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Old 12-02-2008, 17:34   #46
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If I'm on a close reach and the boat starts feeling overpowered, I think the best thing is to head off. Easing sheets is next.

Going closer to the wind just increases boat speed and apparent wind which increases lateral forces on the sails. It's also inviting the lee bow to submerge which would further exacerbate the situation.

Steve B.
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Old 12-02-2008, 19:58   #47
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To be clear, I would not suggest bearing off in a gust when going to windward, just that you have to be careful to decide whether to bear off or head up based on the true wind, not the apparent wind, as depending on the performance of your cat - the apparent wind will often be forward of the beam, even when sailing well off the wind. This took a little learning when I moved from mono-hulls to our cat, as my natural reaction was to always head up in a gust if the wind appeared to be forward of the beam.

And as was pointed out, avoiding gybing in these circumstances is a good idea.

Mark.
The problem can be solved if you can let the sheets go and let the rig weather cok as with a ballestrom or una rig on an unstayed mast. My worst moment was when hit by an adiabatic blast while sailing near a steep headland. The boat was traveling dead downwind and the bows were slowly starting to go under when the gust died away. I am now very much in favor of unstayed rigs, which are standard on the Harry I plan to build..
Robert
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Old 13-02-2008, 10:08   #48
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When on a close reach/beat, heading up does tend to increase the speed of the apparent wind. However, unless the sail is also sheeted in it will also tend to luff the sail, thereby depowering it. Furthermore, as already mentioned, the force vector from the main will also tend to move forward.

In similar conditions, if you head off the sail will still remain full. In addition, the force vector from the main will also move to leeward (toward heeling rather than forward motion), actually increasing your risk of burying the leeward bow. On a beam (or broad) reach however, as has already been pointed out, you should clearly bear off. At that point the maneuver is actually a win/win in terms of the force vector and the apparent wind.

I suppose that some cats/multis could react differently - certainly, in my rather heavy cruising cat with a cutter rig and keels, the boat tends to luff and and the heeling to reduce quite quicky when heading up on a close reach/beat.

On the other hand, although I have not experienced it and although it seems counterintuitive, I can imagine some quicker tris/cats with the ability to point higher being affected more immediately by the increase in apparent wind velocity...

Physics be damned, for the moment, I'd be interested in hearing the experiences of others on particular types of cats/multihulls. How many share my experience and how many share the experience of Steve on his admittedly much faster Dragonfly trimaran? Or is the difference less a product of speed, but more a product of that ability of a particular boat to point higher (ie, a trimaran or a cat with boards versus mini-keels)?

Brad
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Old 13-02-2008, 10:31   #49
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Steve

Your post got me to thinking that we may have highlighted one of the differences between tris and cats. I suspect that in a tri when you are on a close reach or beat and 'feeling overpowered', your real concern is not a wind-driven capsize (which is what I was referring to), but burying the bow of the leeward ama. In that case heading up would indeed put your bows more directly into the waves and momentarily increase the risk of what you are trying to avoid.

I have never sailed a tri, but I do know that it would (should) be able to point much higher than a typical cruising cat and that it should also be less susceptible to wind-driven capsize.

Brad
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Old 13-02-2008, 11:05   #50
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Bear off to avoid capsizing

I've never sailed a cruising cat, but I can relate my experience from sailing a Hobie 16 for 28 years.

I loved to sail on one hull, which requires a delicate balance between tiller control and mainsheet control. When I had the windward hull up as high as it would go, the boat slowed as wind spilled out of the sails. If she started to go over, and I didn't release the mainsheet, I found that if I steered her up into the wind, over she went--capsize! If I steered her down off the wind, she'd get back on her feet and start sailing again.

I found that out by trial and error (and any number of capsizes before I got the hang of it). It really mystified me at first. But then I realized that when performing that downwind maneuver, it felt just like riding a bicycle! If you're riding a bike, going slowly, and start to tip over, what do you do? You steer into the direction that you're falling. Same with the Hobie Cat. You're tipping over downwind, so turn downwind. Just don't go too far down and gybe! Then you really will capsize!

