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Old 24-08-2010, 11:48   #286
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Originally Posted by Event_Horizon View Post
the righting moment increases very rapidly until you begin to fly a hull (usually around 7 degrees-ish) then decreases.
All the curves I have seen show a quite linear function up to about 10-15 degrees (for cats, and to 20 degrees for tris). I attached this curve several posts back. I even put a big red x on it where I would set the fuse. There is very clearly a lot of room to set a fuse to not break under 'normal' cruising (say up to 5 degrees of hull lift = 8ton-ft for the below curve) but still to easily break at hull lift (=25ton-ft for the same curve).

In your example if the hull is lifting to 30 degrees on a cruising cat, I at least, would want the fuse to have already blown (near the top of the curve, whatever angle that is).

I get that people don't want extra complexity and that's an argument I understand. I just happen to honestly not consider a spectra fuse to be 'complex'. We all have fuses in our electrical system to prevent fires. This 'load fuse' seems equally sensible (for a multi). But I am not selling fuses today , so I will leave it there.
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Old 24-08-2010, 13:20   #287
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Following is a link to Chris White's comments on Anna's capsize. Some good insight.


Race Rusults - Chris White Designs
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Old 24-08-2010, 14:13   #288
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Similar situation... auto pilot followed the wind up.....heading alarm went, wind alarm went as it increased to very strong... furled the headsail to a handkerchief at first sign, dropped the main on the traveller and as the wind increased more dropped the main all the way down into the lazy jacks, pulled it back up with three reefs and a tiny piece of jib... kept sailing... 43 foot cat... no big deal.... except it was raining and at night. I think on a cat it is pretty important that you have an auto pilot that will follow the wind and not a heading..... and that can handle the loads generated. Also this type of cat is fairly high performance so the apparent wind is much faster to build and as such precaution needs to be taken. Big powerful cats cannot be left alone.... if theres a big bad cloud coming my way I'm at least going to get a little bit prepared for it.... It just sounds to me like the guy had little to no idea about what could happen ..... maybe a little to much confidence in his boat.
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Old 24-08-2010, 14:19   #289
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Originally Posted by estarzinger View Post
All the curves I have seen show a quite linear function up to about 10-15 degrees (for cats, and to 20 degrees for tris). I attached this curve several posts back. I even put a big red x on it where I would set the fuse. There is very clearly a lot of room to set a fuse to not break under 'normal' cruising (say up to 5 degrees of hull lift = 8ton-ft for the below curve) but still to easily break at hull lift (=25ton-ft for the same curve).

In your example if the hull is lifting to 30 degrees on a cruising cat, I at least, would want the fuse to have already blown (near the top of the curve, whatever angle that is).

I get that people don't want extra complexity and that's an argument I understand. I just happen to honestly not consider a spectra fuse to be 'complex'. We all have fuses in our electrical system to prevent fires. This 'load fuse' seems equally sensible (for a multi). But I am not selling fuses today , so I will leave it there.
As you said, we use fuses in our electrical system, an impulsive load in our electrical system can cause damage, just like on the French cat an instantaneous force could cause component failure. These two scenarios are analogous. This approach makes a lot of sense.

This logic does not work in terms of capsizing. A large multi cannot be capsized 'instantaneously' by forces that wouldn't rip the mast clean off. Go back to your curve. The sum of the area under the curve represents the energy it takes to actually tilt the boat to that position. Your spectra fuse would blow at less than 1/5th the energy it would take to capsize the boat!

To put this in perspective imagine a 10ft. (about 3m) long beam of wood laying on flat ground. You are standing in a hole under one end of the beam so that it is over your head but close enough you can reach up to lift it comfortably. You lift the beam up just of the ground. Feel the weight of it, that is the max righting moment. You decide to be a gust of wind and punch the board so you'd feel the same pressure you felt on your hand when you lifted it up ever so slightly. You punch the board, it only tilts up a few inches, if that, before it clatters back down. Now imagine how hard you'd have to strike the board to make it go vertical and topple over. The difference is power is pretty large if you are even strong enough to do it (not to mention probably hurt your hand so don't seriously try this...without a glove or something). The point is, you can hit the board quite a bit harder than the max righting moment without ever being in remote danger of capsizing it.

