Dumb Anchoring Question

[noelex 77]

Originally Posted by Reefmagnet

I gave a theoretical answer at the start of the thread to a theoretical question, but in a practical scenario with the anchor in 5 ft and the boat in 20 ft consideration needs to be given to what happens if the anchor breaks out. The potential consequences depend on a quite a few situational variables. Sometimes it won't matter at all, and other times it will be critical.

Here's a small twist that this thread got me thinking about. What about anchoring in areas of big tides. Say when tides are 20 ft and you anchor in 10 ft of depth at low tide. This means that the depth will change between 10 and 30 ft. In theory, currents within the anchorage will be strongest mid tide, but wind and surge will usually be stronger at high tide. What does one do in this scenario?

A couple of points
1. when anchors break out they rarely reset. The speed of dragging though will be much higher if you drag into much deeper water. Normally this is not a great problem as deeper water is usually safe

2. Currents do not place much force on the anchor rode. There are tables, but a ball park figure for an average sized boat a 2 Knot current puts the same force as 10 Knott breeze. The biggest problem with current is boats with different underwater profiles will swing differently.

[jackdale]

Originally Posted by Ex-Calif

Bottom line - throw out 200 feet in any water up to 20 feet under keel and sleep soundly.

Not in crowded anchorage you won't sleep well.

[Ex-Calif]

Originally Posted by jackdale

Not in crowded anchorage you won't sleep well.

If I can't lay 5:1 I won't sleep well either. May need to move...

[Maine Sail]

Originally Posted by Ex-Calif

I am always amazed by guys that "drive" into an anchorage and basically fling the hook.

Yeah we call it the Gilligan Toss or the Hollywood Toss.... You'd be amazed how many times we've seen the anchor and a big pile of rode tossed over as far as they can throw the whole mess. Setting it...? "They don't do that in the movies why would I..?"

[w1651]

7 to 1 scope and then climb in your dingy and row out about 300 feet from the stern and drop another anchor. Set that one tie it off at the stern of your boat and enjoy the scenery.
Less swing and more anchoring and peace of mind. If you do drag the bow anchor there's another anchor set to hold until you can reset it.

[sailorchic34]

Well last night I had bow and stern anchors out and set in a tidal slough with a strong current and had a bit of a dragging issue. I had just a little too much slack in the rodes it seems and caused the boat to get just a little side ways to the current. During peak ebb the *&%%$ stern anchor started dragging which put the more and more of the hull in the current, till the hull was parallel to the current. From a past experience, I knew there was too much pressure on the hull. Looking ashore I saw that I was dragging.

The force on the rode was such that my only option was to bouy the bitter end of the dragging stern anchor rode and cast the anchor off. Lucky I got all that done before the bow anchor (down current) started to drag. So lucky me the boat settled bow to the current and held.

At 8:30 PM at slack tide I pulled the boat forward and recovered the buoy and stern anchor. BTW it was a 27-30 pound danford

I had used two anchors (and had used two anchors in the past with good luck) as It was a narrow channel and wanted to stay off to the side, without getting stuck in the mud at low tide. I had 5 to 1 or a bit more scope and a hard set on both anchors. I also knew that holding was soft mud and sometimes marginal.

My fault was having just a little too much slack in the rode. It needed to be fairly tight so the hull would stay pretty close to inline to the current. The problem is once I knew about the problem it was too late for me to adjust the rodes. I don't have a windlass and use my primary wenches to haul the rodes. There was WAY too much force on the stern rode. So much that it bent my stern roller (another thing to fix...)

I don't think I'll use two anchors in a bow/ stern setup like this again in high current locations. The potential for the hull getting a little cockeyed to the current are just too great.. I may look into a Bahama mooring as that keeps the bow to the current.

just fyi

[w1651]

Originally Posted by sailorchic34

Well last night I had bow and stern anchors out and set in a tidal slough with a strong current and had a bit of a dragging issue. I had just a little too much slack in the rodes it seems and caused the boat to get just a little side ways to the current. During peak ebb the *&%%$ stern anchor started dragging which put the more and more of the hull in the current, till the hull was parallel to the current. From a past experience, I knew there was too much pressure on the hull. Looking ashore I saw that I was dragging.

