Less Conventional Approaches to Controlling Yawing

[FSMike]

Why limit uneven length bridles to monohulls? Try it on multis. On tris perhaps securing one line of the bridle to the main hull would work.

[thinwater]

Originally Posted by Snowpetrel

^^ intereting idea. I'll have to give it a try sometime. I guess a dyneema strop prusicked onto the chain would make a secure way to attach the second anchor warp.

Yes, something like that. A soft shackle also works well. Locking chain hook varients can work.

[thinwater]

Originally Posted by FSMike

Why limit uneven length bridles to monohulls? Try it on multis. On tris perhaps securing one line of the bridle to the main hull would work.

On a tri the bridles go to the tips of both floats. Anchor from the center hull is just asking to zig around. (I have one.)

[thinwater]

Originally Posted by fxykty

Our cat in common with most others sits reasonably well in steady winds to an anchor with a long bridle that terminates or is cleated on each bow. However, we recently experienced 40 knot gusts with 25 knot lulls in a minute on two minutes off cycle and yawed terribly. The scope of all chain and 7m polyester bridle legs was 8:1.

The yawing was due to the straightening of the rode during the gusts, then the chain catenary and bridle unstretching (is that a word?) pulling the boat forward 3 or 4 boat lengths and slacking the rode. Then the next gust would come and the boat would turn 30 degrees and drift backward until the rode straightened again and the bridle pulled the boat back in line.

Is there anything to be done to prevent the back and forth yo-yo? As most of the impact at the end of each straightening was on a single bridle leg I don’t think there was any undue load on the anchor. But the accelerations and decelerations were noticeable.

Would using a third bridle leg to a stern cleat to situate the boat at 30 degrees help, at least to stop the yawing if not the back and forth?

Are you using polyester or nylon for the bridle? With all chain, it should be nylon.

If the bridle legs are 7m they are only about 1/2 the optimum length (2x beam).

I would not think 25 knots is light enough to allow much catenary to form. Why do you believe the boat was shooting forward that far? In fact, I wonder if what you are seeing is just yawing aggravated by the gusting wind probably changing direction as well.

Yes, if the deceleration was noticeable, the load on the anchor was certainly undue. every 0.1 G adds one ton of load.

[fxykty]

Originally Posted by thinwater

Are you using polyester or nylon for the bridle? With all chain, it should be nylon.

If the bridle legs are 7m they are only about 1/2 the optimum length (2x beam).

I would not think 25 knots is light enough to allow much catenary to form. Why do you believe the boat was shooting forward that far? In fact, I wonder if what you are seeing is just yawing aggravated by the gusting wind probably changing direction as well.

Yes, if the deceleration was noticeable, the load on the anchor was certainly undue. every 0.1 G adds one ton of load.

Bridle is 20mm 8 braid nylon. Each leg is 7m and our beam between pad eyes is 5.2m so while they’re shorter than 2:1 they’re still long enough that in most anchoring situations we’re shortening them to avoid dragging the bridle on the bottom. We’re building a JSD and we can use the bridle from that system as a storm anchoring bridle to get a longer storm bridle length.

We have 13mm chain and in the 25 knot lulls after the boat steadied the bridle legs were straight but low enough to show the chain was curved. During the gusts once full load was applied we could see the attachment point of the bridle to the chain above the water and the chain from there appeared straight.

I tracked our position on the anchor app - it showed our distance from the anchor varying from 45m to 70m. The winds were from a single direction within 10 degrees as we were in a bay with high sides. With each rebound we were pulled ahead of our steady position before settling back down.

While watching the bridle from the front beam, in the 2m from the end of each bridle leg to the near edge of a chafe protection cover, the observed stretch in just that short section was up to 30cm, so about 15%. The decelerations were during the stretching, so I’m still not sure about the loading.

The anchor is a Spade 140 and the minimum SWL in our system is about 2,000 kg. That’s about the holding power of the anchor, and we certainly didn’t drag, so we didn’t put that much load on it.

