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Thread: Falling off in gusts

  1. #1

    Default Falling off in gusts

    La Gringa and I took four ASA courses back in December, on a 42 ft. Leopard. One of the topics that we kinda briefly skipped over was a statement that while you head up in a gust when sailing a monohull ( most of my sailing experience), with a multihull you fall off in a gust.

    This did not make sense to me at the time, and I meant to explore it further with the instructor. But first I wanted to chew it over and see if I could figure out why one would possibly want to do this.

    Well, I never did get back to that subject. Oh, I checked the right box on the appropriate test sheet, etc. ( we aced all those of course) but I still feel the need to understand this. This sudden rehash is due to the fact that I just installed a Davis weather station here at the house, and about fifteen minutes ago we had a sustained gust here at the house overlooking the Caicos Bank, of 42 kts. And the Mrs. and I started talking about if we were out on a tri or cat we would have hoped to have been on the second reef way before this sucker hit.

    I understand the differences in the rigs, and that a mono can heel to spill wind etc. but WHY would you want to turn a multihull downwind in a gust? Isn't this essentially the same as trimming in? Which is also totally counter to what my first reaction would be.
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    Default Re: Falling off in gusts

    There is an interesting thread on the "Cruisers & Sailing Forum" titled "On the verge of flipping-over a cruising cat".
    Strange circumstances. I would like to know what some of the folks on this site think about it.
    Need to read every post on that thread I think.
    Sail Fast Live Slow

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    Default Re: Falling off in gusts

    In a gust a cat will accelerate significantly. The danger period is specifically before the boat has picked up speed.

    When you luff up, this adds centrifigal force to the hull lift just at that moment of highest danger, and also adds additional apparent wind speed. The resultant acceleration moves the apparent even further forward, and increases the apparent wind speed further.

    Luffing down means that the the centrifigal force acts directly against hull lift at the critical moment, and also acts to reduce apparent wind speed. On the mono, you are not going to see the acceleraation problem, and trade off pinching into the wind for additional VMG
    Insanity is continuing to do the same thing and expecting different results

  4. #4

    Default Re: Falling off in gusts

    I must be having some kind of mental block, because I cannot see that. I cannot see why pointing the bow into the wind can increase apparent speed. Cats slow down very quickly when the wind is on the bows. In fact they are famous for actually stopping in the middle of a tack if you do it too slow.

    falling off exposes more of the sail and windage of the hull to the wind. My spotty logic is telling me this is exactly what you do not want to do. A steep wave hitting you broadside just as you turn parallel to the trough would seem to be another risk.
    Tropical island life in the Devil's Triangle.
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    Default Re: Falling off in gusts

    Gringo -
    What's the difference between apparent wind and true wind? It has to do with the motion of the boat relative to the motion of the wind. If a boat is going 10 knots in a 20 knot wind -- if the boat is going downwind the apparent wind is 10 knots (20-10=10). If the boat turns upwind the apparent wind increases. A sailboat obviously cannot go dead upwind, but it can sail closehauled, resulting in let's say 12 knots boatspeed into 20-25 knots apparent wind.
    You are correct that the boat will come to a stop with the bows directly into the wind, but while it is changing direction into the wind the boat's speed will combine with the true wind, resulting in a higher apparent wind.
    Sail Fast Live Slow

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    Default Re: Falling off in gusts

    Quote Originally Posted by FSMike View Post
    There is an interesting thread on the "Cruisers & Sailing Forum" titled "On the verge of flipping-over a cruising cat".
    Strange circumstances. I would like to know what some of the folks on this site think about it.
    Need to read every post on that thread I think.
    We agree with FSMike that Cruisers Forum discussion (very current and now >130 posts!) is an excellent read...and we note this topic is also discussed elsewhere on this Forum. Cf.

    http://www.multihulls4us.com/forums/...2756#post22756

    The better view seems to be that the most immediate relief to the pressure of a gust is to release sheets (especially the main sheet) in virtually any situation other than where the main is already against the spreader going downwind. Releasing sheets de-powers the vessel quickly and doesn't involve adding to any of capsize forces acting on the vessel.

