Seaworthiness

This is ok if there is a suitable surface for the boat to slide along, too often there is a trough that the boat slides/falls into. Then that energy is dissipated in a violent impact with the sea, like a drop tests but beam on.

No ..please stop saying that.... I'm not and I have said as much several times, I'm trying to illustrate the extremes , the known dynamic responses of different types of vessel. I am not advocating the old seaworthy designs as a desirable current model, I just want you to understand why they are seaworthy. Then we can go on to the compromises knowing exactly what the compromises are and why we choose to compromise.

There are some very seaworthy performance cruisers, there are also some very un-seaworthy ones.

How many of these designers Like Michael Kasten are not qualified Engineers/Architets but just opertunistic yacht designers from a background of personal experience with boats. There is a very important distinction here. I like Kastens approach he is self educated and conservative, his boats are the product of thought and a preperadness to step outside of the current trends.

I'm not and science isn't involved here at all. The paradigm is go-fast we live in a go fast society and this paradigm gets prestige. When is the last time you saw (in a poular sailing magazine) a detailed review and interview of the designer of a Bruce Roberts ? You are in the grip of popular culture.

It is easier to design a skimming dish hullform than a displacement hullform. The flow field is far less complex the keel has an ideal flat plate and many of those inconvenient vortices have simply vanished. Performance rules.

.... you have a very high opinion of computer simulations. The reason big consortiums get leading edge baots is due to the huge amount of money they have availablefor tank testing. Simulation is not very successful for smaller sailing vessels at sea, just too complex.

Tank testing has not changed, wave testing still uses video frame analysis, the force measurements are exactly the same. The difference is that computer controlled tanks are easier to set up to get a breaking wave at position x.

Statistics are meaningless unless we know all the unreported data only then can we extrapolate conclusions. We do know enough to prevent many of these sorts of boats taking paying passengers in controlled waters, why do you thoink we do this? Is it simply because Engineers are a bunch of control freaks or perhaps we have enough science to predict a catastrophic event occasionally.

Again I suspect you wilfully misinterpret what I am trying to say. Modern designs are very different and we can improve significantly on old designs.
It still remains important that you grasp just why some of the old designs are seaworthy, why they didn't founder at all in decades of work at sea despite often encountering ferocious extreme conditions.

Modern designs like the Pogo 40 are in comparison very poor hullforms for survival in extreme conditions. A lot of people seem to have a vested interest in arguing that is is a good hullform. But this is contrary to the discipline of Marine science.

If what I or Guillermo or Marchaj others are saying is inconvenient to the points of view of the proponents of dangerous designs how does that stop discussion? The thread topic is adhered to and you are free to discuss what you like.

That is why I stuck to one rational argument before wrt LPS; not the other host of serious complications and dangers of a B2 knockdown but just the simple relationship to AVS and the time inverted and whether we should consider the implications of this compromise acceptable in a cruising boat.

Whether one option over another is more seaworthy within a given hullform is worthy of discussion too no one is preventing this.

It has not changed this is an incorrect assumption, perhaps born of ignorance? These tendencies can be described and guide the deisgn process, we use the tendencies as guides and reasons for regulatory decisions. A boat with unsafe or safe tendencies is what this is all about. Isn't it?

 

How about a few other points of view on seaworthiness for a change.

John Shuttleworth Multi-hull designer

Seaworthiness - basic concepts
The seaworthiness of a vessel, in broad terms, is the ability of the vessel to provide safety, and comfort for her crew in all weather conditions. The concept of seaworthiness should not only be considered in storm survival conditions, because vessels can be lost in moderate conditions a well as in storms. The effects of fatigue in construction materials and rigging could result in failure in moderate winds, and crew fatigue due to extreme motion could result in errors of judgment, or exhaustion, long before a dangerous situation need otherwise have developed. Collision for instance can occur at any time, and accounts for the loss of a significant number of yachts, and in my opinion is a bigger danger than a storm.
from
http://www.john-shuttleworth.com/Articles/NESTalk.html