From a physics perspective, I think what happens when you steer into the wind is that you create a rotational (centrifugal) force vector that points downwind, perpendicular to the lee hull and away from the turn, and is just enough to tip you over. Turning downwind, the centrifugal force vector points into the wind (away from the direction of the turn), and helps keep the boat upright.

The beauty of sailing a 16' beach cat is that you can feel every nuance of the wind and water and boat with your hands, feet, and even the seat of your pants. I could sense in a split second what the boat was going to do and reacted without consiously thinking.

There's a big difference between a Hobie 16 and a 40' cruising cat. The big cat isn't going to react as fast and you won't have the "feel" of it like you do on a small cat. But I bet the principle is applicable to both. If you start to go over, steer down wind. And dump the main for good measure.

What do you cat drivers think about that?
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Old 13-02-2008, 11:42   #51
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Hud, I think we all agree that you need to let out the sheets to dump the wind. Thereafter, in a cruising cat you also need to immediately reduce sail!

The question here was with respect to an immediate steering response which should allow you the time to let off on the main and jib sheets - not the fastest of maneuvers in many cruising cats, when you start to feel overpowered and are sailing to windward.

You make an interesting point in your comparison to a sailing a Hobie, although I suspect the fact that the Hobie is already flying a hull (precisely what you are trying to avoid doing on a cruising cat) is what makes the difference. In the case of a boat already flying a hull, there would certainly tend to be a disadvantageous weight transfer achieved immediately with a turn to windward (even cars tend to 'roll' to the outside in a turn). This could only add to the existing momentum towards a capsize.

In a cruising cat, you should never fly a hull and the risk of capsize is therefore less contingent upon weight transfer than upon the force and directionality of the wind. Your point however is well taken: should you ever get into a situation in a cruising cat where your windward hull is rising out of the water to a point approaching the maximum righting moment (!!!!) a quick prayer and a turn to leeward would probably be a good idea. Lets face it, with the windward hull flying and the mast raked over alarmingly to leeward, the wind is already being spilled and it is the momentum (and weight transfer) which have now become critical.

Having never flown a hull in my cruising cat (and hoping to never do so!), I can say that a turn to windward while on a close reach or beat causes the sails to luff and depower quite quickly. This gives me the time to let out on the main and jib sheets and then head off.

Brad
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Old 13-02-2008, 12:07   #52
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Originally Posted by Southern Star View Post
Physics be damned, for the moment, I'd be interested in hearing the experiences of others on particular types of cats/multihulls. How many share my experience and how many share the experience of Steve on his admittedly much faster Dragonfly trimaran? Or is the difference less a product of speed, but more a product of that ability of a particular boat to point higher (ie, a trimaran or a cat with boards versus mini-keels)?
Hi Brad - my knowledge here comes from racing beach cats for longer than I care to remember. I believe the physics is, for the most part, applicable to cruising cats but there are obvious differences in degrees of magnitude in causes and effects. On my cruising cat I have never had to alter course to de-power the rig - and I don't expect to. If that's necessary, I'm carrying too much sail and I failed to reduce sail sufficiently earlier OR an unpredictable gust has occured in which case I'd probably perform some combination of luffing and unsheeting. I don't think pointing ability or boards vs keels play a role.

From my small cat experience, when close hauled, heading up to depower with the helm works for the reasons you state after an initial exacerbation of the problem depending on how much hull you have out of the water. Centrifugal force can actually be a player and initially contribute to heeling. But depowering with the helm isn't the racer's first choice - cracking the sheets is (to avoid unnecessary rudder movements). But this can also exacerbate the problem because cracking the sheets takes bend out of the mast and un-flattens the sail, creating more power - if you were really honked down to begin with. In the end, cracking the sheet in combination with pointing up a bit is the way to de-power. If you were trimmed right from the beginning - windward hull just skipping the water - cracking the sheets alone is preferred to take advantage of the puff to accelerate, re-sheeting as the apparent wind goes back forward. On the sophisticated small cats you can play the downhaul to depower (flattening the sail) instead of making coarse sheet adjustments or in combination.