I dove on the anchor after the storm passed and the chain was buried from the 5m marker in thick gloppy mud. It took a lot of work to get the anchor off the bottom.

[thinwater]

Originally Posted by fxykty

Bridle is 20mm 8 braid nylon. Each leg is 7m and our beam between pad eyes is 5.2m so while they’re shorter than 2:1 they’re still long enough that in most anchoring situations we’re shortening them to avoid dragging the bridle on the bottom. We’re building a JSD and we can use the bridle from that system as a storm anchoring bridle to get a longer storm bridle length.

We have 13mm chain and in the 25 knot lulls after the boat steadied the bridle legs were straight but low enough to show the chain was curved. During the gusts once full load was applied we could see the attachment point of the bridle to the chain above the water and the chain from there appeared straight.

I tracked our position on the anchor app - it showed our distance from the anchor varying from 45m to 70m. The winds were from a single direction within 10 degrees as we were in a bay with high sides. With each rebound we were pulled ahead of our steady position before settling back down.

While watching the bridle from the front beam, in the 2m from the end of each bridle leg to the near edge of a chafe protection cover, the observed stretch in just that short section was up to 30cm, so about 15%. The decelerations were during the stretching, so I’m still not sure about the loading.

The anchor is a Spade 140 and the minimum SWL in our system is about 2,000 kg. That’s about the holding power of the anchor, and we certainly didn’t drag, so we didn’t put that much load on it.

I dove on the anchor after the storm passed and the chain was buried from the 5m marker in thick gloppy mud. It took a lot of work to get the anchor off the bottom.

The breaking strength of the leg is about 25,000 pounds. If it is stretching 15% on the rebound, that is about 20% of the BS, or 5000 pound impact load (on top of the base load. It is possible that you are seeing things wrong... but perhaps not. Your holding capacity may also be a bit more than 2000 kg. But the point is those jolts are dangerous.

You can run longer bridles by anchoring them farther back and using good chafing gear. But a simpler solution is to have longer bridles arms and only deploy them when the wind is enough to keep them off the bottom. However, you will need a locking chain hook or soft shackle.

You really do NOT want to use the JSD bridle for anchoring. For starters, a JSD is made from non-stretch line, such as polyester or Dyneema, never nylon. Don Jordan specified low stretch both for chafe and for it's dynamic response. It is also sized for a different working load.

How much chain do you have out? If you are worried about the snubber touching, I would presume about 10 meters, suggesting 70-100 meters of rode. For the boat to sling forward 70 meters begs credulity. The chain would be slack in the lulls, pointing straight down. I must be misunderstanding something.

You are certain the boat is not moving side to side, in an arc? It would be moving forward as well. How much does the compass vary during this motion?

[fxykty]

Originally Posted by thinwater

The breaking strength of the leg is about 25,000 pounds. If it is stretching 15% on the rebound, that is about 20% of the BS, or 5000 pound impact load (on top of the base load. It is possible that you are seeing things wrong... but perhaps not. Your holding capacity may also be a bit more than 2000 kg. But the point is those jolts are dangerous.

You can run longer bridles by anchoring them farther back and using good chafing gear. But a simpler solution is to have longer bridles arms and only deploy them when the wind is enough to keep them off the bottom. However, you will need a locking chain hook or soft shackle.

You really do NOT want to use the JSD bridle for anchoring. For starters, a JSD is made from non-stretch line, such as polyester or Dyneema, never nylon. Don Jordan specified low stretch both for chafe and for it's dynamic response. It is also sized for a different working load.

How much chain do you have out? If you are worried about the snubber touching, I would presume about 10 meters, suggesting 70-100 meters of rode. For the boat to sling forward 70 meters begs credulity. The chain would be slack in the lulls, pointing straight down. I must be misunderstanding something.

You are certain the boat is not moving side to side, in an arc? It would be moving forward as well. How much does the compass vary during this motion?

