Preventing or reducing anchor swinging - Page 4 - SailNet Community
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post #31 of 61 Old 09-11-2007
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To mitigate swinging at the anchor you can take two approaches... assuming the wind in not shifting in direction a lot.

the riding sail, propoerly sized and set will weathercock the boat and reduct yaw... but it will not eliminate it. Once the wind catches the side of the boat or the riding sail, it will push it over and then the wind will catch the other side and push it back. These oscillations will subside in steady winds, but gusty winds will get the yaw going.

Fin keels will yaw more than full keels too.

You can drop a pail or two off the stern in a line to force the stern to drag them causing resistance also reducing yawing.

When you have a cross current it will tend to align the boat off the wind and this too can cause some yawing in brisk winds. It may be possible to balance the forces with a riding sail, or a bridle but this could be tricky.

My sense is that many riding sails are too small to be effective. Shiva's is quite large and is very effective in stopping the yawing at anchor. We use it frequently.

jef
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post #32 of 61 Old 09-11-2007
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Another suggestion in the famous anchoring book, I just blanked out on (seniors moment) a suggestion is given to take advantage of anchor drag. You set out a second anchor off the bow, taking into consideration scope plus highest tide and height of waves.

So in 20 feet of water assuming two more feet of tide was coming in and a 5 foot hight of wave (you only need to compensate for half of the wave so 2.5), you would let out a scope of about 1.2 or .3 of rode with a suitable anchor at the end - around 29 feet. Suitable means just about any anchor as you want the anchor to drag acting as a buffer onto the front end of the boat, slowing its motion down.
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post #33 of 61 Old 11-07-2007 Thread Starter
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Another suggestion in the famous anchoring book, I just blanked out on (seniors moment) a suggestion is given to take advantage of anchor drag. You set out a second anchor off the bow, taking into consideration scope plus highest tide and height of waves.

So in 20 feet of water assuming two more feet of tide was coming in and a 5 foot hight of wave (you only need to compensate for half of the wave so 2.5), you would let out a scope of about 1.2 or .3 of rode with a suitable anchor at the end - around 29 feet. Suitable means just about any anchor as you want the anchor to drag acting as a buffer onto the front end of the boat, slowing its motion down.
Did you mean to say anchor #2 from the stern? I'll have to try that sometime. I don't think a second from the bow would be as effective, as I would not be adding an arm of moment to stop the stern from shifting, rather just another "hinge" point at the bow.

NEW QUESTION:

Recently when using the bridle technique (rode tied to second line, led to aft cleats via rolling hitch) I have had my boat shift up and over the aft line, keelhulling it. I had to spend most of my time at anchor unwrapping the line. I didn't get ti to settle down like in the past. Did I not have enough secondary rode out, or was the angle too steep?

This was in higher winds than previously tested too.

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post #34 of 61 Old 11-07-2007
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Did you mean to say anchor #2 from the stern? I'll have to try that sometime. I don't think a second from the bow would be as effective, as I would not be adding an arm of moment to stop the stern from shifting, rather just another "hinge" point at the bow.
Not very responsible in terms of damage to the seabed. This is a big concern in some areas of the world.

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Recently when using the bridle technique (rode tied to second line, led to aft cleats via rolling hitch) I have had my boat shift up and over the aft line, keelhulling it. I had to spend most of my time at anchor unwrapping the line. I didn't get ti to settle down like in the past. Did I not have enough secondary rode out, or was the angle too steep?

This was in higher winds than previously tested too.
Possibly too much secondary rode. You could try using an anchor kellet to keep the line down so it doesn't come up on the leeward side of the keel, although it does add complexity to the system.

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post #35 of 61 Old 11-08-2007 Thread Starter
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Thanks Mr. Smith

Oh - found one of your anchors yesterday buried on the beach at a nearby lake when I was trying out my metal detector. It says ROCNA 25 and must weigh in at about 40 to 50 pounds... massive bugger, it took both me and my son to haul it out of the sand.

What a strange coincidence that you'd reply to my post on the same day I found one hahaha!

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post #36 of 61 Old 11-09-2007
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Are you serious? How do you think it got there? Didn't steal someone's mooring did ya?

25Kg = 55lb.

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post #37 of 61 Old 11-09-2007 Thread Starter
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Completely serious! I hope it wasn't someone's mooring. There was nothing attached to it but 10' of chain and an open shackle (no pin in it, just the "U" shape).

I guess that someone was anchoring and lost it a year or so ago in the mud, because where we were sweeping would be under about 6-10' of water in the spring.

Why they'd need a big anchor like that is completely out of my scope of understanding.

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post #38 of 61 Old 11-09-2007
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Sounds like they didn't mouse the anchor shackle pin. If that's the case, they probably deserve to lose their anchor... A large boat might require an anchor that size. I have a 28' boat with a 15 KG Rocna on it... a 40' boat might well use a 25 Kg Rocna.
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Completely serious! I hope it wasn't someone's mooring. There was nothing attached to it but 10' of chain and an open shackle (no pin in it, just the "U" shape).

I guess that someone was anchoring and lost it a year or so ago in the mud, because where we were sweeping would be under about 6-10' of water in the spring.

Why they'd need a big anchor like that is completely out of my scope of understanding.

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post #39 of 61 Old 11-14-2007
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We have approx 130' of chain and another 200' of rope. Have only needed to use more than the chain on one occasion and that was more for security than necessity. Generally speaking she lies quite happily at 3:1 scope using a 35lb CQR, if it pipes up increase to 5:1 as needed but it rarely is. Seven tonne displacement, 34' steel hull.

PB had 30' of chain only with a Danforth and it always gave me grief.

I like the chain myself. Only drawback is the rumble and the weight when retrieving but this is easily solved with a snubber and a windlass.

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post #40 of 61 Old 11-16-2007
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I have a 41' , fin keel, in mast main and split back stay. Has anyone used the main (letting out just a bit) as a riding sail.
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