Canting Keel Monos vs Multihulls

Discussion in 'Multihulls' started by brian eiland, Aug 31, 2006.

  1. Vega
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    Vega Senior Member

    Can you explain it?

    Modern Ocean monohulls have an AVS bigger than 115º and a downflooding angle bigger than 100º. Even with a micro-burst, in a sea without breaking waves, the boat will just lie on its side, at 90º. In this position the wind will just not have any rotational effect on the boat. Micro burst don’t take long time to pass, so, when it is over, the boat will right itself up.

    Of course you say: "In normal ocean sailing" and in some situations it is normal to sail in bad weather with breaking waves.

    I was not referring to "normal conditions" because that would lead to a big discussion about what are “Normal Conditions”(read the post again).

    I am just saying that wind alone, in a settled sea, is not enough to capsize a modern oceangoing mono, but can capsize a oceangoing multihull, and this is obviously true.
     
  2. jehardiman
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    jehardiman Senior Member

    Step away for a weekend and look what happens....:D

    Some replies and comments.

    I myself, as a professional NA, would never select a mid-sized cat for my family except as an anchored party float in the most benign of environments. One selects the hullform for the job based upon required criteria. There are serious issues with multi's (power or sail) in certian conditions, just like there are reason to select them for others. The RAO's and cross deck clearence issues of mid sized cats are too severe for me to ever recommend them as "all ocean, all weather" vessel for extended voyaging.

    Sword of Damocles and all that. On one hand you argue that speed and seamanship will preservere, on the other you point out that the multis were lost while trying to speed out of the way. Speed requires the sails to be up, too much sail up is dangerous; given equal seamanship, your margin resides in your hullform. I would concur that speed = safety for small, high speed, motorized combatants; but not for sailing vessels. I would propose that weatherlyness is more important for safety for sailing vessels (.i.e making way to the safe quadrant).

    I concur with Vega here, there are different horses for different courses, and you choose the proper one. My involvment with this thread began with addressing the original quote provided by brian eiland. I just stated that IMHO that quote by Juan K only refered to ocean racers, NOT the sailing community in general. As there has been discussion, that original statement has been proved correct.

    The Westsail 32 Saraband (skipper Dave King) won the light winded (15 to 22 knots) 1988 Pacific Cup.

    Setting that aside, racing for the skippers may be about winning, but not for the sponsers. For the sponsors it is about brand recognition and tax writeoffs. So maybe big multis are selected because they are bigger brand banners (more hull to write on), are more media worthy (i.e. capsize headlines), and greater tax sinks....especially when they turn up down....(that's a pun folks).....;). See my comments on how I feel about big money sponsorship at the bottom of post #131

    I'm not trying to pick on you, but you have good quotes because they are reasoned, which makes it easier to use them as an example. This is a fine example. Here you say seaworthyness is not a factor in hull choice yet you say insensitivity to weight is. For most multihull forms, weight is the primary seaworthyness vs speed issue. Multis capsize because they don't have enough weight, add on enough weight to a moderate (~40') sized multi to give the same angle of zero stability as a mono and you would most likely have speed, pounding, strength, and other issues. To solve this issue the multi must get bigger for the same transport capacity...which brings up the other criteria you mentioned...docking issues. In the real analysis of the hullform, the need to get seaworthyness drove the weight and docking issues.

    Very nice post that sums up a lot of my feeling too. The hullform I'd choose for an afternoon thrill in SF Bay is not the hullform I'd choose to take into the Southern Ocean on a world cruise.

    Capsize/pitchpole/sinking are just different facets of the whole seaworthyness problem. You cannot look at the stability problem as a static situation. It is energy that causes a capsize/pitchpole. As windspeed, seaway, and boatspeed increase, the energy available to cause a capsize/pitchpole also increases. If you look at the RAO's of multis compared to monos, multis frequently have narrow band, peaky, RAO's where monos have broadband, low RAO's. This is problematic because large responses will not give very much, if any, warning especaly when considering random wave spectra response and lack of mass inertia of the multi. It is also important to remember that the operative consideration here is "energy to capsize" vice righting moment because righting moment is only a static, not a dynamic, force. In the final analysis, as a broad generalization, for similar sized vessels, the mass stability of a mono generally requires more energy to cause a capsize than a multi. YMMV.

