What is Too Much Rode?

[hugosalt]

Originally Posted by a64pilot

Brings up the question though, I’m sure there is a point of dimensioning returns, but at what scope does it become counter productive or does it? Meaning is there a point that more equals less holding?

If combo rode/chain...
Years ago before I went to all chain rode when wind was up
I would lay out 10:1 or more rode and being the boat really sailed at anchor
my usual concern was would she pull out the anchor when pulling up just about
broadside to the wind. Less was better as she did not gain as much momentum.
Over the years tried all the much discussed tid bits to settle her down, some even worked most of the time. Going to all chain was the trick.

[Vasco]

Originally Posted by a64pilot

I’ve never had it drag before, but this is the second time this trip, first time was the other day, I let out more chain and it stopped to, but I had a heck of a time raising it, it came up with honestly a three thick steel cable on it, was fun getting the cable off. Cable I’m sure stopped the drag then.
Look at how hard the bend is on the anchor, it was really buried I guess.Attachment 163066

It might be the wire rope on the bottom fouled the anchor and prevented it from setting. I have anchored on top of an old blue plastic tarp before and this prevented the anchor from setting. Cannot see you dragging with even 50 feet out with your anchor in the conditions you were in unless you were in real soupy mud, such as a recently dredged basin,and I doubt that was the case.

I like to sleep at night so,as long as there's swinging room ,I do not anchor with less than 100 ft of chain out, 44# Manson Supreme. I like to anchor in eight feet wherever possible. If it's blowing over 20 I don't bother backing down. Hold at 50 ft and my anchor grabs. Let out another 50 ft. Good for at least 40 knots.

[Dave_S]

This comes from theory not experience which aren't always the same thing.

I have always assumed when you have long lengths of chain out, the pull force on the anchor is from an angle almost parallel to the ground because the weight of the chain. It is impossible for the chain to straighten out with any load.The greater the pull force the more the chain straightens out.

I'm making up numbers here but lets say your boat at its peak applies 1t pull force in line with the chain from the boat end and this is enough to lift the chain a small but meaningful amount off the bottom 70' from the boat at your depth. Then if you have any more than 70' the only real benefit to you is the resistance of the chain to pull through the mud and only that chain beyond the lift mark counts - I think that comes to exactly SFA per foot of chain. But because you don't know if the max lift point is 40' or 100' then more would be better.

My $0.02 worth.

[valhalla360]

Sounds like the anchor didn't set or the mud is so soft, you are just plowing a furrow with it. More chain will help a little but diminishing return as you say is the issue.

100' is less than a 10-1 scope so not excessive if there is room to swing.

I'd start the engine and try backing down again giving it plenty of power and time. If you are moving backwards, it's time to pull it up and reset the anchor. If it's soft mud, it may be time to find a new anchorage.

[44'cruisingcat]

Every bit of chain out is less weight on the boat, so less load on the anchor...

[valhalla360]

Originally Posted by 44'cruisingcat

Every bit of chain out is less weight on the boat, so less load on the anchor...

Not sure if that is true. The boat weighs less but that should mean it sits higher in the water which means more windage which increases the loads.

In the end, 50lbs of chain, is probably such a small amount, you would be hard pressed to tell any difference in the loads.

[El Pinguino]

Originally Posted by 44'cruisingcat

Every bit of chain out is less weight on the boat, so less load on the anchor...

I'm not sure if the weight of 30 metres of 8mm chain ( f'rinstance ) will be of any consequence on a boat with a displacement of , say, 8 tonnes.

If it was then the greater freeboard would create greater windage which would create more load....

Back to the OP.... in hard conditions I've been known to drop out the full 70 metres in 4 or 5 metres of water .... the whole ratio/catenary business stops working in shallow water......

[boom23]

Originally Posted by a64pilot

I’ve never had it drag before, but this is the second time this trip, first time was the other day, I let out more chain and it stopped to, but I had a heck of a time raising it, it came up with honestly a three thick steel cable on it, was fun getting the cable off. Cable I’m sure stopped the drag then.
Look at how hard the bend is on the anchor, it was really buried I guess.Attachment 163066

The following product would have helped: https://www.ultramarine-anchors.com/trip-hook

This is particularly helpful when you lift someone else's anchor chain during med mooring...

[44'cruisingcat]

Originally Posted by El Pinguino

I'm not sure if the weight of 30 metres of 8mm chain ( f'rinstance ) will be of any consequence on a boat with a displacement of , say, 8 tonnes.

If it was then the greater freeboard would create greater windage which would create more load....

Back to the OP.... in hard conditions I've been known to drop out the full 70 metres in 4 or 5 metres of water .... the whole ratio/catenary business stops working in shallow water......

My comment was pretty tongue in cheek, really just saying that more chain out is always a positive, providing there's room. But...

I'd hope an eight ton boat would be using bigger than 8 mm chain.

And do you really think a light boat makes it's anchor work harder than a heavy one?

[El Pinguino]

Originally Posted by 44'cruisingcat

My comment was pretty tongue in cheek, really just saying that more chain out is always a positive, providing there's room. But...

I'd hope an eight ton boat would be using bigger than 8 mm chain.

And do you really think a light boat makes it's anchor work harder than a heavy one?

Well, lots of variables but a heavy boat suggests she will be harder for the wind to push around... light boat with high freeboard to me suggests 'skittish'... sailing around the anchor etc... so yes I think maybe the light boat will give more shock loadings to the anchor and put her more at risk of breaking it out...

