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Old 10-06-2008, 15:31   #16
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Bill, I certainly didn't think this thread was a mono-multi debate or conversation - just a talking point about the subject, which was the capsize.
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Old 10-06-2008, 15:58   #17
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A monohull has about 1/3 the initial stability of a multihull and is thus easier to capsize.
It would be very interesting to see that claim justified by analysis .

Note I am just addressing the veracity of the claim, not wanting a mono vs cat fight - I like both cats and monos.
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Old 10-06-2008, 17:19   #18
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The problem of comparing apples and oranges. The life jacket issue may be a little different for multihulls. While it is critical to have them on while outside the boat, inside it may not matter one way or the other. IMO there may not be any immediate need to get out of the upturned hull. It would be more important to get anyone on the outside into the boat. As you are standing on the overhead in knee deep water the natural urge may be to get out but that should be resisted. These "escape" hatches that some cats have would be better called access hatches. Immersions or survival suits would be a good thing to have especially in non-tropical waters. When everyone is accounted for and things calm down you can rig up ways to get out of the water and gather your stores and emergency supplies.

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My 1/3 figure comes from a stability curve chart in a book by Chris White comparing a 50 foot tri, cat and monohull. The mono develops a maximum righting moment of 65,000 ft. lbs. The cat around 200,000. The tri around 180,000. The cat and tri have different stability curves and at one point the cat is better and at another point in the graph the tri is better so as far as the difference between two and three hulls it's a wash IMO. I posted this graph on another thread discussing this so no need to rehash it all but I just wanted to tell you where I got the statistic.
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Old 10-06-2008, 17:48   #19
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Steve, I am not questioning which has the higher initial stability, cats and tris have considerably higher initial stability than monos (but initial stability is all they do have). I am just questioning the role of initial stability when comparing the propensity of monos and cats to capsize.

I would venture that is very likely that of two cats the one with the highest initial stability will be the least likely to capsize but would be very surprised if the same can be said when comparing cats to monos as the hydrostatics and hydrodynamics between the two are different.

Again, note I am not making any claims as to which of monos or cats is most likely to capsize, just testing the veracity of the role of initial stability when comparing the two. In fact I am not biased one way or the other on the general capsize thing as I think that neither of cats or monos has any innate overall superior ability to resist capsize as they are both capable of capsizing but not necessarily for the same reasons whether that be due to the sailing environment or structural. I believe that the important thing is for skippers to understand what the particular risks are for whichever of the two they happen to sail rather than argue over which is the better in the not capsizing department.

John
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Old 10-06-2008, 18:30   #20
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Keels should not fall off, the end.

Check this story

Fatal yacht counts laid | The Daily Telegraph
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Old 10-06-2008, 18:49   #21
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Originally Posted by MidLandOne View Post
Steve, I am not questioning which has the higher initial stability, cats and tris have considerably higher initial stability than monos (but initial stability is all they do have). I am just questioning the role of initial stability when comparing the propensity of monos and cats to capsize.

I would venture that is very likely that of two cats the one with the highest initial stability will be the least likely to capsize but would be very surprised if the same can be said when comparing cats to monos as the hydrostatics and hydrodynamics between the two are different.

Again, note I am not making any claims as to which of monos or cats is most likely to capsize, just testing the veracity of the role of initial stability when comparing the two. In fact I am not biased one way or the other on the general capsize thing as I think that neither of cats or monos has any innate overall superior ability to resist capsize as they are both capable of capsizing but not necessarily for the same reasons whether that be due to the sailing environment or structural. I believe that the important thing is for skippers to understand what the particular risks are for whichever of the two they happen to sail rather than argue over which is the better in the not capsizing department.

John
It's not hard to find the data. For similar sized boats, a catamaran will usually have between 2 and 4 times the maximum righting moment of a monohull. So the cat will be far less likely to be rolled over in similar conditions.

The advantage the monohull has is that (hopefully) it will self right. Multihulls are very unlikely to, although apparently it has happened.

As evidence of this there is the Queens birthday storm - several monohulls were rolled, some of them more than once, but in every case they self righted. (One monohull did sink, but since there were no survivors we don't know if that was due to being rolled over.) In the same storm the two cats involved did not capsize. But if either of them had, they would almost certainly have stayed that way.
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Old 10-06-2008, 19:20   #22
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For similar sized boats, a catamaran will usually have between 2 and 4 times the maximum righting moment of a monohull. So the cat will be far less likely to be rolled over in similar conditions.
As I say I would like to see the analysis that shows that because cats have higher initial stability than monos that means they have less likelihood of being rolled over in similar conditions. I trust it will be forthcoming.

