Bieker 53 - Exciting high performance cruiser

[estarzinger]

^^ I will comment that the specific case of this capsize - it was a double user error . . . . they should have been full well aware they would get a gust as they came out from behind the island, and they should have been fully able to dump the sheets (and other reactions) instantly (during the whole racing period).

I would not place any 'blame' on this design, except that almost by definition it requires a knowledgeable and alert crew.

[Boatguy30]

Do you have a link to that stability curve graph? A f31 turtled in Mac race last year so unsure about your theory bit sounds good. Comparing righting curve of mono is irrelevant and mono will basically always come backup

[catsketcher]

Attached are curves from John Shuttleworth's page. He is a gun designer.

It shows that tris do have more gradual stability curves, monos even more so.

As to the statement that tri are now used because they have a better stability curve - is just wrong. Crowther knew in the 60s that tris had a smoother curve, the fastest multis have been swinging back and forth from tris to cats and back since the 60s. In the 80s large cats like Royale (an 80ft speedster) was the gun. Then Irens came up with Apricot in 1985 and the game changed to tris. The first multis to break the 80 day record around the world were cats ten years later. The Race in 2000 was a cat fest. Now we are back to tris. It goes back and forth depending on speed.

When a performance cat flips some people go - bad design. When a mono gets wrecked on the shore, keel falls off, hits an object and fills up the same people go "bad seamanship, bad luck". Why the dichotomy? The Beiker is a nice boat that is well designed. You don't have to flip it, but you can. You can flip your car you drive to work. You may if you race it. Is it the car's fault when you do? Are you going to stop using a car because you see one upside down next to the road?

Light cats can capsize but there is much more to safety than capsize. We don't assess safety in cars by their resistance to rolling but by a whole list of criteria. We shouldn't use the same logic in our safety assessment of our boats.

Read the whole article by a real designer if you want to learn some more.

Considerations for Seaworthiness

[catsketcher]

Curves

[Polux]

Originally Posted by catsketcher

Attached are curves from John Shuttleworth's page. He is a gun designer.

It shows that tris do have more gradual stability curves, monos even more so.

As to the statement that tri are now used because they have a better stability curve - is just wrong. .....

If my statement that race trimarans have now substituted cats as top racing offshore boats (that's a fact) because they have a better stability curve, one that allows them to be more easily controlled while racing near the limit, please state in your opinion why is that so.

I am very curious in knowing why do you think that all top offshore racing multihulls are today trimarans.

[Polux]

Note that normally curves are not normally presented with that grid and on the graphic above the cat stability curve looks a lot less abrupt than what she really is.

Here it is a 34ft monohull stability curve the way and with the grid that normally is used:



Imagine that this is the curve that represents the curve of the monohull on Shuttleworth graphic and try to place the cat's curve here and see how abrupt she really is, meaning how fast cat loses stability after reaching max RM. That is why is not advised to sail a cat flying a hull, meaning at max RM, that is also max power and when the boat has less drag.

Remember also that on monohulls, contrary to multihulls, max RM is not used for sailing and it is part of the reserve stability. On monohulls only the RM till about 35º of heel is used for sailing.

Here a better representation taken from Tony Marchaj's "Sailing Theory and Practice.

[Polux]

Regarding that comparison between the stability of a 35ft cruising racer and the stability of a 35ft catamaran, it is way off.

I don't doubt that the cat stability curve is right but regarding the monohull, that he calls a typical 35ft cruiser racer, the Max RM considered is about 10t-feet.

If we consider a modern typical cruiser racer like the Sunfast 3600 the Max RM will be 17.5t-ft, hugely superior to the one considered and with the modification of the monohull stability curve according with that value no way the surface under the stability curve of the cat would be 150% bigger. Maybe just a little bit bigger.



Note: I was posting this on the previous post but run out of time. The monohull stability curve that Tony Marchaj considers on the drawing is the one of a monohull of that time, more than 30 years ago. Now they are quite different with a bigger positive stability but also with a lower AVS and more inverted stability.

