Reversing the engine when digging in the anchor – how much anchor load does this correspond to?

[Bobc]

I have sat and watched people lose swim suits, towels (and even some folding chairs) not to mention beer cans in anchorages. More often than not the offending articles are never retrieved. We have heard of people catching crab pots and supermarket trolleys - and we once caught a 5kg gas cylinder.

If you anchor catches any of these items your anchor will not set - if you simply chuck the anchor over the side in relatively calm conditions you will not know it is fouled unless you try it. You can wait for the wind to pick up, but that might not happen till 2am. It does seem ever so simple to put the line in reverse.

Modern anchor can have a sharp toe - sharp enough to catch more natural items, seaweed or a shell - again - instead of waiting for the wind to pick up - reverse is so much predictable.

These anchors might 'set' but will never offer reliable hold as they simply cannot set deeply - how are you going to find out - unless you test them to near maximum of your yacht's ability to check the hold? Both of these anchors are under the bridge deck of two different catamarans, a common location for the bow roller. You cannot easily see that the anchors have been fouled.

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Read my post again.

"...once the anchor has grabbed and set, I've never had it drag using this method.

There is absolutely no need to use reverse other than maybe in tick-over to help it get a grip in light wind conditions."

If there is no tide and little or no wind, then of course you have to use reverse to set the anchor.

I think maybe the difference here is that your experience is in Australia, and mine is predominantly in the UK/France.

 

[geem]

Read my post again.

"...once the anchor has grabbed and set, I've never had it drag using this method.

There is absolutely no need to use reverse other than maybe in tick-over to help it get a grip in light wind conditions."

If there is no tide and little or no wind, then of course you have to use reverse to set the anchor.

I think maybe the difference here is that your experience is in Australia, and mine is predominantly in the UK/France.

The anchor doesn't know what country it is in. Why should it behave differently?

 

[ghostlymoron]

Hmm, so you just drop the anchor and let it lie?

At least, when you dig in the anchor with reverse engine you will have an idea how good the holding power of the sea bed is.

And in the case of Spade anchor, which we have been using for years, it never has failed to adjust to changing wind directions and reset itself. So, I fully trust that aspect, but I still would like to know what the holding power is at some point...

If your Spade resets itself, why wouldn't it set itself when first deployed?

 

[ghostlymoron]

I do anchor under sail from time to time.

With a CQR, the best approach seems to be to drop the anchor until it is just touching. Wait a little until you have drifted back a little bit. Then dump out a decent amount of chain. About 4:1 minimum.

Tom Cunliffe then recommends making a cup of tea. But I do things very differently.

I make a jar of coffee. And when I have finished that and washed up, the anchor will be dug in properly.

Just to be sure, I could fire up the engine and back down on it. But if the conditions are not going to get stormy over night, it is not necessary in anchorages which I know to have good holding. My biggest concern is that we have enough swinging room and that there are not other boats we are likely to collide with as the wind will almost certainly completely change direction a few times during the night.

Only ever dragged once and that was in poor holding on a stony bottom in windy conditions. I spent most of the night awake waiting for it to happen. Did not drag very far, but as soon as the anchor started moving you heard it loudly in the fore cabin. That kept me up most of the night although we did not need to re-anchor.

Another time, I was concerned that we were on the limit of the holding capacity. It was blowing a gale towards a lee shore. Good holding, all the chain in the locker out and plenty of room.

The only other boat in the bay dragged and ended up on their side on the beach. They got dragged off by the life boat (very expert coxswain) and no apparent damage. But we held solidly and did not move an inch. Although I hardly slept the whole night. I was ready to start the engine and to have it running slow ahead to take some load off the chain which was almost straight - no catenary but with a nylon warp as a shock absorber (needed because of the chop).

My Yachtmaster and round the world friend told me that to anchor under sail you should flake out sufficient scope the approach the anchor point downwind at moderate speed under Genoa alone. Drop the anchor and hang on. The anchor should bite and boat continue to the end of its scope then swing into the wind and stop. I've tried it a few times mainly satisfactory.

 

[Poignard]

If the wind is really strong, there is no dishonour in running the engine to take most of the load off the anchor. You do have to keep a watch, because when the wind dies down ....

That's very interesting. When I have found myself at anchor or on a mooring buoy in very strong gusty winds I ran the engine slow astern to try and keep the chain under tension and stop the boat surging forward in the lulls and snatching when she drops back with her bow at an angle to the wind.

 

[LadyInBed]

If your Spade resets itself, why wouldn't it set itself when first deployed?

That's a good question.
The only thing that I can think of is that on turning the anchor is resetting into a previously ploughed sea bed, but on initial setting it has to plough into virgin bed.

 

[Motor_Sailor]

All ships in Hong Kong harbour (even those on mooring buoys) had to 'raise steam' when the Typhoon Signal Number 8 was raised, so they could steam ahead if needs be when the winds increased further.

If ships were uncrewed or couldn't get their propulsion machinery working, then the harbour tugs would shift them to behind Lantau Island and they could fend for themselves as dead hulks.

