Average Range of Yawing at Anchor in Storms

[thinwater]

Originally Posted by tomlisasail

... I don't understand why deep water makes a better holding situation during heavy winds.

Several things:

• Waves are not as steep.
• More chain gives more catenary.

[newhaul]

Originally Posted by thinwater

Several things:

• Waves are not as steep.
• More chain gives more catenary.

in 50 knots + I ha be anchored my islander in as little as ten feet water( mean low tide)
putting out 30 ft of chain and about 150 ft of rode and I did not use at all that day . Slept well that night though.

[Fuss]

On my 25 ton, high topsided, fin keeled, full skeg cutter, In winds to 20 knots we sail very little at anchor but as the wind increases so does the sailing. In 40 plus knots we can sail thru 120 degrees with heavy snatching at each change. Just like Sailorboy.

I don't like the riding sail, simply because it might cause me problems in increasing winds and also, it doesn't really work for my boat. Last time I tried it, it did make a reduction, however, it makes me nervous at over 50kts and then I want to take it down which then is difficult. I would not want it up in any stronger winds. I only tried it twice.

I experimented with a drogue off the anchor chain and this made a reduction but the drogue was too small. At least in very strong winds, it would be easier to remove than a riding sail.

So I might get a bigger drogue sometime. What I am next going to try is changing the underwater profile from the bow back to the bottom of the keel. To do this I am going to fabricate sunbrella that attaches to the bow and then attaches to the bottom of the keel, so effectively filling in the triangle forward of the keel.
I am sure this will make a difference to the sailing around. BUT, this has yet to be proven. (its only for testing, just in case someone thinks I am leaving it there)

10mm all chain, 60kg bugel anchor.

[thinwater]

Originally Posted by Fuss

On my 25 ton, high topsided, fin keeled, full skeg cutter, In winds to 20 knots we sail very little at anchor but as the wind increases so does the sailing. In 40 plus knots we can sail thru 120 degrees with heavy snatching at each change. Just like Sailorboy.

I don't like the riding sail, simply because it might cause me problems in increasing winds and also, it doesn't really work for my boat. Last time I tried it, it did make a reduction, however, it makes me nervous at over 50kts and then I want to take it down which then is difficult. I would not want it up in any stronger winds. I only tried it twice.

I experimented with a drogue off the anchor chain and this made a reduction but the drogue was too small. At least in very strong winds, it would be easier to remove than a riding sail.

So I might get a bigger drogue sometime. What I am next going to try is changing the underwater profile from the bow back to the bottom of the keel. To do this I am going to fabricate sunbrella that attaches to the bow and then attaches to the bottom of the keel, so effectively filling in the triangle forward of the keel.
I am sure this will make a difference to the sailing around. BUT, this has yet to be proven. (its only for testing, just in case someone thinks I am leaving it there)

10mm all chain, 60kg bugel anchor.

I'm guessing the increase in yawing is because of the chain lifting off the bottom. The other balance factors have not changed.


Please explain why a riding sail make you nervous. I think these problems are solvable with better designs. If the sail reduces yawing, it should be reducing all loads, even though it might not feel that way.

1. Conventional rigging is NOT very efficient. There are better designs.
2. Conventional rigging is NOT very strong (luff is unsupported).


I've done some drogue testing from the bow. It can't hurt, but I was not impressed. The problem is unless the boat is moving pretty fast and the drogue is very big, there is little force.

[a64pilot]

We bought the full Monty of the Sailrite sewing machine, and bought the anchor riding sail to use to learn the machine with.
Near as I can tell, the anchor riding sail makes no difference at all on our boat, we have dual back stays and do not put the sail up on center line.
Heavy winds she seems to stop sailing for some reason, she Sails worst with wind and current in opposition and you hit that magic wind speed where gusts will push her from lieing to the current and then to the wind and back as the wind dies, but that is a gentle thing that you can’t feel below, and only know when you look out.
However with any current at all, a full keel boat will lie completely different than most boats, particularly a Cat. Cats especially will lie to the wind. I assume it’s because there is actually not that much boat under the waterline compared to what’s above, where a full Keel will lie to the the current unless the wind is very strong.

[wsmurdoch]

[QUOTE=thinwater;2868679I've done some drogue testing from the bow. It can't hurt, but I was not impressed. The problem is unless the boat is moving pretty fast and the drogue is very big, there is little force.[/QUOTE]

I have found the same. My cone drogue did little to reduce yawing at anchor. This is a repeat of an old post.

****************
I tried tying a 32 inch cone drogue to the anchor chain just below the water surface to see what effect is would have on the boat shearing about at anchor. I have used as my 'measure of merit' the apparent wind angle because I wanted the boat to stay aligned with the wind to minimize the wind force on the boat.



