Bieker 53 - Exciting high performance cruiser

[Boatguy30]

Which cat was the 13 days one. Did not see any multi in 2011 ARC results

[Palarran]

Originally Posted by donradcliffe

This gets back to the question of allowing catamarans to race in offshore events, like Sydney to Hobart, Newport to Bermuda, Transpac, Transat, etc. The last conversation I had on this with the Transpac and Bermuda organizers was that they were fairly comfortable with professionally crewed boats, but apprehensive about the amateurs. These race organizers REALLY don't want to have to deal with capsized catamarans, especially if there is loss of life. This incident will rekindle those concerns.

Do you think this accident with the loss of two lives should make race committees rethink allowing monohulls? Not allowing multihulls to race is either due to tradition or idiocracy, especially if the reason is concern for a capsize and loss of life.

Two die in Australian offshore race >> Scuttlebutt Sailing News

[cwjohm]

Hi Polux

Referring your average daily KnM post, I find this quite informative.

I had not considered previously that in long passages you could make a certain daily mileage but this may be very different to the mileage you make along the rhumb line. Of course on reflection this is self evident.

It also reinforces my view that 300KnM days are extremely rare even in the fastest of cruising boats. Typically on long passages on "condomarans" I and others I have spoken to typically average 160-170KnM days i.e. an average of 7kn or so. On a fast boat despite the "record" speeds of 20+ a long term average of 10+ over the span of a day is done but not often. The average number I typically hear is around 220KnM days on average or around 9kn average. Of course the difference between 7kn ave and 9kn average can mean the difference between leaving and arriving in daylight.

I tend to think that this issue is not necessarily of great importance to the fast boat owner. Rather it is the opportunity to achieve significant speeds (thrills) albeit possibly fleetingly and of course most important the benefit of a "fast" boat as compared to a condomaran is that it will achieve reasonable speeds under sail more often.

[Polux]

Originally Posted by Boatguy30

Which cat was the 13 days one. Did not see any multi in 2011 ARC results

"By the way that Gunboat 66 made the passage in 11 days, 16 hours and 30 minutes while the cat, that in all these years, have impressed me more made it in 13 days 10 hours, "

In 2011 a Gunboat 66 made it in 11 days 16 hours on a Gunboat 66.

In 2014 a Philocat, the one on the movie, made it in 13 days and 10 hours.

Scroll it down till the multihulls.

https://www.worldcruising.com/conten...by%20class.pdf

[Polux]

Originally Posted by cwjohm

...
I tend to think that this issue is not necessarily of great importance to the fast boat owner. Rather it is the opportunity to achieve significant speeds (thrills) albeit possibly fleetingly and of course most important the benefit of a "fast" boat as compared to a condomaran is that it will achieve reasonable speeds under sail more often.

Yes I agree. A performance cat with enough wind and a knowledgeable crew having fun and sailing the boat on race mode, with somebody at the wheel and others controlling the sails can reach high speeds easily.

A modern performance monohull too but not so easily.

In what regards cruising that's another story and while a cat is sailed to the wind considering gusts (and even so conservatively) a performance monohull is sailed considering apparent wind since on gusts the boat just heels more.

That's what makes for a similar cruising performance even if a performance cruising cat can be sailed downwind faster while racing. Even while racing, on races with upwind legs not always the performance cats are faster as we can see by the results on the fastnet on the last 5 years or so.

Another curious thing and one that I was not expecting is that on the trade winds (ARC) the speeds of performance cats (cruising) are not very different than the one of good condo cats. that's probably for the same reason: on condo cats due to the bigger stability sailors feel more at ease with having more sail up while cruising while on much lighter performance cats sailors just sail more conservatively due to the smaller overall stability.

Where the performance cats are much faster is upwind, on lighter winds and of course, in "race mode" with an experienced crew. But more important than that a performance cat will be sailing when a condo cat will be motoring (light winds).

[fxykty]

Originally Posted by Polux

Yes I agree. A performance cat with enough wind and a knowledgeable crew having fun and sailing the boat on race mode, with somebody at the wheel and others controlling the sails can reach high speeds easily.

A modern performance monohull too but not so easily.

In what regards cruising that's another story and while a cat is sailed to the wind considering gusts (and even so conservatively) a performance monohull is sailed considering apparent wind since on gusts the boat just heels more.

