Anchoring Technique - Three Questions

[Jeff F]

But in sustained heavy winds think the chain is always tensioned enough it’s tight enough to walk on. Think only the snubbers are mitigating shock loads to any appreciable degree.

Appreciate comments, and WRT waves, to my mind that's the biggest challenge. Shock loads can be enormous. My goals are generally to avoid heavy seas underway or at anchor. Without waves it's easy to deal with wind, in my experience.

So I'll happily give up room to swing on a long rode if I can get into shelter from waves on a shorter rode. That's my personal preference, and my practices match that.

I'm still not convinced that adding scope in the absence of waves buys you a lot. The math is available... What's the force required to raise the angle of pull at the anchor to above horizontal at various scope ratios?

 

[psneeld]

Appreciate comments, and WRT waves, to my mind that's the biggest challenge. Shock loads can be enormous. My goals are generally to avoid heavy seas underway or at anchor. Without waves it's easy to deal with wind, in my experience.

So I'll happily give up room to swing on a long rode if I can get into shelter from waves on a shorter rode. That's my personal preference, and my practices match that.

I'm still not convinced that adding scope in the absence of waves buys you a lot. The math is available... What's the force required to raise the angle of pull at the anchor to above horizontal at various scope ratios?

I agree with you on finding a "sheltered" anchorage. My preference when on the ACIW was a creek (or whatever the local name was) that was barely 3-4X as wide as the boat length, preferably with trees on the side where the greatest amount of wind was expected from.

As far as how much wind does it take to stretch your rode? That is pretty boat and tackle dependent.

My 40 Albin with all 5/8 BBB chain, and not full bridge enclosure would be pretty tight somewhere in the high 20's maybe 30 knots IF I had enough out.

In those creeks, it really never straightened out even though I might have had only 75 feet out, if in more open water and gusting 25 to 30 with at least 100 feet out, yes it would be straining my 1/2 inch single snubber.

 

[Stabi]

Saturday morning reading entertainment.

The OP is from the PNW. I really do not think that he usually anchors in 20' or less. Last night we had a tidal swing of over 21'. Tonight will be less at 17'. Five to one will rarely work , especially in a (for us) normal anchorage of 40' or greater, usually greater. I try not to anchor in over 100' of water. 3 to 1 is normal.

While I am not a "professional" , so probably do not know it all, we do anchor out from 100 to 130 nights a year, for the past 23 years.

This pretty much sums up our technique ....in the PNW.

We line up facing the wind direction.
If we are anchoring in 40' of water then while sitting I lay out about 45' of rode. Not enough to foul the anchor, at least not yet.
Hand signals get my wife to reverse throttle at idle and I lay out 120' or more of rode. Minimum about 3X depth.
I watch the rode and get her to go out of gear and let the boat drift back untill I see the boat slow and the rode lift a bit.
THen back into reverse to snug the chain more for another chain lift only more so.
Then out of gear again so the boat can drift forward and slacken the chain.
THe reverse again but in and out so I jerk the rode minimally.
Then I ask for reverse as soon as the boat start to go forward from the chain weight. THis time She stays in reverse and I look for landmarks to sight on, trees in line, rocks in line, logs stranded in line or close enough in line to be a good sight. Almost always that is enough. Once in a while I need to lay out four time the depth but seldom.....................Of course I watch that I am not crowding another boat in which case we also move.

As far as super soft mud, which I have encountered a few times. When backing down, it becomes obvious, so we will either move or switch to a spare fortress anchor with mud palms set in the mud position. If I had not tried to "set" our Ultra anchor, I might not have known that the bottom was super soft and would not set.

 

[C lectric]

I'm curious what size chain are you using? This is for the Palmer 32'?

Ted

Yes, for our Palmer 32'. The chain is 1/4" G43, 275 ft of it plus another 250 of 1/2 rope.
Should have mentioned we look for places at least reasonably protected.

Many have told me the 1/4"is to small but at the time I made that decision I needed to pull it by hand and wanted a lighter ,stronger chain.
My windlass had croaked literally so it was hand bomb it. I figure I could hand bomb the 1/4 G43 but no longer what I had.

 

[Delta Riverat]

Captain told us to toss anchor, play out rode at least 3:1 and then set 2 landmarks 90 degrees apart. Verify position with landmarks.