A sailors opinion

Heavy Displacement. The "displacement" of a vessel is a fancy way to refer to her "weight." It has been my experience that blue-water cruisers are generally much, much heavier than their coastal counter-parts. Consider that most coastal boats at my marina that are actually longer than Candide often have less than half of the weight my boat has. What difference does this make? Well, in rough weather (like on my recent trip to Cuba), Candide managed to stay relatively comfortable compared to some acquaintances who found religion in making the same crossing aboard their 40' Hunter. The crew actually said, "We thought we were going to die! Everybody except the captain was seasick, and we could feel the hull flexing in the waves!" Basically, they bobbed around like a cork for over twenty hours, while Candide remained relatively more stable. In general, heavier is better for an ocean-going boat. From http://www.sleepingwithoars.com/new_page_11.htm


Perhaps a very slightly contrary opinion to mine is held by Dudly Dix who has a high malaise threshold and is a keen racing man.

Dudly Dix sailor and Mono-hull designer. ( Westlawn )

SCA: What did you learn from your experiences in heavy weather in small sailboats, regarding the characteristics most important for safety and survival?
DIX: I live in Cape Town …………. This area is internationally known as the "Cape of Storms", with justification. While we seldom choose to go out in the worst conditions, it is very common to have to fight them to return home after a pleasant day or weekend of sailing.
Sailing in these conditions, I have observed that very few locals ever get into trouble with their sailboats and the rescue statistics are very low. There are boats of all types out there, from ultra-light fin-keelers to very heavy traditional full-keelers, marconi rigs to gaffers. All are capable of handling the conditions.
…….. I come to the conclusion that there is one major factor which contributes to the ability of the boat to deal with extreme weather. That is the need for an experienced, level-headed and capable skipper, with a thorough knowledge of the abilities and limitations of his own boat. Such a skipper will bring his vessel and crew through almost anything. In contrast, even the most seaworthy of boats may be at risk in moderate weather without a competent skipper.
Proponents of heavy full keel boats would argue that my own lightweight fin-keeler (38-ft with displ/length ratio of 120) is an unseaworthy concept. In 15,000 miles of sailing, she has safely brought me through winds and seas that I would have preferred not to experience. Many boats of similar concept have circumnavigated under competent skippers.
That brings me back to the physical characteristics required for a seaworthy boat. The most important is strength, sufficient strength to withstand the loads of sailing in the conditions for which she is intended. If she stays in one piece, the skipper can concentrate on the tactics required to reach the intended destination or shelter. Those tactics will depend on the strengths and weaknesses in the sailing characteristics of the particular boat.
Knowledge of the limitations of the boat will also guide the skipper on how to act in extreme weather, when to stop sailing for his destination and to rather sail for the preservation of his craft. It will then guide him on whether he should be holding her back, allowing the waves to pass over her, or running ahead of the waves under control.
The first option allows her to hold position to some extent but requires immense strength to withstand the tremendous loads involved and reasonably heavy displacement to reduce the amount that the boat is thrown around by the waves. The alternative requires a hull which surfs quickly and is very easy to control downwind, allowing it to spurt away from the danger of breaking waves.
I believe that the other important requirement is watertightness. ………….Whatever type of boat you have, know its strengths and limitations, and seal the leaks.
This was from http://www.smallcraftadvisor.com/content/seaworthiness/index.htm

Unknown author below (not me)
The restless and relentless motion of a boat can invoke the comforting rocking of the womb, or the rising nausea of an eternal rollercoaster ride. Which it is to be will depend on the mood of the wind and sea, the sensitivity of the crew and quite a few aspects of the boat's design. The movement of the boat will also change with the course and boat speed.
A more seaworthy boat will have less movement in a seaway and conserve the energy and wellbeing of the crew. Besides barring enjoyment of a sailing trip, seasickness commonly contributes to the cause of accidents. As too does crew exhaustion from long exposure to being thrown around in bad weather.

 

OK.

What better seaworthy hull/boat do you propose ?

The constraints are :
220 000 € brand new, ready to sail. Available within a year.
Liveable / manageable by a family crew of 4/6 persons.
8 kts minimum cruise speed.

These are down to earth constraints of the real world and you have to cope with them. Otherwise, you are living in a meaningless theorical world.

 

Hei, FC, you don't need so much money. The new A40 is going to be a lot cheaper and the cruising Pogo costs about 180 000 euros, If I remember right.