[44'cruisingcat]

Originally Posted by Polux

If my statement that race trimarans have now substituted cats as top racing offshore boats (that's a fact) because they have a better stability curve, one that allows them to be more easily controlled while racing near the limit, please state in your opinion why is that so.

I am very curious in knowing why do you think that all top offshore racing multihulls are today trimarans.

One reason is that it's easier to get greater rigidity for a given beam with a tri. The centre hull provides a good solid base for the mast, whereas with a racing catamaran, you'd only have a beam to stand the mast on.

[catsketcher]

Originally Posted by Polux

If my statement that race trimarans have now substituted cats as top racing offshore boats (that's a fact) because they have a better stability curve, one that allows them to be more easily controlled while racing near the limit, please state in your opinion why is that so.

I am very curious in knowing why do you think that all top offshore racing multihulls are today trimarans.

Polux - we have known for at least 40 years that tris have a smoother stability curve yet cats have for many years since then been the choice of top boats, but not at the moment. I gave examples and you can find more of you want to.

Probably the real reason for tris being favoured is because they can provide more sideways stability in a race configuration - they can be made wider. Also they can dig in a float bow with wave piercing bows that don't provide huge drag whereas cats have often have a large forebeam that can prove draggy. Also you can play around with volume easier than a cat as the floats and the main hull can have different CBs. Irens made Apricot amazing because he pushed the float CB forward and the GC aft, allowing the tris to power reach like crazy. Tris are fab, but it doesn't make cats less fab either. I have sailed a record breaking tri offshore - an Irens designed ORMA 60 the old Banque Populaire - it was not terribly smooth at all. Bumpy and noisy as all get out but amazing!

The Marchaj graph is way off and this graph was busted 30 years ago by Chris White - yet still it gets trotted out. The cat has nowhere near the area under the stability curve a typical cat would have. Marchaj is an ancient and pretty biased text. The Shuttleworth diagram is old - it was from the 80s but it is bad practice to just update the monos data and not the cat - that is cherry picking.

I will never convince Polux, but in the if someone else does read this, have a read of the Shuttleworth article and read more and more. If you can get to a talk by designers then do so. Some of my best boating memories are about listening to Crowther, Arber, Irens and Newick and asking them questions about the balance of their boats.

Nigel Irens interview - Yachting World

but Steve Callahan has done more interviews than anyone

http://www.stevencallahan.net/proboat.html

We can't distill all the incredible knowledge that these amazing designers have learnt into a few fundamental truths. Yacht design is a spiral where you keep on balancing a hundred different possibilities. Anyone who has built, and especially anyone who has designed and built, knows that boats are the result of many, many deliberations and that saying that a boat's success or failure is down to one, or a few points, is wrong. It's always about the right balance of things. Cats are great, light cats can be great, you just change the balance of the design to suit their needs. That is what we pay designers to do because they must do it very carefully.

[Just Another Sa]

Originally Posted by Polux

If my statement that race trimarans have now substituted cats as top racing offshore boats (that's a fact) because they have a better stability curve, one that allows them to be more easily controlled while racing near the limit, please state in your opinion why is that so.

I am very curious in knowing why do you think that all top offshore racing multihulls are today trimarans.

Nothing to do with shape of static lateral Rm curve.
The modern G-class trimarans offer far better protection from the elements for the crew sailing the boat (not off watch), and they don't have to change position from one hull to the other one like in cats after off watch is over.
Take a look at Macif, which F. Gabart used to make the single handed record around the globe. How would you offer that same level of protection in a cat?
Would you make look like a cruiser with continuous interior from one hull to the other with all the associated windage and weight?