So what does this mean for a fuse?

Well it means that if you have the fuse fail every time it felt the max righting moment, it will fail constantly when you are in no danger of capsizing. That would make it impractical at best.

How then to design a fuse that will work as intended (snap when you really are in danger of capsizing)?

You gamble. You capture a LOT of weather data and data on wind induced multihull capsizes. From this you figure out how often gusts occur that may cause 'false positive' reactions form your fuse, and how strong they are. You look at sustained conditions that are capable of capsizing the boat with and without gusts. There will probably be a large overlap between the force of sustained weather conditions with little variation in gusts and sudden violent gusts able to knock your boat over, however, that is your general range. You might then want to compare this range to catamaran accidents to get an idea of the difference between 'safe forces exceeding the max righting moment' and 'dangerous forces exceeding the max righting moment'. From there its a judgement call and you will still probably have the fuse break often when you're in no danger. Or even worse, potentially not prevent a capsize.

Long story short: A spectra fuse that actually prevents capsizing but doesn't fail often for no reason is extremely complex and tricky to make.
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Old 24-08-2010, 18:29   #290
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A couple of thoughts....

Here is some of the study I did before buying a catamaran. This is all other peoples research.... but if you doubt that this accident was anything to do with poor design or " catamaran " issues... and not "pilot error" I assure you to be mistaken. I feel for the guy, but if you had been in a similar design... ie high performance monohull in this similar situation and had done as much to NOT help yourself I think you too would have had issues and possibly needed rescuing. I honestly cant imagine seeing such a nasty cloud coming and not prepare for it... or even sit by the helm..... in my last web link below.. I particularly like the phrase... " no history of a catamaran capsizing under bare poles has been documented" Has anyone ever heard of a catamaran fliping under bare poles ( not a big fancy wing mast .. but bare poles ? ) .... I think this sums up a lot of what we are discussing. Take the sails down you have an incredibly safe and stable platform....even in heavy breaking seas. The reason this boat capsized is bad seamanship. Pilot / captain error. Many mono hulls have broken because of the same problem..... pilot error. No one really is trying toooooooo hard to sail with 1 reef and a headsail in 62 knots ( just about a category 1 hurricane ) of wind no matter what you're sailing.... it's survival mode......heave too,,,, sea anchors....... run under bare poles.... anything at all that may save your life / boat .... but the crew of this boat did NOTHING AT ALL!!!!!!!!!!!!!!!!!!!! Errrrrrrrrr.... what exactly is the debate? DO nothing on a big powerful catamaran in 62 knots of wind and we are working out forces needed to flip it? I think its pretty clear.

62 knots is almost like sailing in a category 1 hurricane

stability article part 3 by Woods Designs

Catamaran Boat Design

From a report by Lock Crowther.

"This work (tank testing at Southampton Univ) has indicated that the well designed catamaran is remarkably safe in breaking waves up to considerable height, even when beam on, we were unable to capsize a power catamaran yacht in the largest wave which could be generated. This corresponded to a 52' wave for a catamaran of 40' beam. Scaling this down to a typical 24' beam cruising cat means she should be O.K. in a 31' breaking beam sea. An equivalent size mono-hull power boat was easily capsized by a 25' breaking sea, and in tests with conventional yachts after the Fastnet disaster, it was found that a 40' mono-hull yacht could capsized in a 12' breaking sea."
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Old 24-08-2010, 19:39   #291
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sometimes and we know this because its happened before. THINGS GET REALLY BAD FAST.
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Old 24-08-2010, 20:23   #292
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what i meant to say