Nothing about backing down.

 

[Hippocampus]

The differences in practice outlined above seem to vary with region. Been just trying to stress it’s wise to not carry what works 95% of the time in your region to the 5% of the time it won’t or to another region.
I’ve been less interested in poor sets or mild drags that don’t result in damage than to drags that result in damage, groundings or even lost of life. Peter is in a region where one event resulted in all of the above. Failures occurred when snubbers broke, foredecks were sufficiently damaged that rollers, cleats and windlasses were pulled out, boats dragged into each other causing a domino effect, boats Dow flooded from damage. I’ve seen damage in Sopers, the USVI “Hurricane Holel”anchorage at the south eastern tip,Maniposset, rockland and others. PS mentioned a cat 2 event but think these catastrophic events are more common with brief high intensity occurrences such as squalls, Tstorms, and microbursts inside a larger system. The preceding hours (or days) are relatively benign and then you see loading like you can’t believe. Yes cyclonic events do occur but hopefully you have a few days warning. It’s the hyperlocal events that need to be kept in mind.

So I’ve taken to looking at weather a second time about an hour or three before approaching an anchorage. Try to pick a spot where if I do drag it’s on to mud or a non rocky beach. Try to estimate what’s the risk of a burst of brief severe conditions. Pay a lot of attention to positioning to avoid waves in that direction. Tucking into a creek or behind elevated land or trees seems wise as long as it’s not a set up for severe downdrafts. Unfortunately this business of moving isn’t always practical. Along some coasts the best anchoring spots may be full before you get there. Going another 10 or 20 miles from a decent spot to a great but full spot is disappointing. When planning the day pick multiple possible spots and choose when we get there.

So at the risk of sounding belt and suspenders still rather do overkill. If there’s a risk of Tstorms may do our regular twin snubbers on a chain hook and a third to the Sampson post utilizing a knot. In in an open bay may seek deeper water to allow increased scope and a bit of room for a “safe” drag. Enough time to get up and get the engine on. So many things you can do to decrease your risk. Cross the bay or sound so drag is to open water even though it adds miles to your trip.
Talking with folks and reading about bad outcomes have expanded my thinking beyond just scope, bottom, type of anchor and anchoring technique. Many here have wisely pointed out paying attention to direction of exposure to wind and wave is critically important. Some excellent comments on what you can do to decrease risk of a drag by decreasing hunting or pitching.

But would take a critical look at your boat. For me that was brought home looking at boats in various yards that suffered damage. Saw a production sailboat using chain and rope. He didn’t drag but rather the whole unit holding windlass, bow cleats, sprit and rollers was pulled away from the boat. Another attached a single snubber to a SS D down the bow just above the cut water which pulled entirely out and the two halves of the hull were separated there. On several power seen the sprit break free or collapse. Some power boats are designed to primarily go marina to marina. Anchoring is for short breaks not living on the hook. PS appropriately pointed out each situation is different. I’d point out each boat is different. Look at your set up. Your cleats, sprit, backing plates etc. before contemplating anchoring if potentially tough settings.

 

[O C Diver]

Yes, for our Palmer 32'. The chain is 1/4" G43, 275 ft of it plus another 250 of 1/2 rope.
Should have mentioned we look for places at least reasonably protected.

Many have told me the 1/4"is to small but at the time I made that decision I needed to pull it by hand and wanted a lighter ,stronger chain.
My windlass had croaked literally so it was hand bomb it. I figure I could hand bomb the 1/4 G43 but no longer what I had.

:lol:
Half the reason I anchor in skinny water is so I have half a chance at pulling the anchor if the windlass quits.

I don't like anchoring drama in the middle of the night either. Given a choice, I hide in the protected spots also.



Ted

 

[Nick F]

Someone above questioned the effect of water depth on scope requirement, so I ran a few numbers to see what it looks like. I ran for one chain weight only (1.1 lb/ft) and for 20, 50 and 100 foot water depths. The chart shows how much horizontal force at the anchor roller is required to just lift the chain off the bottom, all the way to the anchor. As can be seen, the force is much greater in deeper water.

The force is linearly proportional to the chain weight/ft, so 3/8 chain at, say, 1.6 lb/ft would give forces 45% greater.

