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Old 27-02-2008, 15:07   #91
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Apparent wind

Quote:
Originally Posted by Therapy View Post
This discussion is what I have heard about multihulls in the past.
I have been told (and read here) that for the most part the cruiser need not worry about this stuff because one should be a good sailer and reef for gusts, reef early etc etc.
I feel that is foolish.
You see,
With every motorcycle I bought I soon went to parking lots (empty) that were wet, sandy, dry etc. to learn what some of the limits of the bike (and me!) were. Maybe it is just me but I sort of want to know more stuff.

I want know (and practice in controlled circumstances) what to do if it needs to be done.

Tri - do you have reference to diagrams/drawings/charts that describe/show this stuff of apparent wind velocities and how they change etc. with emphasis on a much faster boat ie; a cat? This is for one that has monohull experience (except Hobie's) that wants to get a cruising cat?

Sorry I don't have that stuff to post but you can probably find it on the web. Agree with learning the limits but so often you don't know what to expect with gusts (e.g. approaching line of dark clouds, or night sailing when you can't "read" the water to windward) and it's good to be able to anticipate a planned tactic and execute with alacrity when needed.

Also monohulls and tris (to a lesser extent) give you a good feel for how hard you're being pressed by the wind... but cats heel so little it can be difficult to judge how hard is hard. So generally speaking in gusty/storm conditions it's a good idea to be conservative and don't try to find the boat's limits (as in your proverbial "parking lots") unless you are in fairly steady and predictable conditions in flat water.

We find that we often go just as fast after we reef as we did when we were still deciding whether to reef, but the boat rides more comfortably and feels safer, so don't hesitate to reef when the thought arises: If you're thinking of it -- it's time.
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Old 27-02-2008, 15:55   #92
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Quote:
Originally Posted by SailFastTri View Post
1 good to be able to anticipate a planned tactic and execute with alacrity when needed.


2 don't try to find the boat's limits (as in your proverbial "parking lots")



3 If you're thinking of it -- it's time.
The web..........yea..........sometimes that is frustrating..............

1 I try to plan ahead.

2 I won't do in my cat (if I ever get one ) just sort of an example of my thoughts.

3 I will heed that.

Thanks.
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Old 27-02-2008, 16:24   #93
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Quote:
Originally Posted by Therapy View Post
This discussion is what I have heard about multihulls in the past.
I have been told (and read here) that for the most part the cruiser need not worry about this stuff because one should be a good sailer and reef for gusts, reef early etc etc.
I feel that is foolish.
You see,
With every motorcycle I bought I soon went to parking lots (empty) that were wet, sandy, dry etc. to learn what some of the limits of the bike (and me!) were. Maybe it is just me but I sort of want to know more stuff.

I want know (and practice in controlled circumstances) what to do if it needs to be done.

Tri - do you have reference to diagrams/drawings/charts that describe/show this stuff of apparent wind velocities and how they change etc. with emphasis on a much faster boat ie; a cat? This is for one that has monohull experience (except Hobie's) that wants to get a cruising cat?
On an earlier post I posted the link to a Privilege 445 apparent polar diagram and did the calculations to show apparent wind speed and true wind angle in the pdf at the bottom of the post. This boat does not show apparent wind increases much more than you would see in a modern monohull. Turning downwind can work in any boat, unless you are so overpowered that the sails make you round up uncontrollably. I show this to people all the time on my monohull to show the importance of lift. As soon as I turn the boat downwind 10 to 20 degrees from a close hauled course, the sails stall, produce less force and the boat immediately heels less. You can continue the turn and further reduce apparent wind.

Unless you've really pushed the limits and getting in trouble with a low performance cruising multi, I don't see that you have to turn downwind in a puff.

Here it is again in the body this time.

