Anchoring in deep water on a slope

[rslifkin]

Originally Posted by Anders

According to the drawing there's a flat area with 50 feet depth? I would drop there and pay out around 200 feet of chain. Why try to anchor on a slope when it's not needed?

I agree with this. Either go deeper to get to the flat area if depth and swing room allow, or anchor on the slope and use dinghy in for a shore tie to keep the pull in the up-slope direction.

[Dockhead]

Originally Posted by noelex 77

To clarify, I am sure Thinwater intended this to indicate anchoring on a downslope is always dicey. An upslope is quite beneficial and dramatically increases the effective scope. Even very short scopes can be used if the direction of pull is constantly along an upslope.

This can be used to advantage. In many cases where there would normally be a severe downslope, tying the stern to shore and dropping the anchor from the bow can be a very effective technique. It converts a severe drawback (the downslope) into an advantage (an upslope).

In places such as Turkey where the bays often drop away quickly this becomes the normal way of “anchoring” (sometimes called Med mooring). Unfortunately, this technique is not commonly considered in many parts of world even in the locations where it can be the most secure option. It is always worth keeping in mind.

What he said.

Basically, never anchor on a slope without a shore tie.

This ties in also to our previous discussions about the "fetish for scope" which affects some cruisers. 3:1 in a good, flat bottom, in deep water, is better than 10:1 on any significant slope and in shallower water. This is a question of geometry - the purpose of more scope is to reduce the angle of pull from the bottom.

Also, the bottom is almost always worse on a slope, than in a deeper place with a flat bottom.

I anchor a lot in the Northern Baltic with rocky, steep-sloping bottoms. The best place to anchor is the deepest part of the cove, even if it means going on short scope. That's where the silt collects and usually covers the rocks, and if hou do drag, you'll end up on an up-slope. Either that or use a shore tie, which is also common local practice.

[s/v Jedi]

Yeah, that’s what I wrote back in post #8: anchor in the 50’ area.

[thinwater]

Originally Posted by noelex 77

To clarify, I am sure Thinwater intended this to indicate anchoring on a downslope is always dicey. An upslope is quite beneficial and dramatically increases the effective scope. Even very short scopes can be used if the direction of pull is constantly along an upslope.

This can be used to advantage. In many cases where there would normally be a severe downslope, tying the stern to shore and dropping the anchor from the bow can be a very effective technique. It converts a severe drawback (the downslope) into an advantage (an upslope).

In places such as Turkey where the bays often drop away quickly this becomes the normal way of “anchoring” (sometimes called Med mooring). Unfortunately, this technique is not commonly considered in many parts of world even in the locations where it can be the most secure option. It is always worth keeping in mind.

Yes, all that. ^^

[rbk]

This scenario is pretty much every anchorage in Alaska, made worse by the 20ft tide swings cause if you’re too close to the slope you can end up on ground. Agree with many others here about anchoring in 50ft, kedge is anchorage is exposed, wouldn’t worry too much if sheltered.

[Dockhead]

Originally Posted by s/v Jedi

Yeah, that’s what I wrote back in post #8: anchor in the 50’ area.

Sure, or even 100' if necessary. Or even 140'.

We weathered a storm in Greenland in 40 meters of water with 100m of heavy chain out. It was the depth of the bottom of that cove -- in the Bear Islands at the back of Scorsebysund. The shallowest flat bottom we could find.


We survived.

[Sailorichiban]

Very normal to anchor “up slope” . If done correctly the most secure way . Typically the bottom will slope away from the shore.
As always use more than sufficient chain.
After many years the only occasion that nearly was a problem; backing down too close on the beach ( excessively close = positive , short dink trip. Negative, inherently risky).
Followed during the night low tide in combination 30+ knots onshore wind. Breakers moved away from shore, some in excess of ten feet. Actually wasn’t a problem, although it was concerning, my opinion was rudder was coming perilously close to grounding.
Immediately shorted scope, possible problem adverted.
Any time precise anchoring is necessary I suggest 2 anchors, I never had an occasion requiring 3, although I have considered it.
Happy Anchoring!

