircraft analysis techniques. Sample calculation results are presented for a typical One Ton yacht. The influence of the sail plan is discussed. The direction for possible improvements are shown and recommendations are made as to the type of generalized hull and sail data which are required to improve this basically simple static analysis.

Seakeeping and the Sailing Yachtsman
Roger Compton*, Bruce Johnson*, and Carl Van Duyne**, *U.S. Naval Academy, Annapolis, Maryland, , **Graduate Student, Stanford University, Palo Alto, California
Waves cause undesirable forces and motions on yachts which vary in severity from mildly uncomfortable to catastrophic. The problems created by waves are receiving serious and increasingly analytical attention from the naval architects who design oceangoing ships. Many of the physical phenomena and engineering principles used to describe and analyze ship seakeeping performance are applicable to the sailing yacht.
Discussion and explanation of such phenomena and principles are the subjects of this paper.

Sailing Yacht Capsizing
Olin J. Stephens, II. Karl L. Kirkman, Hydronautics, Inc., Laurel, MD Robert S. Peterson, NSRDC, Bethesda, MD
The 1979 Fastnet focused attention upon yacht capsizes and resulting damage and loss of life. A classical stability analysis does not clearly reveal some of the characteristics of the modern racing yacht which may exacerbate a capsizing tendency. A review of the mechanism of a single-wave-impact capsize reveals inadequacies in static methods of stability analysis and hints at a connection between recent design trends and an increased frequency of capsize. The paper traces recent design trends, relates these to capsizing by a description of the dynamic mechanism of breaking wave impact, and outlines the unusual oceanography of the 1979 Fastnet which led to a heightened incidence of capsize.

Sailing Yacht Capsizing
Karl L. Kirkman, Hydronautics, Inc., Laurel, MD. Toby Jean Nagle, DTNSRDC, Bethesda, MD. Joseph O. Salsich, U.S. Naval Academy, Annapolis, MD
A joint SNAME/USYRU Project for Safety From Capsizing has led to significant progress in an understanding of the causes and mechanism of the single wave impact capsize. The paper traces the background of the project, outlines the approach selected in pursuing answers to the concerns of the yachting community, presents related findings from other research and describes capsizing model tests and the linear regression of the Fastnet ’79 data.

Model Test Techniques Developed To Investigate The Wind Heeling
Characteristics Of Sailing Vessels And Their Response To Gusts
Barry Deakin, Wolfson Unit, University of Southampton, England
During the development of new stability regulation for the U.K. Department of Transport, doubt was cast over many of the assumptions made when assessing the stability of sailing vessels. In order to investigate the traditional methods a programme of work was undertaken including wind tunnel tests and full scale data acquisition. The work resulted in a much improved understanding of the behavior of sailing vessels and indeed indicated that the conventional methods of stability assessment are invalid, the rules now applied in the U.K. being very different to those in use elsewhere.

Dynamic Performance of Sailing Cruiser by Full-Scale Sea Tests
Yutaka Masuyama, Kanazawa Institute of Technology, Ishikawa, Japan Ichiro Nakamura, Kanazawa Institute of Technology, Ishikawa, Japan Hisayoshi Tatano, Osaka University, Osaka, Japan Ken Takagi, Osaka University, Osaka, Japan
The sailing performance of a 10.6m-LOA cruiser was evaluated by sea test and the results were compared with calculated values and numerical simulations. The sea test was carried out to examine the steady sailing performance as well as the dynamic performance which includes the motion in waves and tacking maneuverability of the boat. The sailing state parameters at the steady condition were compared with the results of the velocity prediction program, and the results were in good agreement.
The motion of the boat in waves was assessed in conjunction with wave measurements using a throw-in type wave meter. These data were analyzed by means of spectral analysis. The results indicated the sail damping effect on the rolling motion quantitatively.
The tacking motion of the boat was also investigated. The trajectory of the boat was measured using differential GPS receivers, and these results were compared with the numerical simulation. The simulation showed good agreement with the sea test data.