    Sinking is an altogether different issue. Boats sink when too much water gets into the people tank. Downflooding through openings is just one issue, there are structural failure issues also. Way too much variability adress except to say that thinner (i.e. lighter), more heavily stressed hulls will be more likely to suffer structural failures leading to flooding than thicker, less heavily stressed ones. As multi have to be built lighter, they are correspondingly more at risk. See my discussion of multis and modern composites in post #70

    Vega, you are on your own on this one. While I concur that it is difficult for wind alone to capsize a mono, the RMS TITANIC lends crediability to "never say never". And "freaky conditions" are a crap shoot. See the studies done by UNO on cross seas capsizing of fishing boats for a good investigation into this topic.

    I concur, fist to finish is just a peer/social thing for owners/sponsors at the bar. At one yacht club I know, the "top dog" measurement was the owners bar tab (how gracious he was), at another it was how much equipment you blew-up that day (how agressive), and at another it was the "very ugly" participation trophy. Remember for sponsors that winning is not the whole idea. Sir Thomas Lipton is the prime example.
     
  3. brian eiland
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    brian eiland Senior Member

    Pride of Baltimore incident

    Have you ever heard of the Pride of Baltimore incident?
    ...couple of excerpts...

    On May 14,1986 returning from Britain on the trade route to the Caribbean, the Pride of Baltimore was struck with what the US Coast Guard later described as a microburst squall 250 miles north of Puerto Rico. The vessel was hit with 80 mile hour winds, capsizing and sinking her. Her Captain and 3 crew were lost, and the remaining 8 crewmembers floated in a partially-inflated life-raft for four days and seven hours with little food or water until they were rescued by the Norwegian tanker Toro.


    It was the well-intentioned desire to replicate these greyhound-like qualities that was part of Pride’s undoing because the original Baltimore clippers needed big crews familiar with their every mood. And whilst the captain and crew of the replica were experienced and well-qualified for the job, a number of problems conspired to bring about a situation that they could not control, leading to her loss on that fateful May day in 1986.

    After the crossing, she cruised the Caribbean island-chain to the Virgin Islands then she set sail for direct passage home to Baltimore. By 13 May she had found a fair breeze to which nearly all her fore and aft sails were set with a double-reef in her mainsail. Her cargo hatches were closed and sealed by the traditional method of hatch boards, canvas covers, battens and wedges leaving just the aft accommodation hatch readily available for crew access. Soon she was in her element, romping along with a force 6 wind on her starboard beam.

    On the morning of her last day afloat, the wind increased to force 7-8 (28-40 knots) at which time weatherboards were placed in the aft accommodation hatch and all hands were called to take in sail. The rig was reduced to just forestaysail and the double-reefed main by which time Pride was broad reaching to the satisfaction of captain and first mate.

    Then, out of nowhere, a 70-80 knot microburst hit the ship, in immediate response to which the main sheet was let go and the helm put up to pay her off the wind, but Pride would have none of it, flatly refusing to respond as the rudder stalled and lost its bite. As a result, the magnificent clipper came beam-up to the wind and heeled alarmingly before rapidly downflooding through her accommodation hatch and galley scuttle, both of which were situated off-centre to port, the side now underwater.

    Pride sank within a minute, leaving her crew in the sea without life jackets or EPIRBS, all of them going down with the ship. However, her two six-person life rafts hydrostatically released themselves, but one tore itself on the rigging and proved useless to the stricken crew. The other raft suffered no damage, but nevertheless malfunctioned and failed to inflate at which time the men then discovered that its hand pump was also non-operational.

    And while all this was going on, the captain and three crewmembers perished leaving the remaining eight men in a wild sea with just the one deflated 6-man life raft.

    Refusing to give in, the eight men spent six hours in the water taking it in turns to inflate the errant raft by mouth until it was buoyant enough to climb aboard and face a very uncertain future with just a few biscuits and minimal water for sustenance.

    During four days adrift, they sighted six ships and one aircraft, all of which failed to see their flares. Then, with flares exhausted, rescue came unexpectedly thanks to an alert watchman on the Norwegian tanker Toro who sighted their flashing torch one night and understood its SOS.

    Ironically, despite her safety gear exceeding survey levels.

    Pride’s crew was saved by a very old technology – morse code! As author Daniel Parrott says: In the end, it was not the satellites, the flares, the international orange, or the specially sealed nickel-cadmium batteries inside the EPIRBS that saved the day. It was a malfunctioning life raft, a flashlight, and an alert crew member on a passing ship … .