Cats have at least 30% more wetted area for the same weight and length than trimarans in light conditions when underpowered and both hulls of the cat have roughly equal displacement, while tris carry over 90% of displacement on the mainhull. Ocean going cats don't prefer gigantic rigs to provide all the required sail area to compensate for that handicap (unlike course racing winged AC-cats) as that positions CofG much higher up, and would increase crew work load while handling the sailplan.
Tris use several headsails with their own furlers (for storing only, not for roller reefing!) and different tack points. The centerhull provides easily all those strong points at the centerline for them. To arrange than in a cat is of course possible with a longitudinal central structure above water, but that increases weight to the same level as tris.
Ps, longitudinal RM component is at least as relevant than lateral component for all multihulls when pushing it.

[Polux]

Originally Posted by catsketcher

Polux - we have known for at least 40 years that tris have a smoother stability curve yet cats have for many years since then been the choice of top boats, but not at the moment. I gave examples and you can find more of you want to.

Probably the real reason for tris being favoured is because they can provide more sideways stability in a race configuration - they can be made wider. ..
..

You have posted the information as relevant, call the designer that wrote the article " a gun designer" and suddenly it seems he doesn't know what he is saying.
[COLOR="Blue"][B]

Besides you pointed the reason why they are faster as offshore racing boats: "Probably the real reason for tris being favoured is because they can provide more sideways stability in a race configuration - they can be made wider. "

And as stability on a multihull is basically a function of beam and weight, being the weight on both configurations not that different on an offshore boat (with space for a crew to live) the beam is what makes the difference in what regards stability.

Equal weight, more beam = more power .....and a more powerful boat with about the same drag is a faster one.

That is why trimarans are the boats that are used for top offshore racing. They have the added advantage of a less brusque stability curve and are a lot more easels controllable (in what regards capsize) when sailed near the limit, near max righting moment.

But you had all that information, meaning all I am saying on the comparison of the Shuttleworth's curves you posted regarding the comparison between a 35ft trimaran and a 35 ft catamaran. We can see clearly that the trimaran has more stability, meaning more power.



Besides that being evident just looking at the curves he says that on the article: "Fig 2. shows the curve of righting moment versus angle of heel for a typical modern 35ft catamaran and trimaran racer cruiser to my design. The trimaran (Type 3 high buoyancy amas) has an overall beam of 32 ft. and the cat ( type 6 ) beam = 23ft. The trimaran has less accommodation, and is lighter than the cat, but because of the wider beam it has greater maximum stability."

[Just Another Sa]

Originally Posted by Polux

If we consider a modern typical cruiser racer like the Sunfast 3600 the Max RM will be 17.5t-ft, hugely superior to the one considered and with the modification of the monohull stability curve according with that value no way the surface under the stability curve of the cat would be 150% bigger. Maybe just a little bit bigger.

No one has written or implied a 150% greater positive area under Rm-curve for a cat. That is your own idea you are shooting down.
Max Gz of 2.5 meters is possible for the cat of that size, more than twice of the max RM of the Sunfast 3600.

[Polux]

Originally Posted by catsketcher

The Marchaj graph is way off and this graph was busted 30 years ago by Chris White - yet still it gets trotted out. The cat has nowhere near the area under the stability curve a typical cat would have. Marchaj is an ancient and pretty biased text. The Shuttleworth diagram is old - it was from the 80s but it is bad practice to just update the monos data and not the cat - that is cherry picking.

.

I assume you wanted to say monohull on the quoted in red?

Yes typically a cruising cat has a considerable bigger stability than a same sized cruising monohull but that can be not true in what regards light performance catamarans.

If that 35ft catamaran was a condo cat, with the double of the weight, that stability curve would have almost the double of the area under it and the stability would have been much bigger than the one of the monohull, even considering the Sunfast 3600 that I had considered.

As I have explained here several times, because in cats the stability is basically a function of beam and weight, performance multihulls of the same size have a much smaller stability than condo cats.

That does not happen necessarily on monohulls. We can see for instance that the Halberg Rassy 34 has a slightly small overall stability than the Sunfast 3600.

