How Much Scope?

[mesquaukee]

Originally Posted by Vasco

I usually try to anchor in less than 10 feet of water if possible. If there's room I put out 100 feet of chain. This way there's no crazy fire drill at four in the morning when a squall comes through. Most of my cruising friends take this approach.

100 ft of 3/8” chain is the minimum in 10 ft of water. In deeper water we prefer 150' of chain if there is room, seems to work no matter how deep the water is. Never understood how a 4:1 scope works with 20 ft of chain and then a rope. The resulting angle of the rode to the bottom is essentially the angle of the shank to the flukes, plow or whatever. Doesn’t seem to be a very good idea for holding in a squall. Had a few off them snatch up on our anchor rode during squalls when they drug.
As Vasco says the 4 in the morning fire drill gets old. We like to stay put.

[GordMay]

Originally Posted by mesquaukee

100 ft of 3/8” chain is the minimum in 10 ft of water...

While we all know that more scope is preferred; unfortunately most “popular” anchorages will most often preclude a scope of ± 9 1/2 :1.

[sailing now]

An old sailor (and there aren't many older than me) once told me "scope is your friend, it doesn't do you a damn bit of good in the locker". I sleep better at 10-1.

[Curmudgeon]

Yeah fine, except that 10 to 1 scope is a hazard in the crowded anchorages I frequent. The chance of dragging anchor is considerably less than the chance of swinging into someone in a moderate breeze-- or having someone swing into you.

[Ziggy]

Originally Posted by Don Lucas

Thanks for replies. I admit I'm not all that experienced and tend to "go by the book". Some more info to maybe help my knowledge base on this one:
1 -depth was 50' when we dropped the hook at high tide with a tide change of about 9' expected, used a 35# CQR with 30' chain for my 39' boat
2 - bottom was rocky ledge and kelp per the guide
3 - was in the lee and wind that night was expected not to shift and to be about 10 knots (but all year the weather people have been telling lies)
4 - guide book stated the holding was poor, but an on-line search stated it was good in "settled conditions" and another article I saw the cruisers said they drug all the way across the anchorage, so I figured the holding was poor generally but Ok given the conditions
5 - I let out about a 4:1 before I set the hook, but I could tell I had drug and the next morning when I pulled it up figured I was about 50' from where I dropped. That amount of drag would have been a problem out in the pack
6 - I was out further off the side from the main mooring anchor field, but there was a 60 footer off my beam further out who also didn't seem to have all that much scope out (they may have been all chain)
7 - maybe possible that where I was the holding was different than out in the "pack" area and those there knew this

thanks for any more guidness, I look forward to the time that I sleep well at night at times like this

Don,

As you can tell from reading this thread, there is plenty of opinions about anchoring, but very little science. Allow me to add a few opinions of my own. You will need develop your own methods based on your experience and whatever sounds reasonable to you.

1) Rocky ledge and kelp makes for poor holding ground, no matter what your scope is. If the conditions are benign, even 2:1 scope will be OK, as your CQR will get entangled in kelp and give you the illusion of security. If the conditions are less benign, you will drag even with 10:1 scope, unless you're lucky enough to hook a rock.

2) In general, I find CQR to have poor holding power, but on a rocky ledge covered with kelp it's probably as good (or as poor) as anything else. By the way, CQR is my secondary anchor.

3) When I want to sleep at night I pick a reasonably protected harbor with a mud or sand bottom and use my 20# Danforth Hi-Tensile, 30 ft of chain, and 5:1 scope of nylon rode. This is not exactly hurricane-class gear, but it has worked for me, over the past 25 years, in winds up to 30-40 kts (not uncommon during summer thunderstorms).

4) When calculating scope, I use the depth of water at high tide plus the height of the bow roller above the water. Also, I don't include the 30' of chain in my scope calculation, just the nylon rode.

5) I always back the engine to set the hook and make sure it's holding. I gradually increase the RPM to 70%-80% of max. If the hook drags, I reanchor.

6) In crowded harbors, tight spots, or when expecting a wind shift, I have used two anchors. It works, but two anchors are a royal pain to set, and an even greater pain to retrieve, so I don't do it very often.

7) It's not infrequent in the evening when the wind dies that we find ourselves too close to another boat. This means pulling up the anchor and trying again.