    If already flat downwind, there doesn't seem to be a lot one can do to relieve pressure from a gust...other than ride it out and then reef (further!? ...or drop sails) at the first opportunity if the gust was uncomfortable and/or pressed the boat to beyond its safe speeds. Happily the flat downwind in a gust situation doesn't present much capsize risk, but it is certainly something to avoid if the wind is accompanied by any sort of fetch. For all of the reasons noted here and elsewhere, attempting to point up from a downwind position in a gust is very risky for a cruising cat.

    If, however, releasing the main sheet is not as handy as the helm (indicative of poor anticipation or just being caught unexpectedly) then it seems the safer course would be to fall off whenever the wind is aft of the beam...and head up if the wind is forward of the beam.

    The 'bottom line' for us looks something like...keep the sheets out of the jammers; err in favour of smaller mainsail area when running downwind; keep watch for gusts in daylight hours; and reduce sail areas as a general rule for night passages.

    ...and we too would welcome the thoughts of others.

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    Default Re: Falling off in gusts

    In the Cruiser's Forum mentioned above I was rightly corrected that heading up in a gust from below a beam reach is a bad thing. I stand corrected. Here is my revised explanation:

    The OP in that article experienced an uncommanded rapid turn into the wind that raised the windward hull out of the water. I think a combination of factors (small wave, heavy weather helm due to sail trim, gust from a more adverse direction, and more) rendered the windward rudder ineffective. The opposite rudder immediately stalled, and the excessive weather helm spun the boat suddenly into the wind. It's shoal draft keels were suddenly trying to plow a ten foot wide furrow in 4' of water, and the inside hull came up, as seen by witnesses some distance away. The key factor was tripping over the keel.

    Does this mean that all cats can do this? The few rabid half-a-maraners lurking on that thread are licking their chops. What needs to be said is:

    A monohull in the same situation would have broached.

    It is not at all evident that this or any other catamaran would have turtled. Why?

    If it were truly likely, there would be a lot more turtled cats to talk about. Perhaps as many as there have been broached monohulls.

    The idea of tripping over a keel presupposes that a cat can change direction 90 degree in seconds. In truth, shoal draft cats are highly directional, many people have said they hold their heading as if they are on rails.

    Meanwhile, back at jumping-to-conclusions-city, should a cat always turn down-wind in a threatening gust?

    No.

    In any dangerous gust, slack the sheets.

    Above a beam reach, a cruising cat should head up in a gust, otherwise head down.

    Thas my story (today) and I'm sticking to it.

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    Default Re: Falling off in gusts

    Quote Originally Posted by Sandy Daugherty View Post
    Meanwhile, back at jumping-to-conclusions-city, should a cat always turn down-wind in a threatening gust?

    No.

    In any dangerous gust, slack the sheets.

    Above a beam reach, a cruising cat should head up in a gust, otherwise head down.

    Thas my story (today) and I'm sticking to it.
    There is never a "one size fits all" answer. When I am at the helm I tend to allow a corner of my mind to look at "what ifs" and experience has shown that this lazy review of potential actions allows a better response in situations that need answers.

    This works for me, but I admit I have an analytical style approach to life.
    Insanity is continuing to do the same thing and expecting different results

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    Default Re: Falling off in gusts

    Quote Originally Posted by Talbot View Post
    There is never a "one size fits all" answer. When I am at the helm I tend to allow a corner of my mind to look at "what ifs" and experience has shown that this lazy review of potential actions allows a better response in situations that need answers.
    Absolutely agree Talbot...and that's sound advice too...but there are readers of these Forums (perhaps with relatively less experience) who are searching for rule-of-thumb responses; for them, the one-size-fits-all is important to know as a starting point.

    The ocean is always the master and we sailors are always the students.

  10. #10

    Default Re: Falling off in gusts

    Quote Originally Posted by D&D View Post
    there are readers of these Forums (perhaps with relatively less experience) who are searching for rule-of-thumb responses; for them, the one-size-fits-all is important to know as a starting point.

    The ocean is always the master and we sailors are always the students.

    Well.....actually.....in my particular case, the "one size fits all" statement in the ASA course did NOT work for me. Still doesn't. It's a question on one of the tests. Says one of the differences I need to learn to sail a catamaran is that now I will fall off in gusts.