For the first 35 minutes (-65 to -30) the boat was swinging away. For the last 30 minutes (-30 to 0) the bridle of the cone was clipped to the chain. It seemed to make little difference in the variation in the apparent wind angle. Watching it in the clear Bahamian water, the drogue took a good part of the swing to come into use, and then the speed was not great enough to cause much drag.



This is a similar earlier test of a riding sail. You can see when it was hoisted. The riding sail cut the variation in the apparent wind direction in half.



This is the riding sail.
***********************

The riding sail was sheeted amidships.

Bill

[thinwater]

Originally Posted by a64pilot

We bought the full Monty of the Sailrite sewing machine, and bought the anchor riding sail to use to learn the machine with.
Near as I can tell, the anchor riding sail makes no difference at all on our boat, we have dual back stays and do not put the sail up on center line....

I too saw very little difference. They help with some boats.


The designs that reliably worked were all V-sails, such as the Fin Delta from Banner Bay and other DIY variations.


Testing. I've got 3 sails and a load cell lined up for the next nice day.

[wsmurdoch]

Originally Posted by thinwater

The designs that reliably worked were all V-sails, such as the Fin Delta from Banner Bay and other DIY variations.

Testing. I've got 3 sails and a load cell lined up for the next nice day.

While I hate to wish bad weather on anyone, I hope you have some solid winds. The December '07 Practical Sailor "test" of the Fin Delta was at a maximum of 10-15 kts and had no measured data.

I'm looking forward to seeing your results. When I decided to get a riding sail for my cutter I considered a conventional flat sail, a V shaped sail (http://www.chava.ru/images/img6.gif), a Y shaped sail (Fin Delta), and even a backwards set flat sail (Good Old Boat - Quit Horsing Around article). I ended up with a conventional flat sail because it was offered on ebay at a price less than the the sailcloth alone by a Florida sailmaker. It was a poor way to make a decision, and I could not find any useful comparison testing.

And, thank you for the link to the ship dragging article. We had a sailboat drag down on us in the cut at Normans Cay two weeks ago, and the diagram of a ship's track in the transition from yawing to dragging on page 4 exactly describes his situation.

Bill

[Montanan]

Originally Posted by olddog57

Forgive me this theoretical consideration: after a wild night at anchor in my very heavy long keeled 34-foot motorsailer (almost 12 ton) with not so much (30-35 kn) wind I thought on this issue, and decided to use asymmetrical bridle (still did not check if it helps)

Sailing at anchor is a kind of self-oscillation.
With an (almost) symmetrical profile and even an (almost) constant wind direction such oscillations are easy to start, as to sail out of the equilibrium state (the chain and the boat both along the wind direction) not much force is needed - say slight wind change is quite enough.
If the profile exposed to the wind is significantly asymmetrical, then the equilibrium state is much more stable - hence any yawing has to be reduced.
So, any asymmetric setup (different length bridle lines, riding sail set at a substantial angle to the center-line) should abate yawing

Thanks OldDog for the explanation, that sounds theoretically sound. I have used the bridle to adjust the bow towards the swell direction when the wind is from a different angle so as to reduce roll because the boat was desiring to set into the wind and to lie a beam on the swells. I'll bias the bridle which I deploy to cleats about a third boats length back from the bow and will adjust to bias against the wind to present a bit of an asymmetric profile to see if that stops the pony ride.

Or I'll try hanging more laundry and towels out on the windward side to dry and to simultaneously be my drying sails.

[thinwater]

Originally Posted by wsmurdoch

While I hate to wish bad weather on anyone, I hope you have some solid winds. The December '07 Practical Sailor "test" of the Fin Delta was at a maximum of 10-15 kts and had no measured data.....
Bill

I submitted an article some months back (still in the publishing cue) where I measured yaw induced loads (up to 3x when yawing hard), things that make it worse (reacher on bowsprit, dinghy on foredeck), and reduction with many methods (chain, kellet, hammerlock, drogue, fender, lift rudder, bridle, push boom to one side, conventional riding sail). I could get the test boat to yaw anywhere from 160 degrees to only 20-30, depending on the set-up.



I've done a lot of anchor testing using load cells, so I am used to relating data over a wide range of conditions.


I've done just enough with riding sails to believe that some designs are much better than others, but not enough to comment yet.

• A good riding sail should be something that can stay up in a storm. It should help in a storm. This should be the main point.
• Like anchors, there is a new generation out there, but I think it has been under recognized. I guess it seems less important. But if a good riding sail can reduce the load by 30-60%, and reducer anchor twitching... that is as big an improvement as new generation anchors brought us. Huge.

One thing I'm pretty sure of (climbing and sailing) is that most anchors hold quite well if well placed and then held still. It's moving that breaks them free or allows them to drag into trash and trip. This is one way chain helps. A riding sail is one more.