That's what makes for a similar cruising performance even if a performance cruising cat can be sailed downwind faster while racing. Even while racing, on races with upwind legs not always the performance cats are faster as we can see by the results on the fastnet on the last 5 years or so.

Well, at FastNet you’re generally comparing larger monohulls with smaller multihulls. But I see in the most recent edition a 70 foot tri beat the first monohull (88 feet) by over 10 hours and 29% faster upwind. An HH66 and Dazcat 1495 finished in 3 days 3/5 hours respectively; while the fastest mono in IRC A finished over an hour behind that and most a half or full day behind. Darn those slow multihulls. How about the result of the recent RORC 600 race - smaller 63 foot tri finished first, not setting a record, while the larger 88 foot mono finished 30 minutes behind and set a record.

Originally Posted by Polux

Another curious thing and one that I was not expecting is that on the trade winds (ARC) the speeds of performance cats (cruising) are not very different than the one of good condo cats.

No, the reason is just as likely that the condo cat crews are motoring in the lighter patches. It’s also confounded by the use of racing crews on some boats. And while sailing in a given breeze, the condo cat will require more sail area (power) to match a performance cat, which may be reefed conservatively but still providing the power needed (and likely going faster anyway due to better hull dynamics). Crews on both boats will be comfortable and not pushing things. The motoring and use of racing crews is why you can’t easily compare performance in an ARC.

Originally Posted by Polux

that's probably for the same reason: on condo cats due to the bigger stability sailors feel more at ease with having more sail up while cruising while on much lighter performance cats sailors just sail more conservatively due to the smaller overall stability.

I’m finally calling BS on your constant refrain of higher displacement equaling higher stability. Stop spreading incorrect information.

Displacement and beam (between hull centrelines, not overall beam) contribute positively to static stability, while sail area and the height of lateral resistance of the sail area detract from static stability. Anything a condo cat gains in stability with displacement it loses in stability due to higher sail area and higher height of lateral resistance.

Add in wave action and you need to also consider the height of centre of gravity. Again, the condo cats do worse on this factor than performance cats.

Create an account on www.multihulldynamics.com and explore SSpd (wind speed in knots to begin lifting a hull) and KSI (wind speed in knots from abeam to capsize) for condo cats and performance cats. Comparing our cat to a Leopard 58, which has twice the displacement, we have SSpd and KSI only one knot less each. Not half!! And that doesn’t account for the much higher height of lateral resistance for the Leopard, which in the formulae is basically a constant factor based on LOA.

Originally Posted by Polux

Where the performance cats are much faster is upwind, on lighter winds and of course, in "race mode" with an experienced crew. But more important than that a performance cat will be sailing when a condo cat will be motoring (light winds).

Much faster in all directions, not just upwind, with less sail area (sailing conservatively as you call it). The difference in hull shapes means a performance boat is more easily driven (less power required) in any direction. Similar effect as for performance monohulls vs cruising (say a J160 vs an Amel 53).

[Polux]

Originally Posted by fxykty

Well, at FastNet you’re generally comparing larger monohulls with smaller multihulls. But I see in the most recent edition a 70 foot tri beat the first monohull (88 feet) by over 10 hours and 29% faster upwind. An HH66 and Dazcat 1495 finished in 3 days 3/5 hours respectively; while the fastest mono in IRC A finished over an hour behind that and most a half or full day behind. Darn those slow multihulls. How about the result of the recent RORC 600 race - smaller 63 foot tri finished first, not setting a record, while the larger 88 foot mono finished 30 minutes behind and set a record.

Racing trimarans are faster than racing monohulls . I only compare performance cruisers with performance cruisers of the same size and that is what I am talking about.

I said that in some editions the wind was favorable to catamarans, on the last one was favorable to cats, on the previous one it was not and on the others it had varied.

If you want to make a comparison you cannot look to only one edition but to the last 5 or 6 ad you will see that I am correct, on some editions performance cruising cats are faster on others are slower due to the different wind and sea conditions.

Originally Posted by fxykty

No, the reason is just as likely that the condo cat crews are motoring in the lighter patches. ..

The beauty of ARC os that most are cruising but also trying to make in fast not to look bad. Because they are cruising they use the engine, like any cruiser would do and the number of engine hours is given at the end of the race. The only ones that are not using the engine are the monohulls from the racing division, a minority.