[Benz]

Sounds like the problem is a poor-holding bottom. Some places just don't hold well, like thin sand over hardpan, or very soupy mud (you want good firm mud, almost clay, for awesome holding). But regardless of bottom, my usual practice is to let the anchor settle itself right in. Unless I'm setting it club-hauled, which is where I come sailing in and use it to stop the boat (I try to do this at a pretty slow speed, though), I just let the wind or current drift the boat back onto the anchor.
Of course, my small outboard can't generate a lot of power in reverse anyway, so backing down for me is moot. But I'm convinced that there's less wisdom to this backing-down mania than its advocates believe.

[44'cruisingcat]

Originally Posted by El Pinguino

Well, lots of variables but a heavy boat suggests she will be harder for the wind to push around... light boat with high freeboard to me suggests 'skittish'... sailing around the anchor etc... so yes I think maybe the light boat will give more shock loadings to the anchor and put her more at risk of breaking it out...

Good heavens!

[noelex 77]

As others have said more scope = better holding. The only exception is if deploying more scope puts the boat further away from the shelter of the land and into an area with stronger wind and/or higher wave action. For some bays this can be a significant factor. In this circumstance it is possible that deploying a large amount of rode could result in the boat less likely to hold than with a more reasonable, but still generous scope.

Holding power increases with more scope, but there is a point of diminishing return where extra scope only produces a very slight increase in holding power. There is some disagreement when this point is reached. Somewhere around a scope of 10:1 to 14:1 is generally quoted as the number where there is little point deploying more rode. That is quite a large span and it would be nice to have a more definitive answer. My opinion is the larger number is generally closer to the truth, but the holding increase when going from 10:1 to 14:1 is only slight. It is also dependent on the depth of water (in shallow water the diminishing return sets in at a longer scope) it is also dependent on the bottom type (in some substrates such as thick mud, chain that is on the bottom will have some grip, so once again the diminishing return sets in at a longer scope). There are a number of other minor factors that come into play, but as a general single rule, if you split the difference consider that deploying more than 12:1 is likely to do little to improve holding. Don't forget to add the height of the bow roller to the depth of water when calculating the scope.

The table used for an anchor's holding ability that is issued by a couple of anchor manufacturers is below. It is only a rough approximation, but I think it useful as a starting point.

Scope Holding
10:1 100%
7:1 85%
5:1 70%
3:1 40%
2:1 10%

It is not unusual to be in an anchorage where the safest scope is not necessarily the longest. In a crowded anchorage If you have good anchoring gear, other boats dragging into you can pose the greatest risk. In these circumstances I sometimes anchor at a relatively moderate scope even when a strongish wind is expected. The less than ideal scope means it is less likely another boat will anchor in front. To do this you need a very good, preferably oversized anchor and use some judgement weighing up the various risks. It should also be remembered that a longer scope increases the swinging circle considerably. Often having a clear 360° swinging circle is safer than a long scope where an unexpected wind change could put you in danger. So think about the scope you deploy rather than automatically equating a very long scope as the safest alternative.

When moving with any speed, an anchor has a tough job getting an initial bite, especially when in difficult substates. Thus when dragging in strong wind, the anchor is likely to continue dragging. Deploying more scope sometimes works to stop a dragging anchor primarily because while letting out the extra rode the force on the anchor is reduced enabling the anchor to gain the important initial bite that allows it to bury properly. Thus it is sometimes difficult to know if letting out more scope has arrested the drag because the longer scope has provided significantly better holding or simply that the anchor has perhaps moved into an area of better holding (seabeds are not very uniform) and the pause in force has allowed the anchor to bite.

If it is an option, rather than simply deploying more scope it is generally much better to raise the anchor and repeat the anchoring process. An anchor that drags will often pick up debris that prevents it working properly. The anchor can look clean when raised but if you look underwater at an anchor that has dragged any distance, it is very likely to have picked up natural or man made debris, hindering its performance. Thus re-anchoring rather than simply letting out more scope is more likely to be successful. If possible, choose a significantly different location within the anchorage when redropping.

[44'cruisingcat]

Originally Posted by El Pinguino

Well, lots of variables but a heavy boat suggests she will be harder for the wind to push around... light boat with high freeboard to me suggests 'skittish'... sailing around the anchor etc... so yes I think maybe the light boat will give more shock loadings to the anchor and put her more at risk of breaking it out...

Seems the guys at Rocna disagree.

http://www.rocna.com/sites/default/f...aph_pounds.jpg

[boatman61]

I am a luddite.. 54 years ago I learnt that when anchoring lay 3.5 times the boat length plus depth for secure anchoring in good to fair weather (calm to 20kts).. increase with wind as needed and its kept me safe..
What I dread are the people who charge in.. stop n drop.. piling chain on top of their anchor as I know damn well if they're in front off me its time to string the fenders.
I pick my position, go slightly past then drop my hook as I start falling back letting the boat lay out the chain.. when 50% is out I hold till boat swings to the wind.. then once more fall off as another quarter goes out.. hold then repeat till required length is laid..
Result.. straight chain and sufficiently dug in anchor.. any further loads will dig her deeper.
Detest boats with rope rodes.. dangerous daysailing cheapskates spouting crap about loads in the bow.. its allowed for by any halfway decent designer.
Thats why some boats have anchor lockers and the crap have wells in the foredeck.
Okay.. Where my flak jacket..