That type of hulls (large transoms) and that approach to oceangoing sailboats (and seaworthiness) had been developed in the Minis, and is know arriving in force to cruising boats. It is one of the main tendencies of modern boat Design, in my opinion. First ocean cruising boat designs that adopted that tendency were Jean Marie Finot designs. He was one of the main responsible for the racing boats that had shown the way, and one of the creators. Now it is an important tendency and is arriving to the big production boats. See for instance the design of the new Sun Fast (that one is going to be even less expensive).

 

I'm an Engineer, I design things from this meaningless theoretical world and other people make them real. Also this is a boat design forum, something some people seem to forget:!: How does what's available alter the fundamental aspects of hullform behaviour?

If you can't afford a new boat with certain desirable features there are other options, the used boat option is generally better for a budget buyer.

The Pogo 40 and similar offerings are riding on the marketing wave of high publicity racing boats. They would make a very satisfying coastal vessel capable of good and exciting club racing. What we are concerned about is these vessels being marketed as family blue water cruisers. Speed and lower cost are not good trade-offs for comfort durability and stability.

 

Mike, I said the best contemporary Naval Architects and the only ones I gave as an example were : Farr, and Finot.
I have quoted Kasten, not by his designs, but by his writings. I believe he is a philosopher.

Don’t you believe that Farr or Finot are qualified NAs?

Note: The Approach on boat Design that was compared was Finot and Farr aproaches versus Marchaj aproach.

It was you who has called Science to the discussion. You have said: “Marchaj put the science of small sailing boat characteristics on the table ... “Sailing Theory And Practice” has been re-written and is current. Aero-hydrodynamics remains definitive and Seaworthiness from the historical depths of 1986 also remains definitive”.

Or: ... But this is contrary to the discipline of Marine science.

I am not saying you are absurd. I am saying that it is absurd to consider unscientific the approach on Boat Design of the best contemporary NAs like Farr or Finot, compared with the approach of Marchaj (in my opinion, of course).

I apologize if you felt offended. It was not my intention.

I feel awkward when you say, regarding twenty and forty-year-old Marchaj’s work: “Aero-hydrodynamics remains definitive and Seaworthiness from the historical depths of 1986 also remains definitive”

This is a very odd statement.

Science is never definitive and if knowledge on Aero-Hidrodinamics had not increased substantially, we would be flying the same airplanes, the cars would look aerodynamically the same and we would be sailing the same kind of boats. This is not (obviously) the case.

In Science and research, 10-year developments in any area are huge, in 20 years you will need a deep actualization; in 40, we would be talking of history of Science.

QUOTE=MikeJohns;119516]
Quoting Vega
The increased knowledge and the use of computer simulations, programs and tank testing have increased the quality of Design and the behavior prediction of the boats to levels only dreamed in Marchaj time.

.... you have a very high opinion of computer simulations.
Tank testing has not changed....
[/QUOTE]

Yes, Computers and complex Software have changed the world and the way people work, including Naval Architecture. Precision in Design is completely different and the information that dedicated Software can give you about the boat you are designing is huge and contributes to better boats.
Today the vulgarization of tank testing and the number of tanks available have transformed testing in a regular practice, even for small boats. Twenty or thirty years ago, tank testing in small boat’s Design was the exception, not the rule.

Compared with the Naval Architects of the 70’s and 80’s, today’s Architechts have also changed. Many in the 70’s and 80’s didn’t have a formal education based on technology, engineer and Science. Now the ones that don’t have that background are the exception, not the rule.

Mike, all tragic accidents make nowadays headlines in the papers. With the amount of information you have in the net, if you don’t find a lot of information about tragedies that take place with the capsizing of cruising boats, it is because that happens in very small numbers, never minding the huge increase in the quantity of boats.

Now you call me Ignorant...but it seems to me that you don’t know what a tendency in Design is.

When Designing a boat or a car, a good Designer is trying to solve old problems with new and better answers. Those new and better answers are what makes progress, what makes the world change and what gives us better cars, better airplanes and better boats.

In the case of an Oceangoing sailboat, a Designer is trying to do a boat that is simultaneously a good performer, as a sailboat and a seaworthy boat.

The old approach to give seaworthiness to an Oceangoing boat, was to make it heavy. It is not difficult to make a heavy sailboat seaworthy but it is impossible to make a heavy boat perform well as a sailboat. Heavy sailboats are slow sailboats on all conditions except with a lot of wind. Heavy sailboats are also expensive boats to build.