That is possible because on monohulls the stability is not only basically a function of beam and weight but the B/D and draft are also factors since they can put the CG of the boat much lower, considering different boats with different characteristics.

As I have said repetitively I am not favoring monohulls, trimarans or catamarans, neither trying to prove that some type is more or less safe than other, I am trying only to put the record straight and allow a better comprehension of the stability characteristics of diferente crafts.

Regarding you saying "Marchaj is an ancient and pretty biased text" that makes very hard to understand why Shuttleworth quotes it as the first reference for his article
http://www.shuttleworthdesign.com/NESTalk.html

yes, the monohull curve on Marchaj graphic has nothing to do with modern monohull stability curves, but I had the care to say and to explain that.

Regarding Shuttleworth article to be outdated I don't think so neither I think those multihull curves are outdated. Since the 90's nothing basically different happened in what regards the design of performance multihull design in what regards stability.

Yes, much had happened in what regards hull design, foils but they are not considerably beamier and certainly not heavier, quite the contrary, so there are not an increase in overall stability.

Regarding performance monohulls they become lighter but they increased draft, have more efficient keels and in some cases they increased B/D and that all means more stability.

The increase in power and stability on monohulls have not only to do with advances in design but with handicap rating. On the 80's and 90's stiffness and power was too much penalized and a powerful boat would not win, so the tendency was for boats with a moderate stiffness.

Fortunately things have changed and today that it is not the case anymore. There was also an increase in racing with one design and box rules (as well as it has become more important regarding top racing), like TP52, class 40, IMOCA, Farr 40, VOR and this had a big influence on performance cruising design that in the 80's was practically linked with handicap racing developments.

Finaly, Shuttleworth site is not an old one. He would not have kept information on it if it was outdated. Look at some designs on his site, really nice contemporary ones. The first one is the one that illustrates the article, an older design, but still quite "modern":

[Polux]

Originally Posted by Just Another Sa

No one has written or implied a 150% greater positive area under Rm-curve for a cat. That is your own idea you are shooting down.
Max Gz of 2.5 meters is possible for the cat of that size, more than twice of the max RM of the Sunfast 3600.

You did not read the thread or the article?

This graphic was posted by catsketcher and what the graphic says (and the article) is that a 35ft performance cat has 150% of the overall stability of a 35ft performance monohull.


Considerations for Seaworthiness

I don't understand the relevance of the diference on Max GZ neither what the GZ has to do with the Max RM. GZ and RM are not the same thing, GZ is the size of the arm and RM is the righting moment.

The GZ of a 35ft performance cat would be considerably bigger than the one of a 35ft performance monohull but the Max RM would typically have not such a big difference because the monohull, due the the ballast, would be considerably heavier.

Anyway the Max RM is not relevant to the boat overall stability, the area under the part of positive part of the RM stability curve is what matters.

On a cat the MAX RM gives a good indication regarding the overall boat stability not necessarily so on a monohull where the AVS has importance in what regards that area. A bigger AVS will increase reserve stability and will increase overall stability.

As that graphic shows the stability curves between a monohull and a multihull are very different and the only thing that can be relevant in what regards comparison is the positive area under the stability RM curve that is representative of the energy needed to capsize the cat or the multihull.

[Polux]

Originally Posted by 44'cruisingcat

One reason is that it's easier to get greater rigidity for a given beam with a tri. The centre hull provides a good solid base for the mast, whereas with a racing catamaran, you'd only have a beam to stand the mast on.

I believe that in what regards offshore racers it has more to do with a bigger beam (more RM) and an easier control in what regards sailing near max RM.

But out of offshore racing trimarans are not necessarily the fastest otherwise the America's cup multihulls would be trimarans and not cats. I believe it has to do with the possibility of designing very narrow hulls since nobody will be living inside.

Also an easier control of the boat at the limit is not so important since the races have a short course, a big top crew that will be alert all times and due the absence of offshore conditions, namely waves.