[Networker]

Awesome and very helpful answers, much appreciated. Never really though about anchoring in deeper water and using shorter scope, I just assumed it wouldn’t work, will give that a try sometime!

[s/v Jedi]

Originally Posted by Networker

Awesome and very helpful answers, much appreciated. Never really though about anchoring in deeper water and using shorter scope, I just assumed it wouldn’t work, will give that a try sometime!

The deeper water is always easier to anchor in and it requires less scope than shallow water

[donradcliffe]

It always depends.

I remember one anchorage in the Greek Islands where I dropped the hook offshore and took a stern line to rocks on the beach. It did not end well. The wind took an unpredicted shift so we were on a lee shore with a dragging anchor. Spent the night motoring against the stern line, then swam ashore and dropped the stern line at first light.

The in the tropical trade wind regions, you usually anchor on the leeward side of the island and the trades pull you offshore. If there is some slope to the bottom, throw out more than the usual scope. Failure to do this can have consequences, as any dragging gets the anchor in deeper water, and eventually you are drifting off to the next island with a hell of a lot of chain hanging straight down. Did I mention that most windlass systems are undersized for bringing up the weight of the anchor and several hundred feet of chain?

And there are anchorages where I have just said "nope" and proceeded 250 miles to the next island. The coral reef islands have really quick drop offs, and if there is no pass, they make very dangerous places. Even if you get your anchor to hold, you have 150+ feet of chain out, and the reef a the reef a boat length or two from the anchor. If the wind dies, you have lost your boat, and I don't care whether its made of milk cartons or steel.

[s/v Jedi]

If there is very little room, you get into what I always call the 1% of times that you need two anchors. Set and test both well, both from the bow in a Bahamian Moor setup.

You still get the negatives of using two anchors, like the rodes may get twisted, but you don’t move onto the reef, which is good

But never use two anchors to compensate for the primary anchor not holding good enough… you need a bigger and/or better anchor in that case, not more of them.

[Dockhead]

Originally Posted by donradcliffe

. . . And there are anchorages where I have just said "nope" and proceeded 250 miles to the next island. The coral reef islands have really quick drop offs, and if there is no pass, they make very dangerous places. Even if you get your anchor to hold, you have 150+ feet of chain out, and the reef a the reef a boat length or two from the anchor. If the wind dies, you have lost your boat, and I don't care whether its made of milk cartons or steel.

Probably the most important anchoring skill of all is the ability to recognize when you simply can't anchor safely, and having the discipline and guts to forgo that post-anchoring drink and keep on sailing.


That is the very definition of seamanship

[Dockhead]

Originally Posted by Sailorichiban

Very normal to anchor “up slope” . If done correctly the most secure way . Typically the bottom will slope away from the shore . . .

Very normal for whom? Not for me!

Reasons NOT to do it this way:

1. Wind shifts and your anchor pops out.
2. Wind kicks up and you're in the surf.
3. Your boat is in shallower water than the anchor -- what if you need to put out more chain? Or you drag?
4. Anchoring off a lee shore?! The only way you're doing this without a shore tie, is if the wind is blowing you onshore.

The only time it's OK to anchor on a slope off a beach, in my opinion, is when the wind is blowing offshore, is not expected to change, and you have a shore tie on. Multiple anchors don't help in this situation.

And never anchor off a lee shore! Surely that's about as basic as it gets, and needs no explanation.

[RaymondR]

Originally Posted by fxykty

Maybe a picture, because I can’t figure out which way you’re setting either anchor wrt the island or side of channel.

As illustrated.

[Don C L]

Originally Posted by s/v Jedi

The deeper water is always easier to anchor in and it requires less scope than shallow water

Hmmm... this seems true, but I'd like to see the mathematical proof of it...