Fore and Aft Anchors

capta

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Jun 4, 2009
4,766
Pearson 530 Admiralty Bay, Bequia SVG
I know that when setting an anchor one should use a scope of 7:1 ~ 10:1 based on conditions of the seabed and surface. But if one wants to set a stern anchor, should one use the same scope as the bow anchor? Or, can one get away with lesser scope? The purpose of the aft anchor is to reduce the swing of the boat while at anchor.

Thoughts?
Since I moved up to the proper anchor and chain (88# Rocna & 1/2" chain) we have moved down from 10:1 to 7:1 and now to 3:1 (as I was originally taught, 5:1 with line & chain). The boat rides better and much more quietly since we no longer drag all that chain across the bottom, and our chain appears to be wearing more slowly as more is suspended.
Can't say we won't drag tonight, but we haven't once, in 6 years of sailing full time in the islands, at anchor most nights.
As for a stern anchor, we usually use a 1" line and 50 feet of 3/8" chain with a 55 Fortress about 7:1. It's light enough to drag before the Number 1 anchor and allow the boat to sit as she pleases still well anchored. We most often do this somewhere like Prickly Bay, Grenada where the swell hits you broadside when you are anchored bow to wind. So, hauling the boat around to sit more comfortably to the swell leaves the boat broadside to the wind. Add a 3 AM squall and you don't want both anchors to drag, which they might do if the stern anchor didn't. Sometimes, if the squall is particularly vicious, I'll proactively cast it free with a fender tied to it and retrieve it after the squall.
 
Last edited:
Feb 14, 2014
7,400
Hunter 430 Waveland, MS
Looked it up...
"Bob Ogg, co-inventor of the Danforth anchor, recommends setting one anchor into the wind or current, and a second anchor 180° away. Then take both lines to the bow of the boat. This allows the boat to swing around in a relatively small arc, yet will allow the boat to pull against an anchor without causing it to reset when wind or current change."
 

capta

.
Jun 4, 2009
4,766
Pearson 530 Admiralty Bay, Bequia SVG
Looked it up...
"Bob Ogg, co-inventor of the Danforth anchor, recommends setting one anchor into the wind or current, and a second anchor 180° away. Then take both lines to the bow of the boat. This allows the boat to swing around in a relatively small arc, yet will allow the boat to pull against an anchor without causing it to reset when wind or current change."
Depends on the situation. That's called a Bahamian moor and it's normally used when you have a current change of 180 degrees a couple of times a day. Wouldn't work very well in the scenario I posted above and you would hope you weren't somewhere where you would have to do that in a hurricane! lol
 
Jul 27, 2011
4,989
Bavaria 38E Alamitos Bay
Bahamian Moors are most commonly used in narrow, tidally-influenced rivers or inlets; so, Iv'e read. You don't want the boat sweeping out a 400-ft diameter four times a day.
 
Feb 14, 2014
7,400
Hunter 430 Waveland, MS
you would hope you weren't somewhere where you would have to do that in a hurricane! lol
Well guess what I am going to do, if we have a storm surge of 10+ feet?

1) Go up the Pearl River north of the NASA Saturn Rocket fuel locks.
2) Tie stern off too a big huge pine tree.
3) Drop the two bow anchors in a Y
4) leave a iPad on boat with battery bank booster [follow me set]
5) get picked up by a friend in small boat
6) Pray my insurance is paid up:cowbell:
 
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Mar 26, 2011
3,401
Corsair F-24 MK I Deale, MD
Anchored fore-aft, the force can be enormous if the wind comes on the beam. You will need all the scope and holding capacity you can get. Or the stern anchor will drag, holding you slightly beam to the wind. Overall, the only time to anchor fore-aft is in a canal or other place that is protected.

The main question is why do you need to control swing?

Your boat yaws and that might loosen the anchor. There are better solutions:
  • Remove windage from the bow. Dinghies, reacher etc.
  • Use a bridle. Excelent for multihulls, less so for monos.
  • Lift the rudder. Really helps... if you can.
  • If rope rode, try a kellet (only works in lighter winds).
  • Hammerlock. Lower a small anchor on very short scope from the bow. It will set just enough to stop the swing without causing complications. But it will dig up the bottom a bit.
  • Riding sail. A pain to rig, but very effective.
  • Set two anchors in a V, about 90-120 degrees. One of the anchors should have a shorter rode, NOT led to a locker, or the tangles will be epic when the wind shifts. Even better, attach the second anchor to the rode.
Not much room. First, you want to swing with other boats. But sometimes you are off to the side and this does not matter.
  • Set two anchors in a V, about 100-140 degrees. Same as above. Much safer than fore aft. However, BOTH anchors must be large enough to hold. Very often, one of these is pivoting fluke, which is safe because the range of angle is limited.
 
Jun 11, 2004
1,621
Oday 31 Redondo Beach
The main question is why do you need to control swing?
Because the breeze shifts 180 in the middle of the night (now in opposition to the constant swell) and you don't want to blow out broadside to the swell and roll your mast and brains out for the rest of the night.
 

capta

.
Jun 4, 2009
4,766
Pearson 530 Admiralty Bay, Bequia SVG
Well guess what I am going to do, if we have a storm surge of 10+ feet?

1) Go up the Pearl River north of the NASA Saturn Rocket fuel locks.
2) Tie stern off too a big huge pine tree.
3) Drop the two bow anchors in a Y
4) leave a iPad on boat with battery bank booster [follow me set]
5) get picked up by a friend in small boat
6) Pray my insurance is paid up:cowbell:
The only time I've ever been that smart was when Andrew had his beady eye on Miami and my boat was in Las Olas. Every other time I've stayed with the boat and worked my as* off.
 
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Mar 26, 2011
3,401
Corsair F-24 MK I Deale, MD
Because the breeze shifts 180 in the middle of the night (now in opposition to the constant swell) and you don't want to blow out broadside to the swell and roll your mast and brains out for the rest of the night.
True enough.

Every anchoring situation has its own requirements.
 
Nov 26, 2012
2,315
Catalina 250 Bodega Bay CA
If you use a bow beach tie then a stern anchor back set is usually used. If you tie up for the night in Tomales Bay CA your may well use this concept. I have for years, and use 2 stern anchors at 45 degrees many times. The reason is wind reversals from N. to South do occur at night! Enjoyed the discussion. Chief
 
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