Development of Proposed ISO 12217 Single Stability Index for Mono-Hull Sailing Craft
Dr. Peter van Oossanen, Van Oossanen & Associates, Wageningen, The Netherlands
For more than 5 years now, Working Group 22 of Technical Committee 188 of the International Standards Organization (ISO) has been developing a standard for the assessment and categorization of the stability of pleasure craft with a length up to 24 m. This work became necessary when the European Union decided to issue a Directive on Pleasure Craft, facilitating the export and import of pleasure craft to and from the various countries comprising the European Union. All newly-built pleasure craft up to 24 m in length, to be marketed in the European Union, must comply with the stability standard being developed, and some 50 other ISO standards, covering all aspects of structure, materials, equipment, etc, as of June 1998.
To support the work of Working Group 22, The Netherlands carried out a comprehensive study for Part 2 of ISO 12217, covering the stability of mono-hull sailing craft. Together with the French, Swedish and UK delegates, this work finally lead to the development of a single stability index. Working Group 22, in September 1996, unanimously agreed to adopt this concept for the assessment and categorization of the stability of mono-hull sailing vessels. This paper gives a description of some of the work that was carried out by the Netherlands in this regard and gives a description of the single STability IndeX (STIX) concept and the way the STIX value is determined from the various stability and buoyancy properties of sailing vessels.

The Effect of Pitch Moment of Inertia in Body Axes on the Performance of a Yacht in Waves
C.J. Sutcliffe, Univ. of Liverpool, Dept. of Mechanical Engineering, Liverpool, UK A. Millward, Univ. of Liverpool, Dept. of Mechanical Engineering, Liverpool, UK
Observation of full size yachts sailing upwind in a seaway has shown that, because of the presence of the sails, the yacht is constrained to move in body axes (parallel to the mast) rather than in earth axes (normal to the water). It is thought that this is due to the effect of the sails in the air and the keel and other appendages in the water providing a large damping force which resists any motion normal to the mast line. An experimental project has been carried out therefore to investigate the effect of this change in motion axes on the forces and motions induced by the seaway.

The Re-Righting of Sailing Yachts in Waves - A Comparison of Different Hull Forms
Martin Renilson, Australian Maritime College, Australia
Jonathan R. Binns, Australian Maritime College, Australia
Andrew Tuite, Crowther Multihull Designs, Australia
The re-righting performance of three yacht hulls has been assessed experimentally. The three hulls are considered to be representative of modern racing yachts. It has been shown that two different experimental techniques provide the same relative results between the three hulls, leading to the same conclusions. Correlation of re-righting performance with basic hydrostatic parameters has been shown for these three hulls, however a simple case when this correlation is non-existent is noted.

A Time-Domain Simulation for Predicting the Downwind Performance of Yachts in Waves
Dougal Harris, Curtin University of Technology, Perth, Western Australia.
Giles Thomas, Curtin University of Technology, Perth, Western Australia.
Martin Renilson, Australian Maritime College, Launceston, Tasmania, Australia.
Yachts racing in many of today's high profile races, such as the America's Cup and the Volvo Ocean Race, spend much time sailing downwind in following seas. The development of a method for predicting the performance of yachts sailing downwind in waves would therefore provide a valuable design tool for racing yacht designers.
This paper describes the development of a time-domain simulation for predicting the performance of yachts sailing in irregular seas for apparent wind angles between 90 and 180 degrees. The simulation output may be used to either directly compare different designs or augment existing polar plots for the effect of a following sea.
The simulation is comprised of three main modules: the wave induced longitudinal force, the resistance force and the sail aerodynamic force. The resistance and wave force modules have been validated through semi-captive model experiments. Results from the complete simulation have been compared with those obtained from free running model experiments.
Numerical experiments on a number of hull and rig configurations have been conducted using the simulation. Results are presented with conclusions being drawn on the effect of hull form and environmental conditions on downwind performance.

Model Tests to Study Capsize and Stability of Sailing Multihulls
Barry Deakin, Wolfson Unit MTIA, University of Southampton, UK
Sailing multihull cruising yachts cannot be righted from a capsize without external assistance, and so they present a difficult problem for regulatory authorities concerned with commercial operation of such craft. A standard is required which enables their stability to be assessed at a similar level to that of monohull yachts. Unfortunately their stability characteristics and behaviour are very different to those of monohulls, and the normal methods of assessment are not appropriate. Some aspects of multihull capsizing are addressed, with a discussion of the results of an innovative programme of wind tunnel and towing tank tests. It is hoped that the paper will be of assistance in directing others in their assessment of multihull safety, and will provide a technical basis for further discussion of the subject.

More...

