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Old 08-06-2008, 10:08   #61
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Big Difference between preventing a capsize in a Multi that righting one.

Following this thread and doing some vector analysis I have noted that people are equating stoping a vessel from turning turtle and righting one. Using Conserv dimensions to do the math I think we can assume that the vessel would be pivoting about the lee hull in a knockdown. When the the top of the mast hits the water the angle on the deck will be about 100 degrees or about 10 past vertical. Because the lee hull is not airborne, we can neglect the weight in the calculations. To make the math simple I assumed that 60% of the vessel weight would be in the airborne windward hull( probably an over estimation, but for simplicity I also neglected the weight of the rig and sails which probably offsets the error). Multiplying 7200# *20 (also simplified since this assumes all of the weight is located at the maximum distance from the pivot point) by the cos of 80 degrees we get a vertical turtling moment (torque) of roughly 25000 ft#s. That is 25000 ft# pulling the boat over. Once the sails hit horizontal they are not contributing to the rolling forces. To correct some information here, a standard scuba tank contains about 80 cubic feet of air at sea level pressure. Each cubic foot of air can displace 64# of sea water, thus a standard scuba tank discharged into some sort of balloon structure can provide 5120# of flotation. Placing this balloon at the end of a mast 58 feet above the deck it would provide moment arm of nearly 300,000 ft#. This would mean that a scuba tank full of air could easily prevent a multihull from capsizing. It would seem to me that the earlier proposal of using some sort of inflatable float at the end of the mast would be quite effective. To reduce weight aloft I would think that one would want to have the scuba tank in the hull and a tube running to a relatively light weight float at the top of the mast.

To right an overturned vessel one would need to apply a torque of 144000 ft# to begin the process of pivoting the same vessel about a lower hull of a fully inverted vessel. Given the the fact that the mast is now some 60 feet underwater the air in a scuba tank can now displace only about 1/3 of the water it can at sea level, or about 1700# and since it would be pulling vertically it would apply virtually no torque.

Of course all of these calculations assume a flat sea and neglect the forces of the wind on the bottom of the hull once the windward hull lifts out of the water, but I think it presents a reasonable approximation of the differences between righting an inverted cat and preventing it from going all the way over in the first place.
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Old 08-06-2008, 10:40   #62
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Sorry about the delay in my response, don’t come here often.
Yes the boat was the paragon (not paragon I, no such boat).

However the assumptions made by big cat about beam, sail area and mast height are not correct. The beam is 24 which raises the righting moment to about 162000 lbs (using his formula) the other info I don’t have at my disposal at work however, if I recall the actual sail area was less and I don’t think the mast was quite 60' so those numbers aren't much good either.
Anyway, after the incident we (Paragon) (and the USCG) spent a lot of time and $ redoing all the stability calcs and it was determined that the boat should not have flipped in the conditions experienced that day.
Of course the problem with all that is that it did happen, it happened because the underside of the boat was exposed to the wind force in effect creating an additional amount of "sail area" sufficient to flip her over.
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"But I do wonder at why a beligerantly defensive monohuller would want to spend time in a multihull topic; is it possible he wants to save us from ourselves, or is he secretly *multicurious*?"
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Is this comment directed at me? I do hope not as I am not a "beligerantly defensive monohuller" I posted here because I thought that my experiance in the flipping event might be of interest to the orininal poster, he asked if anyone had experiance with this - I do, that makes my imput of some value at least I would think so.
If you Sandy are infering that the capsize I was involved in was the result of a bad decision on my part. You werent there so you can have no idea of any part of it, or the events that lead up to the capsize. Suffice it to say I didn't loose my job at Paragon.
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Old 08-06-2008, 12:05   #63
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. Placing this balloon at the end of a mast 58 feet above the deck it would provide moment arm of nearly 300,000 ft#.
I think this sounds OK but I don't think a mast with a float would last long in any kind of sea. It would simply fail and make all that air and tubing etc a waste. IMO.
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Old 08-06-2008, 12:25   #64
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Not directed at you Andy. I reviewed the Coast Guard Report at the NTSB, and I DO NOT second guess competent investigators. If 80% of all accidents begin with human error, then 2 out of 10 just get zapped by something else. And no, I don't believe that the decisions made that put you in precisely the wrong place at the wrong time are culpable. You were doing your job. If you want to learn more about microbursts, research Dennis Fujita.
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Old 08-06-2008, 12:40   #65
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Follow up for Capt. Andy & Capt. Bill

Captain Bill, you're right about the amount of air in a typical scuba tank. So, my visions of the number of bottles needed can be considerably reduced.