 

[MathiasW]

These are interesting photos. It must be a nightmare to clear weed etc from an anchor on a catamaran like that. How do you get access to clear it? Do you have to partially unrig the trampoline netting?

Use a dinghy ???

 

[Poignard]

All ships in Hong Kong harbour (even those on mooring buoys) had to 'raise steam' when the Typhoon Signal Number 8 was raised, so they could steam ahead if needs be when the winds increased further.

If ships were uncrewed or couldn't get their propulsion machinery working, then the harbour tugs would shift them to behind Lantau Island and they could fend for themselves as dead hulks.

When I was in the Royal Hong Kong Police I remember going on board a decrepit Taiwanese ship one night to find out why she wasn't showing an anchor light. She was a 'dead ship', having lost all power. No generators working, even the emergency generator wouldn't start. Her old man seemed on the verge of a nervous breakdown and didn't even know if she had an oil anchor lamp on board. Eventually one was found in the forepeak and the regulations were satisfied and so were we. Next day she was gone.

 

[MathiasW]

If your Spade resets itself, why wouldn't it set itself when first deployed?

Well, the difference is obvious, isn't it. When the anchor is set and wind direction changes, it will stay buried and just rotate. So it is not coming free and then have to reset itself. That is very different from when you are launching it and it has to get hold for the first time....

 

[westernman]

That's very interesting. When I have found myself at anchor or on a mooring buoy in very strong gusty winds I ran the engine slow astern to try and keep the chain under tension and stop the boat surging forward in the lulls and snatching when she drops back with her bow at an angle to the wind.

We never had lulls in my day.

This is in conditions where there is no catenary left in the anchor chain. I.e. it is really bar tight.
I have never surged forward in those conditions.

The only time I had something like that was tied up along side a dock in windy and rough conditions. The boat surged back and forth on the spring lines. I fiddled with the length of the lines and then it all calmed down.

 

[Poignard]

We never had lulls in my day.

Nothing like a nice lull or two. Especially with a cup of tea.

 

[geem]

If your Spade resets itself, why wouldn't it set itself when first deployed?

If you don't set it it might foul something on the bottom or you will wrap your own chain around the fluke that is just sat on the surface. You will only find this out in the middle of the night when it drags or you hit something

 

[MathiasW]

From a practical point of view for most yachts if you set the anchor in light wind by gradually ramping up to full reverse power and leaving this for around thirty seconds the depth of anchor set will be equivalent to an anchor that was simply dropped when the yacht has experienced about 25 knots of wind.

After setting in the above manner If the wind stays below 25 knots and does not change in direction the anchor will remain unchanged. If the wind rises above 25 knots the anchor will have to burry deeper to hold the yacht in position.

This rough rule of thumb holds true for most sailing yachts although there are exceptions. The biggest variable is the efficiency of the propeller in reverse

I have just verified with my Anchor Chain Calculator tool - The 831 kp I got from the engine calculation correspond to 41 kn of wind (in a flat sea with no waves). With a lot of waves and no snubber at all, this comes down to 25 kn indeed! Using a good snubber it will be good till 35 kn or so. Thus, I conclude this number makes sense now for me...

 

[thinwater]

These are interesting photos. It must be a nightmare to clear weed etc from an anchor on a catamaran like that. How do you get access to clear it? Do you have to partially unrig the trampoline netting?

Not at all. Reach down and grab the bridle, and bring it up to the front beam. Now, whether they do that is a different question.

There is no absolute reason that multihull anchors cannot be rigged over rollers on the bow. Many are. But it is nice to move the weight closer to the center. Whether it is better overall can be debated.

 

[Neeves]

These are interesting photos. It must be a nightmare to clear weed etc from an anchor on a catamaran like that. How do you get access to clear it? Do you have to partially unrig the trampoline netting?

These anchors were on cats on swing moorings in the same mooring field as we keep ours. They picked up the ribbon grass in the last place they anchored - so the anchors would not have set very deep. The lower, or second picture, the bow roller is part of the structure of the cat and the roller itself, in the middle of the stainless plate, completely hides the anchor as the only 'view' is through the slot in the plate. Cleaning the anchor - you need to get in your dinghy and get under the tramp and pull the weed off by hand. The clearance between water and bridge deck, at its lowest, will be around 1m - you would need to lie in the dinghy, face up, drift underneath, pull off the weed - it really needs 2 people one adjusting the position of the dinghy.

Our windlass is very roughly located as theirs is, ours is slightly further forward, but our bow roller is almost at the bow and the chain is houses in a 'U' shaped channel. The advantage of having all the weight just forward of the mast is balanced by the terrible anchor access.

You can do what thin water suggests and drop the anchor sufficient and then pull the anchor aboard at the bow using the bridle - these cats are quite big and have hefty gear - its easier from the dinghy (though not very sensible at the end of a long passage and its dark . To clean you would need to pull and anchor on deck or hang over the forward cross beam - none of the options are ideal.

Jonathan

 

[Neeves]

That's very interesting. When I have found myself at anchor or on a mooring buoy in very strong gusty winds I ran the engine slow astern to try and keep the chain under tension and stop the boat surging forward in the lulls and snatching when she drops back with her bow at an angle to the wind.