Good point regarding the JSD - there seems to be a lot of confusion about the drogue line and bridle composition but I’ll take your word that I should make the bridle from Dyneema. In that case I’ll need a separate storm anchor bridle, or reconfigure the existing anchor bridle. We already use a screw pin shackle to attach the bridle to the chain. Chafing protection for running bridle arms onto the deck is a major PITA, but we’ll consider it.

The boat moved up to 25m back and forth, not 70. At minimum extension we were 45m from the anchor and at maximum extension 70m from the anchor. At minimum extension we were forward of our normal lull position, I think due to rebound momentum.

We were in 7-9.5m of water (depending on tide) with all 60m of chain out and the bridle shackle to the end of the chain, for a total of about 66m.

I also kept a track on iSailor and it showed the vast majority of the movement was straight up and down, with the boat drifting back yawed to one side or the other during gusts, hanging straight on the end of the rode fully extended for the rest of a gust, then rebounding straight forward during the lull before settling to a minimal extension, still straight forward. Compass heading varied up to 30 degrees to either side during the drifts, but COG was roughly in line.

Maybe a bucket on a line off one of the sterns, or one from each, would keep the boat from rebounding so far forward?

[thinwater]

Originally Posted by fxykty

Good point regarding the JSD - there seems to be a lot of confusion about the drogue line and bridle composition but I’ll take your word that I should make the bridle from Dyneema. In that case I’ll need a separate storm anchor bridle, or reconfigure the existing anchor bridle. We already use a screw pin shackle to attach the bridle to the chain. Chafing protection for running bridle arms onto the deck is a major PITA, but we’ll consider it.

The boat moved up to 25m back and forth, not 70. At minimum extension we were 45m from the anchor and at maximum extension 70m from the anchor. At minimum extension we were forward of our normal lull position, I think due to rebound momentum.

We were in 7-9.5m of water (depending on tide) with all 60m of chain out and the bridle shackle to the end of the chain, for a total of about 66m.

I also kept a track on iSailor and it showed the vast majority of the movement was straight up and down, with the boat drifting back yawed to one side or the other during gusts, hanging straight on the end of the rode fully extended for the rest of a gust, then rebounding straight forward during the lull before settling to a minimal extension, still straight forward. Compass heading varied up to 30 degrees to either side during the drifts, but COG was roughly in line.

Maybe a bucket on a line off one of the sterns, or one from each, would keep the boat from rebounding so far forward?

What you are describing is very unusual. The chain has to store enough energy in the last few feet of extension to basically launch the boat forward, probably at about 3 knots to start. The wind needs to drop from 45 to 25 almost instantly, which does happen. Does that sound right? A bucket would be useless, generating only 10 pounds of drag at that speed. A full-size drogue for your boat (Seabrake 48?) would only generate about 450 pounds, which would make a difference. A Seabrake 30 would only generate about 180 pounds, which might be enough. Unless you have such a drogue, I can't think of anything you would have on board that would do. You might also try a hammerlock anchor off the front beam, in the center. I would try that first.

Interesting.

[fxykty]

Originally Posted by thinwater

What you are describing is very unusual. The chain has to store enough energy in the last few feet of extension to basically launch the boat forward, probably at about 3 knots to start. The wind needs to drop from 45 to 25 almost instantly, which does happen. Does that sound right? A bucket would be useless, generating only 10 pounds of drag at that speed. A full-size drogue for your boat (Seabrake 48?) would only generate about 450 pounds, which would make a difference. A Seabrake 30 would only generate about 180 pounds, which might be enough. Unless you have such a drogue, I can't think of anything you would have on board that would do. You might also try a hammerlock anchor off the front beam, in the center. I would try that first.

Interesting.

I think not just the stored energy in the lifted chain but also in the stretched bridle legs.

Won’t the hammerlock foul the lazy rode coming down from the bow roller, which is just behind the front beam?

