Anchor sizing questions

[kmacdonald]

Originally Posted by arsenelupiga

large anchor seem to be promoted by uk based sailors. I can only think that this has something to do with tradition. I guess in olden days this may have worked.

Math however does not support that. Chain centenary is the most important. Forces may nearly straighten 30 m chain, but will not do this to 60 m chain. Nope, your cleat will go first. I carry 120 m of chain for these pesky nights when one chooses to anchor in 40m instead of risking trip in shallow anchorage.

The dinosaurs are gone for the most part but apparently there are a few stragglers left.
Go as light as possible to get the job done.

[arsenelupiga]

Originally Posted by kmacdonald

The dinosaurs are gone for the most part but apparently there are a few stragglers left.
Go as light as possible to get the job done.

i hope this is not meant to be cynical for your own good.

Large anchor and short chain will damage hull structure, rigging etc, because of large forces. You do not want that, unless you want to destroy your boat for insurance purposes.

You want to use centenary to soften forces when you get these 60+ kn gusts. This setup actually weights much more. Extra 30 m of 10mm chain weights 70 kg, 2x increase in anchor maybe 20 kg.

[kmacdonald]

Originally Posted by arsenelupiga

i hope this is not meant to be cynical for your own good.

Large anchor and short chain will damage hull structure, rigging etc, because of large forces. You do not want that, unless you want to destroy your boat for insurance purposes.

You want to use centenary to soften forces when you get these 60+ kn gusts. This setup actually weights much more. Extra 30 m of 10mm chain weights 70 kg, 2x increase in anchor maybe 20 kg.

Do you have a single example of hull structural damage from using a light anchor?

[Mike OReilly]

I don’t know why this topics generates such confusion or animosity. An anchor holds based on the force it can exert against the substrate. This is mostly an effect of surface area of the anchor, as well as the downward (digging) force vector.

Size matters … seems silly to have to say this, but some people seem to miss this point. The bigger the fluke area the larger the force. This is why a larger anchor of the same type produces more holding power — its surface area is bigger.

Mass of the anchor is a proxy for fluke size. It’s an easier number to use, and works well when comparing similar anchors. It’s not mass, per-say, that is the critical factor. It is the force created by the anchor against the substrate. Some anchors, namely Danforth-style (including Fortress) are designed with a higher fluke to mass ratio. So these anchors are generally lighter. But the mass-as-proxy-for-holding still applies here; the heavier (larger) the Fortress, the more holding power it can produce.

Mass (weight) also plays other critical factors in anchoring. A heavier anchor is generally easier to set and to get dug in. As long as your boat can create sufficient force to dig in the anchor, bigger is going to be better. It is possible to go too big such that your boat can’t generate sufficient force. A heavier anchor will generally reset easier.

All of the above is tempered by the type of substrate anchoring into. As we all know, large Danforth-style anchors produce the most holding power for the given size. But we also know the best conditions for these anchors is a bottom that is in the sandy, thick muddy, soft clay range. Danforth/Fortress style anchors perform poorly in hard bottoms, or weeds. Plow anchors do better in these latter areas.

The new-generation style anchors seem to do well over a wider area than the older style. This is why most people recommend going to one of these anchors.

Moving onto rode, an anchor only holds by producing a force vector horizontal to the substrate. It is impossible to achieve a perfect horizontal pull from point (the boat) that is angled to the anchor. This is why we use long and heavy rodes to keep the pull angle as shallow as possible.

Heavy rode (chain) also contributes to holding power. Catenary is most significant for deep water anchoring. A long chain produces a significant downward force which acts to maintain the horizontal pull on the anchor, and is also a significant energy dampener. In shallow waters, a long chain that is dragging on the bottom will produce significant friction (depending on the substrate). This too acts as a dampener, and adds to the holding capacity of the system.

I boil all this down to a simple recommendation: for your bower anchor, get the largest new-gen anchor you and your boat’s system can reasonably manage. Use as much chain as your boat can manage without compromising other factors.

[boom23]

Originally Posted by Mike OReilly

I boil all this down to a simple recommendation: for your bower anchor, get the largest new-gen anchor you and your boat’s system can reasonably manage. Use as much chain as your boat can manage without compromising other factors.

I agree with you 100%.

I am waiting for the arguments...

[Jim Cate]

Originally Posted by boom23

I agree with you 100%.

I am waiting for the arguments...

Why wait? Just read over the preceding 60+ posts!

Looks to me like most of the folks who are actually long term anchor-outs in unfamiliar waters support the 'as big as you can manage well' view.

We do...

Jim

[kmacdonald]

Originally Posted by Mike OReilly

I boil all this down to a simple recommendation: for your bower anchor, get the largest new-gen anchor you and your boat’s system can reasonably manage. Use as much chain as your boat can manage without compromising other factors.

