Seaworthiness

Some interesting findings about today's extreme racing machines and the effect of wider beams.
(Extracted from a Richard Slater 2003 submission to the AYF)

"In an ISAF meeting in September 1997 organised to review Open Class safety, Groupe Finot (designers of many winning Open class boats) presented a paper to the meeting on security of Open 50 footer and 60 footers.
Part of their paper was on stability and the ability of an Open class boat to re-right itself after being inverted. Their recommendations on how to make the Open class boats more likely to re-right after being inverted were:

1. The moderated width of the boat
2. The volume of superstructures
3. The tightness of the mast
4. Flood ability
5. The canting keel
6. The inflation of volume

Moderating the beam of the boats will assist in their ability to recover from being inverted (the most extreme of predicaments) but the class rule that limits static heel has proven that designers are forced to increase beam, in order to satisfy the static heel requirement.
In the Open class, designers have now learned the need to look at the Limit of Positive Stability (LPS) as a key tool in determining a boat’s resistance to capsize. The class has now moved to including a high Limit of Positive Stability (called in the IMOCA rule – Angle of vanishing stability, or AVS) of 127.5 degrees.....
......
In the following examples, Reichel Pugh has designed boats to fit within the 10 degree static heel rule. The boats in this study have the following characteristics:
• Equal Lengths
• Equal Displacements
• Equal Vertical Center of Gravity
• Equal Keel Draft
• Equal Cant Angle (40 deg)
• Wide Boat has 15% more hull surface area, 39% more deck surface area and 23% more wetted surface area.

One boat satisfies the 10 degree static heel limit by reducing the cant of it’s keel to 18 degrees off centre. The other boat is a wide beam boat (similar design concept to satisfy the static heel limit as we see in IMOCA boats).

Their inverted stability range:
Wide Boat: 137° to 252° (115 degrees)
Narrow Boat: NONE
(See attached image)

These plots are then a comparison of a well built narrow boat compared to a wide boat that would have impossibly low structural weight and VCG.
In reality the wide boat would:
• Have more structural weight and less bulb weight, for constant displacement.
• Have a vertical centre of gravity significantly higher.
• Have significant increase in its range of inverted stability and decrease in its upright righting arm values.

With realistic VCG the wide boat would have the following values: Compare with "Fully Canted to Windward" stability curve.
Righting arm at 30 deg heel = 1.40 m (1.80 m on plot).
Righting arm at 160 deg heel = -1.76 m (-1.80 m on plot).
Inverted stability range = 150 deg, (116 deg on plot).
The plots show that this unrealistically advantaged wide boat still has a significant range of inverted stability. Even with the keel canted to 40 deg the boat would need further assistance to self right, shifting of water ballast etc."

(The bolded is mine, taken from the graph)

 

What about a substantial masthead float to prevent a total 180 degree capsize?
Such an item would use a gas cylinder to inflate the float and it would operate if the boat were heeled over to 85 degrees or so. It could be installed within the mast, out of harms way and would provide a huge self righting force to the boat, in the event of a knockdown.

Any inflatable boat manufacturer has all the knowledge, I would think.
Of course, it wouldn't be as spectacular as my other idea of a rocket assist pyrotechnic at the top of the mast to bring the vessel upright. Of course, the sailor would have to hope the rocket would not immediately capsize the boat in the opposite direction! Up own, up down, give a bloke a chance!

Pericles

 

Pericles,
Now there is an idea worth patenting. It could deploy automatically.

 

Guillermo,
Did Reichel Pugh, give the width of the boats in the two examples, or any other criteria,such as freeboard height?

 

Yet it is quite possible that the boats motion contributed significantly to the ability both mental and physical of those poor wretches.
However the argument was that the B.390 from an intrinsic safety point of view had fatal flaws, not only did it have a poor area under its GZ curve but it was also prone to excessive inversion time (as with most low LPS boats) . I think that a sensible and safe blue water “family” cruiser should return upright within a comfortable time for a person without breathing …shouldn’t it ?

Most boats do not sail in ocean conditions but they are designed for them. Consequently the scantlings end up with a very large safety factor for the weekend coastal sailor.

The masts and rigging of many of these boats is still original. We know that stainless steel rigging has a finite life yet the rigs stay up. We know that Aluminum alloy has a finite number of stress cycles before it fails, yet these masts are not failing. Good design? Or over weight, over conservative design?