8) Maybe 10:1 scope is OK in an open roadstead in the Bahamas, but I find it completely impractical in a typical New England harbor.

Take these opinions with a grain of salt--your mileage may vary.

[DRS]

10:1 here and you would have knocked on the doors of all your neighbours. deapth at low tide was 23 feet and high was 30.
45 pound plow, mud bottom, 5 to 10kn breeze, 100 feet of chain.
Not saying its right just pointing out it's some times necessary

[DRS]

OOPS wrong picture attached in previous post, although the comments are fitting. This was the actual anchorage.

[mesquaukee]

Originally Posted by GordMay

While we all know that more scope is preferred; unfortunately most “popular” anchorages will most often preclude a scope of ± 9 1/2 :1.

That 10:1 scope is really 7:1 when one includes the height of the bow roller (5 feet).
A light wind shift may straighten out 50-60 feet of it.
If you are anchoring where the weather is noted for having a 40-60 knot squalls blow through 2 or 3 times a week with winds that rapidly change direction having less than 100 feet of chain out is problematic. Another problem is those that insist on using a dim energy saving anchor light that cannot be seen in a blow with heavy rain.
We have managed to catch a number of boats on our bow due to light ground tackle and an inadequate anchor light. At least during a squall if you can see the dragging boat you could fire up the engine and motor over to one side.
During a 70 knot squall a 44 ft boats anchor rode up our chain to the bow roller and their 25 feet of chain ground its way up our side to the bulwarks. Fortunately we had our customary gear out and we held that boat too, that was in the slippery ooze covering the bottom in Isla Mujeres. It was entertaining thinking about the number of boats we could have rounded up if we had broken out.
Yes there are a lot of crowded anchorages in which case we put out 2 anchors where squall frequently happen so we do not have to worry whether we are on or off the boat.
We carry 300 ft of 3/8” chain, 600 ft ¾” line and 115, 75, 66, 45, 35 lbs anchors of various types. Two anchors and rodes are ready to be dropped; a third can be ready in under 5 minutes.

[s/v Jedi]

You only need as much scope as needed to not drag the anchor. We like 5:1 when other boats have that too (we ask the neighbors before anchoring) but when there's no room (or we compensate for our length), we sleep good with 3:1. But we know it'll take more than 50 kts to start us dragging at 3:1 with good holding. We also know (not voluntary) that 5:1 is good enough to hold during 120 kts. We have a 176 lb. original Bruce.

So, you must try and see. Once you get the experience, you know. When you don't try, you don't know. Every boat is different, every anchor is different and every bottom type is different.

When we can drag the anchor with the engine in reverse, we don't consider ourselves to be securely anchored (like when there's rock) and we keep anchor watch. The GPS always keeps anchor watch.

About setting the anchor: don't use electric "down" with the windlass. Use the clutch. Let the anchor go down as fast as it wants, putting a nice crater in the bottom, good for starting the set. Let the chain run out freely while backing down until you get 5:1 scope. Now tighten the clutch so that it is still just slipping. This will set the anchor or it will never set in that spot. After that, use electric up or down to adjust to the scope you want, but always set at 5:1, not less, not more.

cheers,
Nick.

[Pelagic]

Don......Those who never test their anchors holding will be "tested" sooner or later.

seems like the captain had a license to kill

[sailorboy1]

So those that know me know this is only my second season and my first boat. So I admit LOTS of things are new when I do them and this just continues my scope story/question.

Last night we anchored in Provincetown MA, which is a shell hard bottom. Picked my general area for dropping the hook based on depth and expected wind during the night. Motored up to the area and looked it over and asked another boat that was there how the holding was and how much scope he had out. He said his plow was holding well and he had a 4:1 out (and I could tell it was a mixed chain/rope as all I could see was rope so his setup was just like mine).

So we dropped the hook, played out a 4:1 based on bow roller height, drifted back and then powered up to set. Since I had been playing with the GPS I set the anchor alarm and also marked the spot I was at so I could see the track). During the next 4 hours the wind was light and we appeared to be set and not dragging. Since we had dropped at low tide I decided to let out some more line, but could only do so much as if the wind shifted I would swing into the guy next to me. There I made probably a big mistake: the GPS was lighting up the whole aft of the boat and the the sky above so I turned it off.