Absolutely not. Put the weight in the anchor, not the chain. Why do people resist the science? Looks to me like most of the folks who understand the physics and are actually long term anchor-outs in unfamiliar waters support this. Sure, prior to nylon anchor line, chain was dominant but lets face it, nylon has been around a long time and has been well proven.

[vyc2014]

Where are you cruising? Whats the water depth and sea floor material? I use a Fortress 35 for sand conditions. Nothing better. For other conditions, I have 250 ft. of 10mm chain on a Manson Supreme. I dragged once in a storm in FL keys years ago, but i was set in the wrong direction and these waves of fronts coming off Cuba in June blew up in the Gulf Stream and they were pure nasty.

[dkenny64]

good choice on going with the Manson anchor..
for a reason that no one has mentioned..


retrieving...if the anchor is stuck good..like you want.


if you pull the chain/chain/rode tight and drive over the anchor the shackle will slide to the front of the anchor and pull it out.. rocna doesn't have this nor does mantus.. not that those are bad anchors at all..but if you cannot get it out.. well you have to cut the the line/chain..


my preference is all chain with a snubber..
last summer wife took out boat out..
anchored in what should have been a shelters area from the wind..
but during the night a storm blew in from the opposite direction..now we
have 40-60knt storm winds and a mile of open fetch for waves..
we didn't drag..45lbs manson( i think). all chain.. yep it was well buried in mud. best guess the wind caused the boat heel about 5 degrees



-dkenny64

[TonyDove]

Interesting thread … lots of the usual approaches discussed to good effect.

Slightly off topic … but just adding my pet fetish into the mix. Why oh why do boat manufacturers and naval architects insist on putting the anchor and chain locker right up in the bow? Even worse is a tendency to provide only a chain locker or a very minimal anchor locker … with nowhere to stow the anchor out of the way. This further leads people to undersize their ground tackle … to fit the locker instead of the size of boat.

This is the last place you want that weight when sailing (or motoring). Older designs used to put the windlass back nearer the mast … with a swage pipe leading the chain down to the bottom of the bilges for the chain locker … keeping the weight central and low … exactly where you want it to be. This position also has the benefit of providing much more room around the foredeck for the crew to work when anchoring instead of pushing all the effort up around the pulpit and forestay. And once the anchor is up … please don't carry it on the bow roller … bring it back and lower it through a hatch … again, storing it low and central. Do you think that makes the anchor less accessible? How often do you really need to unexpectedly and urgently drop anchor? It takes very little time to pull the anchor back up through the hatch and launch it over the bow roller. And wherever you stow your anchor … please strap the brute down when you stow it … you don't want something that sharp and heavy bouncing around, especially in a roll-over.

Okay … I know … 'older designs' like this were so far in the past that their wisdom seems to have evaporated in the mists of time.

Happy sailing and happy restful anchoring

[Mike OReilly]

Originally Posted by kmacdonald

Absolutely not. Put the weight in the anchor, not the chain. Why do people resist the science? Looks to me like most of the folks who understand the physics and are actually long term anchor-outs in unfamiliar waters support this. Sure, prior to nylon anchor line, chain was dominant but lets face it, nylon has been around a long time and has been well proven.

What part of "for your bower anchor, get the largest new-gen anchor you and your boat’s system can reasonably manage” is unclear? After that I said get as much chain as you can manage. Most long-term anchor outs support this. I only see one or two saying something else.

I’m a physics guy (studied astro-physics if details are required). Once the forces are sufficient to completely straighten out a the rode is reached, the chain ceases to provide any catenery or friction benefit. Yes … agreed. Until that point, these two ARE significant factors. I don’t know about you, but I have only ever seen my all-chain rode bone-hard perhaps once or twice.

I just weathered another three-day Newfoundland gale — winds. Sustained winds to 40 knots. Metre+ seas in the anchorage. My all-chain rode and substantial snubbers would stretch out, then relax, then stretch, and relax. Catenary and snubber acted as physics dictates, resulting in easy movement on the rode, with little overall time spent fully stretched out.

[kmacdonald]

Mike, most here are saying use all chain rode. If you do that you could get by with a smaller anchor since the catenary effectively increases scope resulting in higher holding power. Now if you use nylon rode and a bigger anchor but less effective scope the holding power may be the same but way less total weight. The rational approach is to design your ground tackle to get the job done with the lightest weight possible. The all chain, biggest anchor possible minimizes a rational approach but is consistent with "very old" thinking. Do you also upsize you standing and running? Mast section also? What about engine size----biggest that will fit regardless of hull speed limitations? Then there's hull layup----kevlar reinforced? I guess we better upsize the shaft also.