[FSMike]

Originally Posted by thinwater

On a tri the bridles go to the tips of both floats. Anchor from the center hull is just asking to zig around. (I have one.)

thinwater -
I didn't say to attach the anchor to the center hull, I said to try attaching one leg of the bridle to the center hull.
One leg of the bridle to the vaka, and one leg to an ama.
Such an arrangement could be used to keep the boat cocked into the wind, and hopefully keep the amount of yawing to a minimum.

[thinwater]

Originally Posted by FSMike

thinwater -
I didn't say to attach the anchor to the center hull, I said to try attaching one leg of the bridle to the center hull.
One leg of the bridle to the vaka, and one leg to an ama.
Such an arrangement could be used to keep the boat cocked into the wind, and hopefully keep the amount of yawing to a minimum.

First, my boat yaws less than 10 degrees as it is; the bridle is very wide and lifting the rudder moves the under water COE very far forward. It probably yaws lass than that, but it's always hard to measure so closely with the wind swinging. Second, this can be accomplished more robustly by attaching them to the amas and adjusting the legs; same angle, if that is desired. The problem with using the main hull is that IF the wind gets just slightly to the wrong side, most tris will yaw like crazy.

[thinwater]

Originally Posted by fxykty

I think not just the stored energy in the lifted chain but also in the stretched bridle legs.

Won’t the hammerlock foul the lazy rode coming down from the bow roller, which is just behind the front beam?

Yes, stored in both.

Tangles are not likely, because the hammerlock is practically straight down. only about 1-2 meters more chain than the depth. Try it, nothing to lose.

[wsmurdoch]

Originally Posted by thinwater

You really do NOT want to use the JSD bridle for anchoring. For starters, a JSD is made from non-stretch line, such as polyester or Dyneema, never nylon. Don Jordan specified low stretch both for chafe and for it's dynamic response.

Don Jordan's report (Investigation of the Use of Drogues to Improve the Safety of Sailing Yachts) is dated May 1987. Dyneema was commercialized in 1990. Don Jordan's recommended material in the report is double braided nylon.

[thinwater]

Originally Posted by wsmurdoch

Don Jordan's report (Investigation of the Use of Drogues to Improve the Safety of Sailing Yachts) is dated May 1987. Dyneema was commercialized in 1990. Don Jordan's recommended material in the report is double braided nylon.

His non-stretch recommendation came later. However, he did hint at it in the report (page 52). He never explains the apparent conflict. He did not consider this report to be finished work, including the design of the cones. I did not say Dyneema, I said low stretch.



I guess you make your choice. However, Fiorentino and Seabrake both specify reduced stretch for this reason. I've done a lot of drogue test, and IMO, if you have a lot of stretch you increase the risk with no significant reduction in force. If you were trying to steady yourself in the surf, would you rather have a bungee cord or a firm line, and these lines are very long and stretchy. The drogue provides the give, the line does not need to.

I'm not a huge Dyneema fan for this. I find Dyneema hard to handle and prefer polyester for drogue testing. There are reasons you never handle naked Dyneema on a boat. But I accept why people would do this for the space savings, for something they may never use, and I have no reason to believe, nor is there any information suggesting that it is a safety problem in this application. So I stay out of that argument.

An aside. Don Jordan also advised people NOT to use common cable thimbles (what is used 98% of the time) but to use reinforced thimbles. There have been cases of the thimbles distorting under load and cutting the bridle lines. Another problem with nylon, it seems, it that thimbles ALWAYS loosen under load because the line stretches.

[Panope]

Originally Posted by thinwater

Tangles are not likely, because the hammerlock is practically straight down. only about 1-2 meters more chain than the depth. Try it, nothing to lose.

Thinwater,

Great thread, thanks for posting.

I was unfamiliar with the term "Hammerlock Moor" so I did a quick Google search to learn more about it.

In several seamanship publications, the Hammerlock anchor is described as being dropped at the point of maximum yawing/swinging and using a short scope (not nearly vertical) forming a "V" type moor. They also mention the "nearly vertical" (anchor just touching bottom underfoot)technique separately but do not give a proper name for it.

Do you have a good source for clarifying the term "Hammerlock Moor"?

Steve