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Old 31-08-2010, 12:51   #376
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The lee board is used anytime sailing upwind in a cat of that design... there is no little keels under the hull so the only way to stop the boat sailing sideways upwind is to have dagger boards. When this is up the boat can slide down the waves and I imagine in this case would be a contributing factor along with Pilot error.... It would not be unusual in a cat of this size to be sailing upwind with both daggerboards down... standard upwind configuration. However as the wind increases, there is more need for the boat to be able to slide. If we were racing this boat, we would have had someone on the help, someone on the main and daggerboards, but they both would have been down all the way. WE would have reefed or at least turned the boat as the wind veered and increased, dumped the main and if necessary the headsail sheet also. With two people onboard, someone...anyone should have at least followed the wind shift up and dumped the main... I think if either of theses two things had happened this boat would have sailed on like nothing really happened. Pilot error...not caused just because the dagger board was down.. contributing factor yes... but not the reason why this happened.
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Old 31-08-2010, 14:03   #377
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Originally Posted by sailingaway221 View Post
The lee board is used anytime sailing upwind in a cat of that design...
Yes.

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there is no little keels under the hull so the only way to stop the boat sailing sideways upwind is to have dagger boards.
Actually there are little keels on this boat.

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It would not be unusual in a cat of this size to be sailing upwind with both daggerboards down... standard upwind configuration.
No, this boat has asymmetric boards. Upwind the standard configuration will be some lee board and no weather board. And, what's size got to do with it?

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If we were racing this boat... they both would have been down all the way.
That would be slow since the weather board would just be adding drag.

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...not caused just because the dagger board was down..
Yes. The conversation has been ranging out from the specifics of Anna's loss a bit to more general tactics, lessons and thoughts which seems like a good thing to me. There is an unusual complication in this case: the board that was deployed was asymmetric. Keeping in mind that leeway is subtracted from the apparent wind, that the heeling moment increases as the board takes a larger share of the leeway load, that the lift from the boards increases quickly with increased boat speed and that asymmetric boards continue to operate at low or even negative leeway it is very likely that there was some additional contribution to the both the heeling force and moment compared to what one would have with symmetric boards. Too, with a symmetric set-up one can sail with just the wx board which will ventilate as it nears the surface increasing leeway and reducing heeling force and heeling moment which might be significant. From a performance standpoint asymmetric boards are very attractive (eg. all competitive C class cats use them) but their contribution to seaworthiness is, I think, still a bit of a mystery.

Tom
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Old 31-08-2010, 14:19   #378
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TSM, thanks you're right ... I've been sailing my tornado too long. The little keels though are actually to protect the hull and rudders during groundings, not to stop leeway.
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Old 31-08-2010, 14:33   #379
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The little keels though are actually to protect the hull and rudders during groundings, not to stop leeway.
Absolutely right. I've got a similar arrangement on my boat and the little keels are not much good as anti-leeway devices. And, on my boat with symmetrical boards I sail with both down to weather most of the time because it increases performance, too.

Tom
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Old 31-08-2010, 14:58   #380
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On my Atlantic 55, I do not have the fixed keels; the original owner did not want the extra wetted surface area (a completely different topic). Anyway, our boards are symetrical and I have decided that I like them this way for several reasons:

1) I can chose whether the windward or leeward board is the one I want to deploy. In general, if we want a board down in bad weather, we deploy the windward one.

2) If you break a board, you can quite happily go along with just one. We broke one and continued cruising while we had repairs made.

3) If you do break a board, you have a natural plug to use for molding a new one.

4) Tacking is less of a rigamarole when you don't have to lower one and raise the other.

5) Asymetrical boards can get tough (maybe impossible) to raise once you load them up.

All of these points aside, I understand that asymetrical boards will give you better upwind performance (I don't know how much, but racing boats value it).

I often use both boards when beating under the assumption that it helps minimize leeway (just based on the notion that I have more surface area). We were happy with our upwind performance with symetricals.
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Old 31-08-2010, 18:13   #381
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Steve,

I hope I'm wrong, but I doubt very much that Anna will be repaired. From what I understand she washed across a reef losing her rig, cabin and probably much of her deck hardware and part of her deck. The stern sections are in a bad way and, with her lovely sheer, the bows are likely damaged as well. I just don't see repair as being cost effective, but like I said, here's hoping I'm wrong.