Let's go the extreme and ditch the engineering and just oversize everything. Or do we just oversize the ground tackle? IMHO if you look at the anchor on the bow and don't question if its big enough you have over sized you anchor, not the other way around.

[wingssail]

Originally Posted by Jim Cate

Why wait? Just read over the preceding 60+ posts!

Looks to me like most of the folks who are actually long term anchor-outs in unfamiliar waters support the 'as big as you can manage well' view.

We do...

Jim

Not to be a contrarian but we are very happy with a 44lb Bruce on the bow with 300ft 5/16HT chain on our 43' 8ton boat. In 20 years since we put this on the boat we've not ever had a dragging problem due to impossible bottom conditions which was not evident during setting. If the anchor set well it never dragged. We have been anchored in 60kts of wind and 2ft chop in a sheltered bay near Cape of Good Hope. We changed to the storm anchor as the wind built but our standard anchor was doing fine https://wingssail.blogspot.com/2011/...of-africa.html.

We carry a large fortress on a 300' nylon rode with 35' chain, which is never used.
We carry a 66lb Bruce as a storm anchor which we have set instead of the 44lb about twice (after shackling it to the chain in place of the 44).
We have a stern anchor and a dingy anchor.
Our windlass is 10' back from the bow. Our chain locker is 10' further aft than that. Both chain and rope rodes are in that locker.

Our reasoning:
We keep the weight out of the bow, hence a proper sized anchor, not simply the biggest we can carry up there. Same reason for the lighter 5/16HT chain.
We use all chain for the catenary and chafe resistance (on bottom).
We have multiple anchors for back-up and emergency.

To the OP:
Your 41ft fin keel performance oriented boat will sail better with lighter weight ground tackle in the bow. This does make a difference. Chose a good, modern anchor, of proper size, not simply huge. To sleep well carefully pick your anchoring spot (keeping in mind what it will be like in a wind shift) and set your anchor well, very well. use 5:1 rode in normal conditions, 7:1 if wind is expected. 3:1 in tight places with little chance of weather. Here is a difference than others recommend. You need less scope in really deep water. If the water is 65' deep, 4:1 is plenty; you will still have 200ft of chain sitting on the bottom. I have anchored in 90' of water with 3:1 scope.
Stay out of the open roadstead anchorages. I will sail 100 miles extra distance to get a bullet proof anchorage. I like it quiet. Wind is OK, waves, I don't like. Others may say they will sleep well with a huge anchor, but if there are big waves in the anchorage and the wind is howling, they will still be up all night, not sleeping through it like a baby.
Finally, use an electronic anchor watch. If you swing the wrong way or move, the electronics will wake you up.

[Mike OReilly]

Originally Posted by kmacdonald

Mike, most here are saying use all chain rode. If you do that you could get by with a smaller anchor since the catenary effectively increases scope resulting in higher holding power. Now if you use nylon rode and a bigger anchor but less effective scope the holding power may be the same but way less total weight. The rational approach is to design your ground tackle to get the job done with the lightest weight possible. The all chain, biggest anchor possible minimizes a rational approach but is consistent with "very old" thinking. ...

Those of us who cruise to a variety of areas, and who anchor out a lot, don’t have the luxury of knowing exactly what the conditions we will face. So we design a system with the widest possible range of success.

Sure… if you know exactly what you’re going to face, all the time, then design your anchor system to deal with exactly that. If I knew my anchoring was always going to be in soft but firm substrate, I’d ditch the Rocna and stick a Danforth or Fortress up there for my bower. But that’s not how I cruise.

As for nylon vs chain, there are benefits to each. For long-term cruisers who venture into uncertain waters, chain is superior. But nylon has some advantages. And for light, smaller boats, the benefits may outweigh the negatives. If your boat is highly affected by bow weight, then you have to take this into account when designing your anchor system. Most cruising boats are less affected by weight, but some certainly are.

[wingssail]

Snubbers.

Here is another observation:

Most cruisers use a snubber, or two (a bridle) on their anchor line. The snubber, being stretchy, takes shock away from their normal chain rode.

We found that in really bad anchorage conditions with lots of wind and wave action the nylon line on our snubber would stretch and chafe on the bow roller, especially if the boat was swinging.

We tried putting hose over the snubber to protect it against chafe. The nylon heated as it stretched and it melted the anti chafe hose and continued to chafe the snubber. We carry two snubbers. Both were showing definite chafe were they went over the bow roller. (we have two rollers, one for the chain, one for the snubber).

Finally we learned to put a non-stretchy section of line in the snubber system. This non stretchy line does not heat up and it does not chafe going over the roller when encased in a section of hose. Beyond the non-stretchy line our snubber has 15ft of nylon which can absorb the waves and heavy winds which might otherwise shock the chain.