Gerritsma,J.,and Keuning,J.A.,"Performance of Light and Heavy Displacement Sailing Yachts in Waves",Proceedings of the Second Tampa Bay Sailing Yacht Symposium,The Society of Naval Architects and Marine Engineers,1988

Joint Committee on Safety from Capsizing. 1985. Final Report of the Directors. United States Yacht Racing Union, Newport and Society of Naval Architects and Marine Engineers, New York.

 

The following post (#41) was originally posted under the title Open 60 & 50 (IOMCA) rule should be changed started by Stephen Ditmore. Post # 41 is being reposted here per Guillermo’s request to discuss and comment on the aspects that pertain to seaworthiness.

Source: http://www.boatdesign.net/forums/showthread.php?t=15206&page=3

 

Let me quote an 'old book' (Marchaj's seawortiness book, 1996 revised edition, pages 273 and 274):

"...(the roll decrement curve) demostrates in some quantitative sense the critical dependence of damping on boat speed. There are plotted three roll decrement curves ......relevant to calm sea conditions in which, nevertheless, heavy rolling may be incurred due to aerodynamic forces alone. One curve applies to the situation when the boat makes no headway, and the two others when she's moving ahead. The advantegeous effect of speed on damping efficiency of the hull underbody is dramatic. A hull itself, even without keel or bilge keels may have sufficient inherent damping when under way...
A further illustration of the influence of speed on rolling is given...This time the model was tested in small waves of steepness ratio (Hw/Lw = 1/43 and 1/86), and ultimate rolling angles were plotted against the wave direction. Quite conspicuous peaks in the two set of curves (for two different speed-length ratios) are indicative of resonance conditions when the rolling period of the boat is about the same as the period of encountered waves. It will be seen that when resonance occurs, the influence of damping action is greatest....These test results give some quantitative answer to the question of why, in a survival situation, active rather than passive tactics are usually successful and those who are able to maintain some speed and directional control fare better...
...data are relevant to to boat behaviour in relatively small waves of low steepness. Since...the maximum angle of roll depends on the wave slope, in stormy, steep waves an accumulation of rolling may be rapid indeed and extreme slopes may be lethal to small boats. Although it is unlikely that a boat with efficient damping can be capsized through synchronism alone, resonance may be a contributory factor....
The old rule still holds and always will, namely: in survival conditions when no sail can possibly be carried it is the waves of a storm, not its winds, that the mariner has to fear the most"

(italics are mine)

Cheers.

 

Well, Tom: it seems we have coincide while posting. Thanks for bringing your post at Stephen's thread into this one. I would appreciate very much if you could give me your opinion on the seaworthiness of what you call skimming dishes. In my opinion the clue is they are seaworthy (from the seakeeping point of view) while at speed (see my previous post), because of the huge damping effect of sails (if no instability is reached), hull and appendages. My concern is the actual tendency to bring this kind of speed-borned seakeeping ability into the cruising boats market, relating seaworthiness to it, as if it were the ultimate survival tactic. On the other hand, I see seakindliness as an important factor not only to crews' comfort but safety (I'm not talking racing boats here, but cruising ones), seakindliness which is not at all reached with those extreme beamy hulls. What's your opinion?
Cheers.

 

Hum, STIX definitively penalizes low AVSs and it can penalize Beam, but what you seem not to have understood is that a boat is always a compromise between a lot of factors. You assume that a boat with what you call “ excessive beam” (like the POGO40) can’t have a high STIX number for its length.

And of course, you are wrong, the STIX and the boat stability depend on the way all the factors and compromises are put together in a meaningful and harmonious way, with special relevance on the CG of the boat.


If you were right, then the Pogo 40 would have a very poor STIX as you wrongly have assumed from the beginning.


There is no contradiction about what I think of STIX. I have said and I maintain:


“STIX is only an easily understandable index (but found through a complicated calculation that takes into account a lot of different stability factors) that is in my opinion, the most sophisticated stability screening tool available.... STIX is just a number and its interpretation could not be simpler: The bigger, the better”.



About the STIX I share the RYA, Paul Miller and Ben Johnson opinions:


The RYA view about STIX:

“STIX is arguably the most sophisticated stability screening tool yet available." ….
“

http://www.rya.org.uk/NR/rdonlyres/...tabilityIntro.pdf#search="stabilityintro pdf% 22


The Paul Miller view (D. Engr., from the Dept. of Naval Architecture of the United States Naval Academy):


“The Best we have…”


Bob Johnson view: (Naval architect, the Island Packets designer and the U.S. participant on the international work group of designers and naval architects responsible for developing STIX):

… STIX standard, I think, encompasses all critical stability factors in an analytical method that is based on established principles of naval architecture, sound methodology, and correlates well with real-world experience for real boats. No other single stability-assessment method .. is as comprehensive as STIX.



