Characteristics of Offshore Yachts

[leftbrainstuff]

Originally Posted by mstrebe

Characteristics of offshore yachts is an excellent book that anyone considering an offshore boat should read. That said, most keelboats are made to its parameters these days. It's actually hard to find hulls with very serious violations.

Secondly, it takes both good seamanship and a seaworthy boat to safely cross an ocean, but both of those factors merely reduce risk, they don't eliminate it. Fools can be lucky in bathtubs, and professional sailors can die in a battleship. One-off anecdotes of success or failure mean nothing when you're talking about risk, they serve merely to reinforce incorrect cognitive biases for or against something. You can't prove anything with an anecdote.

There's no such thing as a perfectly safe boat in every storm, and no such thing as a sailor who can face down any typhoon every time in any boat.

What turns anecdotes into useful information is compiling a lot of them into statistics. Once is an accident. Twice is a trend. Ten times is a characteristic. The more information we compile about seaworthiness, the more seaworthy boats we can make.

In the Fastnet '79 race, many boats that lied ahull were capsized, but none that hove-to were. Because we're talking about hundreds of boats, that provides real statistics that mean something. It proves that regardless of type, keeping the bow (or stern) to the waves is vastly safer than letting the boat simply drift. A wave 1/3 the LWL of a boat can capsize it from the aft quarter, but a boat can survive waves longer than its LWL if its met bow on. That's a dramatic safety factor that requires constant seamanship during a storm--you're much safer if you tend your direction during a storm and don't just batten down and pray.

The new stability index (STIX)-based CE regulations in Europe are having a dramatic effect on manufacturers. My boat (which for me is a weekender) was build to have an All-Ocean rating--but only just barely. If you run the numbers, you can see that Beneteau modified the boat's design to be safer in order to achieve the A rating they wanted for the boat. So you've got a marketing factor ("All ocean rated") with real meaning in these CE regulations. I think it's going to save lives ultimately, as manufacturer's cannot simply self-certify a boat as being "blue water". It now has to mean something.

The Stability Index itself is based on insurance actuarial data and statistics from disasters like FastNET and Sydney-Hobart. It's not complete, but it is good solid statistical information about what makes a boat safe, compiled into numbers that boats can be built to. That's how disasters come to have future meaning that benefits all.

Finally, while the physics remain the same, our ability to model them with finite state analysis and computational fluid dynamics (CFD) make it possible to run simulations of hulls in storms thousands of times over to test permutations of ideas and effects of seemingly minor changes on stability and recovery. This is also vastly improving form stability of hulls and providing exact information about what is required of a keel to right a boat.

It was CFD modeling that proved that in fact a boat needn't avoid being beamy to return upright, because guess what? In a storm, there's ALWAYS another wave that will start the return roll. As long as the boat is more stable right-side up than upside down, it will return to right-side up.

Click on my boat and you'll see a boat decried as a floating hotel. It's all there, open interior plan, care taken with interior design, beamy.

Well, it's CE all ocean rated, it will roll back over within 3 minutes if it's turtled despite its beam, it'll float on either side with its companionway above water should it loose its keel, and its hull form has been tested in a CFD virtual storm thousands of times over with waves hitting from every direction.

And before you say that computer simulations are meaningless and statistics won't save anyone, please back your opinion up with something besides bloviation and anecdotes.

Its good to see some solid engineering and analysis being applied to vessel design.

The existing ocean ratings are more akin to hotel star ratings. If you have feature or equipment on the list you get a rating. Great marketing aspect but has no correlation with survivability.

And survivability is the non functional parameter we are talking about here. Survivability implies that the system is robust, meets minimum performance criteria, can be repaired in service and can be managed in survival conditions.

Modelling and simulation is great, as is statistical analysis providing we have a clear definition of the requirements and can validate in service. The problem is we lack a clear definition of survivability and how will it be applied in practice.

In most cases we dont have statistically valid data for what is a wide ranging broadband data set We only have individual vessel data sets. The ocean and wind is highly variable, unlike road data, which requires very large test sets to deliver validation. A single stability rating will not solve this problem but may eventually lead to better boat designs. The static stability index for SUVs acts similarly.

I have 30 years of engineering analysis and testing in motorsport, automotive and defence. Unless modelling, simulation and analysis is correlated in practical, repeatable, real world tests it is very dangerous to trust those results.

In automotive, defence and motorsport there are specific and legislative tests that are mandated and for which we have good historical evidence. Until we see the same for sailboats I dont expect any improvement in survivability in the near term.

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[Cap Erict3]

It should be noted that Don Jordan did much to assuage the weather concerns of sailors. After the Fastnet disaster he chose not to attempt to build an unsinkable vessel, but to design a viable strategy and equipment to allow a vessel to survive those devastating conditions.

While the design elements that will help a vessel to remain afloat, return to an upright position and retain maneuverability have long been known, those elements will continue to take a back seat to other aspects of sailboat design.

The boats that I have seen that were truly designed to function after submersion were submarines.

Never saw one fly a spinnaker.


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Looking for another pretty place to work on the boat.

[Terra Nova]

Cap--good post.

TN is built like a submarine, with her flush deck. This photo illustrates how much camber is in the deck.

[Cap Erict3]

Thanks. Sweet boat.

Fair winds


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Looking for another pretty place to work on the boat.

[mitiempo]

Originally Posted by skipmac

Obviously if you're talking about short trips, day sails, coastal cruising, etc the very rough, rule of thumb, approximate guidelines I listed (somewhat tongue in cheek) do not apply. And of course local conditions and regional weather phenomena also apply. As they say on the internet, YMMV.[/COLOR]

Some of the best sailing around here is a trip around Vancouver Island. There is a race around as well - the Van Isle 360.