I agree that a float at the masthead wouldn't right a capsized catamaran, because the vector is wrong. You'd have to flood one hull and pump the other one dry for it to do any good-that would give you a favorable vector, and reduce the amount of air needed as well, as the masthead wouldn't be deep in the sea. You'd need a water bag off the upward hull to pull against to finish righting the boat, and a gin pole to give some leverage would help as well.

Derek Kelsall experimented with catamaran righting once, long ago. He posted about it either on his website, or on the KSS Yahoo group.

Most catamarans, unlike BigCat 65, would need airbags in the 'upward' hull to pump them dry because their hulls are so open, and would probably need waterbags to fill to weight the 'downward' hull for the same reason. Of course, the water-filled hull would start to lift the other hull, so maybe you wouldn't need an airbag in that hull after all.

Obviously, this would all be a problem in a big swell. Your typical trade wind swell is about 12' high, and this wouldn't be fun in 12' swells. You'd have to try to get the wind on the right side of the boat, so that it would help to right the boat instead of trying to capsize it again, too.

I really don't think the idea of preventing a capsize with an airbag is a practical idea. It would take a rather large airbag, and that would greatly increase your risk of capsize in bad weather.

Captain Andy, I don't know the accurate figures for the mast height and sail area of the Paragon-I got my figures from the internet for the Conser 47, but yours may have had a lower rig. I knew that the beam was 24'. The formula for stability uses not the overall beam, but, as stated, the centerline of one hull to the centerline of the other hull. I mentioned that the hulls were rather narrow, and guestimated a hull beam of 4' for use in the formula based on a drawing I saw online.

My estimates of your sail height were very rough work indeed-do you have any recollection of how high up the mast the heads of your sails were when triple reefed? I was guessing a little less than halfway.
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Old 08-06-2008, 13:35   #66
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It's in the news-monohull capsize near Texas

News accounts agree the boat lost its keel. Some say the boat was still floating with the crew on the bottom of the hull, and others seem to say they were in a liferaft. Apparently, a 38' monohull.

5 of 6 crew members rescued after A&M boat capsizes | Chron.com - Houston Chronicle
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Old 08-06-2008, 14:04   #67
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Thoughs on righting a capsized catamaran at sea

Using the 'flood one hull' method of catamaran righting described above, you might not need an airbag at the masthead, because if you could get access to a halyard, you could attach that to an inflatable dingy and pull from the inflatable dingy with a handy-billy.

You would also want to deploy a sea anchor from the cat, to try to get a favorable angle to the wind, or at least, to avoid an unfavorable one. So, let's say you did all this, and now had one hull overhead and the other straight down below the water, and the cat was pointing into the wind and swell.

Next, you'd need to take a line from the 'up' hull down to a water bag on the 'up' hull's keel side, and use a second handy-billy to pull down. At the same time, you'd want to pump the 'down' hull out. The person doing that might be on the side of the deck house. I can see the need of two dingys here, or at least an inflatable dinghy and an open-deck kayak.

Of course, if you succeeded, the person pulling down towards the water bag would be under the hull that was coming down, so look out!
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Old 08-06-2008, 14:57   #68
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Why not design an airbag bladder system which deploys similar to the way air bags deploy on a car. They can flush mounted from the deck 1 ft down the entire length of both hulls and be automatically deployed when an onboard gyro senses a beam pitch greater than 70 degrees. When the mast passes 70 degrees the air bladders deploy, but unlike an automobiles airbags, they don't deflate but rather remain inflated. That should act to counteract the forces carrying the boat over and 'bounce' the submerging hull upwards thus reversing the direction. Considering that too much sail in high winds is usually responsible for tipping the cat, as it bounces back in the other direction, there should be adequate wind force to prevent capsizing in the opposing direction. If it weren't then the air bladders on the opposing side would deploy if 70 degrees were breached in that direction thus stabilising the vessel allowing for other countermeasures to be employed.

