Seaworthiness

Vega,
Ha, I watched video one and just about busted a gut laughing. This boat is 90 degrees broadside to the waves at least twice in the 40 seconds it takes to play the video. There is almost no directional stability (Big Mistake) the storm jib is doing little if no good at al at keeping the boat moving; partly because it is rotating through an arc of 120 degrees or so. Try to keep an optimum angle of incidence under that scenario. Mike is right though, it is a lumbering tub. The Deshaws designs might be a better example of a narrower beam sea kindly cruiser that still has a good measure of speed.
In your second video I couldn’t see enough sailing. Check out this video of the 2006 Velex 5 oceans race during the storm outside the Bay of Biscay. The International Sailing Federation had this to say of the conditions.

http://www.yachtinguniverse.com/CPG/displayimage.php?album=1&pos=22

Cheminées Poujoulat is sailing heavily reefed, and fairly stable for the conditions. It is an excellent example of what Guillermo is talking about in post 353.

And he goes into a little more detail in post 372

Also your similar coment in post 374

Now imagine the skipper in the first video, who is obviously a little ‘sea challenged’ trying to sail an Open 60 in a storm, or even a cruising derivative of such; he would probably have a storm jib up, and it would be bobbling all over the place, don’t you think?

Guillermo speaks from a technical viewpoint. His opinion is conservative, leaning toward safety in a broad scope of environmental conditions, while considering the sailing proficiency of average cruising folk. I am careful not to judge Guillermo too harshly for his views; I personally have seen my viewpoint on safety change over time. When I was in my early 20’s I was a radical skier; I would fly off cliffs and do flips and all kinds of other stupid human tricks. I can’t tell you how many times I buried the tips of my skis in the snow because I didn’t make it out of a layout in time. I just went to the slope to watch my 10 year old son on his new snowboard, and all ready he is taking jumps, tricking and the like. It scares me now.

Even with my more conservative views, I would jump on board one of those Open 60’s in a heartbeat, with only one thing to say: Lets put this baby on the rail and see what she can do!!

 

This guy too?
http://web.usna.navy.mil/~phmiller/offshore.ppt#1

This link was posted by Paulo at: http://boatdesign.net/forums/showpost.php?p=85533&postcount=5
In Paulo's words there: "...but a very well made document (and a very complete and nice one)..."

Cheers

 

That guy pointed out exactly what some of us have been saying!

Only 11% of accidents are do to design or equipment failure, the rest are human error. (89%)

He also states that increasing preparation, training, cost, attitude, and routing reduce risk.

That sound familiar?

But of course this is boatdesign.net not sailordesign.net, so we must focus on some percentage of the 11% that are not caused by human error.

Randy

 

Randy,
don't be tough on me...

I agree with you on the huge influence of human factors on boating safety, but what I'm interested here is in discussing intrinsecal seaworthiness properties of designs, from the point of view of stability, seakeeping abilities, seakindliness, watertightness, buoyancy, etc. Why don't you open one or more threads on seaworthiness from the point of view of seamanship, safety equipments, structural integrity, etc? I will gladly collaborate there.

For sure things are not 'quimically pure' and every matter influence the rest, of course, but you know what I mean. Maybe the name of this thread, and even my very first post in it, is confusing. Probably it should have been called "Stability and Seaworthiness"
Cheers.

 

Let's talk about those 11% due to design or equipment failure.

Let's look at 2005 data from RNLI (Royal National Lifeboat Institute) the ones responsible for sea rescue in Great Britain (published on January edition of Yachting Monthly). These Data regards only sailing boats:

Launches:

Machinery failure: 799

Fouled propeller: 256

Sail failure: 131

Dragging Anchor: 14

Steering failure: 95

Unsure of position: 13

Adverse conditions: 240

Vessel overdue: 2

Man overboard: 19

Ill crewman: 53

Some conclusions:

In 2005 RNLI Lifeboats were launched 1622 times.

65% the problem was: Machinery failure and Fouled propeller. This seems to be the major problem in sailboat seaworthiness.

No reports of launches for capsized boats.

There was 13 guys that had put out a mayday because they didn’t really know what was their position.

 

But that an uninteresting discussion. Anyone knows that a 10 000 T rescue tug is more seaworthy/stable than an Optimist .

 

Randy
I think you will find this data skewed by the nature of the vessels and the operators. Many trailer launched power boat opertors are renown for their less than ideal seamanship and are probably responsible for the majority of data on which this is based. Cruising sailboats of the 40 foot class that Guillermo wanted to discuss are to be expected to be better manned and more responsible.

Well found cruising boats seldom get into trouble the occasional boat sinks but it is hard to collate the data. I am also not sure that we have seen enough Pogo 40's cruising types (actually blue water cruising) yet to justify their defense with such statistics anyway.