The work to create STIX was, like Guillermo said: “based on a thoroughful research of yachts with desirable and undesirable characteristics”. the works that have taken 5 years and have joined the more knowledgeable minds in this Industry are described by Dr. Peter van Oossanen, referring to the Dutch contribution:

“For more than 5 years now, Working Group 22 of Technical Committee 188 of the International Standards Organization (ISO) has been developing a standard for the assessment and categorization of the stability of pleasure craft with a length up to 24 m.

To support the work of Working Group 22, The Netherlands carried out a comprehensive study for Part 2 of ISO 12217, covering the stability of mono-hull sailing craft. Together with the French, Swedish and UK delegates, this work finally lead to the development of a single stability index. Working Group 22, in September 1996, unanimously agreed to adopt this concept for the assessment and categorization of the stability of mono-hull sailing vessels”.


About STIX and seaworthiness, referring to the POGO40 you have said:

About the RM1200, the boat you refer to when you say (qualifying the POGO), “things are even worse”. You have said:

From the beginning I have said that you were completely wrong about the stability of this boat. You should have given more credit to the opinion of Jean Marie Finot (the Pogo 40 designer) or the opinion of Owens and Clarke. They have said that this kind of boat is a safe oceangoing boat and they obviously know what they are talking about, because they knew the stability characteristics of this kind of boat and you obviously don’t.


When you say that “probably her STIX (POGO40) is as low as the RMs one” you are not referring to the “real” ISO STIX of the RM1200 (38.3) but to the wrong STIX that you have calculated for that boat, and that is : 32.9.


So you are assuming that the POGO40 has a stability comparable with other STIX33 boats, like:


OCEANIS 321, STIX 33; OCEANIS 343 STIX 34; FIRST 33.7, STIX 32.



But that is ridiculous, because the POGO 40 has a ISO 12217 STIX of 44.7.



You should compare the POGO stability with the stability of boats with an equivalent STIX, like:


Swan44, STIX 38; Westerly Ocean43, STIX 40; Oceanis 523, STIX 46; Beneteau50, STIX 41; Island Packet 370, STIX 43.


And these are all seaworthy oceangoing boats.


It makes no sense, to say about a boat, that has a 44.7 STIX:

 

The only thing that can be concluded is that Guillermo formulaes are not valid for rather light boats bulb ballasted.

One thing clearly wrong is the moment of inertia, used for roll period and acceleration. I fear Guillermo formula for inertia is based on the displacement only. But a ligth 12m boat with a bulb and draft above 2.20m (2.25 for the didi 38, 2.20 for the pogo 40, 2.38 for the A40) and a 19 m mast clearly have a higher moment of inertia of the more classical 10m boat of the same weigth, but with a fin keel (a la IOR) with 1.9m draft and a 15 m mast.
None of the old formulae would have predicted an AVS of over 140° for the 4T empty 11.5m didi 38.

 

What you call the skimming dish" can be also seaworthy in a cruising context.

The Pogo 40, the boat that we are discussing, is a boat that comes from a line of smaller cruiser racers that have their origin in the 6.5 racing minis. They have a racing version and a cruising version. Both boats have identical stability and use water ballast. The Pogos are very popular in France. They sell a lot more of cruising Pogos than racing Pogos.

The Pogo is a Finot designed boat, but it is not only Finot that is designing cruising fast and seaworthy “skiming dishes”. See this one and take a look at the owner’s letter (end of the page).

http://www.owenclarkedesign.com/default.asp?m=da&id=11196

 

There is no need for shouting and rudeness, but Guillermo, I think it's a point here about deep bulbs, and maybe water tanks in bilges too, both features will increase the inertia and make for longer roll periods. It is an old rule of thumb, concentrate your ballast lengthwise but distribute it sideways.

 

Well, those are not "my" formulae and I have already agreed they may not be accurate for very deep bulb finned boats. Anyhow I keep considering them pretty useful to assess a boat at a glance, in lack of better information. I've found they may even work quite well for cruising boats with 'standard' depth bulbed keels. There are some examples of that at the STIX thread.