All cruisers would use the engine on a Transat so it is about how a boat is efficient or not doing a Transat, not about racing.

Regarding catamarans even the fast ones use generally the engine. For instance that Gunboat 66 that made an incredible passage used the engine for almost 60 hours. That fast Philocat used the engine too.

Originally Posted by fxykty

I’m finally calling BS on your constant refrain of higher displacement equaling higher stability. Stop spreading incorrect information...

Add in wave action and you need to also consider the height of centre of gravity. Again, the condo cats do worse on this factor than performance cats.

Your lack of knowledge regarding this is dangerous to the ones that believe your words.

I have already told you that you can find a significant number of performance cruising cats with 50ft or over that have capsized and cannot find a single condo cat of that size that has capsized.

Since for each performance cat there are at least 4 or 5 condo cats you should have 5 times more capsizes of condo cats (of that size) than performance cats and not none.

Only this should tell you that you are wrong and should make you try to understand why ou are wrong, trying to be more informed about the subject.

Monohulls due to different B/D and due to different drafts that put the CG of the ballast lower or higher can have very different CG.

The cats not having ballast don't have a big difference in what regards CG being them performance or not. Sure a performance cat has a lower CG but the difference is minimal if we compare with diferente types of monohulls.

The RM is obtained by GZ*Displacement and the total energy required to capsize the boat is equal to the positive area under the RM stability curve.

The GZ curve of same length monohulls can be considerably different due to the very different CG of diferent monohulls .

On same lenght cats due to very similar CG a the GZ curves have essentially to due with beam and that's why some cat designers use the simplified formula for stability that I had posted before, one that does not consider CG but only beam and displacement.

So, yes on cats, in what regards two stability, you have two factors: beam and displacement. So obviously displacement, contrary to what you say is determinate for cat stability since it is one of the factors.

Regarding sail area it is true that a cat with more weight needs more sail area but anybody familiarized with boat design can tell you that performance is not directly proportional to the increase in sail area and that a boat with the double of the weight and the same size is very far from having or needing the double of the sail area.

Also, a simple verification regarding models on the water will tell you (if you don't know that already) that performance boats, being them cats or monohulls have a much bigger SA/D than cruising boats, being them condo cats or cruising monohulls.

I have not a performance cat neither a condo cat and I am not biased on this discussion.

Recently a famous boat designer with many monohull and cat designs, including many race boats, bought a cat (one of his designs) for sailing with the family. When asked why he chose a condo cat over a performance cat he told that it was for safety reasons, to sail in a more relaxed way and that the speed that condo cat provided was already more than enough.

Obviously I am not saying that a performance light performance cat is dangerous only that it has to be sailed more conservatively than a condo cat, not in a so relaxed way and it demands a more experienced crew not being a great choice for a solo sailo or even for a couple unless they are both experienced sailors (it is rarely the case) unless they do only coastal sailing (meaning mostly day sail).

If I had a cat I would have a performance one, I like particularly the Sig 45 but that does not mean that I ignore its stability characteristics or the care I should have while sailing that kind of boat. Certainly not in a relaxed way but then I like to sail in a sportive way. My wife would not agree to me dough and I don't know if I could convince her to let me have one. I suspect not.

Originally Posted by fxykty

Much faster in all directions, not just upwind, with less sail area (sailing conservatively as you call it). The difference in hull shapes means a performance boat is more easily driven (less power required) in any direction. Similar effect as for performance monohulls vs cruising (say a J160 vs an Amel 53).

Who says the opposite? I am only saying, after many years looking at the ARC performance, that on a cruising Transat generally condo cats are only slightly slower than performance cats, a much smaller difference than their absolute performance may suppose.

I gave an explanation, you can find another but the fact remains.

And regarding racing crews it is very unlikely that you will have racing crews or more sportive crews on condo cats than on performance cats. Regarding fuel consumption, in some cases there are differences but on others not.

[fxykty]

Originally Posted by Polux

Racing trimarans are faster than racing monohulls . I only compare performance cruisers with performance cruisers of the same size and that is what I am talking about.

I said that in some editions the wind was favorable to catamarans, on the last one was favorable to cats, on the previous one it was not and on the others it had varied.

If you want to make a comparison you cannot look to only one edition but to the last 5 or 6 ad you will see that I am correct, on some editions performance cruising cats are faster on others are slower due to the different wind and sea conditions.



