Range of positive stability

[Dolfiman]

A local guy here on the forum...
Gerr Marine Naval Architects and Yacht Designers http://www.gerrmarine.com/index.html
...is well worth a look.

His article in direct reference with the thread is there :
http://www.gerrmarine.com/Articles/StabilityPart2.pdf

The specific issue of upside down stability of these beamy "flat iron" shape racing boats fit for Vendée Globe downwind conditions dramatically arose after the third race 96-97 and the death of Gerry Roufs, then second, following the capsize in heavy seas of his Groupe LG 2 (photo), later found upside down. Tony Bullimore also faced the same situation during the race, his boat Exide Challenger staying upside down after the capsize, and he was miraculously rescued after 5 days of survival inside. Idem for Thierry Dubois, his boat Amnesty International stayed upside down. The year after, during the Around Alone race, PRB the boat of Isabelle Autissier capsized and stayed upside down. In those days, the boats were designed with absolutely flat deck (>> suction effect when upside down) a very small roof protuberance and a minimal keel-bulb ballast, both conditions leading to a great amount of stability upside down that slope and energy of rough sea waves could not overcome to recover the upright position. After all that, a lot of critics arose, crisis meetings of all stakeholders to save such races, that led to more strict rules and stability figures with regard this scenario, and in particular greater AVS and the areas rule of 5/1 . On their side, Naval architects developed more rounded deck shape + more rounded and developed roof and cabin, anyway useful to offer better confort and protection for the sailor, as it was claimed necessary by the winner Christophe Auguin ("An improvement of the performance can only go through a greater confort of the sailor") : photo of the new PRB (Roxy on this photo) winner of the following Vendée Globe 2000 race with Michel Desjoyaux, with a lot more roundness of the deck and cabin/roof development.

 

[MikeJohns]

The two such boats in which people were killed were both abandoned and both floated by themselves all through the storm, with hatches open. They were both recovered later. If the boats were so unsafe, they would not have floated by themselves with hatches open through a storm.

If you read the report you'll note the comment that the hatches were left open after the rescue which was quite late, the storm had moderated significantly before the yachts were abandoned. And what about the 5 other boats that didn't make it through the storm ( all presumed to have sunk) that were abandoned earlier?

 

[MikeJohns]

In the Fastnet 125 people were taken off boats successfully and 15 died, many of the deaths in the process of abandoning their vessel. But close to four thousand people swung into action to alter the very statistics you are incorrectly trying to infer data from. Which is crew deaths. Look at "would have died" if you want meaningful statistics.

I haven't read the Marchaj book in eons but arguably, its points can be disputed in significant ways. For example, I think it claims that the small IOR boats in the '79 Fastnet (which inspired the book) were dangerous. However, the deaths in those boats were basically caused by poor securing of equipment. ......................

You need to read both the inquiry into the Fastnet and Marchaj's Seaworthiness. What he did was show why dangerous aspects of a vessels RAO's occurred and why some of the undesirable traits were being driven by rating rules of the day. All Marchajs work has been repeated and reinforced by a host of researchers in several countries. The worlds leading research organisation for this field is Wolfston and work by Barry Deakin is also worth reading. Newer knowledge has refined MArchaj's work but not negated it.

Barry Deakin was also scathing of the ideology you appear to espouse. Such as his comments to the 98 S-H coroner when he basically said "we keep on telling people ( what's wrong with the boats) but they just don't seem to get it...... "

.....All else being roughly equal, a lighter boat will go faster and also be at least risk of encountering rough conditions. Conditions rough enough to roll or sink a small boat are rare. Even if there is a chance that they may be more dangerous in rough conditions, this risk could easily be offset by the fact that they spend less time doing an equivalent passage and therefore have less chance of encountering such conditions.

Capability for speed isn't any indicator for cruising passage times. The speed is dictated by comfort and ease of sail handling by a short handed crew, usually where one person has to be able to handle sail. Racing is a completely different paradigm. I have never seen much difference in reality cruising.

 

[M&M Ovenden]

Risk is always based on hazards and exposure. It's a qualitative assessment that has bias. In my case I don't think I'd put much value on reducing the exposure time to reduce the risk. My money would always be on mitigating the hazards. My thoughts for what it's worth.