A couple of hours later was awoke to the sound of lines banging (weren't mine at the time), so knowing this met that the wind had picked up I popped up for a look. We had swung with a wind change and the wind was at 20 knots (was like 5-8 when we dropped), but we looked to still be set (was now 1 am of course and high tide was in 20 minutes). So go back to bed, but don't get to sleep because now my lines are banging so go up to take care of that (it's been about 10 minutes). I look around and realize we are WAY far away from where we just were and and had even drifted past the breakwater (good thing it was full moon and clear as I don't know if I would have noticed otherwise).

I turn the GPS on (destorying my night vision) and it of course goes right into alarm. I also notice the guy who said he was holding with 4:1 is pulling anchor and moving. So I start the drill to pull the anchor and move as I was dragging and worried about the breakwater. Fire up the engine and motor forward and my wife goes forward to bring the rode in (I don't know why I allowed this). After a while I can tell there is a problem and go forward to help. Turns out she had cut her thumb before coming on deck while closing a hatch and it is bleeding alot more than she realized. So since the rode is tried off and the wind is now blowing into open water: I tell her to go below and take care of the cut. While she does this I mark a new pointr on the GPS and it seems we are dug in and holding even though we probably only have a 3:1 out because were in the process of pulling it up.

My wife comes back on deck and sits down all woozy, turns out the thumb cut is a lot worse than she knew. So I figure there is no way she is going to be able to help move the boat. So decide since we are past the breakwater and if we were to keep dragging would go across the bay for around a 1/2 mile before we get to the next group of boats, and the anchor seems set, that I would just stay were I was even though it is pretty open and it's going to be a tossing. So I go let out more scope to get 7:1 (tides going out now and anymore and I figure I'm swinging into the lobster pot floats). While up at the bow I can see all the blood on the deck in the moonlight (if could safely take the dingy in I would be taking her for medical attention). And of course I stay up the rest of the night as the wind increased.

Once daylight came I could get a good look around and figure we drug a good 300-400 feet during the time we first popped up and the 10 minutes later. Now I'm waiting for conditions to change and watching the wind as if it shifts it is going put be windward of the breakwater. But since the anchor is good and set and we are short handed on the boat I'm going to stay this way till things are better or I just have to move.

Bottom line is 4:1 is enough my ass!!! Maybe all chain in a sand bottom is a completey protected cove. Maybe!

PS - just rebandaged my wife's thumb, that's thge end to that nail.

[s/v Jedi]

Don,

What type and weight anchor do you have?

You wrote that you used the engine to set the anchor. Can you describe how you do that, i.e. how long and how many rpm's etc. Your problem is either with the anchor setting procedure or the anchor breaks loose with the wind shift and has a hard time resetting.

If you post the info, I can help more. The only thing I can write now is that we found the best scope to set the anchor is 5:1. If we want a 4:1 scope, we first set the anchor at 5:1 and after that shorten the rode.

ciao!
Nick.

[Bash]

Nick, as per his previous post, he was using a 35# CQR with 30' of chain for a 39' boat.

Don, common wisdom is that your chain should minimally be as long as your boat. I should think that going with 50' of chain will contribute greatly to your ability to set the hook well. If you're going to continue to anchor in such deep water, however, I would advise going to at least 100' of chain.

[Cheechako]

Your scenario has been repeated many times, at least once by allof us I'm sure! I never anchor with less than 5:1. If exposed it's likely to be 7:1. Of course that's easy to say if you have an electric windlass. Sure 100 ft of chain would be nice but a real backbreaker to retrieve if you had to do it by hand. If you have a windlass then yes and go for 150ft! You anchor is undersized for a 39 ft boat. Most cruisers would use a 35# CQR on a 30-35 ft boat . You should step up to 45# minimum for sure. Wind shifts are the problem with all anchors (except reportedly with the new designs not so much) I snorkeled my anchor a lot in the carribean. One day in the Tobago keys it was blowing pretty steady 35 with gusts to 40. I watched the all chain rode for a long time. This was a 42 ft cat with a lot of windage. The anchor was buried completey but you could tell where it was. The last 20-25 ft of chain never came up out of the sand. (caveat: it would be different in those winds with a heavy chop, this water was flat... no fetch)

[Bash]

apologies. I seem to have forgotten that some boats don't have a windlass. still trying to shake the cobwebs out this morning.