The beauty of ARC os that most are cruising but also trying to make in fast not to look bad. Because they are cruising they use the engine, like any cruiser would do and the number of engine hours is given at the end of the race. The only ones that are not using the engine are the monohulls from the racing division, a minority.

All cruisers would use the engine on a Transat so it is about how a boat is efficient or not doing a Transat, not about racing.

Regarding catamarans even the fast ones use generally the engine. For instance that Gunboat 66 that made an incredible passage used the engine for almost 60 hours. That fast Philocat used the engine too.



Your lack of knowledge regarding this is dangerous to the ones that believe your words.

I have already told you that you can find a significant number of performance cruising cats with 50ft or over that have capsized and cannot find a single condo cat of that size that has capsized.

Since for each performance cat there are at least 4 or 5 condo cats you should have 5 times more capsizes of condo cats (of that size) than performance cats and not none.

Only this should tell you that you are wrong and should make you try to understand why ou are wrong, trying to be more informed about the subject.

Monohulls due to different B/D and due to different drafts that put the CG of the ballast lower or higher can have very different CG.

The cats not having ballast don't have a big difference in what regards CG being them performance or not. Sure a performance cat has a lower CG but the difference is minimal if we compare with diferente types of monohulls.

The RM is obtained by GZ*Displacement and the total energy required to capsize the boat is equal to the positive area under the RM stability curve.

The GZ curve of same length monohulls can be considerably different due to the very different CG of diferent monohulls .

On same lenght cats due to very similar CG a the GZ curves have essentially to due with beam and that's why some cat designers use the simplified formula for stability that I had posted before, one that does not consider CG but only beam and displacement.

So, yes on cats, in what regards two stability, you have two factors: beam and displacement. So obviously displacement, contrary to what you say is determinate for cat stability since it is one of the factors.

Regarding sail area it is true that a cat with more weight needs more sail area but anybody familiarized with boat design can tell you that performance is not directly proportional to the increase in sail area and that a boat with the double of the weight and the same size is very far from having or needing the double of the sail area.

Also, a simple verification regarding models on the water will tell you (if you don't know that already) that performance boats, being them cats or monohulls have a much bigger SA/D than cruising boats, being them condo cats or cruising monohulls.

I have not a performance cat neither a condo cat and I am not biased on this discussion.

Recently a famous boat designer with many monohull and cat designs, including many race boats, bought a cat (one of his designs) for sailing with the family. When asked why he chose a condo cat over a performance cat he told that it was for safety reasons, to sail in a more relaxed way and that the speed that condo cat provided was already more than enough.

Obviously I am not saying that a performance light performance cat is dangerous only that it has to be sailed more conservatively than a condo cat, not in a so relaxed way and it demands a more experienced crew not being a great choice for a solo sailo or even for a couple unless they are both experienced sailors (it is rarely the case) unless they do only coastal sailing (meaning mostly day sail).

If I had a cat I would have a performance one, I like particularly the Sig 45 but that does not mean that I ignore its stability characteristics or the care I should have while sailing that kind of boat. Certainly not in a relaxed way but then I like to sail in a sportive way. My wife would not agree to me dough and I don't know if I could convince her to let me have one. I suspect not.



Who says the opposite? I am only saying, after many years looking at the ARC performance, that on a cruising Transat generally condo cats are only slightly slower than performance cats, a much smaller difference than their absolute performance may suppose.

I gave an explanation, you can find another but the fact remains.

And regarding racing crews it is very unlikely that you will have racing crews or more sportive crews on condo cats than on performance cats. Regarding fuel consumption, in some cases there are differences but on others not.

OMG, Pollux, neither of us is a naval architect so nobody else should be taking our postings as gospel. Hopefully we are both somewhat informed and not completely wrong.

Bottom line, I agree that a condo cat is less likely to capsize. But zero - that is demonstrably not true. Here is one, http://www.yachtingmonthly.com/news/...r-a-year-34308. I’m sure more diligent searching will find more. But I totally disagree that a performance cat of half the displacement of a same length condo cat is twice as likely to capsize. That is the message you’re spreading, and it is simply not true.