On small cats flying chutes, the opposite is true. You NEVER go DDW on a small cat, so assuming you're starting on the wind to some degree when hit with a puff flying a chute, you immediately depower by turning downwind. Heading up only worsens the problem.

On a reach a neat trick to use when getting overpowered is to sheet in on the jib to close off the slot. Otherwise, luff or sheet out.

Are you sorry you asked?

Dave
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Old 13-02-2008, 14:35   #53
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Thanks Dave - everything you have said makes perfect sense. And I agree completely that you should never find yourself in situation where you are that close to the line in terms of a wind-driven capsize in a cruising cat. The thread started with someone expressing concern about capsizing in heavy air in a cruising cat, and the discussion led to differences in approach and techniqes between cats (and now tris) and monos.

And if you took my reference to my personal experience as meaning that I was close to a wind-driven capsize, I apologize. I was talking about a few occasions when there was an unexptected increase in wind velocity and the gusts exceeded what I felt comfortable with in the absence of reefing. I headed up and found that, as with any boat, the heeling pressures reduced almost immediately. This allowed me to let out the sheets and roller-reef the jib (rather large on my masthead rig) and then proceed on without any further drama.

My point is (was) that if you are feeling overpowered while sailing to windward, you should head up and not off, as well as let out the sheets; when on a beam reach or below, you tend to bear off rather than up. And I gather you agree with these basic propositions.

Your point with respect to the mainsail on most cruising cats is also well taken. Rather than letting out the mainsheet, one should really be moving the traveller to leeward as, yes, more camber in the sail tends to increase rather than decrease heeling/power.

My cat, with its cutter rig, tends to obtain most of its power from the headsails rather than the main and accordingly, this is less of a problem. My first line of defence is let out the jib sheets and then to reef the jib, rather than the main.

On the other hand, on the vast majority of cruising cats equipped with fractional rigs and huge mainsails the answer is to reduce the power of the mainsail first by moving the traveller to leeward. On most boats this is a somewhat slower process than merely releasing the sheet; in that case, heading up first in order to depower the sails might still be the best first response to excessive gusts.

In any case, I really appreciate your imput. My actual on-water experience in a cat is miniscule in comparison to yours, so its reassuring to find that my understanding of the physics of sails ( and my experience to date, however limited) is not completely off the mark.

Brad
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Old 13-02-2008, 15:18   #54
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Great discussion, guys.

Thanks.

Somehow, thinking about my hull shape and the general heft of the cat I'm closing on, I think it's only going to slide sideways when the winds pick up to that level anyway. ha ha
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Old 13-02-2008, 15:53   #55
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Great discussion, guys.

Thanks.

Somehow, thinking about my hull shape and the general heft of the cat I'm closing on, I think it's only going to slide sideways when the winds pick up to that level anyway. ha ha
Sliding sideways reminded me of a book. I'm pretty sure it was Phil Weld with Moxie. His storm tactics were to take down sails, raise the daggerboards, and lie ahull. The boat would slide/surf sideways down the breaking waves. I doubt this technique would work on boats with fixed keels.

John
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Old 13-02-2008, 16:36   #56
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Sliding sideways reminded me of a book. I'm pretty sure it was Phil Weld with Moxie. His storm tactics were to take down sails, raise the daggerboards, and lie ahull. The boat would slide/surf sideways down the breaking waves. I doubt this technique would work on boats with fixed keels.

John

There's a story on the internet about the Queen's Birthday Storm in '94 which hit around around Tonga and the Northern Cook group. Many boats were caught in this storm, I believe the weather event was later called "a bomb'.

Catamarans caught in 30 meter seas and 100 mph winds essentially did as you suggest. All came through shaken but alive. None of the Cats were dismasted where as all monohulls in the same storm were rolled and dismasted.