Vancouver Island nudges 50 degrees N on the north end. The closest land to the west when on the outside is Japan.

Even Victoria is 48 Degrees N and is south of the border between Canada and the US.

[K_V_B]

Originally Posted by mitiempo

Some of the best sailing around here is a trip around Vancouver Island. There is a race around as well - the Van Isle 360.

Vancouver Island nudges 50 degrees N on the north end. The closest land to the west when on the outside is Japan.

Even Victoria is 48 Degrees N and is south of the border between Canada and the US.

People here will sail Beneteaus as far north as the Lofoten, and think nothing of it. And that's 70° north. People often forget how far north Europe really is. The French Mediterranean coast is already north of latitude 40, which is why to us the idea that this is an extreme latitude is somewhat silly...


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[El Pinguino]

Its all about the warm currents....that and the fetch.... oh and the hype... 'roaring forties' has a nice sort of a sound to it...

Meanwhile.... 33 days out of NZ....48* S ....

[Steadman Uhlich]

Originally Posted by El Pinguino

Its all about the warm currents....that and the fetch.... oh and the hype... 'roaring forties' has a nice sort of a sound to it...

Meanwhile.... 33 days out of NZ....48* S ....

Good photo to prove a good point.

So says a former Latitude 38 Sailor.

_________________

[skipmac]

And to see the other side of the coin. Here's a GRIB from passageweather.com for the North Atlantic this week.


Note that the bottom edge of this system is just about 40 north latitude.

[skipmac]

And here's the GRIBs for 12 May showing the wind forecast between 40 and 50 south just below Australia and moving east.

No, I guess there's never any strong winds at 40 south or 40 north either. Perfect areas for daysailing.

[hpeer]

50°North, Labradore coast, June.

Here is where the "polar zone" dips furthest South.

[Exile]

Originally Posted by hpeer

50°North, Labradore coast, June.

Here is where the "polar zone" dips furthest South.

I guess we now know why you like steel cutters.

[Capt Phil]

After about 30 years of commercial work at sea in the PNW fishing, towing logs and barges and beach combing, then nearly 30 more years of doing deliveries on the west coast from Alaska to Panama in both directions, my definition of a capable 'blue water' sailor/cruiser is that it reaches port safely, with minimal gear failures and arrives with as many as she leaves with. Pretty objective, I think! Cheers, Phil

[estarzinger]

This topic is very complicated. It has not been successfully completely covered in any book I have yet seen (including Desirable and Undesirable Characteristics of Offshore Yachts).

Just for example, consider the french centerboard boats (like the Ovni and it's various sisters). These designs have been used very extensively by the french in the southern ocean, and they have an excellent track record in severe storms. Their two primary positive characteristic are (1) their ability to slide sideways in big breaking waves, rather be tripped over their keels and roll, and (2) their ability to be perfectly balanced & track straight downwind even when heeled on the side of big waves. But they would score extremely low on the "desirable' book scale, and the books authors did not really even consider much less study them because they are not a racing design (not very good upwind in racing terms). So, this whole design approach/space was not explored by that book.

In our own boat we choose to build in both massive initial stability and a very high AVS. This combination meant we were very hard to knock over (the high initial stability) but also likely to bounce back up quickly if knocked over (the high AVS). This combination is also not really considered by the book's authors because it requires more ballast than a racing boat will want to carry (a competitive IMS boat our rig size/length will carry only 65% of our ballast). But in our experience it is a terrific heavy weather cruising combination.

Also, quite honestly racers did not in the fastnet and still do not really take heavy weather totally seriously. Note that in the hobart storm none/zero tried to use any sort of drag device much less the prefered series drogue solution (yes we can debate that but IMHO that is clearly the prefered solution is that situation for those sort of boat designs), and many used clearly poorly balanced sail plans when trying to run off. And many had storm sails that were too big. And many admitted in interviews afterwards they did not understand weather charts and forecasts very well. And this all in a race which was run under safety rules developed from the fastnet experience with racing skippers who get more strong weather than most. I was once told by the chair of the bermuda race that "offshore racing is being unseamanlike as fast as possible' - that was obviously tongue in cheek but he was conveying a basic truth about racing - speed, particularly in light airs, is vastly more important than heavy weather considerations (thus no-one carrying series drogues because they are 'too heavy and unlikely to be used').

. . . as to the debate about the relative contribution of the skipper vs that of the boat design . . . The physics and the tank tests say that any boat design (even the most 'desirable') can be rolled by a breaking wave higher than it's beam if it is poorly managed by the skipper. It might still be rolled even if the most skilled skipper is on board but with very significantly lower probability because there is much that skilled skipper can do to reduce the probability. This is borne out in real world experience (in both the cruising and racing fleets).

It is also possible to design a boat that will survive a hurricane with even the most unskilled skipper, but that boat will not be the most fun to sail, and is not reflective of really any design that is typically on the market today. The closest practical example I have ever seen is Ralph and Debra's Northern lights (a custom 40' steel ketch somewhat along Josha lines but with many many custom features from the vastly experienced owners). But very few owners today would want that sort of boat. And Ralph and Debra are vastly skilled offshore sailors (in addition to having this tank) (note: they just sold the boat).

Finally, I might note that I was asked a few years ago by the CCA to manage/edit a new edition of the "desirable" Book. After some consideration I declined because I considered the topic too complex and did not think we could do it justice.

[mstrebe]

Excellent post estarzinger!


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