AWA BS AWS TWA
170 8 12.1 174
150 8.5 12.2 162
130 9.5 12.5 163
110 11 13.4 141
90 13 15.2 131
70 11 20.9 101
45 7.5 24.6 60
TWS=20
AWA= apparent wind angle
BS= boat speed
AWS= apparent wind speed
TWA= true wind speed
AWA and BS from polar diagram of Privilege 445

Here's some polars for beach cats:

http://www.mwilsonrae.com.ar/Tornado/CurvasPolares.pdf


From the Tornado polar:

TWA BS AWA AWS
60 12 27 19.1
75 13.2 34 17.3
80 13.5 47 13.5
90 14 36 17.2
110 13 44 13.5
120 12 69 10.8

TWS = 10

Note how the apparent wind speed rises again at a TWA of 90 degrees, and that it is 1.7 times as strong as the true wind. I don't have the data, but I would guess that you would see this kind of behavior on large racing cats and tris, and maybe even performance oriented cruising multis. This is where I would really worry about the zone.

John
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Old 27-02-2008, 17:09   #94
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Originally Posted by cal40john View Post
Unless you've really pushed the limits and getting in trouble with a low performance cruising multi, I don't see that you have to turn downwind in a puff.

John
I don't understand why you specify "low performance"....
In my experience the higher the performance of the boat, the more likely this tactic is to be needed. Higher performance boats are, for a given size, lighter with more sail area (have taller rigs) and are more likely to be overpowered. (Looking at the polars you posted, all of the boat designs slow as the course approaches 180 degrees.)

I thought this discussion thread applied specifically to the situation of "really pushed the limits and getting in trouble".
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Old 27-02-2008, 18:22   #95
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Quote:
Originally Posted by SailFastTri View Post
I don't understand why you specify "low performance"....
In my experience the higher the performance of the boat, the more likely this tactic is to be needed. Higher performance boats are, for a given size, lighter with more sail area (have taller rigs) and are more likely to be overpowered. (Looking at the polars you posted, all of the boat designs slow as the course approaches 180 degrees.)
That's exactly the point I've been trying to make. I think a majority of the multis sold to the off shore cruising community would be classed as a lower performance multi and therefore have less likelyhood to use this tactic.

Even an iceboat is going to go slower than windspeed DDW.

Quote:
Originally Posted by SailFastTri View Post
I thought this discussion thread applied specifically to the situation of "really pushed the limits and getting in trouble".
You're right. What I probably read into several of the posts that wasn't actually in them, was bearing off is the only tactic available to you in a puff, no matter what the conditions.

John
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Old 27-02-2008, 19:38   #96
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I plan on having an unstayed rig and all you have to do is release the sheet. I have experienced being overpowered dead downwind from an adiabatic bullet. It was a bit disconcerting. In general I agree that on a fast boat when not hard on , turn down wind
Robert
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Old 28-02-2008, 14:32   #97
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Flipped Cats

Most of the cat flippings I have heard of were either going across the front of very large waves with the sail almost square to the wind, or from sailing over the top of a large wave and burying the nose--the aft then being lifted and the wind helping her over into the pitchpole, or river bar crossings.

With a cruising yacht I think the way to go is to sail defensively, and this applies to multihulls in particular. Reef early and if necessary reef again.

I would rather head for shelter or wait out a blow than to try to bash along hoping to make it home in a sea where the wave height far exceeds the beam of the boat just so I can get to work the next day. I would prefer to survive and get to work the day or two after--

Sometimes one encounters freak waves in rough conditions.

It only ever happened to me once, but two waves added themselves as I went up the sides of them on the quarter, and I looked to leeward and saw a huge hole in the ocean, with apparently large waves all around it. I thought how little I would fancy being down there--when the tri fell off the top of the wave and dropped straight into the hole, submerging most of the leeward ama. I looked up at waves which appeared ready to bury me--and the hole just filled as the waves moved on and we were again sailing in a moderate sort of sea.

The water depth was about fifty feet--

Now, had I been in sailing parallel to the waves I am sure I had a real chance of being overturned, in this brief and unusual situation.

It takes unusual circumstances to produce unusual events--at least some of the time. If there are waves of two metres--expect the odd wave of as much as three or four times that height. If the sea is comparatively shallow and the wind is strong and gusting even more strongly, those waves can become steeply faced, perhaps breaking.

In a mono, comfort dictates the way you will sail to a great extent. Because cats and tris are deceptively comfortable, one can be in a potentially dangerous situation before one becomes aware of it unless one has sufficient rough water experience.