I am getting fed up with you with your constant refrain that displacement equals stability. That is only part of the equation and is missing other factors that have just as much bearing as displacement and beam: sail area (absolute sail area, not the SA/D ratio - of course a lighter boat will have a higher SA/D) and the height of the centre of effort (for static stability, that is before a boat begins to heel). The point here is that the benefit to stability of greater displacement is offset to some greater or lesser degree by sail area and the vertical position of that sail area. Unless the condo cat is designed to motor (which I suppose is true as their fuel tanks are usually huge) then they will have a relatively large rig to provide enough power to keep moving in lighter airs.

Most performance catamarans, particularly over 45 feet, are less than 20% less static stability than their heavier condo cat sisters (using the SSpd and KSI numbers I referenced earlier - true formulae for stability and not the back of a napkin estimation that you favour).

Regarding sailing relaxed on a performance cat, absolutely. You reef down to well below what is needed, often to reduce the speed to keep the passage making comfortable, and you’re still reeling off big days because your performance cat is easily driven. The effective SA/D ratio on passages falls way down due to reefing. Other than in very light winds, no need to run gennakers or spinnakers. Seems safe to me and doesn’t require significantly more vigilance than any other type of boat. And you have the option to step on the gas and have some fun with “sportive” sailing if you want - condo cat, not so much.


Finally, the Atlantic ARC is not a typical ocean passage as it is extraordinarily downwind relative to the South Pacific, Indian Ocean and South Atlantic coconut milk run routes. Let alone the variety of cross wind passages to get out of cyclone zones. And of course when new models of boats are introduced they are usually entered into the Atlantic ARC with a larger crew as a marketing effort - it’s not just mom and pop crews. Boat performance in the ARC is interesting, but it doesn’t have much to do with real world cruising performance.

[TJ D]

Hey, Polux-You are a naval architect, aren't you?

I hereby officially retract my 300/day claim as well. I should have said 250! And not 'easily', either. The boat must be somewhat aggressively sailed (but still not in race mode).

I sort of thought that anyone who would take on a passage shorthanded on a boat like this would be understood to be quite skilled.

But, that is perhaps an assumption that doesn't hold up.

Let the argument resume...

[Polux]

Originally Posted by TJ D

Hey, Polux-You are a naval architect, aren't you?

I hereby officially retract my 300/day claim as well. I should have said 250! And not 'easily', either. The boat must be somewhat aggressively sailed (but still not in race mode).

I sort of thought that anyone who would take on a passage shorthanded on a boat like this would be understood to be quite skilled.

But, that is perhaps an assumption that doesn't hold up.

Let the argument resume...

No just an architect with interest is naval architecture, like Finot LOL.

I am half kidding, Finot was really an Architect with an interest in naval architecture (not a former education in Naval Architecture) but his work speaks for himself. I have not designed boats but that is not needed to know about stability. It is only to have the knowledge.

In what regards basic stuff I have some articles about on my blog that are intended to provide sailors with a grasp on the subject.

[Polux]

Originally Posted by fxykty

....
Bottom line, I agree that a condo cat is less likely to capsize. But zero - that is demonstrably not true. Here is one, Missing Sunsail yacht found after a year - Yachting Monthly. I’m sure more diligent searching will find more. But I totally disagree that a performance cat of half the displacement of a same length condo cat is twice as likely to capsize. That is the message you’re spreading, and it is simply not true.

It seems that you have some difficulty in understanding what I say. I said that are several performance cats with 50ft or over that have capsized on the last 10 years or so and that I don't know of any condo cat with 50ft or over that had capsized.

Just looking at that cat you posted we can see that it is far from 50ft (much less over 50ft) in fact if I am not mistaken it is a 44ft boat, so, please read what I say and stop saying that I am saying things that are not true.

Originally Posted by fxykty

I am getting fed up with you with your constant refrain that displacement equals stability. That is only part of the equation and is missing other factors that have just as much bearing as displacement and beam: sail area (absolute sail area, not the SA/D ratio - of course a lighter boat will have a higher SA/D) and the height of the centre of effort (for static stability, that is before a boat begins to heel). .....

And you keep misunderstanding and misquoting me, I never said that displacement equals stability, I said that in what regards cats and in an approximated way, displacement is one of the factors regarding static stability, the other one is beam.

The approximation is close enough for being used by cat designers that have not a solid formation in physics and mathematics, for designing cats.