I had suggested before that it would be indicative to look at the racing fleets and that we would expect to find the opposite data ie 89% to equipment failure being the cause of rescue.

Human error at sea also accompanies the topics of motion comfort and fatigue which have a very great effect on human capability both mental and physical.
[Except when it comes to racing since maniacal maniacs seem to be immune to motion sickness (Thats for Chris .. CT )]

 

I admit and respect it can be of no interest to you. So, what are you doing here?

 

Trying to find what is lowest cost "feature" to increase seaworthiness. And trying to understand why AVS is a concern for sailboats and not for powerboats in ISO 12217.

 

Tom, thanks for the Video, it is a nice one and it exemplifies better what I was saying about the kind of motion of this kind of boats in tough conditions. As you have said, the boat is stable and I will point out that the skipper can even stand without having to grab the boat with one hand. He is working with both hands and that says a lot about the boat motion on bad weather.

But I don’t agree with your conclusion when you say:

.

This idea is also expressed in the (wrong) opinion he has about the Pogo40:

Guillermo has the opinion that this kind of boats are only seaworthy at speed.

Obviously that is not what you see on that video. The boat is going slowly. The skipper is putting a storm head sail (and not a small one) but even with that sail on, the boat would still be sailing far away from hull speed.

That contradicts Guillermo’s statements. He states that this kind of boats is only “seaworthy at speed”, but the movie shows that this kind of boat moving slowly can be very seaworthy, while maintaining a very controllable and easy motion.

http://www.yachtinguniverse.com/CPG/displayimage.php?album=1&pos=22

Note: the bold marks on Guillermo posts are mine.

I agree with you, Guillermo is saying the same thing by other words.

He is saying that this kind of boats (Pogo 40 and Open 60s) is only stable at speed and that the righting arm at “low (initial) end” of the stability curve (at 0 speed) is bad when compared with a good oceangoing cruising boat of more traditional design.

But that is also not true.

 

Yes, I thought exactly the same thing. It is one of the first things I noticed.

I can see some discrepancy in how we interpret what we are seeing. Maybe our emphasis has been overly biased as each of us privy to this discussion, tries to persuade one another. Perhaps we are not considering other interrelated aspects of stability that may be an overriding contributing factor.

For instance, there is some confusion as to what Guillermo means by “while at speed”. I did not take that to mean ‘as fast as the can go’; I took it to mean a non quantified speed, or another way of putting it an ‘aspect of stability derived from velocity.’

In any case, I believe the fact that the boat is moving at a velocity that allows the boat to maintain directional stability is very important. Especially since the boat is operating under autopilot.

Consider the lumbering tub (video 1 in Vega’s post #374) I question how much hysteresis is playing a part in the skipper’s inability to control the boat. As a refresher: hydrodynamic hysteresis is the time lag in generating steady flow over a lift generating foil after a change in angle of incidence. The boat with a long keel/rudder combination will be less affected by extremely energized wave patterns than a boat with high aspect ratio keel and rudder, BUT once the flow over the low aspect ratio long keel/rudder has been disturbed to the point that lift has disintegrated, The boat will have to travel a greater distance to reestablish flow to the point where directional stability can be maintained. In the case of the lumbering tub, the boat is yawing so drastically as to cause the skipper to impart drastic rudder angles to try to maintain control; the boat is not traveling far enough to reestablish sufficient lift. There are several problems in this particular case

1. Not enough speed.
2. Not caring enough sail to generate sufficient velocity.
3. Less overall weight might be beneficial. (not from ballast)
4. The effects of hysteresis are creating too great a time lag between changes in rudder incidence angles

Although the Racing Open 60 has very high aspect ratio keel and rudders, it is also much, much lighter for its size than the lumbering tub, it is able to carry more sail for its displacement, and when reefed, it is able to maintain sufficient speed to generate necessary hydrodynamic forces, this is key. Is this what Guillermo means by “while at speed”; I guess he will have to clarify. There are other secondary considerations for instance: The effectiveness of the auto pilot may be dependent on the quick rudder response of the high aspect rudder of the Open 60, in turn, the effectiveness of the rudder may be augmented by the autopilots ability to adjust course deviations more efficiently, quicker, with less deviation from an ideal angle of attack; to some degree this is dependent on an unknown critical velocity for the given conditions.(Unknown by us, not the designer… at least we hope)
As it is not important to me weather or not I win a debate, let me be the first to concede that I believe Vega has made some good points and given some examples of modern trends that should be considered, especially in the wake of new gear, and building materials that have come forth in the last decade. Vega has shown some examples where flexibility has been designed into the vessel to help mitigate some of the seaworthiness issues. At the same time, it is a disservice to Guillermo and others who have brought up points to consider, to conclude that the examples presented are proof that Guillermo must be incorrect. It is not necessary for me to judge who’s opinion is right or wrong; I need only to identify those statements that I know to be correct, and apply them to my particular design. I have made these observations, in part based on points that Guillermo has made.