 

[Caballero II]

Interesting to hear some of you don't actively set as well. I mean, I can see how it may not be necessary if you are ON the boat, and stay on the boat, with an anchor alarm set, but are you telling me you still don't set the anchor and then get off your boat overnight or even for many hours? You hope the anchor sets on it's own instead of in a controlled manner by yourself? I realize the anchor does this at any wind/current shift, but the concept seems crazy to me. Maybe I just haven't done it enough and I'm over thinking it

I do think you may be over-thinking this. I've never seen seas seriously over stress when I've only got 1:1 or 2:1 out. I start dropping to 5:1 length out, let the boat drift back as I do this. Let it soak a bit, and only then put a little reverse idle on it. If it holds there, I increase bit by bit until I'm convinced it's a good set. It depends a lot on what your anchor is. You didn't say.

 

[Hippocampus]

Someone above questioned the effect of water depth on scope requirement, so I ran a few numbers to see what it looks like. I ran for one chain weight only (1.1 lb/ft) and for 20, 50 and 100 foot water depths. The chart shows how much horizontal force at the anchor roller is required to just lift the chain off the bottom, all the way to the anchor. As can be seen, the force is much greater in deeper water.

The force is linearly proportional to the chain weight/ft, so 3/8 chain at, say, 1.6 lb/ft would give forces 45% greater.

Not fully understanding what this graph is showing.

Would think if there’s enough force to lift the chain off the bottom that force is felt by the boat but also an equal force by the anchor. That force on the anchor is the horizontal force from wind and wave but also the horizontal vector of the chain weight given its at a diagonal. Think anchor sizing is for a good bottom so don’t mind going a size up. But don’t exceed capacity of the windlass for weight of chain (when up and down) plus weight of chain plus shock load from chop and waves.

Having anchored where the water is clear it doesn’t take much. From personal observations ~20kts with 100’ out in 20’ of water with a typical 40-50’ boat little if any chain is resting on the bottom. So yes the forces are considerable. Use your engine so chain is only lifted when up and down. Then lift is the amount of chain weight as determined by water depth. For us with a lofrans I won’t anchor in more than 40’unless forced to. Windlass is approaching its limit if there’s a moment when chain is tighter. Also snubbers aren’t a sometime thing. People wreck windlasses and then say “but we were never in a storm or gale. “.
I’m much more conservative now being on power. On sail if my windlass failed I could run a line tied to the chain and brought to a powered 2 speed primary. Even stick in a snatch block to get 3:1 purchase. On the trawler I only have the windlass.

 

[rslifkin]

I’m much more conservative now being on power. On sail if my windlass failed I could run a line tied to the chain and brought to a powered 2 speed primary. Even stick in a snatch block to get 3:1 purchase. On the trawler I only have the windlass.

My plan for that has been that if the windlass fails, try the manual backup. If that's not adequate to retrieve the gear, then dump it and buoy it. And then it's time to head for the nearest source of windlass repair parts (and come back for the ground tackle).

 

[psneeld]

I found the horizontal windlass manuals that I have used to be easy but pretty slow, the verticals a bit harder (due to ergonomics) but faster if not a heavy load.

 

[rslifkin]

I found the horizontal windlass manuals that I have used to be easy but pretty slow, the verticals a bit harder (due to ergonomics) but faster if not a heavy load.

That agrees with my assessment, although the verticals may be a bit less annoying in the sense that (given no nearby obstructions on the deck) you can just grind in circles like a sailboat winch vs the ratcheting back and forth with the manual retrieve on most horizontal windlasses.

 

[Hippocampus]

Not to worried about electric motor failing. Rather worried about mechanical guts of the thing. You get a fairly long lever arm so think even a fat old man could retrieve if it’s just the motor.

 

[rslifkin]

Not to worried about electric motor failing. Rather worried about mechanical guts of the thing. You get a fairly long lever arm so think even a fat old man could retrieve if it’s just the motor.

On my windlass (Maxwell HRC10) the manual backup requires the clutch to be released, so the gearbox, etc. is out of the equation. As long as the chainwheel is still in place and can rotate on the shaft with the clutch released, the manual backup will work. A failure beyond that point isn't impossible, but I consider it relatively unlikely.