For those who love good sea stories. Here's the link to the tale as told by the Captain of the New Zealand Navy rescue ship HMNZS Monowai.

Queens Birthday Storm 1994 - HMNZS MONOWAI
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Old 13-02-2008, 17:16   #57
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Another account of the Queens Birthday Storm: [PUP] Multihulls in the deep blue

Ramtha is still cruising - currently in our local marina.
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Old 13-02-2008, 17:29   #58
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lack of experience

Llamedos,
That was intentional reef to the lower level as a new "cruising" crew. Remember the warning "winds may be 40% higher than forcast" The gust factor is 50% hence 20kts to 30ts means 20kts with up to 30kts gusts & then th 40% comes into the story. If you are crewed with 6 strong guys & are racing then you will take a different view. The reference to the Storm of 1994 & the "Ramha" is why I like my cat!! I know Bill & Robin very well & if you can get the video of this event you will see just how bad the sea can get!!. One point comes to mind from this event & Bill related how this could have helped was the donning of the wetsuit. Bill had lost all steering & tried to keep control by engines. This went on for days & fatigue/cold was taking its toll. If he had put on the wetsuit earlier then he would have not been knocked about as much & much warmer. If things are not going well then you must depower the main before doing anything. Bearing off is not a good idea. (The video was taken from the NZ navy boat & I saw it on the Discovery Channel. Bill had a tape & I will ask if he still has a copy) All the cats stayed upright one mono was lost with all crew, most rolled many times. The faster boats in front keeped going & were OK. Unforcasted weather!! Once in a lifetime event?

Regards Bill Goodward
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Old 13-02-2008, 20:40   #59
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this could have helped was the donning of the wetsuit. Bill had lost all steering & tried to keep control by engines. This went on for days & fatigue/cold was taking its toll. If he had put on the wetsuit earlier then he would have not been knocked about as much & much warmer.

Points taken, Bill.

Well, at least in one way I'll be ready for rough stuff... being from New England, I have a semi-dry suit!! It leaks a little water when you're underwater, but wearing it on deck with booties, gloves and full hood, you'd stay toasty in the worst of spray.

I hope I never need it to steer! ha ha
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Old 14-02-2008, 04:02   #60
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Hud, I think we all agree that you need to let out the sheets to dump the wind. Thereafter, in a cruising cat you also need to immediately reduce sail!

The question here was with respect to an immediate steering response which should allow you the time to let off on the main and jib sheets - not the fastest of maneuvers in many cruising cats, when you start to feel overpowered and are sailing to windward.

You make an interesting point in your comparison to a sailing a Hobie, although I suspect the fact that the Hobie is already flying a hull (precisely what you are trying to avoid doing on a cruising cat) is what makes the difference. In the case of a boat already flying a hull, there would certainly tend to be a disadvantageous weight transfer achieved immediately with a turn to windward (even cars tend to 'roll' to the outside in a turn). This could only add to the existing momentum towards a capsize.

In a cruising cat, you should never fly a hull and the risk of capsize is therefore less contingent upon weight transfer than upon the force and directionality of the wind. Your point however is well taken: should you ever get into a situation in a cruising cat where your windward hull is rising out of the water to a point approaching the maximum righting moment (!!!!) a quick prayer and a turn to leeward would probably be a good idea. Lets face it, with the windward hull flying and the mast raked over alarmingly to leeward, the wind is already being spilled and it is the momentum (and weight transfer) which have now become critical.

Having never flown a hull in my cruising cat (and hoping to never do so!), I can say that a turn to windward while on a close reach or beat causes the sails to luff and depower quite quickly. This gives me the time to let out on the main and jib sheets and then head off.

Brad
Hi, Brad.

I'm a little confused by your post--I can't decide if you're agreeing or disagreeing with me.

My point was, re-stated in different words, was meant to address one issue only: if your hull is in the air, if the boat is going over, do the "counter-intuitive" thing and turn downwind, not upwind to save yourself.
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