    I just see that as not a very good universal rule. Maybe on a run? Broad reach? My first inclinations are to head into the wind, or slack the mainsheet. turning broadside just doesn't feel right. But again, I have owned a small monohull for 19 years. And have a total of two weeks sailing cruising catamarans.
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    Default Re: Falling off in gusts

    Quote Originally Posted by Gringo View Post
    in my particular case, the "one size fits all" statement in the ASA course did NOT work for me. Still doesn't. It's a question on one of the tests. Says one of the differences I need to learn to sail a catamaran is that now I will fall off in gusts.
    Very good point Gringo. We stand corrected...and now modify our remarks to the extent that the rule-of-thumb needs to be the right one!

    It seems extraordinary, judging by our experience and the many posts on this and other relevant forums, that it should be formally taught as a universal rule to fall off when sailing a cat and encountering a gust.

    Anyway, slack the mainsheet is the spot-on first reaction. Then helm down for wind aft of the beam and helm-up for wind forward of the beam.

    We too admit to being lifetime monohull sailors now recently (~3yrs ago) converted to the 'dark side'...of beautiful, flat and roomy sailing!

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    Default Re: Falling off in gusts

    Quote Originally Posted by Gringo View Post
    Well.....actually.....in my particular case, the "one size fits all" statement in the ASA course did NOT work for me. Still doesn't. It's a question on one of the tests. Says one of the differences I need to learn to sail a catamaran is that now I will fall off in gusts.

    I just see that as not a very good universal rule. Maybe on a run? Broad reach? My first inclinations are to head into the wind, or slack the mainsheet. turning broadside just doesn't feel right. But again, I have owned a small monohull for 19 years. And have a total of two weeks sailing cruising catamarans.
    I think the problem you are having is that you are looking at this as a major change of course. we are addressing this in the same way you would if luffing up in a mono i.e. a 10 - 20 degree course shift.
    Insanity is continuing to do the same thing and expecting different results

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    Default Re: Falling off in gusts

    Quote Originally Posted by D&D View Post
    Very good point Gringo. We stand corrected...and now modify our remarks to the extent that the rule-of-thumb needs to be the right one!

    It seems extraordinary, judging by our experience and the many posts on this and other relevant forums, that it should be formally taught as a universal rule to fall off when sailing a cat and encountering a gust.

    Anyway, slack the mainsheet is the spot-on first reaction. Then helm down for wind aft of the beam and helm-up for wind forward of the beam.

    We too admit to being lifetime monohull sailors now recently (~3yrs ago) converted to the 'dark side'...of beautiful, flat and roomy sailing!
    I think the real answer is "it depends". Yes, a fundamental, general, difference between a mono and cat is to fall off in a gust, but...

    In thinking about our experience on a cruising cat, I think the FIRST reaction is to change heading (down or up depending on conditions; point of sail, sea state, room etc), followed by easing the traveler, easing the main and so on. I can't envision sailing for extended periods with the main sheet in my hand and "out of the jammer".

    On CF, the OP seems to have reluctantly concluded that he cannot control the boat solely by steering, but he still seems pretty convinced that there is a design flaw in the FP Lipari. I wasn't there and have never seen the boat, so I can't judge whether he's right.

    Fair Winds,
    Mike

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    Default Re: Falling off in gusts

    Quote Originally Posted by Yoga O View Post
    On CF, the OP seems to have reluctantly concluded that he cannot control the boat solely by steering, but he still seems pretty convinced that there is a design flaw in the FP Lipari. I wasn't there and have never seen the boat, so I can't judge whether he's right.
    Mike
    My reading of their situation has always been that the design flaw was with the crew rather than the boat.

    If you push a boat to the limits, and the limits suddenly get worse, this is not a boat problem, but an attitude of mind problem.
    Insanity is continuing to do the same thing and expecting different results

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    Default Re: Falling off in gusts

    I don't think there is a standard response for either monos or cats - except for, as suggested above, "it depends" or "it doesn't matter". In the least, any "standard" rule would have to be more case specific, addressing both apparent wind angle and other parameters such as sea state and wind speed relative to need-to-depower.

    When I'm cruising and everything is stable, the only thing I do in (significant) gusts is, well, see if my trolling baits are still OK. Cruising boats should be able to ride out typical gusts with no reaction whatsoever from the skipper.