    Pride of Baltimore’s loss became the subject of two inquiries, neither laying blame on anything or anyone, but the lessons were fairly obvious to all, making it clear that catastrophic loss is often the result of many small things accumulating to become one very deadly problem.

    In the case of Pride, she was knocked down by a vicious gust with too much sail set aft rather than further inboard closer to her longitudinal centre. Had she been flying the foresail instead of the mainsail there would have been less area aloft and she would almost certainly have answered her helm when turned to port to run off the wind.

    Her low topsides, with their lack of reserve buoyancy plus closed gun ports in the bulwarks, exacerbated the heeling moment as water came aboard faster than it could run away, allowing more time for it enter the hull and then spread below decks unchecked by any bulkheads. And as for the tiller: it was not seen as a problem, but I still wonder if it really suited a vessel of that size.

    To the credit of all those involved in the first Pride, her loss did not send them running for cover, to the contrary the lessons learned were incorporated into a replacement ship, aptly named Pride of Baltimore II; every bit as attractive as the first but with modern concepts of seaworthiness firmly in mind. She has higher topsides, bulkheads, external ballast and is a bigger vessel with a smaller rig, allowing her to continue the legacy of being a wandering goodwill ambassador as well as a fitting memorial to those who lost their lives on the first Pride.

    As for the Lucas family, we visited the port of Baltimore ‘between clippers’ so did not hear of the plans for a replacement vessel until many years later.

    But less than one year later we experienced a microburst that put us on our ears whilst sailing back to the Caribbean, so we can very definitely bear witness to their unbelievable suddenness and unmanageable force during which well honed instincts can completely fail you.

    On one hand our incident proved the value of ‘being ready for anything’, but it also showed that luck plays a huge part in surviving something as sudden and violent as those meteorological misfits.
     
  4. RHough
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    RHough Retro Dude

    LOL ... you gave me time to come up with reasoned responses ...

    No, I pointed out that the multi's capsized not due a fault of the boat, but due to a lack of crew. If the multi's had capsized while their crew was making every effort to prevent the capsize, I would concede the point. In the cases we are disucssing, I think single-handed sailing played a larger part in the capsizes than the seaworthiness of the boats.

    I agree that weatheryness is an important safety factor. Many modern multi's are at least as weatherly as comparable mono's. Farrier's tri's seem to be able to point about as high as a mono of the same length and sail about the same speeds (from the reports I've read). They are also able to achieve higher VMG by pointing lower and sailing faster, an option not available to the mono's.

    I agree wholeheartedly. If we consider the question of the future of canting keels in relation to ocean racing multi's, I don't think any boat that requires ballast will be an odds-on choice to win an open class race. I'm sure someone will correct me, but I am not aware of anyone choosing a mono-hull for ocean racing when the rules allowed a multi-hull choice. Now that I've typed that, I seem to remeber a 230+ ft mono in the OSTAR ... :( However, there can be no argument that almost all the outright major ocean records are held by multi's. As good as they are the VO70's are still about 20% slower than the big ocean multi's.

    If, on the other hand, we consider canting keel mono's vs multi's for all weather cruising, the discussion is completely different. What does not make sense to me is trying to draw conclusions about all weather cruisers from single-handed racing data. As I've stated before, I think powered moving ballast systems are a very viable choice for cruising mono's. My opinion of such powered systems on racing boats is well known, they are not legal and should be banned.

    PFFFTTT! :D Point to you. However, that was the first race run under the Pac Cup Handicap. The ratings for the Pac Cup were hotly debated at the time and I doubt that the Westsail would fare so well under the current version. :)

    Here we have the basis for another debate. My feeling is that the quest for line honours drove many Corinthian sailors to build bigger, faster, boats. The IOR was nicknamed Invest Or Retire for that reason. The desire to be first to finish predates big sponsorship by quite a number of years.

    The mass media does favour fast boats and accidents at sea, no argument. First to finish makes headlines, first to finish on corrected time rarely gets even a sidebar. This is true in most sports, handicap golf championship results don't make the front page of the sports section, neither do handicap bowling league results. About the only "sport" that gets handicap races on TV is bracket drag racing ... and then only as a filler while they re-build the engines of the top fuel cars between rounds.

    I don't know if I should crawl into a corner and cry or thank you for the compliment. :)

    Have you ever looked at the abilities of two boats with the same weight? If we compare two boats of say 20,000 pounds displacement, wouldn't the multi be much larger? What effect would that have on seaworthiness? The sail area needed to drive the boats should be about the same (the multi would suffer in light air). Would a 20,000 pound multi be easier to capsize than a mono with the same SA/D?