 

[Nick F]

Not fully understanding what this graph is showing. . . .

s.

Hippo - I was trying to quantify the effect of depth on the scope required to give the same holding power. As the graph shows, you can get the same ultimate holding power at shorter scope when in deeper water.

 

[mickand]

Watching folks arriving at an anchorage, I'm always amazed by some dropping their anchor while still traveling forward.
I watch my chartplotter speed drop to near zero, engage reverse, watch the speed start to increase from zero and deploy the anchor/chain. My interval spray paint will tell me when to stop the windlass, I'll come to neutral (speed now maybe 1 to 1.5kts) and I'll leave the helm, walk to the bow and hopefully watch the chain tighten. I will maybe engage reverse at idle after a few minutes and again watch speed and catenary angle to ensure a good bite.
Once satisfied, I'll fit the bridle and relax.

 

[CarlF]

My practice is:

I use 5:1 scope measured for high tide (including height of bow). This makes my swinging radius compatible with both 3:1 and 7:1 neighbors. The exception is the CQR and Delta anchor that really needs 7:1

Let the whole 5:1 out but don’t let the boat drift back too fast. Anchors can jump and not catch if you are moving faster than 2kts while trying to set. In strong wind or current a few bursts of forward may be necessary to keep the speed OK. If you are losing your balance when the anchor sets, you are too fast.

In soupy mud bottoms you need to set the anchor with multiple light pulls over 20 minutes to give the anchor time to sink into the mud between pulls.

After the anchor is initially set I’ll use about 2000 rpm for 15 seconds to test the set. The RPM isn’t as important as the visual force on the chain. The chain should rise out of the water and be “bar tight” ”. The reason to do this is that an “idle set” will often hold on a bit of rock or with the anchor on its side. The “bar tight” set will drag if the anchor was not well buried.

 

[O C Diver]

Someone above questioned the effect of water depth on scope requirement, so I ran a few numbers to see what it looks like. I ran for one chain weight only (1.1 lb/ft) and for 20, 50 and 100 foot water depths. The chart shows how much horizontal force at the anchor roller is required to just lift the chain off the bottom, all the way to the anchor. As can be seen, the force is much greater in deeper water.

The force is linearly proportional to the chain weight/ft, so 3/8 chain at, say, 1.6 lb/ft would give forces 45% greater.

Your graph doesn't surprise me, but I'm curious how you came up with the formula, equation, or whatever gives you the numbers. If it's a simple equation, could you post it so that I could substitute other values for my own use.

Ted

 

[Hobbit]

We have a 280 lb. anchor with 70' of 1/2" chain connected to 1/2 steel cable 2:1 or 3:1 max if its going to blow. Try to avoid exposure to 40 kts of wind but have stayed put in 30 kts in mud bottom. Never dragged in 30 years...touch wood. Reverse slowly watch cable tighten up and boat swings around.... it weighs 45 tons. I see a lot of sailors trying to set a 50 lb anchor doing 3 to 5 kts makes for good entertainment.

 

[Nick F]

Your graph doesn't surprise me, but I'm curious how you came up with the formula, equation, or whatever gives you the numbers. If it's a simple equation, could you post it so that I could substitute other values for my own use.

Ted

Hi Ted - the formula for a catenary is well established, although a bit tricky to work with. You can see it here in Wikipedia (https://en.wikipedia.org/wiki/Catenary#Equation)

The basic shape formula is

y = a*cosh(x/a) where a is a "shape factor". (Note: cosh, not cos)

I used Excel to calculate out a number of different cases. To get each combination of depth and scope that I wanted I had to iterate several tries of input values ("a" and "x-scaling").

Let me know if you want the XL file.

Here is another graph I made, comparing different depths at the same 500lb limit load.

 

[O C Diver]

Hi Ted - the formula for a catenary is well established, although a bit tricky to work with. You can see it here in Wikipedia (https://en.wikipedia.org/wiki/Catenary#Equation)

The basic shape formula is

y = a*cosh(x/a) where a is a "shape factor". (Note: cosh, not cos)

I used Excel to calculate out a number of different cases. To get each combination of depth and scope that I wanted I had to iterate several tries of input values ("a" and "x-scaling").