    When I raced small cats I can remember doing both - heading up or falling off when close hauled - depending on the total picture. Very pertinent here is the magnitude of the gust and the magnitude of the helm adjustment. Head up too quickly on a small cat already flying a hull and the centrifugal force may take you over. Fall off too quickly and pearling the lee bow may trip you up. Then there's the combination of heading up/falling off in tandem with depowering the rig: significantly easing the main sheet (if already fully close hauled) or trimming the downhaul (to flatten the main) or trimming the jib sheet (to close the slot). On boats with bendy masts, trimming the main sheet - if you have any left - will actually depower the rig via flattening the sail. Same as honking down on the downhaul. Ease the sheet just a little and you actually power up - by un-flattening the sail. Then there's working the traveler......

    I definitely recall that most of the time on small tippy cats I would first head up in a puff to depower the main by spilling air - without touching any sail controls. But I'm talking about just twitching the tiller in manageable puffs. Already close hauled on the small cats (with rotating rigs) the luff of the main will likely already be luffing - all the work is being done by the aft 2/3 of the sail. Heading up a bit depowers the rig by increasing the luffed sail area. Apparently (pun intended), this can compensate for any increase in apparent wind velocity. If you don't head up, the puff with fill some of that luffed portion and power you up.

    Inherent in all of this is the fact that any puff on any closehauled boat (not simultaneous with a lift or header) will first appear to be a lift due to the instant increase in apparent wind angle - until the boat speed responds. So not doing anything on the helm is defacto falling off. That said, in reality, most puffs and lulls are accompanied by lifts or headers so it still "depends"....

    Off course, none of this applies to cruising boats, IMHO. On a cruising mono or cruising cat I don't think it matters much at all because these boats are not that close to disaster to begin with that heading up or falling off (before adjusting sails) will correct. If it does matter, you're not cruising or you're over canvassed. If you nonetheless find yourself in an over powered situation, "it depends".....

    2 Hulls Dave

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    Default Re: Falling off in gusts

    I was writing my post while Dave posted his, but I am going to include it all anyway. I do agree with Dave regarding small cats.

    While I have owned my current boat just 18 months, I have owned, sailed and raced Hobie Cats for the past 31 years. I think some of what I learned on those boats can be applied here.

    While I am sure it can be terrifying on a cruising catamaran, flying a hull can be a thrilling, yet inefficient way to sail a Hobie Cat. In a gust as the hull lifts, the sail wants to spill the wind. Novice skippers (and monohull sailors) usually panic at the thought of going over and tend to head up. However one can get into trouble that way, as the wind can now get under the trampoline and continue to lift and further causing instability. Many a Hobie has gone over that way.

    I think to head up in a cruising cat would cause the same instability, as now the wind could get under the boat as well!

    Of course on a Hobie Cat another reaction is to immediately spill the main, which is many times easier to do on a Hobie than a cruising cat.

    I found that by heading down on my Hobie, the boat accelerates but the windward hull comes down. That initial burst of speed can be unnerving to the inexperienced or monohull sailor not familiar with such acceleration. As I head down not only do I flatten the boat and accelerate, but get that little extra time to reconsider my sail trim, traveler position, crew placement etc., and I am that much closer to the next mark. If I am up in the air that isn't really possible.

    As this thread has progressed, I have looked in both Gregor Tarjan's "Catamarans -- Every Sailor's Guide (2006)" and Charles Kanter's "Cruising in Catamarans (2002)" but I have not been able to find specific mention of this topic. However I did find the following:

    Charles Kanter states, "Monohulls relieve excess pressure from wind gusts by heeling or rounding up. Multihulls do it by accelerating...A gust comes along, the monohull heels smartly, recovering when the gust passes...The multihull on the other hand, not heeling, leads someone unfamiliar with its energy relieving techniques to question the possibility of capsize. The basic energy relieving technique of a multihull is acceleration. In actual mathematical measurement, it takes only a little acceleration to equal the power absorbing ability of much heeling...Even a little increase in speed absorbs an enormous amount of energy." Kanter also mentions Chris White discussing the basic mathematical aspects involved as they relate to why monohull people are forever talking about capsize in "The Cruising Multihull."

    Gregor Tarjan states, "Whereas a monohull will round up in a gust, a stable cat will absorb the energy of the wind and translate it into forward momentum and simply accelerate the boat."