In what regards beam today there is not a difference between the beam of performance cats and condo cats, regarding same length cats. That is why in that case displacement is a determinant factor in what regards the difference of stability between condo cats and performance cats with the same length.

For having the same stability of a smaller condo cat a performance cat has to be bigger, that means more weight and more beam than it would have if it had the same size of the condo cat.

That is why condo cats builders start their offshore boats at 38ft (there are lots of them with 40ft) while performance cat manufacturers start their lines with 42/45 ft boats and that's why really light performance cats, like the Bieker, have normally 50ft or over.

Sail area is a completely different issue than boat stability. Stability is what allows the boat to carry a bigger or smaller sail area depending on a bigger or smaller stability.

Again there are some formulas to calculate a safe sail area for a cat, that are used by the same cat designers that use the simplified formulas to calculate static stability. Sometimes the formula to determine cat stability incorporates the one to find the safe sail area for a given stability.

Of course those formulas give you only a good idea of the sail area a given stability is able to carry in what regard a cat sailing with full sail area.

The stability of a cat remains the same if you sail with a reefed boat or not what varies is the rotating moment created by the wind on the sails.

If you have two cats with the same beam one with the double of the weight than the one with half the weight has about half the stability meaning that it would only need half the energy to be capsized.

Of course the heavier cat will need more sail but it does not need the double of the sail and if you will check you will see that there are some performance cats that have just a bit less sail area than condo cats with the same length and beam, having the performance cat a much smaller displacement.

I hope that the information I provided is useful, at least to some, in what regards to understand better stability. Unless you put again in my mouth things I did not said I will finish this here. I believe all this is already sufficiently clear.

But I would like to say again that nothing of this means that performance cats are dangerous. They demand more experience sailors, they need size to have a better safety margin (the lighter the bigger) and they should be sailed more conservatively than condo cats.

I personally prefer them to condo cats even if obviously the majority of sailors prefer condo cats. That's why there are 4 or 5 condo cats for each performance cat. None is better than the other, just different types of boats with different advantages and disadvantages.

[fxykty]

Last one too, we are generally in agreement except on one point (that twice the displacement equals twice the stability that as sailors we need to care about). I’m starting to think that is simply the two of us meaning two different things but using the same word.

Originally Posted by Polux

It seems that you have some difficulty in understanding what I say. I said that are several performance cats with 50ft or over that have capsized on the last 10 years or so and that I don't know of any condo cat with 50ft or over that had capsized.

Just looking at that cat we can see that it is far from 50ft (much less over 50ft) in fact if I am not mistaken it is a 44ft boat, so, please read what I say and stop saying that I am saying things that are not true.

A length constraint in capsized cruising (not racing, like the Bieker 53) boats certainly shallows the pool of boats. I can think of two Atlantic 47 that capsized while cruising, but am not sure of larger performance cats in the range you’ve referenced.

As for 50 feet and over condo cats - not many of those cruising the oceans. Possibly no more than there are performance cats of that size. The vast majority of cruising condo catamarans are in the low to mid 40s, with cruising performance cats perhaps 5-10 foot longer on average. Other than in charter operations, how often have you seen over 50 foot condo cats?

Originally Posted by Polux

And you keep misunderstanding and misquoting me, I never said that displacement equals stability, I said that in what regards cats and in an approximated way, displacement is one of the factors regarding static stability, the other one is beam.

Here’s where we differ - you refer to static stability and I’m referring to dynamic stability, that is, what happens once the cat begins to heel. That’s why I refer to other factors and that just referring to displacement (and beam) is misleading for real world comparisons. Maybe we can say we’re both right?

Originally Posted by Polux

The approximation is close enough for being used by cat designers that have not a solid formation in physics and mathematics, for designing cats.

In what regards beam today there is not a difference between the beam of performance cats and condo cats, regarding same length cats. That is why in that case displacement is a determinant factor in what regards the difference of stability between condo cats and performance cats with the same length.

For having the same stability of a smaller condo cat a performance cat has to be bigger, that means more weight and more beam than it would have if it had the same size of the condo cat.

That is why condo cats builders start their offshore boats at 38ft (there are lots of them with 40ft) while performance cat manufacturers start their lines with 42/45 ft boats and that's why really light performance cats, like the Bieker, have normally 50ft or over.

It’s also about getting a reasonable accommodation plan and load carrying capacity in narrower hulls. Increased relative stability is a bonus.