Sometimes and we know this because its happened before. THINGS GET REALLY BAD FAST.Its a great discussion so far as it mostly has been neglectring the rude mono multi thing. I was about to say yes cats have done the davey jones thing bared poled but then I need to check myselfon the story
I was going to use. Off the gut yes but I need to go back and reread the story's. There will always be a story a defense of the sea to do the unthinkable. If you have ever surfesd the side of a 60' wave you would know the moment was about the preperation the crew the durability and as a 4' flourescent light bulb wanders past you in deafening winds prudence wins out. I think multi hulls can do some amazing things and then so can a mono. Computing the stability and ratios comes down to a small component. Having fusible links that protect you and epirbs are not the moment. The moment is making the right choices maybe its prudence. It may be hours leaning on the helm as your exhausted and needing /wanting sleep but still fealing for the anticipated draft after a lull. Or knowing the 4th wave isnt going to be regular and is going to come broadside and shake the whole boat drench you face on and spill by without a care. The sequential need for every resonse to be right. But thats not usual sailing. You can take righting moments and reputed designers. Ill take vigilance and experience. If you dont have experience double up on the vigilance. I have never flipped a cat or pitched a mono. I have sailed in winds that ranged from 60 to 80 knots for three days it took several more for the seas to calm. The crew was the most important asset. At one point we decided to put out more sail more because we needed the forward moment in the troughs as the wind came down a bit. A slightley different angle anyway hadn't seen that side of the discussion
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Old 24-08-2010, 21:23   #293
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@sailingaway221/sabray

You both are absolutely right. Nobody is contesting that the best way to avoid accidents is preparation/training/experience. However, as an engineer you learn quickly that you can absolutely never ever rely on the user to operate whatever you design safely with even a shred of self preservation or common sense. There will always be someone out there that will flawlessly make every wrong decision promptly and confidently.
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Old 24-08-2010, 22:16   #294
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Changing tack a little here, getting back to the subject of Anna.

Now that Anna is in Tonga and has written on one of her hulls that she is under Salvor possession has anyone heard what the latest is with her?

Has she now been righted and pumped out?

If she is repairable, and the last photo I saw although still upturned looked promising apart from not knowing the extent of the underwater damage, does anyone know if the owner intends to get her back up and going again or is he just gonna leave her to the insurance company, I assume that she was insured.

Are there any up to date photos?
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Old 25-08-2010, 00:44   #295
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Changing tack a little here, getting back to the subject of Anna.

Now that Anna is in Tonga and has written on one of her hulls that she is under Salvor possession has anyone heard what the latest is with her?

Has she now been righted and pumped out?

If she is repairable, and the last photo I saw although still upturned looked promising apart from not knowing the extent of the underwater damage, does anyone know if the owner intends to get her back up and going again or is he just gonna leave her to the insurance company, I assume that she was insured.

Are there any up to date photos?
Got a picture of that?
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Old 25-08-2010, 01:14   #296
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Got a picture of that?

Yes, take a look at post #247 which has the photo and an accompanying story. I'd like to get an update of what has happened since then.

Steve
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Old 25-08-2010, 08:25   #297
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Well it means that if you have the fuse fail every time it felt the max righting moment, it will fail constantly when you are in no danger of capsizing.
Event,

Your are positing that in 'normal sailing' these HP cats regularly see shock loads higher than their max right moment (but with not enough total energy to push them over). If that is true I understand and agree with your point . . . but do you have any evidence that is true?

I am positing that the 'normal sailing shock loads' are well under the maximum righting moment and I submit as evidence the sizing of the harken hardware, which is all sized for safe working load (for instance the traveller system has a 7500lb max working load) at just about where I suggested the fuse should be set and less than I calculated the max righting moment world be. If this is correct, then do you agree that the fuse is not so tricky?
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Old 25-08-2010, 10:01   #298
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" no history of a catamaran capsizing under bare poles has been documented"

Actually, that's not true any longer. A Catana 42 capsized in the bay of Biscay, bare poles with a para-anchor out. The delivery captain told me it actually 'reverse pitchpoled' while there was slack in the para-anchor rode. As we get more and more cats out cruising, mother nature is showing she can do pretty much anything. Pretty much no 'never will happen' statement can survive sustained contact with the ocean - not on a mono hull and not on a multi.