Near islands we get "Bullets" of wind which can last up to a minute or sometimes more. They are a product of wind reacting to the island topography. They will rip sails, break rigging and one has to watch out for them all the time. I think they would be capable of flipping a small cat and breaking gear on a large one.

Some multis do not have a lot of bouyancy in the bows, and are a bit slow to rise to a sea, especially if they are carrying a lot of chain and a decent anchor etc. This could be a disaster if one surfed down a steep freak wave. As soon as it starts to get rugged I head for shelter, and I move stuff aft to lighten the bows as much as possible.

A little trepidation might be a good thing--complacency certainly kills people--but panic is not. If you are sailing a multi in really bad seas and are unconcerned--perhaps you should be--just a little.
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Old 28-02-2008, 18:08   #98
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Bearing in mind that we are talking about a very rare situation indeed (where the direction you steer is a critical tactic), I still believe that for a cruising cat that is suddenly overpowered while beating or on a close reach, there are some real benefits to turning to windward:

1. The sails will almost immediately begin to luff, reducing the power and heeling force that is generated. The boat that turns to leeward in such a situation will still have his sails drawing fully, except that with the sails being sheeted in too far for the angle of the wind, even more of the force will be directed towards heeling than forward motion.

2. If heading up from a beat/close reach, you will now also (assuming the waves are coming from roughly the same direction as the wind), be putting more of the bow into the oncoming waves. On the other hand if one heads off, you will be exposing more of the beam of the boat towards the waves, greatly increasing the risk of wave induced (or at least assisted) capsize.

Gregor Tarjan in his book Catamarans, The Complete Guide for Cruising Sailors, International Marine, Camden Maine, 2008 says at page 185 that:" Beam seas are the most dangerous for a multihull and should be avoided at any cost, even if only for seconds." If you choose to head off while overpowered on a beat/close reach, this is precisely what you will be doing. And of course, you will still have your sails drawing fully, as described above.

On the other hand (as I suggested in an earlier post), Tarjan does agree that " if you are overpowered by a strong beam wind, I prefer to reef the mainsail by running downwind"(loc. cit.). Of course in this case, you are actually turning away from the seas (in this case your stern quarter) and reducing apparent wind speed.

Apparent wind is a phenomenon that affects both multihulls and monohulls: if dead upwind, the apparent wind is the sum of the actual wind speed and the speed of the boat; if dead downwind, the apparent wind speed is the actual wind speed less the speed of the boat. So yes, if on a beat (or close reach), the apparent wind speed will increase as you head up. On the other hand, the sails will almost immediately begin to luff, reducing the forces generated by the sails, both forward and to the side. Further, as already discussed, you will also be moving the force of the waves from the side towards the bows. These two factors are clearly more significant than the centrifugal forces generated by a slight turn to windward and the slight increase in apparent wind (slight as you are already sailing to windward).

It should also be remembered that it is often easier to reef your sails while heading into the wind (and this is what you ultimately need to do in situations where you are overpowered). And finally, if you are headed directly into the wind/waves, there is absolutely no heeling force being generated by either the wind or waves while you attempt to reduce sail. If you remain exactly where you were when overpowered, you will find the task of reefing much more difficult and dangerous.

As to letting off on the sheets - a good tactic in a dinghy, but without moving the traveller to leeward, you will primarily increase the camber in the mainsail and therewith increase heeling: you need flat sails in heavy air.

In sum I (and some others) still believe that when you are close hauled, it is important to turn to windward as your first line of defence in preparation for reefing. If you have the wind off the beam, however, it is just as important to do the reverse and turn downwind prior to reefing. My experience (and limited understanding of physics) suggest that one tactic should not be used in all scenarios.

Brad
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Old 28-02-2008, 20:03   #99
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Quote:
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are some real benefits to turning to windward: Brad

Brad I dunno about this.

If I do manage to turn into the wind in a blow, with my windage the wind is just going to blow me around again. I've had it happen in 50 knot winds, which changed my mind on storm tactics.
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Old 28-02-2008, 21:32   #100
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Brad's post causes some concern to me too. I started to post a few replies -- even deleted one because I don't want to appear too contentious as a newbie on this board. However I've owned trimarans for 9 years and believe rounding up can be hazardous if you are truly at the limits of stability when starting the move.