As an aside, our 55 foot cat has a dynamic stability rating about 5% less than a Leopard 58 that weighs twice as much. Not half. Even though the static stability is half. Which one matters more for a cruising boat on the ocean?

Also note that legally cat designs have to satisfy a dynamic stability formula, not static. Refer to https://www.law.cornell.edu/cfr/text/46/171.057

Originally Posted by Polux

Sail area is a completely different issue than boat stability. Stability is what allows the boat to carry a bigger or smaller sail area depending on a bigger or smaller stability.

Ummm, no, sail area is a factor in dynamic stability. Once the boat has wind operating on it, sail area and the position of the sail area matter. And for behaviour in waves and greater angles of heel you need to include the height of the centre of gravity. I expect condo cats don’t do so well with that, so this also keeps performance cats from being as poor stability-wise as your displacement and beam only mantra.

Originally Posted by Polux

Again there are some formulas to calculate a safe sail area for a cat, that are used by the same cat designers that use the simplified formulas to calculate static stability. Sometimes the formula to determine cat stability incorporates the one to find the safe sail area for a given stability.

Of course those formulas give you only a good idea of the sail area a given stability is able to carry in what regard a cat sailing with full sail area.

The stability of a cat remains the same if you sail with a reefed boat or not what varies is the rotating moment created by the wind on the sails.

If you have two cats with the same beam one with the double of the weight than the one with half the weight has about half the stability meaning that it would only need half the energy to be capsized.

Of course the heavier cat will need more sail but it does not need the double of the sail and if you will check you will see that there are some performance cats that have just a bit less sail area than condo cats with the same length and beam, having the performance cat a much smaller displacement.

Half the energy to lift a hull. After that, dynamic stability takes over. It’s a long way from lifting a hull to capsizing - granted, it can happen quickly, even for a Hobie 16, which has significant positive righting moment through 70 degrees. Performance cats generally have much higher angle of heel before righting moment goes negative - the righting moment curve has a lower maximum height but extends further towards higher angles of heel, so overall stability is no worse. Designs like the Seawind with raised hull cabins quite possibly have a righting moment curves past 90 degrees, even though given their lighter displacements their static stabilities are lower than comparable size and heavier condo cats.

And yes, the maximum righting moment (aka static stability) calculation can be used to calculate rig scantlings, though sail area depends on other calculations to determine power requirements.

Originally Posted by Polux

I hope that the information I provided is useful, at least to some, in what regards to understand better stability. Unless you put again in my mouth things I did not said I will finish this here. I believe all this is already sufficiently clear.

Agreed, surely we’re both tired of this. The take away for others - stability is calculated both static and dynamic, and each means something different. Though as we’ve seen from something like IRMA, no amount of static stability helps in extreme conditions.

Originally Posted by Polux

But I would like to say again that nothing of this means that performance cats are dangerous. They demand more experience sailors, they need size to have a better safety margin (the lighter the bigger) and they should be sailed more conservatively than condo cats.

I personally prefer them to condo cats even if obviously the majority of sailors prefer condo cats. That's why there are 4 or 5 condo cats for each performance cat. None is better than the other, just different types of boats with different advantages and disadvantages.

+1

[tp12]

I think it's important to make a distinguishing point at this juncture of the thread. Performance cats only demand more experienced sailors when they are sailed close to the edge of their performance envelope. Like all sailboats, you can reduce sail for the conditions. Sailing a performance cat conservatively, well within its limits, does not require the same experience.

You can cruise like that and open her up occasionally when experienced crew are aboard or when you've gained that experience yourself. This is no different to how people get used to powerful motorcycles, or cars.

There's a saying in motorcycle racing "the throttle goes both ways"

[Franziska]

@tp12

Fully agree.

[Just Another Sa]

Originally Posted by fxykty

Also note that legally cat designs have to satisfy a dynamic stability formula, not static. Refer to https://www.law.cornell.edu/cfr/text/46/171.057

Where on this planet is that law enforced?
Please inform us so we all know to never go there to sail in our illegal boats.
It practically dictates that only condocats are legal, and not all of those meet the criteria even on protected waters.
Surely all cats ever used on olympics as well as hobie 16 are totally illegal then in the country there that law applies. They would need to reduce their upwind sail area more than 90% to be legal and no downwind sails at all.
The most absurd law I ever saw anywhere.