"but the crew of this boat did NOTHING AT ALL!!!!!!!!!!!!!!!!!!!! Errrrrrrrrr.... "

I think that's rather harsh and in fact not true. They were doing things, perhaps not the right things and perhaps not fast enough, but that's hindsight. They had sailed thru squalls before and had gotten used to a routine that worked, but obviously was not up to the task for the final squall.

There is no question that if the crew had done exactly the right things fast enough they would have been ok. My point is, again, doublehanded with passagemaking fatigue and distraction, are you absolutely dead certain you would do exactly the right things fast enough?

From an operational point of view I find it interesting that dropping the mainsail entirely is a popular option/recommendation for squally sailing. On Hawk we drop in the deepest reef pretty commonly, but try to avoid dropping it entirely. In the sort of squally/variable conditions, we can poke along with the deep reef in but really need the motor if we have the main away entirely. And we can rehoist from the deep reef at any angle but its much more of a production to put it back up from entirely down.

Just out of curiosity:
Those of you who do this (drop the mainsail a lot), have you done anything in your set-up to make it easier or more convenient?

I presume you who do that then just motor thru the squalls and less wind between them?

Do you then have to turn up into the wind to rehoist your mainsails or have you got lazy jacks set-up that allows an offwind hoist? Do you have powered main halyard winches?

Do you throw sail ties over it or just let it sit in the lazy jacks?
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Old 25-08-2010, 12:43   #299
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Event,

Your are positing that in 'normal sailing' these HP cats regularly see shock loads higher than their max right moment (but with not enough total energy to push them over). If that is true I understand and agree with your point . . . but do you have any evidence that is true?

I am positing that the 'normal sailing shock loads' are well under the maximum righting moment and I submit as evidence the sizing of the harken hardware, which is all sized for safe working load (for instance the traveller system has a 7500lb max working load) at just about where I suggested the fuse should be set and less than I calculated the max righting moment world be. If this is correct, then do you agree that the fuse is not so tricky?
Obviously we are being fantastic speculation artists at this point. I'm not sure what make/model or exact tolerances of the rigging or the forces imparted on them during capsize of that particular cat. However, I do believe that the rigging on cats is intentionally designed to be able to handle loads in excess of the maximum righting moment. Of course there are examples like gunboats with sexy videos where they are flying a hull. But even just a month or two ago there was a member on this forum talking about how he accidentally flew a hull on a FP Lipari. No damage to the rigging was reported. However, what this indicates to me is that if high volume production cruising cats are fitted with rigging that can withstand forces well in excess of the max righting moment, it's because they need to.

I also suspect that the rigging on Anna is closer to that of the Gunboat than Lipari and could probably fly a hull for fun (without damaging the boat)...if you had a special enough captian

However, I admit that if your assumptions are valid a fuse would be a viable option.
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Old 25-08-2010, 14:47   #300
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Following is a link to Chris White's comments on Anna's capsize. Some good insight.


Race Rusults - Chris White Designs

Thats a great read!
The STACS idea is terrific as a drill for monohulls as well.

I do note he must have been reading my earlier posts saying to dump the main sheet and have the engin running!!


I clipped each of his lines here so read the whole thing as its great advice (stuff we already know anyway, but its nice to have it layed out)
Quote:
STACS: it stacks the deck in your favor.
S – sail area
T - trim
A- autopilot
C- course
S- sheets

S- Sail area. Sail area should be adjusted to deal with the expected increased velocity of gusts
T- Trim. Typically this means moving the main traveler to leeward somewhat and easing the sheets if not reducing sail further.

A- Autopilot. When the squall is at least a couple minutes away turn off the autopilot and take control of the steering. This will enable rapid response should an overpowering gust occur.

C- Course. ...true wind forward of the beam) and a dangerous gust occurs it is normal practice to turn into the wind enough to de-power the sails. Ideally the course can be held on the edge between flogging the sails and overpowering the boat until either the squall subsides or sail can be further reduced.

S- Sheets. In the case of an overpowering gust the first sheet to ease is the main sheet. ...
http://www.chriswhitedesigns.com/news/anna_capsize/lessons_learned.shtml
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