Modern designers are trying to find better Design solutions to the old problem. They want a better sailboat, a boat that can be as seaworthy as the old heavy ones, but also a boat with a good sailing performance in all wind conditions, and if possible, inexpensive to build.

Modern approach is not based on weight (slow boat/expensive boat). New and stronger materials make possible the construction of strong and light boats. The seaworthiness of the boat comes from variable solutions, that go from different dynamics of new types of hulls, in bad weather and waves (comparing with old heavy boats), to lowering the CG of the boat by concentrating the ballast on deep bulbs and so on.

This modern approach has several tendencies, all having light boats in common. These tendencies result from the several successful ways that Designers have found to answer the old Design problem. All new ways that result in light fast and seaworthy sailboats tend to give way to Design tendencies.

A single and isolated successful Design is not a new tendency. But when one NA begins to make different similar boats, that work on the same principles and are fast and seaworthy, normally it will soon be followed by others that will work with the same kind of criteria and ... Voilá, we have a new tendency.

Some tendencies:
- The French aluminum deriveurs (centerboarders) initially designed by Caroff (I think) and then by many French NAs, like Philipe Briand and many others.
- Boats with long and narrow fin keels with a bulb on the bottom and with substantial form stability.
- Large transom boats with a very narrow keel with a bulb and a huge form stability.
- A very recent one, the canting-keel....and many others and all the above in different combinations.

I have given you the names of Farr an Finot as example, because they have been among the most creative contemporary Naval Architects and in a way or another, they have contributed to many of the modern tendencies in Oceangoing Sailboats. Of course there are many others that have contributed too.

Regards

 

Mike, Guillermo, et.al.: I'd hoped you would respond to my call for a change. Do we have some common ground here?

 

Leo posted a good one about CFD a while back

The CFD research done to date has been done mainly with speed in mind and with sea worthiness hardly even entering the priority list.

Ask yourself - What was the goal of this research? !

We need to thread carefully when it comes to accepting new "scientific research" or history will repeat itself, as it generally does

Mikey

 

Vega, it would not be quite correct to make a comparison with the aero industry here, once again the goals of the research were different. Efficiency and safety were higher up on the priority list than speed.

Wing profiles of today are much more efficient than 30 years ago, they also stall later and less abrupt, i.e., they are more forgiving. The end result of the research would have looked very different if the priority list had been different

Mikey

 

Stephen,
I'm a little bit lazy these weeks. Also I have experienced a home computer problem and, on top of this, a lot of work at the office and some family obligations are 'distracting' me from the forums. I'll be with you there ASAP.
Cheers.

 

Let's know what Phil Sharp, who dominated the Class 40 at the last Route du Rhum, says about driving a Pogo 40:

"I helm a lot, about 14-16 hours a day. Whenever I'm not eating or sleeping. Going downwind you really need to be on the ball to push the boat. The autopilot couldn't cope. At the bottom of a wave you get a hell of a lot of lee helm, for example, and the autopilot would just set it off into a crash gybe. On bigger boats you might get away with it, but these boats are twitchy and can flip out with less warning"

 

NIce post CT49 (By the way, I suggest people using nicknames to sign with their real first name at least, just to be able to refer to posters by their name instead of the nick. Although several members have informed about their names, sometimes it's difficult to remember them all, so signature could be useful to this end).

Discrepancies among reputed scientists are quite common and usually constructive. Whith time, the strongest and better defining the real world theories are the ones who supersede.

Naval Architecture has been turning around quite a lot of time now, and extensive, scientific and profound research has been done throughout all these years by naval architects at all times, improving a bit on each turn. The analyzing tools are better each day, and calculations are done in a fraction of what it was not so long ago. When I was at the university we still integrated by Simpson at hand and the like, and now we have all those computer programs easying our lives.

But the basic principles remain the same they were 35 years ago, and when computers begin to produce stupid results one needs to go to basics to know what's happening and solve the problem. I deal with two well reputed naval architecture programs at my office and I know how tricky they may be and how careful you have to be to not be caught in a major mistake.

From my point of view, basic principles regarding seaworthiness are still 100% valid and strongly supported by experience. New materials are allowing us to structurally design in a way it was not possible some years ago, certainly, but the basic designing principles remain pretty much the same.