    Yep, the flooded vessel must be denser than water. Water in the people tank won't sink most multi's. :)

    Great post! Gets the small grey cells working for sure!
     
  5. Vega
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    Vega Senior Member

    Brian, this is an entertaining story but it has nothing to do with the case.

    I have said:

    I am talking of modern boats and you are talking about a century old design. That boat probably would have an AVS inferior to 90º, and as you can see by the story its downflooding angle was not better.

    They say that they have learned the lesson and that the Baltimore II would have exterior Ballast and better stability. But even this one can not be considered, by any means, a modern boat.

    The situation I was talking here was precisely a Micro-Burst (or a tornado). It was dark and I only have seen the “thing” in the radar. The boat laid at 80/90º for an eternity (more than 1minute, less than 3, I think) and it carried practically no sail. It was a 36 modern lightweight cruising boat, not an especially seaworthy boat. When the huge wind suddenly disappeared (and returned to 35k) the boat returned to the upright position. The water didn’t even enter the cockpit, or in the exterior luggage spaces. Except a sail (third reef and lose) that was thorn out of the mast and a shredded banner, there was no damage, except in the confidence of my daughter that was closed inside the boat.

    The first photo is from the Baltimore I, the second from Baltimore II

    Regards
     

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  6. yipster
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    yipster designer

    good boat you have coming up again, than again saying above depend on (cats) stability, windspeed and such and recalculating that experience is hard aft.
    dont think a cat -i'm generalising- turns upside down every 10.000 miles, maybe a similar cases study may give more insight
     
  7. brian eiland
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    brian eiland Senior Member

    Blown Over in a Settled Sea

    I understand what you are getting at Vega. I just took issue with this portion of your statement;
    I personnally experienced a total knockdown off the coast of Cape Fear/Hatteras in a traditional long keel 47 wood ketch I once owned. It was a beautiful sailing evening and I was under full sail with all the port lights open. A sudden burst of wind knocked us over on our side and water poured in thru the relatively small round port lights. Had the very big engine access hatch in the cockpit floor opened and allowed the sea to flow in as a giant gulp, I'm sure we might have floundered.

    Later that same evening a huge frontal passage came to sea from the land in what I can only describe as the most intense electrical storm I have ever witnessed, accompanied by a 'wall of wind'. Luck would have it I was forwarned by the earlier incident of being blown over on our side, so I was prepared for this.
     
  8. Vega
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    Vega Senior Member

    :p :p :p Yipster, it is not a good boat, but a normal big production inexpensive36ft sailboat. Any modern Class A boat would have performed the same way, and if you go to the STIX thread you are going to see that I agree with Guillermo about the inadequacy of the actual parameters that define a class A boat (too low).

    Fact is that I don't consider my boat as a true oceangoing boat.

    About one cat capsize for each 10 000 miles:p :p I completely agree with you. I was just analyzing my complete sailing experience and seeing what would have happened if I had sailed a cat. Of course, I am not a lucky guy, but I don’t trust in luck either. I am more the kind of guy that thinks that If can happen, sooner or latter, it will happen:rolleyes: .
     
  9. yipster
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    yipster designer

    hi vega, i read those microburst ( windsheer ) can do over 130m windspeeds toppling even motorcruisers
    its certainly a big concern and self richtning is a good thing
     
  10. Crag Cay
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    Crag Cay Senior Member

    I think there needs to be a little more clarity in the terms used. Capsize can mean different things to different people.

    Of course a mono hull can be knocked down (to 90 degrees) by wind alone in a flat sea, but then it would have to be incredibly badly designed or have the assistance of another factor (breaking waves, down flooding, shifting ballast, etc) to continue to the inverted position. 'Washing the Windex', as we call it, has been a feature of a number of designs I have raced since the late 70's. Even if inverted a return to upright has long been held as a 'desirable characteristic of the offshore yacht'.

    However these racing multihulls have apparently, enough of a wind lever in their wing masts to be knocked down in hurricane plus wind speeds alone, even under bare poles. Once knocked down, they need no further factors to continue to an unrecoverable 'turtle'.

    A couple of other points: we need to make sure we always compare apples with apples. I would like to see comparative 'seaworthiness' evaluations between a number of designs all having (say) 10000 lbs of displacement. One would be a small, heavy displacement cruiser, a larger (LOA) lightweight flyer, a high performance tri, and a Wharram cat. Some of these students looking for final year project should make a start.