One could equally, if not worrying about the analytical and practical facts of the matter of the causes of capsizes, make a similar glib claim that because monos have a much higher stability beyond where a cat loses its initial stability that monos are less likely to be rolled over (in fact ballasted monos retain stability well past 90 degrees).

I suggest (and know ) that the dynamics of capsize are far more complex that that.
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Old 10-06-2008, 19:25   #23
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I believe any designer/builder, barring one off true racing boats, that build boats that loose keels are criminally liable. Granted there are circumstances, such as running boats aground and damaging the structure that would mitigate this, but if the boat is undamaged the keel must stay attached. I don't like the direction I see mono design and build going.

I also believe capsize of mono's is a very rare occurance, whereas a knockdown is common, the two should not be confused.

Multis have much more initial stability or as some well known multi designers are known to say, "they carry sail to beat hell". Mono's have ultimate stability and thus a knockdown is not a big deal. That's why they can't carry sail to beat hell.

Last weekend was the 85th running of the Mills Race: about 150 boats. The midwest has been plagued by one nasty front after another and the fleet was pasted by one late Saturday night. My brother in law was driving an old IOR 1 ton upwind and they were knocked down to it's beam ends for 3 or 4 minutes. He said the breeze went from 15 to 20 (#3 and a full main) to 50 knots instantly. No rain, no warning, no nothing, just bang, they were down. Several mono's lost people overboard, all were recovered, one rig came down, countless sails were shredded, none of the 145 mono's sunk. In the multi fleet (five boats), two boats cartwheeled, one went over the other stayed on its feet. The crew of the capsized tri was picked up by a Melges 32, the Melges went on to finish the race with extra crew. Not sure where the tri ended up but the word is the boat broke up and sank (not sure though). To me this is an example of ultimate stability compared to a very high initial stability.

So to answer the thread begun by Bill, yes monos can capsize but mostly it will be a catastrophic event like loosing a keel but it should not be compared to a knockdown.
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Old 10-06-2008, 19:30   #24
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Here:

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Quote:
Originally Posted by MidLandOne View Post
As I say I would like to see the analysis that shows that because cats have higher initial stability than monos that means they have less likelihood of being rolled over in similar conditions. I trust it will be forthcoming.

One could equally, if not worrying about the analytical and practical facts of the matter of the causes of capsizes, make a similar glib claim that because monos have a much higher stability beyond where a cat loses its initial stability that monos are less likely to be rolled over (in fact ballasted monos retain stability well past 90 degrees).

I suggest (and know ) that the dynamics of capsize are far more complex that that.
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Old 10-06-2008, 20:21   #25
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Just a note - the stability curve in the link is not typical of ballasted monos at all. Maximum righting moment will be normally be between something like 50 degrees and 80 degrees, around 60 is typical so not the 90 degrees in the graph in the link.

These are static curves, of course, and are only one part of a vessel's resistance to capsize (although for a mono they gather importance for ability to recover from capsize).

Getting back to the curves, it should also be kept in mind that the total area under the curve from zero heel to loss of stability (or if considering just to knockdown for a mono, then to 90 degrees) is important as it is proportional to the energy required to capsize the vessel.
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Old 11-06-2008, 08:04   #26
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Lets move the stability discussion somewhere else--the question of criminal liability for the loss of the keel is more important. Read the article Dana-Tenacity posted on the Australian race boat that lost its keel...the builder's design engineer and a welder are being tried on four counts of manslaughter.

As boatowners, you would prefer that your keels didn't fall off, and would applaud some system which rewarded boatbuilders for making safe keels and penalized them for making unsafe ones. However, imagine you want a new boat, and the designer/builder says--"Life is too short to risk time in prison, mate--get someone else to build your boat."

When was the last time a car or aircraft designer or builder was tried for manslaughter when someone died?? Now how about a racing car, where the designer is paid to improve performance by shaving design margins?

Do you think someone should go to jail because the keel fell off the Cynthia Woods?
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Old 11-06-2008, 08:40   #27
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I'd sure like to know why it fell off. Stories I've seen suggest that the wind and sea state weren't astonishingly bad.