Now I'm certainly no engineer, but if an engineer were to say that either the forces would be too great for the air bladder to prevent capsize, or that there is no method currently available to inflate as quickly as would be necessary - it would seem that such a system would still be useful post capsize. Once the vessel has already turtled, pull a life-raft style cord which deploys the bladders on on hull. Pull the 'cork' as it were to fill the other hull with water thus sinking it. Then dive to pull the cord for the bladder on the inside of the sunken hull to inflate the bladder and voila - that hull should raise as it's being pumped out.....
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Old 08-06-2008, 15:02   #69
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Some questions:
Assuming that the float on your masthead is working, and that the top of the mast is on the surface of the water - just how would you get enough leverage to lift the mast 10 to 15 feet out of the water in order to bring it perpendicular to the sea? Or are you assuming that you will be able to sink the boat on its side to the centerline? If that’s the idea how will you then re-float the sunken hull? Also how do you get enough weight into one hull for it to sink? If Cats don’t sink, how do you sink them with materials on board? If you have enough weight to sink one hull that you are able to shift from one hull to another wouldn’t that weight combined with the rest of the boat be enough to possibly sink the whole boat, or at least slow it down enough to negate the speed advantage that cats have over mono's?

An observation: I don’t know if you have ever done any work on an upside down cat, if not let me tell you -- first off unless you have a hatch built into the bottom of the hull getting inside the boat will be very difficult if not impossible. After a flip you will likely have a lot of tangled gear and wreckage in and under the boat. Then the sea state will also make any kind of work esp. dangerous, the boat and whatever is tangled, broken or fouled under the boat and in the water around will not be moving together but rather grinding against each other increasing the risks and difficulty of any self rescue.

I'm not saying that it cant be done, but just that any intellectual discussion of what to do will be unlikely to come close to the reality of what needs to and what can be done.


When I am driving a cat now I will have attached to the stern life lines low to the deck a small bag with a mask, fins and a "spare air" tank (five to ten minutes of air) ready for me to use. Doesn’t cost much (esp. compared to my life raft) and could make the difference between life and death for me or my crew / passengers.
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Old 08-06-2008, 16:29   #70
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[COLOR=black]Some questions:
[COLOR=black]first off unless you have a hatch built into the bottom of the hull getting inside the boat will be very difficult if not impossible. After a flip you will likely have a lot of tangled gear and wreckage in and under the boat. Then the sea state will also make any kind of work esp. dangerous, the boat and whatever is tangled, broken or fouled under the boat and in the water around will not be moving together but rather grinding against each other increasing the risks and difficulty of any self rescue. [
Another option is to have tools and a marked section to cut through the hull, the key for survivability on an upside down multi is designing and planning, see for example Ian farriers design specs for inverted F41.

Capt Andy - I was also wondering what was the design of the boat you were on that went over.
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Old 08-06-2008, 16:29   #71
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I think this sounds OK but I don't think a mast with a float would last long in any kind of sea. It would simply fail and make all that air and tubing etc a waste. IMO.
I agree, such a float might not have to last very long. A cat in this position would be vey unstable in any sort of sea(like the conditions required to knock it down in the first place). If my calculations are correct the CG in this postion would only be about three feet past vertical. Anything that rocked the hull even a small amount past vertical would cause the boat to right itself, assuming the sheets were loose.

Someone else pointed out that there was nothing that would inflate fast enough. Automotive airbags inflate in less than 1/200th of a second, so perhaps a airbag type gas generator would be better than a scuba tank, noting that only about 1/10th of a scuba tanks volume is required to stop the mast from sinking.

Fortunately I have not inverted my cat, but in my youth I liked to sail sunfish to the edge and sometimes a little bit past. My experience was that a capsize was kind of a slow motion thing, especially once the sail hit the water. I would think that something that would inflate in 2 seconds would be fast enough. Does anybody know how long it took for that cat to invert?
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Old 08-06-2008, 17:21   #72
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less than a secound from start to being upside down
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Old 08-06-2008, 17:24   #73
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less than a secound from start to being upside down
So much for the 2 second theory.
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Old 08-06-2008, 17:25   #74
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So much for the 2 second theory.
If you watch some videos (not too many and I can't find the one from yesterday) it is a lot longer than that.
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Old 08-06-2008, 17:27   #75
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Factor as stated it was a "consor 47"

the tools would have to be stored in a spot accesable once the boat was upside down, or you would need a foolproof way to retreive them IMHO.

Part of the problem is thinking that you could actually do any work, I believe that in any kind of weather it would be nessisary to first wait for the conditions to improve before begining any work (other than trying to stay with the boat). Seas would be washing across the bridge deck and depending on the initial weight of the boat the brige deck may or may not be submerged adding even more problems.
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