Rig failure tends to kill and seriously injure people as well as disabling the vessel so factors of safety have always been high on rigs.
Masts are durable for a different reason other than excessive fatigue resistance; the primary mode of failure is buckling and the wall thickness is chosen accordingly, they are loaded in principally in compression which is not significantly fatigue inducing .
The shrouds in tension are prone to fatigue, Modern annealed stainless wire is less prone but It is common to find fractures in rigging wire and almost as frequently stress fractures in SS chain-plates and consumables like shackles. A simple flouro dye wipe can be very illuminating.

There are very good manmade structures designed to the limit with a minimum of material they are called Aircraft.

I don't think so, the sea can be a much crueler mistress than the sky, for example the C130's can fly with impunity right through the eyes of strongest hurricanes without over-stressing its airframe (where I read the USAF routinely fly to measure the wind-speeds around the centre for the path/severity predictors).
The problem with the sea is that conditions can be very unpredictable and as they say “**** happens” and usually it was totally unexpected..

Seamanship is more demanding to guarantee safety (is this a good argument ? ) but I don’t agree that it makes a better seaman, perhaps you just reduce your options.

Prudent seamen have always slowed down for heavy weather and under some situations the most prudent action is to Heave-to, not just to stop and wait as a storm tactic but also to effect repairs or just rest. These options are not safe seamanship for the 40’s class in big seas because of the propensity of the vessels to surf sideways and get into a violent inversion. They must try and use a drogue with all its attendant pros and cons.

Which will tell you that the unpredictable event that broke your boat was strong enough to break your boat. The Americas cup boats are a good example of just how unpredictable some of the loads are, despite batteries of strain gauges and instruments, and millions of dollars in the design and construction. Cross a sheet to an opposing winch and the boat snaps in half!

I think you need to accept that there are pros and cons with any hull-form and that includes the 40’s style racers (Particularly in some conditions). We haven’t mentioned other factors related to comfort like dryness, cockpit security and shelter.

Without access to the design data I cannot prove my concerns that they are unsuited to cruising. [If this design data would vindicate these vessels of the criticism they enjoy from many technical and skilled people in the yachting world why don’t they publish it ?] However we can do a technical risk assessment .

Risk assessment can consider both Leading and Lagging indicators i.e. we can predict that something will occur through prediction, or we can count the occurrences.

So far the concerns are mostly leading because this is still a relatively rare phenomena, we would expect them to sit in most respects when being raced somewhere between the Minis and the open 60’s. (Note that the 60’s have proven considerably more seaworthy than the 50’s).

So far we have seen one race and relatively little ocean cruising, and marketing claims of family cruising, reeling off effortless miles while enjoying cool beers.

Did anyone watch the “Pirates of the Caribbean” footage on Utube site the video is cut when the boat rounds up after the wave hits it on the quarter and more footage is spliced in.

 

Are you sure you posted the correct plot?

I don't see any negative values over -.4

 

As with certain Cats for many years now.

It is going to depend on the dynamics of the knockdown. If it is a violent inversion its drag will probably add to a dismasting, but it would help if the mast rig was intact and the vessel inverted. Probably better just to have a bigger mast (sealed) . Counter to all intuition the vessel may be less likely to be knocked down if you put a heavy mass there instead (on top) ....funny old world

 

RHough
I believe Guillermo has posted this before, the info comes from the following PDF, entitled:
‘Submission to Modify the Australian Yachting Federation Special Regulations ….Resistance to Capsize’.
It is a good read as there is opinion from Finot Design,Merfyn Owen(Owen Clark Design),Manolo Ruiz de Elvira chairman of the ITC(2003) and James Dadd, class measurer involved with rule changes to the Volvo 70 rule(2003)

www.yachting.org.au/site/yachting/ayf/downloads/Technical/Agendas/Stability Submission Paper.pdf

 

Thank you, it is indeed a good read. The paper was written with a purpose, it is an editorial (in that is not a study of capsize resistance or inversion). The purpose of the paper is obviously to get the rules changed so that previously excluded boats can race. It cannot be considered objective.

It is interesting, however to see what it does say about stability and inversion:

SUMMARY OF SUBMISSION
The main reasons for including a limit on a boat’s static angle of heel are no longer valid.
A Static Angle of Heel Rule fails in its purpose to make boats resistant to capsize.
The only true test available of a boat’s resistance to capsize is its limit of positive stability and its stability analysis.

[bolded mine]

So when is a boat capsized?
RRS 21 states:
CAPSIZED, ANCHORED OR AGROUND; RESCUING
If possible, a boat shall avoid a boat that is capsized or has not regained control after capsizing, is anchored or aground, or is trying to help a person or vessel in danger. A boat is capsized when her masthead is in the water.