If already pinched close upwind (very close) maybe (big maybe) that move is viable, but otherwise you'd be better served to depower the main and jib and don't turn upwind until the boat slows. Turning upwind will increase apparent wind and the centrifugal force from the turn (acting on weight aloft) will tend to assist the wind in lifting the windward hull.

Executed with alacrity, a turn downwind will almost never add any concerns about broadside waves.
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Old 29-02-2008, 06:06   #101
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In my experience it is faster when sailing to windward to depower by luffing up, then commence the correct procedure for reefing: start the diesels to keep your heading, let out the jib sheet, move the traveller to leeward, then reef. The increase in apparent wind will be very small (you are already sailing to windward) and very short (the sails should start to luff almost instantly when you pinch up). This is a procedure I used on one occasion in gusts over 50 knots (which coincidentally knocked down a 60 foot charter schooner only 2 miles from my position).

On the other hand, I will admit that I have never been overpowered past the point of stability. As I said in an earlier post, if I were ever to find myself lifting the windward hull out of the water, I would no doubt turn to leeward as you suggest. At that point the immediate centrifugal force of the turn might bring the windward hull back down (so long as it was not simultaneously hit on the beam by a large wave). Thereafter I would have to let out the jib and pray that I am able to get the traveller out before I jibe, all while trying to maintain a proper heading after a turn that was commenced by 'turning with alacrity' to leeward with massively overtrimmed sails. Really, once you have started to lift the windward hull, you can choose your poison.

Brad



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Old 29-02-2008, 06:21   #102
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if you are truly at the limits of stability when starting
I understand Brad's points and think Larry nails the distinction here. How close to the "edge" are we talking about?

From years of racing small cats and crossing the "edge" many, many, many times, I can make the argument that whether one should head up or down in a puff depends on a split second decision of how close to the edge you are and whether you've prepared based on your observations of the upwind conditions. Is the puff a lift or a header? Is it small, moderate or big? Is the sea state conducive to heading up or down? Is there a conveniently placed and timed wave to take advantage of or avoid in combination with the current or expected conditions? How much leeward bow freeboard is left? Is there also a crab pot you need to avoid?

Once you've sailed a small cat sufficiently enough to really, really know the boat - including capsizing it enough times to know how and why and when it will - you can make these split second decisions and be right most of the time. Twitching the tiller up or down in combination with sawing the sheets/downhaul in or out can keep you right on that edge or send you too far to either side. There is no one answer, IMHO, if you're close to the edge. If you're not close to the edge, you can do anything you want - including nothing.

I hope I never have to make a split second decision like this in my cruising cat. If I do I have already made mistakes WAY earlier.

Dave
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Old 29-02-2008, 06:57   #103
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This is truly interesting, but wouldn't the prudent sailor already have reduced sail by now? Why is we are sailing on the edge? I can understand a racer doing this, but not a cruiser. Next time I head south I will play with both these tactics in less than on the edge scenario. I am telling you folks, this is one extremely informative group of people.

I am on a car site also, and one fella's quote is.....
not one of us is as smart as all of us...................
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Old 29-02-2008, 07:30   #104
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[quote=Southern Star;138959] the correct procedure for reefing: start the diesels to keep your heading, let out the jib sheet, move the traveller to leeward, then reef.
snip
let out the jib and pray that I am able to get the traveller out before I jibe, all while trying to maintain a proper heading after a turn that was commenced by 'turning with alacrity' to leeward with massively overtrimmed sails.

G'day,

Hard to think of a better argument for an unstayed rig with self vanging boom.

On any point of sail, in any wind strength, release the sheet. The boat stops with the sail pointing into the wind. Lock the helm so the waves don't damage the rudders. Stroll forward and put the reef in, or leave the sail as is and have a cuppa while the squall blows over.

There is the added advantage that the mast would have flexed automatically in the higher wind, so the boat probably would not have been overpowered anyway.

There is a thread at http://www.cruisersforum.com/forums/...sts-12995.html for anyone who wants to know more.

regards,

Rob
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Old 29-02-2008, 07:54   #105
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I think this entire conversation is boat dependent. There is no one answer.
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