Mike

Yeah it will be interesting to see what happens with her. It intrigues me why they would bother with the additional expense of loading her onto the ship to take her back to NZ if they were not going to attempt a repair. If insurance assessors just wanted to inspect her you would think it would be a cheaper option just to put her on the hard in Tonga and fly in to check her out.
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Old 31-08-2010, 22:01   #382
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Apparently their policy required a crew of 3 when on blue water cruises.
My carrier doesn't require 3 for a blue water passage. Two is considered enough for an A57.
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Old 01-09-2010, 06:58   #383
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Tom, sorry for the delay in responding. I am not suggesting that the Atlantic is in an ultimate sense unsafe or unseaworthy - quite to the contrary, I think that they are incredible boats and would love some day to have one. I also agree that one cannot make a direct comparison with monohulls in terms of design features.

Nevertheless, even in multihulls, increased displacement increases resistance to capsize; a lower CE for the sailplan and a lower SA/D ratio for the sailplan does the same. Furthermore, assymetric boards, when deployed, not only reduce leeway in comparison to LAR's keels, but also increase the risk of 'tripping' when suddenly overpowered.

Yes, by reefing one can lower both the CE and SA/D ratio. However, it stirkes me that for many cruising couples (who are/can be inattentive), a heavier cat with a lower SA/D ratio and LAR's keels would be more forgiving and hence, in a sense, more 'seaworthy' for their purposes. Yes, one can get into a reductio ad absurdum analysis and I am not proposing that the mulithull equivalent of a Westsail 32 would be the best option (indeed, in terms of performance and a comfortable motion, weight is the enemy of any mulithull).

Nevertheless, I still believe that due in part to the light displacement/relatively high SA/D ratio and performance underbody, the Atlantic would be more susceptible to capsize than many of her more pedestrian cousins unless particular attention is paid to correct sail and board trim.

Brad
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Old 01-09-2010, 15:08   #384
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Tom, sorry for the delay in responding.
No need to apologize -- I promised to add to my post but haven't gotten around to it so I'm already way behind in the karmic accounting on this one. And here I am rushing again...

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...
Nevertheless, even in multihulls, increased displacement increases resistance to capsize; a lower CE for the sailplan and a lower SA/D ratio for the sailplan does the same. Furthermore, assymetric boards, when deployed, not only reduce leeway in comparison to LAR's keels, but also increase the risk of 'tripping' when suddenly overpowered.
Yes... But, design is holistic and I think sometimes it's possible to miss the big picture when concentrating on specifics. Quickly here are some design balancing acts that deserve some consideration. It's true that increasing displacement increases the resistance to capsize but it is also true that additional beam multiplies the effects of displacement and inertia also adding to resistance to capsize. But drag through the water is a function of displacement. Roughly speaking resistance to capsize is a function of displacement times effective beam and even more roughly speaking drag is proportional to speed to some exponent times displacement. So, while it is true that displacement increases resistance to capsize it is also true that a boat that is lighter but wider can have an equal or greater resistance to capsize and less drag. All else being equal the wider boat will be faster with the same amount of sail set and a similar exposure to wind capsize risk and, as a result of the added inertia, less exposure to breaking wave capsize. In theory at least and all else being equal the wider, lighter boat with the same righting moment costs more than the narrow heavy one by most metrics but it is both faster and more seaworthy for the similar levels of wind capsize risk. Also, when adding displacement what happens to the center of gravity will have effects on the boats resistance to wave capsize. Higher CG's increase the risk of capsize in waves. And the distribution of the weight also effects wave capsize resistance. So, particularly when looking at catamarans, it is not enough to look at D or even SA/D when considering wave and wind risk.

You're right that lowering the CE of the sail plan reduces the heeling moment. But I think you may be assuming that boats with lower SA/D's have lower centroids as a matter of course. However, it often happens that as designs get heavier they get taller -- bridge deck accommodations grow up and out and fore and aft. The rig then gets pushed up to accommodate the accommodations. A yacht with minimal bridge deck clutter can have a lower boom and lower and lower cut jibs and a lower air draft for the same sail area. Also taller yachts have greater air drag makes them slower upwind and, very slightly, increases their vulnerability to wind capsize. So, a designer could draw a yacht with less accommodation and more sail area that would have the same CE and less drag and a similar wind induced capsize risk than a yacht with a taller accommodation plan. So, lowering the CE is a good thing in terms of capsize resistance but one should not assume that cruising designs have significantly lower CE's as a matter of course.