Let me know if you want the XL file.

Here is another graph I made, comparing defferent depths at the same 500lb limit load.

Thanks Nick! That graph gives me a close enough idea. I was looking to make an equivalent comparison (depth and scope) for 20' with a scope of 1:7. Basically wanted to know at what depths a reduced scope would give an equivalent effect on the rode.

Ted

 

[Jeff F]

Generally, sc

ope is the ratio of chain length in the water in relationship to depth when the chain is taunt.



Is there a snubber in your equation that changes the ratio,?



Ted

Normally I add about 6' to rode length when I rig the snubber.

I had to think about your scope definition. So yeah, I suppose when the chain is taut there would only be 24' in the water. It's a sobering thought.

 

[Takoradi]

There are strong opinions between the power-set camp and the dump-and-forget camp. Both sides are entrenched and frankly, they talk past each other.

I am firmly in the power set camp and do not understand the no-set approach. To my mind, exceptions to power-set are few. While I've never anchored in soupy mud, it makes sense to delay a set and let an anchor soak while it works its way through the goop. But I'd still want to give it a set after a while. The biggest variable for me is scope which varies mostly on water depth, expected conditions, and how crowded an anchorage is. For my tiny 75hp Perkins, I typically bring the RPMs up to around 1000 and hold it for 15 seconds or so until I can verify I'm not dragging. I might go longer if there are other issues such as expected weather.

A story. For golfers in the crowd, you've probably watched the AT&T ProAm at Pebble Beach CA and noticed s bunch of boats anchored off Stillwater Cove. It affords very modest protection from typical northerly weather patterns. A few miles to the south is Whalers Cove which is shown as an anchorage with decent protection from uncommon southerly weather. If a boat were to use the drop-and-forget technique, they'd be at severe risk. Best I can tell is that the bottom resembles a concrete tarmac.

Left untethered, a boat will lay more or less broadside to the wind. It's why boats 'sail' at anchor and why you're confounded a bit

Peter View attachment 141145

So I spent some time as a tek diver and am familiar with that stretch of ocean. At the time, if it wasn’t about diving, I didn’t pay it much attention. We noticed the crowds up on the cliffs but it took us all day until we were back at the dock to realize it was the ProAm! Sandy bottom with lots of boulders and rocks.

Tak

 

[tozz]

Thanks Nick! That graph gives me a close enough idea. I was looking to make an equivalent comparison (depth and scope) for 20' with a scope of 1:7. Basically wanted to know at what depths a reduced scope would give an equivalent effect on the rode.

Ted

ah, yes, that is interesting. So if i look at the graph and extrapolate out a bit you are saying that you would get the equivalent effect at 7:1 at 20' that you would at .... about 4:1 at 50' and looks about 3:1 at 100'?

-tozz

 

[Nick F]

ah, yes, that is interesting. So if i look at the graph and extrapolate out a bit you are saying that you would get the equivalent effect at 7:1 at 20' that you would at .... about 4:1 at 50' and looks about 3:1 at 100'?

-tozz

Yes - exactly. I, too, found this interesting and somewhat surprising.
Nick

 

[Delta Riverat]

Makes sense.

7:1 at 20 = 140 feet
4:1 at 50 = 200 feet
3:1 at 100 = 300 feet

 

[Simi 60]

With our 7.5ft draft and 60 tonne (66 ton) if we have 7ft under keel at high we put 40m (131ft) out (first mark)
If we have 25ft under keel at high we put out the same.
And that's worked for us up to around 40 knots.

Recently we sat out a week of 35 to 40 knots in a coral lagoon, 25 ft under keel and breaking waves at high tide with zero issue.
But the long 20mm nylon snubber with 8mm dyneema at the roller for chafe sure copped a workout.

 

[Hippocampus]

More chain means more catenary effect and more weight. Think when thinking rode length equation is different for chain than rope even with a heavy kellet.

This can be an issue as UHMWPE one can be as strong or stronger than steel for much less weight. Doesn’t rust and keeps weight off the bow. Seems a perfect rode but even with snubbers and kellets behaves differently.

 

[Mako]

Member @Larmex99 anchors with a captive reel winch with Dyneema. He would be a good source for feedback if someone is considering similar.