I think you would be better to use a decent snubber than run the engine.

Have a look at Mathias spread sheet and input the data, you will see how the snubber will solve, or reduce, the problems.

The art of snubbing, in the nicest possible way - Mysailing

How to: Dealing with Snatch Loads in an Anchorage

Anchor Snubber Tips

There is an updated article in YM, I think the July issue 2021, which focusses on snubbers on a monohull (and should be available in your local library).

If you can rig a bridle, easy on most monohulls then try this article

A Snubber & Hook for all Occasions - Practical Sailor

A bridle is advantageous as it helps to manage veering caused by wind sheer, you get the same advantage if you use 2 anchors in a 'V'.

A good snubber needs to be about deck length, or longer if you want to cater for strong winds. If you cannot see the snubber stretching - its too thick and inelastic. (Our snubbers are 30m for each arm of 10mm kermantle dynamic climbing rope, 38' cat (still roughly the same as a 45' AWB) and 7t in full cruising mode (400l of water 200l of fuel). Our bridle effectively means we use a mixed rode and if you read the articles - a maximum of 10m is forward of the bow.

If you want to understand the issues with having inadequate (and by implication no snubbers) read the article I posted earlier on the storm.

You can of course use heavy chain and take advantage of catenary, instead of elasticity of a snubber, which is what NormanS does - but, if nothing else, some yachts (like cats) are very susceptible to extra weight

Jonathan

 

[Neeves]

We never had lulls in my day.

This is in conditions where there is no catenary left in the anchor chain. I.e. it is really bar tight.
I have never surged forward in those conditions.

The only time I had something like that was tied up along side a dock in windy and rough conditions. The boat surged back and forth on the spring lines. I fiddled with the length of the lines and then it all calmed down.

The problem with a bar tight chain, when the chain looks to have no catenary (but does have catenary - but none of any use) is that your anchor is under the same tension as you see (or feel) at your bow. If the chain is bar tight that implies to me some decent wind and decent wind results in chop - so your bow is going up and down and the bar tight chain is also going up and down (as is the shackle attached to your anchor). The holding capacity of an anchor is measured under ideal conditions - a straight and steady rode - holding capacity is NOT measured with the shank continuously lifted and not lifted.

Now get a big shovel and go down to your local beach and stick the blade of the shovel, say at 45 degrees, into the sand at the waters edge. Lift the handle. Now jiggle the handle for a minute or two and now lift the shovel - which is easier the un-jiggled or the jiggled shovel? You can do the same experiment at home - make up some mortar, cement - take your trowel and lift some of the mix - now jiggle the trowel and the mix all round your trowel with 'liquify' (which is why cement trucks keep the load moving - it stays liquid through all the mix.

If you dive on your anchor (choose warm water, but with a bit of chop running) and touch your anchor when all the chain is lifted off the seabed (so around 6:1 scope, 30m of chain and all the chain will be off the seabed at 17/20 knots. - you will find it is constantly twitching (nice technical term). The movement of the yacht is transmitted along the chain - even though there is plenty of catenary. If the anchor is twitching it will reduce the shear strength of the seabed in which the anchor is set and its holding capacity reduced (like my shovel experiment).

You can reduce all this negativity by using a snubber.

Snubbers are cheap as chips, some 3 ply nylon - depends on yacht size 8mm to 12mm (30' - 50'). Invest in a bit over deck length. Secure at transom, run to bow (sort out how to get it outboard sensibly) - attach to chain - job done (the articles give more detail, are a bit more wordy and have some pictures! ). If you run your engines slowly - you will have a blocked exhaust elbow in no time - and that's a real bummer (and can be much more pricey than a 12m of 10mm nylon). I cannot say that a nylon snubber will be quiet - they can squeak - but even that can be managed.

Think outside the box.

Jonathan

 

[Stemar]

I cannot say that a nylon snubber will be quiet

Mine was a hellava lot quieter than chain shifting in the bow roller!

 

[Slowboat35]

I find it rather surprising that anyone would not make an effort to dig an anchor in.
If your anchor is going to plough a furrow across Newtown Creek with a few Hp's help then it's going to do the same in the oncoming gale. Wouldn't you rather discover this charactaristic while you still have time to deal with it?
Granted, if no gale is coming then probably no need to use full revs, but surely prudence and basic seamanship dictates that you ensure the anchor has got a bite? A pile of chain sitting on top of the anchor holds a boat deceptively well until the wind begins to whistle, as anyone who's sailed the Greek Islands with charter boats around can attest...

Re pull available under power, there is a rule of thumb amongst tuggies that approximates 1 ton of bollard pull per 100Hp. PBO's 2009 featherng/folding propellor test was run with 21Hp. The baseline standard 3 bladed prop provided 260Kg bollard pull in ahead and 180Kg in astern which corresponds quite well with that.
How that translates at the far end of an anchor rode is anyone's guess, but suffice to say it'll be a fair bit less. Quite how much force the previously quoted 30Kt wind exerts on an anchored boat is equally up for debate but I'd wager its substantially if not dramatically more than the engine's bollard pull

Me, I'll continue to dig in, thanks, and do so under full power if I think it's going to get boisterous.