Cheers,
Mark

 

[CT249]

In the Fastnet 125 people were taken off boats successfully and 15 died, many of the deaths in the process of abandoning their vessel. But close to four thousand people swung into action to alter the very statistics you are incorrectly trying to infer data from. Which is crew deaths. Look at "would have died" if you want meaningful statistics.

Nothing I can find indicates that the boats that some call "seaworthy" would have fared better than the boats that some call "unseaworthy" were it not for rescues.

You need to read both the inquiry into the Fastnet and Marchaj's Seaworthiness. What he did was show why dangerous aspects of a vessels RAO's occurred and why some of the undesirable traits were being driven by rating rules of the day. All Marchajs work has been repeated and reinforced by a host of researchers in several countries. The worlds leading research organisation for this field is Wolfston and work by Barry Deakin is also worth reading. Newer knowledge has refined MArchaj's work but not negated it.

Barry Deakin was also scathing of the ideology you appear to espouse. Such as his comments to the 98 S-H coroner when he basically said "we keep on telling people ( what's wrong with the boats) but they just don't seem to get it...... "

He is if course entitled to his professional opinion but he is not necessarily any more correct than other professionals in the field.

Capability for speed isn't any indicator for cruising passage times. The speed is dictated by comfort and ease of sail handling by a short handed crew, usually where one person has to be able to handle sail. Racing is a completely different paradigm. I have never seen much difference in reality cruising.

One person's experience is not conclusive proof.

 

[CT249]

If you read the report you'll note the comment that the hatches were left open after the rescue which was quite late, the storm had moderated significantly before the yachts were abandoned. And what about the 5 other boats that didn't make it through the storm ( all presumed to have sunk) that were abandoned earlier?

I looked at Trophy and Ariadne because of the number of deaths involved. Ariadne capsized around 0100 on 14 August and was abandoned afterwards with the main hatchboards out and the main hatch open. She was recovered after the race despite having the broken mast still attached.

Trophy rolled about midnight on Sunday/Monday and was abandoned very early Monday morning. She was recovered after the race and although my books are in storage I believe she had hatches open. When her crew hopped into the raft it was because she was expected to sink so it would appear highly unlikely that they closed the hatches.

Table 2.1 of the Fastnet report shows when survey respondents felt the weather was at its worst. Twenty two percent felt that it was worst from midnight on the 13/14th to 2am. Thirty percent felt that it was worst from 2 am to 4 am on the 14th. Twenty nine percent felt that it was at its worst from 4 am to 6 am on the 14th. It is therefore apparent that boats that were abandoned early in the period when the storm was at its peak (as seen by those who were there) survived with hatches open, as I said.

Grimalkin got into trouble later and had the main hatche open when Ward was picked up.

The boats that sank included Magic (small and light, design unknown), Polar Bear (wooden boat similar to a UFO 34, not very new or radical and quite similar to an S&S 34), Charioteer (OOD34, not an IOR design), Gringo (unknown design) and apparently one other I cannot identify. Funnily enough, no one seems to have analysed the non-racing boats in the area, which suffered six deaths - four on a Val 31 tri and two on a cruising yacht. Of course, that means that unless there were 120 cruising boats in the area, they suffered more fatalities pro rata than the racers. Even if we confine the analysis to the monos, unless there were 40 cruising monos caught in the area at the time the cruising monos suffered worse than the racers.

The simple reality is that on the occasions when there has been significant analysis of large fleets of sailing yachts that have been caught offshore in severe conditions, we see that getting inverted only causes a small, albeit tragic, proportion of fatalities and losses. Furthermore, the boats that have been lost, lost crew, inverted or been close to it include heavyweight cruising types, "classics", slender pre-IOR types with very high LPSs such as S&S 34s and Cole 43s and Ohlson 35s, etc. The types that attract most criticism do not suffer more casualties, pro rata.