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Old 11-06-2008, 12:34   #28
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On the lifejacket issue, I decided to have only manual auto inflating jackets onboard.

The downside is that if I hit the water unconscious that I will die. But given that most of the intended sailing will be singlehanded I do not consider this such a downside as it may first appear.

The upside is that it will not (or at least very unlikely) go off accidently, either at an awkward moment where a sudden restriction of movement could be a problem (ie if I went overboard attached to a lifeline), plus also if I ever took on serious water and was still at the stage of trying to fix things I would still want the option of an auto inflating life jacket available at that time or much later.....given that although I may not wear a lifejacket as much as I could / should when wearing it (attached to my Waterproofs) I do so above and below decks.

And of course me being me replacement of the automatic bit of the lifejacket may not happen at the first available opportunity

Of course this is my judgement based on my circumstances and my own experiance, and the decision has been made in the full knowledge and acceptance that ......it may be the wrong one. But IMO that is what life (and messing around in boats!) is all about making yer own decisions and then living with the consequences (or in this case, not!).



In regard to Keels falling off - I reckon my main keel will only fall off if I hit a reef at speeds far in excess of what the boat could ever achieve (my calculator says 83 knots ).....far more likely that the boat becoming "detached" from the Keel (by breaking up on a reef) will be more of a problem at that point.

Although I have never had a keel drop off I will convey my (2nd and 3rd hand) understandings.

From what I understand, keels fall off racing monos by a combination of design and build. From the design being too aggressive to last the intend life span and / or from the build not following the exact specs to the last 'nth degree......or the boat having exceed it's design life / be outside it's safety zone.....or have been used more aggressively for extended periods that the designer intended / allowed for.

IMO Keels falling off cruising mono's is either a former racing boat built for speed with the trade off made being over long term durability from stresses (hey, it's a racing boat - they are meant to be built like that!) OR a design b#llock being dropped by the manufacturer, which may of course not reveal itself for many years, in an attempt both for performance and cost effective build. Of course good old fashioned cost cutting in design and / or build can never be ruled out given the average boat builders prediliction for sooner or later running out of money and going broke.......

I recall years past that my Father had a wooden sailing boat (well, more motor than sail) with a full length keel that was maybe 18 inches deep, essential made of a lump of metal (I forget exactly what) bolted to the bottom of the hull. Every couple of years he would draw one or two of the Keel bolts and if needed he would replace them with new. The boat was maybe 10 years old when bought and owned her for around 15 years and during that time he replaced all the bolts at least once. By the time he got around to replacing all the originals (maybe 10 on a 27 Foot boat - I forget) some of them were badly wasted away in the middle even though they looked ok on the surface and 1 or 2 he was lucky to get out in one piece. I should mention that this was not a leaky old wooden boat, in fact he was often ribbed that whilst some people were concerned (or not!) about water in the bilge he got upset with dust. He honestly would dust the bilges!....but I beleive that part of the reason for the deterioration in the keel bolts was due to them passing through wood, which combined with a bit of seawater seepage (upwards!) created a reaction that "ate" the metal bolts.....so perhaps all other things being equal with an encapsulated keel and glassed over heads to the Keel Bolts not so much to worry about...........
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Old 11-06-2008, 14:56   #29
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The issue of the keels falling of is NOT an issue that any of us should be concerned about. you people dont understand the concept of a racing hull.
"IF IT DOSENT BREAK, IT WAS BUILT TO HEAVY FOR RACING"
This is a common remark made by many who race from those in 5.5s all the way up to the 70 and 80 foot super sleds.
FROM EXPERANCE we would shave all we could off a boat to including cutting out major bulkheads and replacing them with wall paper covered foam boards to get an edge on the next guy.. I remember buying "AIR-X" material made Spinnakers and then hope that they would make it through the next race..
When your racing, your living life on the edge, and your boat is built on the fact that extreme use will break it.. look at our past history concerning the Americas Cup Boats, They not only have spare masts but they have spare boats...
And this issue about the righting moments of a mono hull compared to a multi hull.
The primary stablazation of a multi hull May in fact be better than a mono,
BUT when it comes to secondary stabization, a mono hull increases as the boat lays over, dumping the wind and trying to pull the balast out of the water..
The effect of secondary stabazation is increased or compounded as the boat lays over, dumping the wind from the sails and lifting the keel from the water.
In a multi Hull, there is NO secondary stabazation, only a balance between primary and secondary, that a fine line where you fly the hull.
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