(that is a pretty broad definition)

This explanation of capsize is not intended to be the definition of what it is to capsize, if it was intended to be a definition within the Racing Rules of Sailing, ‘capsize’ and its meaning would be included as a ‘Definition’.

I propose that consideration must also be given to the ability of a boat to re-right itself after being inclined to extreme angles. This might include angles beyond when a masthead is in the water.

In the NSW State Coroner’s Inquest into the 1998 Sydney to Hobart Yacht Race, Mr John Abernathy made the following findings in regards to stability:

2. Relying on the experiments of Dr. Renilson I find:-
(a) That the lower a vessel's limit of Positive Stability the more susceptible it is to being knocked down and being inverted;
(b) In general the higher a vessel's limit of Positive Stability the sooner it will be righted from the inverted position;
(c) Because of the different deck configurations of vessels no recovery time from the inverted position can be accurately predicted for any limit of Positive Stability.

If this is true, what can we use to predict how long a boat might stay inverted (so Mike can stop holding his breath)?

The paper (3 years old) advocates moderate beam. What is moderate beam?

I looked at 10 "41 foot" boats and found the average beam to be 13.2 feet. The range was 12.96 to 13.833. These are cruising boats, Bavaria to Jeanneau ... Dehler and Jeanneau build skinny 12.96' beam boats, that Hans Christian is 13.25, the Island Packet wad the slimmest at 12.91

By this standard the Pogo 40 at 14.4' is (OMG!) 9% wider.

If you compare LWL to beam the average is 2.72. The Pogo's LWL (40) gives it a beam of 14.67' I think this makes the Pogo's beam fall within the range that I would consider normal. Certainly not "extreme".

I don't see how that paper condemns moderate boats like the Pogo 40. It certainly does not make a case for static stability making boats more seaworthy.

 

I’m not sure why the preoccupation with inversion times anyway; rarely do you here anyone suggesting it should be less than a minuet, but in fact if you are concerned about someone on deck living, then that is about all the time you have, or less. To get a good idea how people react when suddenly dunked under water, find yourself a good sized brick, fasten a hook to it and when your buddy isn’t looking snap it on his belt and chuck him overboard. O-K seriously, I have been in a couple of situations as a diver where someone I was diving with suddenly lost air. Both cases they panicked, and if I hadn’t been right there, they would have drowned. Even if someone is tethered, there first reaction is to unsnap so they can get air, which of course makes it very likely that they are going to be separated from the boat. If people are inside when a boat inverts, it is a different story; I personally think that for a cruising boat, some form of inside steering, or even a pilot house is a huge safety advantage in dangerous weather conditions.

 

Mike makes my point:

The boat's motion ... possibly ... oh please ... who had control over the boats motion? Do you expect the boat to chose the weather to make a passage in? Did the boat decide to have enough sail up to suffer from repeated knock-downs?

Of course C130's fly through hurricanes ... how is this relevant to not operating outside of design limits? It rather reinforces what I said. If the limits of the design are known, it is operator error to operate outside those limits.

As far as the sea being so cruel ... when you fly the wings off an airplane, the probability of finding it still flying after you have bailed out is zero. Quite unlike finding a B390 floating upright after being abandon.

Does anyone think that air is stable and predictable compared to the sea? (hint: What causes the sea state?)

I don't think so, here are two possible ways to arrive at scantlings:

1. After careful engineering studies, and a thorough knowledge of the material, we have decided that the hull of our fiberglass boat should be X thick.

2. Gee, this new fiberglass stuff seems to be stronger than wood, if we make a copy of this hull and make it just as thick as the wood, we don't have to do any research. We can just build 'em and sell 'em.

Which is more likely? The large "safety factor" is just lazy design, otherwise known as "margin for error" ... as in "I don't know, so I'll make it heavier".

Again I don't agree. The same formulas used to design rigs with wooden masts and iron rigging are still in use. The simple fact that not every bit of timber has the same properties as every other bit of timber forces over specification. When you then figure the moments of the wooden mast and use them for alloy, you end up with wasted weight. Just the nature of the material should allow different engineering. That wooden mast of unknown quality of both material and construction had to be too heavy. Aluminum doesn't rot when it is not varnished, alloy spars don't fail because someone skimped on the glue or used butt blocks instead of swallow tails.