[Alan Mighty]

You've of course read:

Earl Hinz, The complete book of anchoring (1986):

reduce the sheering motion of a boat in strong, gusty winds. In this situation neither a riding sail nor the use of the rudder can be expected to have much effect in steadying the boat while excessive loads are being put on the ground tackle and the anchor’s set is severely tested

and

Yabuki, Takamoto, Yamashita, and Saitoh, "On the development of an anchor watch supporting system for small merchant ships" (2011):

1 A ship at single anchor starts horsing at the wind velocity of 10 m/s and the shock load caused by horsing acts on her cable. Ship sheers violently back and forth across the wind when it is at 16 m/s or more and the shock load increases remarkably.

2 The secondary short-scope anchor is very effective to reduce horsing in stormy weather.

[RaymondR]

I put a second anchor out in a V configuration, go below and try to ignore it. Tried all sorts of other stuff over the years and the second anchor appears the easiest and most practical.

[Alan Mighty]

Originally Posted by RaymondR

I put a second anchor out in a V configuration, go below and try to ignore it.

The officers on USS Muliphen, which today lies somewhere on the seabed off Florida, were the ones who invented and refined the hammerlock moor in 1954 while weathering three hurricanes. They reckoned you need something more than a simple equal armed V to survive a rotational storm - particularly because you have to predict on which side the storm passes and how the winds are going to swing.

They came up with two forms of the hammerlock moor (named of course after wrestling hold): the hammerlock V-moor and the hammerlock X-moor. Both involve asymmetry, but in the V-moor the hammerlock leads fair while in the hammerlock X-moor both rodes cross.

See attached graphic: Prince Figure 2

The idea being that the secondary anchor, at short stay (reduced scope) stops the yawing. The Muliphen could reduce the arc of yaw from 80 degrees to 5 degrees.

If the wind is not expected to shift direction, then the angle between the two rodes is 90 degrees and a line joining the two anchors should be close to being at right angles to the expected wind direction.

In a rotational storm (i.e. a hurricane, a cyclone, a typhoon) passes, the Muliphen hammerlock moor was designed to allow the secondary anchor to drag so the vessel (or the whole anchor bridle system) turns to face into the seas and wind.

See attached graphic: Prince Figure 4

When facing a rotational storm, if the secondary anchor drags into line with the primary anchor, all benefit of the hammerlock is lost and yawing recommences and imperils the primary anchor.

When facing a rotational storm, if the secondary anchor does not drag as the storm passes, for instance turning the vessel so it puts its load on the secondary anchor, then either the secondary anchor has to be lifted and re-set or the scopes of each the two anchors have to be adjusted to keep make the former secondary the primary.

That's when you need an able-bodied and disciplined crew to lift the short stay anchor and reset it, to keep the angle between the primary rode and the secondary rode around 90 degrees.

On the Muliphen, the engines were used to keep the angle of the primary rode, as it left the water, at 30 degrees to 60 degrees.

The research done by Yabuki et al. on small cargo ships used a scope of 1.25:1 to 1.5:1 for the short stay anchor.

Yabuki et al. used a 600 tonne cargo ship in their research. They adjusted the length of the primary rode as the wind speed grew, with the idea of maintaining the length of chain laying on the bottom - the counterpart in a way of USS Muliphen steaming at anchor while monitoring the angle of the chain and trying to keep that parameter under control.

Yabuki and co. aimed to keep about 55 metres (2 shackles) on the bottom at any wind speed. So Yabuki et al. started with 5 shackles (about 130 m if my math is right - Japanese cargo ship captains follow rules of thumb such as fair weather scope = (3 times depth + the length of the ship)) - at 20 knots, increased that to 8 shackles at 40 knots. They reckoned that when a vessel does the figure 8 horsing (the combination yaw & sway that WAFI call "sailing at anchor") the centre of the figure 8 is located just where the chain lifts from the bottom.

The point of that (monitoring the centre of your figure of 8 horsing) is that once the centre is close to your anchor, it's too late and you're dragging anchor.

Yabuki san and friends reckoned that once the anchor drags, letting out more chain does nothing much except lighten the bow.

[thinwater]

^^ Interestingly, I recently read a US Navy report that basically said that a hammerlock mooring could become ineffective as the storm rose, since the wind force would progressively increase, but the resistance of the second anchor would not. This is primarily a problem if the scope on the hammer anchor is too short.


Comparing ship behavior to yachts is interesting but not directly applicable. The comments on scope and dragging make this obvious. Still interesting, just significantly off-topic. I assume you knew that.



I've read Eric Hinz. That was 33 years ago and we've learned a few more things since then. Smart guy, but he also said a riding sail should be sheeted amidships, which is dead wrong (it should be sheeted to one side--makers and experienced sailors agree on this). Aerodynamics was apparently not his strong suit.
----
There is still much to learn.

[newhaul]

Try setting your riding sail up the backstay and sheeted to one side . It will cause you to sail to one side a bit then you should hold pretty steady on that point of sail. Adjust your sheeting point to obtain the sailing point that seems most comfortable for your vessel and conditions.