The force on the rode was such that my only option was to bouy the bitter end of the dragging stern anchor rode and cast the anchor off. Lucky I got all that done before the bow anchor (down current) started to drag. So lucky me the boat settled bow to the current and held.

At 8:30 PM at slack tide I pulled the boat forward and recovered the buoy and stern anchor. BTW it was a 27-30 pound danford

I had used two anchors (and had used two anchors in the past with good luck) as It was a narrow channel and wanted to stay off to the side, without getting stuck in the mud at low tide. I had 5 to 1 or a bit more scope and a hard set on both anchors. I also knew that holding was soft mud and sometimes marginal.

My fault was having just a little too much slack in the rode. It needed to be fairly tight so the hull would stay pretty close to inline to the current. The problem is once I knew about the problem it was too late for me to adjust the rodes. I don't have a windlass and use my primary wenches to haul the rodes. There was WAY too much force on the stern rode. So much that it bent my stern roller (another thing to fix...)

I don't think I'll use two anchors in a bow/ stern setup like this again in high current locations. The potential for the hull getting a little cockeyed to the current are just too great.. I may look into a Bahama mooring as that keeps the bow to the current.

just fyi

Your right mud doesn't take well to holding a 34 ft boat in a strong current. I think a Bahama setup is the best for that condition.
But the original question was about anchoring along the beach with a good slope the further you get off it. If 5 to 1 scope was sufficient (and I don't think it is) or not.
Not knowing or thinking the current is that strong and only tide fluctuations to consider as well as wind I went with a stern anchor set up. I have used it before at Egemont key with a lot of luck but if I went to the other side of the island I would use a Bahama set up and not leave the boat.

Has anyone ever broke an Anchor?

[Waterway Guide]

I still think you're much safer with either just one, well-set anchor off the bow, or a Bahamian Moor (1 anchor set fore, one aft, both off the bow). The discussion here supports the theory that boats get in trouble with an anchor tied to the stern, especially when another is tied to the bow.
And anchors do break, but not commonly. I think all the ones I've known were from part of a fluke bending or breaking when partially stuck in a rock or roots. I don't think it happens when well buried (of course, chain links, shackles, and swivels can break, too).

[Pelagic]

Originally Posted by GordMay

Exactly. You anchor according to the significant forces (wind, current, waves, or some vector of them).
I'd calculate my scope, depending upon the deepest depth within my entire swinging circle; always trying to avoid very steep drop-off slopes.

It is very rare when I would disagree with Gord, but in this case…
you set your anchor towards the closest danger and then with your radar, note the CPA and then record anything closer as a dragging situation.

Currents and wind change often ( Day/night thermals, squalls etc) but that danger is fixed… so it is important to know how close your set anchor should keep you off of a known danger.

You should always set first towards danger with your anchor, confirm holding at substantial astern propulsion, before letting the elements of the moment take over.

[Ex-Calif]

Originally Posted by Pelagic

It is very rare when I would disagree with Gord, but in this case…
you set your anchor towards the closest danger and then with your radar, note the CPA and then record anything closer as a dragging situation.

Currents and wind change often ( Day/night thermals, squalls etc) but that danger is fixed… so it is important to know how close your set anchor should keep you off of a known danger.

You should always set first towards danger with your anchor, confirm holding at substantial astern propulsion, before letting the elements of the moment take over.

I think this is nice in theory but with significant beam wind or tide I would have real trouble holding stern to without kiteing.

Its hard enough to hold head to when backing down.

[Pelagic]

Hi Dan….That is a fairly common scenario…. when it is too difficult to set towards your closest danger you set for prevailing conditions, but when it changes to light conditions, you back towards nearest danger and set your safety indexes.


Years of experiencing squalls at anchor has made me a believer of knowing when I am dragging towards a known danger.

[sctpc]

Managing your anchor