Paulo:
I would like to check out by myself that POGO 40 STIX number you mention and, if confirmed, I will happily recognize my feelings about the POGO STIX numbers were wrong. Do you have her stability curve for the MOC condition? Cruising or racing version?

About the RM 1200, I've told you: Don't be so sure about what you have been said. Remember: stability tests to calculate STIX are not mandatory, and manufactures have always a commercial interest. So we must take what they say with some beneficial mistrust, specially when they keep this kind of info away from their publicity. I'll analyze that boat in more deepness at the STIX thread, and we'll find out (When I come back home from this trip).

In spite of your remarkable efforts (and pretty twisting posts), I'm afraid I still think you have lack of knowledge when discussing these matters. Remember you even didn't knew what FL, FB, FR and WAV were in the STIX formulae some weeks ago. It's amazing how you discuss matters, pontificate on them and scorn better formed people's opinions, when you only have a very superficial knowledge.

Cheers.

 

Absolutely. But I would like to bring your attention to the fact that many of those cruising boats derived from racing versions, do have 'standard' depth keels, not the deep racing ones, so inertia may be pretty less (If my memory don't fail I think there's a cruising version of the DIDI 40 with 1,60 m keel).

I find amazing the lack of accurate (and many times misleading) info many manufactures and even designers use at their marketing material.

Cheers.

 

My apologies for waiting so long to post, but I consider it prudent to give the subject some thought before offering an opinion. I reread through the posts; although there are many excellent observations, it is apparent that there is little consensus on what criteria should be included in the definition of a seaworthy vessel; which in turn makes it impossible to prioritize by significance or magnitude the various components that encompass a concise definition of seaworthiness.

Some might say “Not true, we have the STIX number by which we can make comparisons.”

If this were a forum for the general public, or for sailing enthusiasts of all types, I would say that the STIX number is good stating point to evaluate a variety of boats on the subject of stability. But that is not the case here. Most of the participants on this forum are boat builders, or designers. Let us remember that the STIX number is a numeric rating that assures compliance to an ISO standard to insure a degree of uniformity in safety matters for which builders have to show compliance. In short, it as born out of the need to show government mandated compliance. Keep in mind that the working group that developed the STIX system was made up of educators, boat builders, regulatory personnel, and certification personnel; many if not most were not trained naval architects. The current STIX formula was chosen because it was the only system that the working group could agree upon. It by no means provides us with a basis for a sophisticated treatise on the subject of seaworthiness.

Guillermo has made a straightforward request in post 1:
“Let's discuss here what we understand by 'seaworthiness'…”

So let us discuss the fundamental design characteristics that are pertinent in order to increase the probability of a boat and her crew to survive in extreme conditions; irregardless of how they may have happened upon their dismal circumstance.(sleeping, drunk, tactical err, racing nut, dog slow boat, ego)

I think Guillermo’s inclination to press beyond the confines of the STIX formula is warranted; his willingness to resist accepting restrictive all encompassing formulas will aid him in producing innovative design ideas. For those who have been lulled into accepting the fairly restrictive STIX definition of stability I have introduced a list that I believe more fully encompasses the parameters that make up a seaworthy vessel. This is by no means an exhaustive list, but if we are not including at least these items, and considering them in the broader scope of our arguments, then can we really boast that we are yacht designers?

Static Stability
Dynamic Stability
Hull Form
Mass distribution (and center of gravity)
Moment of Inertia
Aerodynamic induced rolling
Rolling induced by waves
Orbital velocity induced roll
Ruder and appendage induced rolling
Wave induced broaching
Aerodynamic induced broaching
Weightlessness do to extreme sinusoidal wave forms
Heaving motion and capsize probability
Rolling induced by heaving motion
Parametric excitation and initial heal angle
Hull form contribution to broaching
Period of encounter
Resonant magnification
Metacentric height
Dynamic metacentric stability
Heavy verses light displacement
Center of gravity as it relates to displacement
Mass distribution as it relates to displacement
Mass distribution and its effects on moment of inertia
Wave anatomy and displacement interaction
Damping of undesirable motions
Aerodynamic damping
Damping do to appendages
Form damping
Velocity effect on damping
Curve of declining angles
Capsize probability of a single breaking wave
Directional stability
Ruder control
Redundancy of control systems
Safety systems and probability of use
Boat strength
Acceleration tolerance