1 Maintaining speed, or forward momentum at or above the critical velocity that produces directional stability is critical for any vessel in heavy storm conditions.

2 Speed-borne sea keeping aids considerably in the stability of a vessel due to hydrodynamic and aerodynamic damping. (This can actually be seen in the video clip of the Open 60’s posted earlier. Notice the first boat is traveling slowly and is rocking fairly hard to starboard each time it passes over a wave; the second boat is traveling much faster, and is crashing through waves at considerable speed, watch the top of the mast, and you will see the boat is rock solid.)

3. Zero speed (or 'frozen pictures') characteristics are the ones more relevant to survival conditions when boat speed has come to very low figures.(a direct quote from Guillermo)
I take this to mean when the boat can no longer maintain directional stability, or there has been some sort of damage that has stopped the boat, in which case the boat will very quickly turn broadside to the waves, and stay that way.

4. When designing a boat for cruising, a designer must take a more careful look at static stability, as dynamic stability, including velocity is more difficult to maintain in a cruising boat which is heavier by nature.

5. Light displacement should not come at the expense of adequate ballast.

 

You are right of course, yet when I pointed out what to me were obvious errors in judgement and actions that I describe as poor seamanship, the poor Beneteau 390 still got the blame.

I think your conclusion places the Beneteau 390 incident right in the 89% human error bucket and there is not a darn thing wrong with the boat.

The subject of scantlings has come up more than once to condemn light displacement boats and defend heavy displacement. If you don't know what you are doing, the only way to insure a low failure rate is to design things so lightly stressed that the long term fatigue is negligible. If aircraft were designed that way they probably would not fly. As evidence that boats are grossly over built (much heavier than they need to be) I offer a tour of almost any marina. Look at all the 30 year old boats that are still sailing with ZERO maintenance. No tests of structural integrity needed, they are tanks. 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?

Why not design with a knowledge of the materials, make the hull no heavier than it has to be and enjoy the benefits of lower production costs (less material used) and a lower CG for the same displacement? I don't think anyone would argue against a lower CG (all else being equal).

There is a concern that the new boats can be pushed past their limits. So? If I over rev the engine in my car I can damage it. Is that a design flaw? Light aircraft (where there is a greater chance of death from structure failure than sailing) can have the wings literally flown off of them if the pilot does not operate within the limits of the design. Can we not trust sailors to be as prudent as pilots?

If you can find data to support your supposition that "it would be indicative to look at the racing fleets and that we would expect to find the opposite data ie 89% to equipment failure being the cause of rescue."

I will counter that it is human error to push equipment to failure and we are right back where we started. I will also note that as far as I know there were 0 failures of Class40 boats due to design flaws. 89% of 0 is still 0. Of course centuries of sailors knowing that they had to back off under some conditions was undone by heavy, near bullet-proof boats. It became normal to push the boats as hard as you were able, since they were hard to break. Boats with limits force sailors to become prudent seaman again. The only difference is that they are doing it at 20 knots instead of 8.

How about designing a instrument system for yachts that reads how close to the design limit the boat is being operated? Rigging stress gauges and a G meter might be a good start. When conditions threaten the structure the instruments warn the operator and it is up to the sailor to back off. Just like the red-line on a tachometer or airspeed indicator. Now if a designer does not know what those limits are ... I suggest they don't design boats that are capable of performance that will expose their ignorance. Of course just about anyone can design and build a low performance, heavy, lightly stressed boat ... not much challenge there. Kind of like building a "safe" car with a lawn mower engine. It never goes fast enough to do any damage.

Why try to design so the sailor does not have to be aware? It doesn't work for airplanes, it didn't work for cars (until the advent of computer controls that now limit wheel spin and engine RPM).

I think that no matter what evidence is presented, the people that don't like modern hull shapes will find some unmeasurable quality to condemn them. Then try to make it sound like scientific fact.

 

So you have to admit it has some interest....
In my opinion, AVS is more relevant to sailing boats than to motorboats just because they have sails, so more prone to wind induced knockdowns than motorboats. And that concern on wind induced knockdowns for sailing boats appears not only at ISO 12217 but also at any other stability criteria bodies I know. Of course AVS is not the only way to express the concern.

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.
(Page 160)

It is clear that the limit of positive stability was considered in the coroner’s report the key determinant to a boats ability to resist capsize.

Cheers.

 

Tom,
I subscribe 100% your last post. Even when you say: "....Vega has made some good points and given some examples of modern trends that should be considered..."
Cheers.

P.S. Your interpretation of my "While at speed" is correct.

 

This a perfect example of your mixing on my words.
Really: Either you understand nothing of what I post (which may be my fault for not expressing things with enough clarity for everybody to understand) or you just want to play a 'winning' game which is in fact already quite boring.
(Or both things...)
Cheers.