    I think the key here is "stable cat" as he states later in the book, "When close-hauled in a monohull in windy conditions, standard practice is to head up when hit with a gust. This prevents excessive heeling, which could result in a knockdown. On a high-performance cruising multihull luffing up is still the best course of action when you're temporarily overpowered while sailing very close to the wind..."

    Interesting to note, according to his bio Gregor has over 80,000 miles on monohulls and multihulls and has crewed on boats ranging from America's Cup Yachts to 102' cats. As a merchant marine officer, he is a USCG licensed captain and member of The Society of Naval Architects and Marine Engineers.

    Gregor also states "Unlike Hobie Cats or very light displacement catamarans, a cruising catamaran will never lift a hull. I have never lifted a hull on a cruising multihull...On a well-designed cat, theoretically, the shrouds will act as safety valves and break before the main hull could lift...The only time I flew a hull on larger multihulls was on racers, such as Formula 40 cats, 60' tris or 120' racing cats such as "Club Med."

    My boat, a Morrelli & Melvin designed coastal cruiser, is less than the 2:1 length to beam standard, and I have had the sensation that the windward hull wants to lift. Observers however, have told me that is not even close, so I have to believe it is just me getting used to the boat.

    My inclination is to believe there is nothing wrong with the design of the FP that started the whole discussion.

    Marshall
    "People sail for fun and no one has yet convinced me that it's more fun to go slow than it is to go fast." -- Dick Newick

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    Default Re: Falling off in gusts

    Quote Originally Posted by Yoga O View Post
    I can't envision sailing for extended periods with the main sheet in my hand and "out of the jammer".
    "Out of the jammer" (to us) means on a loaded (including a self-tailing) winch. So not in the hand, but at least able to be released more quickly than opening a jammer under heavy pressure.

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    Default Re: Falling off in gusts

    Quote Originally Posted by searenitysail View Post
    Gregor also states "Unlike Hobie Cats or very light displacement catamarans, a cruising catamaran will never lift a hull. I have never lifted a hull on a cruising multihull...On a well-designed cat, theoretically, the shrouds will act as safety valves and break before the main hull could lift...The only time I flew a hull on larger multihulls was on racers...
    The currency of Gregor's above observation seems to us to be the central issue of the CF thread. It is logically inevtitable that there will be a point where, as designers of 'cruising' vessels push the design envelope further toward larger sail plans to acheive light air performance, Gregor's observations above may cease to apply so strictly (especially the "never lift a hull" bit) simply because the "cruising catamaran" may, by design evolution, be moving closer to the "racer". The CF thread (to us anyway) poses the question...are we there yet?

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    Default Re: Falling off in gusts

    I suspect that it is possible to force any boat beyond its limits to the point of compromising safety. The difference is, most of the time, a mono pushed beyond its limits will fill and sink, either through downflooding of hatches or total capsize. The cat may go over, but it will still float. Much better place to wait for rescue than an inflatable raft or worse! Of course, lucky monohullers who are knocked down will return to an upright position, hopefully with a boat not full of water. THE CAT IS STILL SAFER!!!! Even more so if sailed sensibly.

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    Default Re: Falling off in gusts

    Tried to get Gregor Tarjan into the discussion by emailing him link to both forums. Unfortunately, he didn't choose to enter. He did email me the following, though.

    Marshall

    Dear Marshall:

    I am sorry for the late response but I just returned from a (sail) trip.

    You know - this question is a very personal one. There is no right or wrong way of doing things. Personally in very strong wind - high/short wave conditions , if close hauled I would feather the cat to windward and luff up instead of taking a big roundabout turn to leeward exposing the boat to beam seas…and possibly accelerating.

    On the other hand in the same conditions sailing really deep, say at 140 apparent, I would do the opposite. Run off and depower.

    This is of course assuming that wind and waves are in harmony (coming from the same direction) …which sometimes is not the case as I have found out last week off Cabo Cruz in Spain.

    It is always the least way of resistance. Sailing safe is about reducing loads whenever and wherever.

    Just an opinion.

    Stay well,

    Gregor

    "People sail for fun and no one has yet convinced me that it's more fun to go slow than it is to go fast." -- Dick Newick

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