Cheers.

 

Paulo (Vega)

The NA’s designing yachts compromise too. Farr has produced some very nice boats, also some very poor ones. Even boats that killed people when the keel fell off because the scantling rules were deficient. (Rising Farrister). The successful yacht designer operates in a social environment that is demanding certain types of boats. Designs are usually commissioned by a manufacturer that has to sell them into a market. The designer is stuck with a design brief that says “Contemporary fast yacht that will perform well in the club racing” tand they have to toe the line. (line up for the race). I am not sure that the argument works the other way, “that they must be great boats because they have qualified designers”.

Don’t confuse model resistance towing and dynamic capsize wave tank tests very few if any of the designers for any class of sailboat test their designs this way. That is why I said the design has nothing to do with science.

Definitive in science (and engineering) means the most reliable complete and authoritative source to date that has not been shown to be erroneous by further study and that it is accepted enough as representative of current knowledge to be applied . we have to rely on definitive sources. That is why you will find Marchaj referred to in most all NA academic research papers, modern books on NA and yacht design.

I know this is not your first language but when I said

“It has not changed this is an incorrect assumption, perhaps born of ignorance? “
You appear to have taken a rather egotistical view of this and took some of my points…?

The definition of ignorant is “lacking in knowledge” if you re read that sentence as

“It has not changed this is an incorrect assumption, perhaps born of lack of knowledge? “
you will hopefully see what I am actually trying to say, It was in reply to you suggesting that the science of current and 20 year old studies was somehow different, I was trying to say that if YOU “Paulo” studied the old boats and the science of their motion and apply that science to new baot designs you will find that the science of their hydrodynamics has not changed. But I presumed you lacked knowledge of the motion of old boats and the application of the science to those types of vessel which would be common unless it had been directed study.

It should not have been taken as an insult.

I am also a bit confused over your “I am not saying you are absurd. …………..I apologize if you felt offended. It was not my intention.”

I was unaware of and took no offence.

Communication with you seems rather fraught with emotional peril.

 

A smaller boat driven hard in extreme circumstances will always be more difficult to drive than a much bigger boat. That's perfectly normal.

A small increase in speed makes all the difference regarding the ability to use the auto-pilot and the way the boat behaves. If you are racing (and leading) you will want all extra knot decimals you can get, so it is normal that Sharp stayed a lot at the helm.

Last season I have made a small and fast passage (90 miles) driven my boat hard. I have done 8k average speed and I went to 12, 13K several times. To drive my cruising boat like that I had to be at the helm all the time. I have done so, because I was having fun. When I arrived I moored alongside a cruiser-racer and talking with the skipper, it turned out that he had made the same passage, leaving some time earlier. We where talking about the great sailing that we had and talking about speed, it turned out that its much faster sailboat had done an average speed of 7K, one knot less than my average speed.

The reason? He had been on auto-pilot most of the time.

 

If you do not design things that are cost effective, they are simply not used. The cost MUST be less than the profits.
Anti locking brakes for cars are a perfect example.
I do not know how old is this principle, but forty years ago, some cars nobody knows already had antilock brakes (jansen interceptor). It needed a very low cost system to make the system law mandatory in 2003 for new cars.

For the boats, there should be in the western world over 10000 sailboats in the 40 ft (beneteau, bavaria, janneau to name a few), like the oceanis 390 that a single 1 among 552 capsized. And yet you have only ONE report 10 year old. So, there is NO need to increase seaworthiness, except if you propose a NO cost, or very low cost solution.

I do not agree on this one. For instance, Archimede principle is millenium old. But for a long time, you had no way to compute volume and CoG except by hand with limited mathematics. Chebicheff and Simpson integration are only century old. And now, any hull cad software can compute this for you in near real time.

Navier Stoke equation arealso century old. But now, we do not have mathematical tools to fully solve these equations.

I would conclude that seaworthiness is not a problem. There is aboout no interest to put so much money to increase speed and/or efficiency of a boat that do not reaches its destination because it capsizes before.

I hope you know the lastest Airbus is naturaly aerodynamically UNstable. (aft centered). Like all recent aircrafts. This for efficiency. The stability is gained back with electronic controls.