 

[Dolfiman]

Table 2.1 of the Fastnet report shows when survey respondents felt the weather was at its worst. Twenty two percent felt that it was worst from midnight on the 13/14th to 2am. Thirty percent felt that it was worst from 2 am to 4 am on the 14th. Twenty nine percent felt that it was at its worst from 4 am to 6 am on the 14th.

I can bring my testimony as I was that night at the mooring in Valentia bay (Ireland) not far from the Fasnet fleet. There were two successive wind hits of equal violence, the South-West one and the North-West one. During the South-West wind, our boat (a 12 m sailing boat) was very shaken and the mooring line was pulling hard. At around midnight - 1 am, the wind came down quite completely and the moonlight was sufficient to see the clouds spin around us as if we were in the center of the whirlpool, incredible spectacle. It was obvious that we would be soon touched by the North West for which we were not sheltered and we decided to swifltly change our place in the bay to have a better protection from that wind direction . We did it as soon as possible, putting the secondary mooring line attached to the main one so to have ~ 50 m of mooring line with two anchors, and we finished the maneuver in the N-W forcing (fortunately in those days, there were very few boats in the bay and so plenty of place to maneuver and moor). During the rest of the night, we relayed on deck to check that we were not slipping, ..... and in the morning we learned by the BBC what had happened for the Fastnet boats.

 

[MikeJohns]

For any sailboat full inversion is the most dangerous response to wave action that can occur in a seaway. There’s an ideology that likes to confuse knockdowns with full capsize. Any boat can be knocked down to 90 degrees. You can’t really avoid that by design without going to extremes for any hullform.

Nockdowns are very likely for any boat in extreme heavy weather, what happens as response has more to do with Seamanship than vessel design( you can add a luck factor as well). But we can predict reliably which boats are most likely to get back up unscathed and carry on, and which boats are very likely to be inverted by the same impact. We can also predict which boats are likely to be uncontrollable, unable to heave-to reliably or have an intolerable motion in extreme conditions.

……..four on a Val 31 tri and two on a cruising yacht. Of course, that means that unless there were 120 cruising boats in the area, they suffered more fatalities pro rata than the racers………………….The types that attract most criticism do not suffer more casualties, pro rata.

Bad seamanship also contributes to unnecessary risk with crew unnecessarily on deck or even sitting on the rail in heavy weather on any boat. People can die on very seaworthy boats but not because of an innate fault in the boat.

However, once again you are trying to use fatalities as a valid statistic. There were 15 rescue helicopters (that flew 200 hours airtime) and a whole fleet of rescue vessels from 3 nations directed by professional land based SAR teams. You cannot use fatalities validly as any indication of seaworthiness wherever there's an SAR response altering the stats.

He is if course entitled to his professional opinion but he is not necessarily any more correct than other professionals in the field.

Barry Deakin is relaying the findings of several high profile research institutions not just venturing an opinion. There are several research establishments around the globe that have conducted vigorous independent research. It’s all used for standards for commercial sailing vessel requirements too. The classic being the MCA guidelines for commercial sailing craft.

Which other professionals in that field do you think disagree, and do you have a reference to their published papers, journals, conference presentations ? I’ve never seen anything.

 

[CT249]

How do you know how reliable the predictions of, for example, being uncontrollable are? What large scale statistical databank is being used to ensure that the predictions are correct?

You imply that the stats were radically altered by SAR. On what evidence do you base that claim? Have you carried out an analysis of the boat types that were involved in the rescues? How have you calculated what would have occurred had SAR not been available in each case? Why do you believe that the rate at which boats sank in the major races that have been studied was radically altered by SAR? What crew were saved by SAR from what light boats? What light boats were saved from sinking by SAR? If you are going to make the claim, surely you should have some evidence.

As we have discussed earlier, Dovell for example disagrees that light boats were more likely to encounter issues in the '98 Hobart. You ascribed that to his own bias. However, have you explored the possible bias from the "other side"? Have you considered the possibility that people who do ocean races may actually have a bit more knowledge about the factors involved in actually doing the sport than those who do not actually do the sport?

