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Old 14-12-2008, 12:10   #1
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Tacking a Catamaran - Interesting question

A friend of ours just bought a catamaran, and was asking about coming about in high seas. Whether to do it in the trough or on the crest. After a bit of thought I could not come up with a standard rule of thumb. I told him it would depend on the waves: as in height and intervals. Any thoughts?
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Old 14-12-2008, 13:31   #2
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They tack relatively slowly, compared to monohulls, that the chances of being in the trough and then on top of a swell during a tack is pretty good...unless you have a really long wave period. I don't think it makes much difference.
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Old 15-12-2008, 08:46   #3
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Use the shape of the Seas

I believe it would depend upon whether the sea was ahead or from aft and, if from aft, whether it was overtaking or not. In any case it is a timing issue, with the objective being to use the acceleration down the face of a wave to give one the inertia to carry through the eye of the wind while in the trough and fall off on the new tack as the yacht rises to the next wave. In really heavy seas and strong air, we have found it easier--on the crew and the equipment--to gybe the yacht around to a new tack, with the actual gybe being made as one accelerates into a trough as the apparent wind is reduced and the the rig is somewhat sheltered from the wind. While we sail a mono, I suspect the same would hold for a cat although it may be a bit tougher for a cat in steep seas as a cat will attempt to float perpendicular to the face of the water and may slip sideways on the back of a wave unless the helm is brought down smartly as the crest passes. Not a fun exercise in any yacht, but a necessary skill

FWIW...

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Old 16-12-2008, 00:09   #4
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I am surprised this hasn't gotten more response. I am eagerly awaiting reponses.

I have ideas but they would only be guesses. Dave of Maxingout would surely have an opinion.

It might get more play in the multihull forum. I'll move it if you like Denny. Just let me know.
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Old 16-12-2008, 02:31   #5
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I think its bullshit. Spin the wheel whenever you want to.
This thing about people being too scared to turn into the wind in a strom is garbage. When you need to turn upwind just do it.


Mark
PS I'm open to others thoughts as I have never been in a big enough swell to not allow me to do what I want.
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Old 16-12-2008, 05:30   #6
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A Cruisng catamaran has twin engines, yes? I would not want to get caught in irons trying to tack through the wind in a big head sea. I think I would consider using the engines to get me through the tack ( one engine forward, one reverse). The goal is to get through the turn as quickly as possible without losing way.

By coming about, do you mean tacking through the wind and then falling off to make a full 180 degree turn, to a broad reach? I think I'd start my turn on the top backside of the wave, get through the turn before the trough ( if possible ) and then quickly fall off the next wave face taking the sea on the quarter.

I'm just trying to picture the turn in your question, not make a judgement as to whether the downwind heading is the correct strategy.

Of course, conditions can only be accurately determined when you're in them.

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Old 16-12-2008, 06:36   #7
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Quote:
Originally Posted by Ex-Calif View Post
I am surprised this hasn't gotten more response. I am eagerly awaiting reponses.

I have ideas but they would only be guesses. Dave of Maxingout would surely have an opinion.

It might get more play in the multihull forum. I'll move it if you like Denny. Just let me know.
Sure Dan and if you would provide link please
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Old 16-12-2008, 06:41   #8
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Lets say fulll 180 degree turn so, a tack and fall off to full 180 degree turn was the question
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Old 16-12-2008, 06:46   #9
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The issue of whether one is sailing into a head-sea or with the seas or in an over taking sea has relevance because of the motion of the water in the waves and the resulting effect that has on the yacht's rudder(s) and ability to respond. In waves, the water rotates in a circular fashion in the direction of the wave's travel, reaching a relative maximum at the crest of the wave and a relative minimum in a trough. If one is traveling against a head sea, the water flow across the rudder(s) is at a relative maximum at the top of a wave giving one the greatest rudder control at that point. Coincidentally, however, at the top of a wave the yacht also has the greatest wind-load on her forequarters, blowing her to leeward away from her tack, hence one wants to begin the tack at the top of the wave as the yacht passes over the crest and then use the yacht's acceleration down the back of the wave, where the forequaters become somewhat sheltered from the wind, to carry through the tack. If the wave period is too short, however, as it could be in a developing sea, one might not have time to fully pass through the eye before the next wave forces one's stern to windward, denying the tack. At that point one has no choice but to gybe.

Running up wind but down sea (such as to windward in a northeasterly in the Gulf Stream), unless one is traveling faster than the sea--i.e. the sea is not overtaking--the speed of the circular water flow at a wave crest can reduce or entirely eliminate rudder control, and in a situation where the water flow signigicantly exceeds the speed of the yacht, the effect of the rudder(s) can actually be reversed (turning the wheel to starboard results in the yacht's head backing to port, away from the tack) as, from the rudder's view-point, it's as if the yacht were moving backward through the water. Accordingly, unless one is moving significantly faster than the seas, positive rudder control can only be assured in the troughs, at which point the yacht is again, momentarily sheltered from the wind.

FWIW...

s/v HyLyte
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Old 16-12-2008, 13:45   #10
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Start your motors, and push & pull her through the turn. Use every tool available to you to accomplish any job. When you get to know the boat you will know how she behaves. Fortunately for me. I haven't seen that situation in my cat YET!......i2f
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Old 16-12-2008, 13:55   #11
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Why don't issues like this ever come up when catamaran enthusiasts are telling us how superior they are??
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Old 16-12-2008, 14:05   #12
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Quote:
JusDreaming: "Lets say fulll 180 degree turn so, a tack and fall off to full 180 degree turn was the question"
Why tack? If the objective is to reverse course, falling off on the existing tack and gybing is the easiest, safest, course of action.
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Old 16-12-2008, 20:07   #13
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Every time I gybe its an opportunity for the gooseneck or the traveler to fail, so I would rather tack, but I have a monohull.

From my old Hobie days, I would always tack going up a wave when my speed through the water was best. The only problem was that when you tack the Hobie, you have to go to the stern to swing the hiking stick around the traveler, and big air under the trampoline would blow you over backwards--not quite as much as problem for cruising cats.

Sidenote to Jim--haven't they thrown you and Ann out of Oz yet???
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Old 16-12-2008, 21:41   #14
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Hi guys - Just moved this thread from the Seamanship Forum to see if the cat guys had any opinions.
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Old 16-12-2008, 21:45   #15
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I remeber racing dinghy's in college. There were five or six foot seas and 25 knot winds with stronger gusts. I found that when you got to the bottom of the wave it was nearly impossible to tack. I realized that there was not enough wind in the trough of a wave. Applying this to a 10 or 20 foot wave the majority of the sail area is blocked by the waves so I would think that you would want to start your tack at the top of a wave as Hylyte explained.
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