    Finally, I don't think the notion of speed being a guaranteed method of storm avoidance can be relied upon completely. In order to avoid storms, you have to predict where they are going to be. In 79 and 87, two (F12+) storms have hit the south coast of the UK completely unknown to the forecasters. These were both in mid summer or autumn, (rather than mid winter) and came across the most highly observed and forecast waters in the world. So if the Met Office can be so wrong here every ten years or so, what are the chances of a 100 percent correct forecast in an area slightly more remote than the English Channel?
     
  11. jehardiman
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    jehardiman Senior Member

    Ok, getting really picky to ensure that everyone understands the comparison.....

    For the same length and wind speed profile, a similiar weight modern multi would capsize sooner than a modern keel ballasted mono given "normal" design, no downflooding, static and flat water, and the same SA/D. This is not opinion, it is simple physics and has to do with the seperation between B and G and the width and windage of the hull. Draw up the free body diagrams and do the energy calculation to capsize yourself.

    The real cincher in the problem is that the cat has maximum overturning resistance at the start of the event, but then losses righting moment and resistance to capsizing as the event progresses until the windage of the hull overpowers the minimal righting moment well before the heel angle reaches 90 degrees. The mono has minimal resistance as the even starts, but righting moment increases until it reaches maximum when the overturning moment is minimum, theryby arresting the capsize while still having residual righting energy available to accomidate seaway effects.

    Hands down, a mono is my choice if I always want the boat to come up from a knockdown.
     
  12. jehardiman
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    jehardiman Senior Member

    I have heard several NA's that looked at this event say that the changes made to her the original 1800's design contributed significantly to the loss. This is especally true about changing the deck hatches from 18" scuttles on CL to open ladder accommodations off CL to allow visitors below in a ship that was never designed for that. This coulped with the increase in height (a reglatory requirement) and non-freeing ability of the bulwarks led to the rapid downflooding. The question remains though if she would have risen from the knockdown in her original design. A lot of similar vessels in the 1800's didn't.
     
  13. Crag Cay
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    Crag Cay Senior Member

    The only comparative graphs I can find at the moment are in Derek Harvey's multihull boat, where he shows the calculated GZ curves for a modern style 35ft mono, tri and cat. From these he claims it takes 50 percent more energy to wind capsize the cat to AVS (85 degrees), and 70 percent more energy to capsize the tri to its AVS (90 degrees) compared to the monohull.

    In the book's example, he only constains LOA and allows all the other dimensions to vary so as to represent typical examples of each at that LOA. In your statement you also constrain Displacement and SA/D. Do you think this is realistic for the three different styles of boat of similar length ? And if so do you think it would be the reason for you and him taking apparently opposing views?
     
  14. jehardiman
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    jehardiman Senior Member

    I haven't seen the analysis you cite, but I am very sure of the limits I palced upon my statement above....basically because it is impossible to capsize the mono within the limits I cited....i.e. with no waves and no downflooding, the mono will always right itself....unless you increase the beam and decrease the draft to skimming dish proportions. The mono hullform and weight distribution (i.e. KG<KB) I would use would always right from a masthead in the water. A multi can never achieve that condition (KG<KB).
     

  15. Vega
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    Vega Senior Member

    On the 2006 June edition of Yachting world a comparison was made between an Oceanis 50 and a Lagoon 410, two boats that belong to the Beneteau group.

    The Beneteau displaces 12 020kg and the Lagoon displaces 7240kg.

    It can be said that it is an unfair comparison between a mono with 15.0m and a cat with 12.4m. Apparently they didn't think so, and I agree with them.
    What counts in a cruising boat, besides seaworthiness and the way it sails, it is the interior space and the price. Regarding those two factors it is an even match. I believe that, for the same buyer these two boats can be an option.

    The Oceanis costs 224,801 euros and the Lagoon 259,932 euros.

    I will post the wind polar and the GZ curves of the two boats.

    The force needed to capsize each of them will correspond to the area below the positive part of the RM curve. The one posted is the GZ curve. As the Beneteau displaces more than the lagoon, for having the correct areas we will need to have a correction factor of 1.66 (12020/7240) to compensate the superior displacement of the beneteau. This means that if we take into consideration the areas of the GZ curve, the beneteau area has to be multiplied by 1.66.

    It’s too late, and I have no time to comment on this data know. Be my guests, and have a go at it;) .
     

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