There still appears to be no statistical evidence that the "dangerous" boats and their crews are becoming casualties at a significantly higher rate. If they are more dangerous then it would appear to be only by a small margin. The chances of dying while doing an offshore race in Australia are very close to the chances of dying while staying at home. Therefore it appears that we may at most have a very marginal improvement in a very, very small risk - one that sits very, very low on the risks faced by the average racing sailor.

Given that we have an alleged but unquantified increase, which appears to be statistically very small, in a very, very low risk then it is not at all silly to accept it for the sake of having what most racing sailors believe to be a boat that is more fun to sail on.

Given that it is extremely well known that humans are very poor at assessing risks and tend to vastly over-rate the danger they face from rare but "catastrophic" events and under-rate the danger of more mundane ones, it is perfectly logical to investigate the statistical likelihood of inversion and see that it is very, very small and therefore should be seen as such. We'd probably get a far greater increase in life expectancy if we go sailing more often, because we feel the boats are fun to sail, and therefore get more exercise.

 

[MikeJohns]

........ What light boats were saved from sinking by SAR? If you are going to make the claim, surely you should have some evidence.

Well it’s you that’s inferring vessel qualities from fatalities without doing that very research. I have said you should identify the “would have died” and add those to the fatalities before it can be at all meaningful.

Dovell for example disagrees that light boats were more likely to encounter issues in the '98 Hobart.

Dovell is not a researcher at all. That Deakins peers have alternate views is not true. Deakin’s peers are numerous not one of them has ever disagreed with his statement to the S-H inquiry and those comments are quite factual backed by a lot of research particularly by The Wolfston Institute.

… Have you considered the possibility that people who do ocean races may actually have a bit more knowledge about the factors involved in actually doing the sport than those who do not actually do the sport?

I’ve had a lot to do with racers and race boats and I’d say only a few have any idea outside of popular culture . A lot of them in the 98 S-H didn't even understand how a marine forecast worked let alone what you should do in heavy weather for prudent seamanship.

The problem with Naval Architecture is that much of it is not intuitive at all, a classic case is that people often feel the safe on dangerous boats because they can’t tell the difference between a dangerous seakindliness and seaworthy seakindliness.
Also we are talking about rigorous peer reviewed and repeated scientific inquiry which is necessarily impartial. It trumps gut feelings every time.

.The chances of dying while doing an offshore race in Australia are ……………very low on the risks faced by the average racing sailor.

Precisely because the state and an efficient SAR service comes and gets you when you get into trouble.
That’s not a service available for many cruisers, you can’t be airlifted or picked up by a rescue launch within a few hours. But that's the level of service that skews your observations.

 

[kvsgkvng]

If the ballast-to-displacement ratio is near or above 50% and the keel is deep (and strong to take bending moment) enough, no matter what form is the hull the righting GZ curve is going to be in the vicinity of 120* Presuming most of the ballast is in the bulb at the bottom of the keel.
With this in thought, if the boat is wider the resisting moment is greater (the boat is "stiff"). The problem for cruising is that flat belly is going to pound like crazy for light to moderate displacement boat. Large barges don't pound unless in category 5 storm.
JMHO.

 

[gilberj]

since Fastnet 79....39 years ago there has been a lot of work done by competent professionals, almost all working within their area of passion. A number of new standards have been developed. All new boats are built today in Europe and in other places are built to the ISO standards.....12217-2 mainly ( dealing with assessing the boat for different types of sea D for Estuary/lakes etc, and A for offshore) but there are other ISO standards dealing with watertight integrity and drainage and construction. ( I don't have the standard numbers for these others handy.)
There is a further development called the STIX number, which is derived from the ISO standards...mainly 12217-2. An off shore racing boat needs a STIX number of 32 or greater. Generally the minimum AVS is considered to be 130, though there are some fiddles on that.
In simple terms the intent is to have a strong righting lever when the boat is knocked down to mast in the water...90-95 degrees. You really immerse the stick (roll over) and about 70% of boats will loose the rig, making it a survival situation.
A more recent development is been to stipulate a small maximum stability in the inverted condition. This can be accomplished by having a high volume cabin shape/deck combination. The mast(s) can be designed and built to be buoyant, or a ballistic (inflatable) float designed into the a goal post frame otherwise used to hold the solar panels and radar etc.