Funny you should mention dye testing. Just finished having a professional service do some testing on some rod rigging. When I asked a certified non-destructive testing company point blank if there was a non-destructive test to estimate the remaining fatigue life of SS wire or rod, the answer was no. As far as I know, the material must be tested to failure. Once the number of cycles to failure is known, a replacement schedule is set. Samples are then taken out of service and tested to failure to evaluate the accuracy of the estimated cycles on which the replacement schedule was based. Bottom-line, rigging can pass a dye test today, and fail due to fatigue next week.

So if we adopt your position that "the sea can be a much crueler mistress than the sky" ... why aren't boats designed to the same standards as aircraft?

I'll argue that slowing down to the point of reducing stability is folly. The idea that the most prudent action is to heave-to comes from days when the boats had no other choice. By golly if it was good for boats that would open their seams and sink if you tried to sail them, it must be good for boats that can take loads that would break the old ones in two. If the only trick in your book is one that new designs are not meant to perform, I'm sure it would make you conclude that the design was unsafe. Not unsafe by any objective measure however. Effect repairs? Why did you break it? Rest? Set the AP and keep sailing while you rest ... "the propensity of the vessels to surf sideways and get into a violent inversion." I'd like to read the accounts of the Class 40's that have inverted after surfing sideways, I am not aware of them. Can you provide a link?

More smoke and mirrors ... the crew put loads on the hull for which it was not designed. That failure had nothing to do with unpredictable loads, it was part of the 89% human error group. The "state of the art" in sailboats is almost laughable when compared to aircraft or professional auto racing. I really get a kick out of calling events like the VO70 the "Formula 1" of sailing. The level of engineering and testing that goes into F1 makes the VO70's look like High School shop Friday night dragsters.

I agree. Just don't label them unseaworthy based on a subjective measure. It is misleading, perhaps not intentionally, but misleading none the less

Anyone ever see a video of a car spinning out because the driver had the throttle wide open? And wasn't that round-up after a gybe when they didn't have enough horsepower to move the keel fast enough? Pretty hard to take obvious crew error and use it to comment on design.

Good to have you back Mike, you are a wonderful sparring partner!

Randy

 

There are two problems in this endless thread.

One problem is how to build "seaworthiness", for a hull, and how to measure it. And comparing comparable boats. I have already said that you cannot compare an optimist seaworthiness with a 10 000 tons rescue tug. I am not even sure you can compare a olson 30 http://www.olson30.org/theboat/olson30.html and a nicholson 31 http://www.yachtsnet.co.uk/archives/nicholson-31/nicholson-31.htm . Although beyond similarities in their names , both boats have about surprisingly same length, similar beam, same draft,both sold over hundred , and still sailing with active communities 25 years after the last unit built. (wich I think tend to proove some recognized qualities over time )

The only difference is one is 3600 lbs and have an average used price of 15000$. For the other, you have to multiply both figures by 4.

I think comparing seaworthiness for equal cost is the only possibility.


And the second issue, which would be more at its place is the community / Open discussion forum, would be "What is the acceptable minimum seaworthiness for an offshore cruiser". It is a purely personnal emotional psychological items. Some people think the mandatory minimum is QM II, anything smaller is a safety risk. Other DO have successfully crossed oceans in row boats.

 

Absolutely I couldn't agree with you more, a number of people have drowned because their tethers were either caught or initially too short to reach the surface and the boat took several minutes to right, in these cases the pull was too strong on the lines to allow them to be unclipped and presumably no knife was available. This has happened several times in various vessels all with low LPS's.
As you say if they did manage to get free there is a danger of being seperated from the boat too although it is probably a lower risk than that of drowning. The other consideration is an unconcious tehtered crewman, they are basically dead if such a boat inverts.

 

A agree.
One man from Trondheim crossed the north atlantic from Iceland to Norway in a kayak!
How do you make a kayak more seaworty, or safer?
That is the extreme "low end" in cost,
but how do you make an old 30 feet sailboat costing 10 to 20.000USD as seaworthy as possible? And would you take you children off shore in it?

This discussion is in the stability forum.
What about windows and hatches that brake under a wave?
Do we have any statistics on what makes a boat sink?

 

"a number of people" "several times" "various vessels"

This is typical of a urban legend. There is absolutely NOTHING verifiable in what you said. The only thing, it looks it MAY be probable. But I repeat, nothing is verifiable in what you allegate.

If ever you have HARD facts abouts this, please just tell us your controlable sources, how many people you facts concerned, and how many people have been reported killed while boating the SAME year, SAME country.