I'm not sold on asymmetric boards for long range cruising. I understand the performance argument but even on racing boats that allow them and race much of their time dead upwind their performance is not totally game changing (eg. A class cats). I would expect in most cruising where even the "upwind" passages tend to be fetches that the additional realized performance would be very small. They cost more to build and need more attention when sailing and reduce your options... Hmmm... If I were to go that route I would consider a design where the tip was flexible enough to wash out as the loads increased which would help with some of those issues but they still seem darned expensive in money and opportunity to me.

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Yes, by reefing one can lower both the CE and SA/D ratio. However, it stirkes me that for many cruising couples (who are/can be inattentive), a heavier cat with a lower SA/D ratio and LAR's keels would be more forgiving and hence, in a sense, more 'seaworthy' for their purposes. Yes, one can get into a reductio ad absurdum analysis and I am not proposing that the mulithull equivalent of a Westsail 32 would be the best option (indeed, in terms of performance and a comfortable motion, weight is the enemy of any mulithull).
FWIW, low aspect ratio keels may increase "tripping" more than a typical deployed dagger board... I'm thinking I'm already being over wonkish but low aspect keels are surprisingly effective in increasing roll resistance... OTOH, experience in beach cats suggests that boards may not be notably faster on the points of sail that many of us go out of our way to sail on... So many choices

Anyway, yes a design with a lower CE and lower SA/RM (D does not imply RM in multies) with plain sail set will be more forgiving than a an equivalent design where either of those factors is raised. But, there is not way to make a conventional multi immune from wind capsize so the operators will still need to be aware of their risks. And, it doesn't always follow that the faster, lighter boat has higher CE's or SA/RM's...

The stability of multis is all "form" stability so rules of thumb that work for keel yachts are not always valid. I'm not sure what a Westsail equivalent cat would look like but it might end up super wide rather than super heavy...

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Nevertheless, I still believe that due in part to the light displacement/relatively high SA/D ratio and performance underbody, the Atlantic would be more susceptible to capsize than many of her more pedestrian cousins unless particular attention is paid to correct sail and board trim.

Brad
Perhaps, but as rigged the designer gives her a wind capsize number around 60 knots... That's a lot of resistance to wind capsize. No? Is it really obvious that a more "conventional" cruising cat of similar size would have done better? At some point all multis become "unforgiving". I feel the same way about reefing my cat as I do about turning the gas off at the bottle each time we use the stove. You can get away with lots of mistakes, maybe a lifetime of them and the odds of any single lapse causing disaster are very small. But the potential disaster is so great that it should never be ignored.

Anyway, bottom line: Displacement alone is a poor indicator of multihull seaworthiness. I've yet to see a number that encompass all the important factors in multihull wind or wave risk. You have to consider whole designs.

Tom
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Old 01-09-2010, 18:11   #385
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Excuse my laziness, but I haven't found the time to figure this out on my own but...when you have the asymmetric keels on a cruising cat, why aren't they designed so the weather side is deployed?
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Old 01-09-2010, 19:30   #386
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you mean daggers? I would be engaging the leewards if I was pushing and wanted lift. You can set the weatherside but if your heeled up the bite is limited. Depending on the boat you can play with the lift and depth and which side your dipping.It was mentioned earlier I believe
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Old 01-09-2010, 19:44   #387
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Excuse my laziness, but I haven't found the time to figure this out on my own but...when you have the asymmetric keels on a cruising cat, why aren't they designed so the weather side is deployed?
Tradition? Some issues come to mind. First, the board would ideally need to be moved significantly aft to balance the boat and that could lead to a lot of design changes. Second, the board would be less effective when moved aft as more of it would be working in the disturbed flow around the hull and less effective to wx as it would have effectively less span. Third, there is less experience doing it that way so getting the location right would be chancier. And so on... But, I think that's a question too far. I'm still trying to get my head around why one would go for asymmetric boards at all on a cruising yacht. Of course, jibing boards make perfect sense...

Tom
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Old 01-09-2010, 20:10   #388
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I'm still trying to get my head around why one would go for asymmetric boards at all on a cruising yacht. Of course, jibing boards make perfect sense...

Tom
I suspect the same reason people put large spoilers on street cars...
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Old 07-10-2010, 16:20   #389
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What is the latest with Anna?

I would expect that the ship carrying Anna back to NZ would have arrived by now. I was wondering if any of our NZ members or visiting cruisers in the area have spotted her and know what is planned for her? I have heard that she has quite severe damage but still wonder if repair is a possibility?

Some photos would be great if anyone has some.
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Old 16-11-2010, 20:48   #390
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one year old and they had to go back in for repairs? I know this is only one incident and my heart goes out to them, but I'm becoming less and less a fan of Cats.
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