All chain vs 100'

[svinvictus2]

Originally Posted by sanibel sailor

When I started sailing, I always had rope rodes with a short (15'-30') section of chain. On a prior boat, I swapped to all chain, about 300'. I had 150 in the forepeak and pulled 1500 back into the forward bilge. Don't recall ever using the extra 150'. I have some chain now for my current boat. I am thinking about using 100 feet of chain backed up with a couple hundred feet of nylon rather than all chain. It seems i will get nearly all the benefit of chain with significant weight (and cost) savings.

Current dreams are Florida to Cuba, NW Caribbean/Panama and westwards.

We've been based in the Caribbean for many years now where we carry 250' of chain. There is an argument for chain and rode bot the benefits of both security and ease, no splice, seem to out weigh other areas. While sailing in the North East i preferred the combo only because we were once almost hit by a passing ship and saved our selves by quickly cutting the rode and getting out of there.

It may be more expensive with added weight bur you can sleep well at night.

[Wrong]

There's plenty of good advice from experienced boaters in this thread. However one issue not mentioned is the hazard a boat using lots of rode presents to surrounding boats anchored on all chain. All chain, by virtue of its weight and friction against the bottom prevents a boat from wandering, especially in a windrode situation, too far. Not so if a boat has deployed a significant amount of rode in proportion to chain... This boat is prone to 'sail around its anchor', so far in fact that a collision with surrounding boats anchored with all chain is a real possibility.

[noelex 77]

Originally Posted by Lodesman

I submit that a few degrees difference between 7:1 and 10:1 scope has a negligible effect on the holding power of the anchor. Do you have test data that compares anchor pull to shank angle?

I am not sure why 7:1 and 10:1 are specifically being discussed. The general principle of increasing an anchor's holding power as you let out more rope (or chain) rode, is true irrespective of scope. This is contrary to your suggestion that letting out more rope "does nothing to improve the holding power of the anchor and only increases the diameter of your swinging circle."

The law of diminishing returns starts to take effect at larger scopes and once the angle of gets around 5° the benefits become very slight. So most feel there is little practical benefit over around 10:1 to 14:1 depending on who you believe.

To answer your specific example, several anchor manufacturers suggest the holding power increase from 5:1 to 7:1 is about 15%. I have no way of verifying these numbers, but they seem a reasonable ball park figure to me.

I am curious to understand that while you believe "a few degrees difference between 7:1 and 10:1 scope has a negligible effect on the holding power of the anchor". You nevertheless feel that the very small change in angle from chain catenary seen in strong wind and moderate depths is so essential.

If anchored at 10:1, which would be reasonable in strong wind, the maximum change in going from rope with zero weight to a hypothetical infinitely heavy chain would be only 5.7° and this theoretical maximium is independent of all factors apart from bottom slope.

Originally Posted by Lodesman

I submit if you have most of the chain off the bottom, you're using too little.

It would be nice to keep the chain on the bottom and the pull on the anchor at 0° relative to the seabed, unfortunately that is just not practically possible in strong wind. This can be shown by theoretical calculations or practical observation.

It is possible in light to moderate winds, but holding in these conditions with a good anchor is not normally an issue.

[ddavis4464]

I see from all the responses that you should have gotten the idea it depends on where you want to anchor. Let me make one other observation. Ideally you should have enough chain rode to anchor with a 7:1 scope. If you are anchoring in 85ft of water that is a lot of chain. In twenty feet of water it would be 140ft. You can add a rope tail if necessary to anchor in deeper water on the odd occasion, it will not drag the bottom but remain on the catenary. Often you need to size your chain so that bow can handle the weight of the necessary chain. The minimum size chain can be imputed by estimating the wind profile of the boat and then computing the forces at say hundred miles per hour. Get all that right, with a big anchor 2# per 1000 of displacement and you'll be good to a cat 3. Good Luck. Danny

[Cheechako]

Originally Posted by Wrong

There's plenty of good advice from experienced boaters in this thread. However one issue not mentioned is the hazard a boat using lots of rode presents to surrounding boats anchored on all chain. All chain, by virtue of its weight and friction against the bottom prevents a boat from wandering, especially in a windrode situation, too far. Not so if a boat has deployed a significant amount of rode in proportion to chain... This boat is prone to 'sail around its anchor', so far in fact that a collision with surrounding boats anchored with all chain is a real possibility.

Yeah, good point. Let's face it , all chain is best, but others arrangements are doable if done and maintained properly.
The pictures above of chain against rock and coral are very typical, but even 100ft of chain with nylon backup will likely solve that issue most of the time.

[wsmurdoch]

Originally Posted by Lodesman

Do you have test data that compares anchor pull to shank angle?

Earl R. Hinz, "The Complete Book of Anchoring and Mooring", 2nd Ed.

p 99, Fig 5-3 titled "Effect of scope on anchor holding power for the all-rope rode."

Rope anchor rode scope, Holding power efficiency-percent; 2:1, 17%; 4:1, 56%; 6:1, 72%; 8:1, 79%; 10:1, 86%; infinite, 100%.

p 97, Fig 5-1 titled "Anchor lead angle effects."

Rode lead angle, Relative holding power; 0 deg, mud 1, sand 1; 4 deg, mud .8, sand .6; 8 deg, mud .7, sand .45; 12 deg, mud .65, sand .4 .

(both graphs read by eye.)

The data comes from R.J. Taylor, "Interactions of Anchors with Soil and Anchor Design", p 20.

https://archive.org/stream/interacti...e/n49/mode/2up

[Stu Jackson]

It's not likehere haven't been entire books written about this stuff.

Maine Sail also did a great writeup about anchor scope.

And a friend of mine who crusied from BC to Mexico wrote this:

with 100ft of chain. The rest of the world can debate all they like. When I pull into a place like Bodega Bay at midnight and the fog is so thick I can't see the jetty 50 feet away to make an entrance, I drop my hook in the rolling ocean swells with the surf crashing (Foster says it's like staying in a cheap Best Western beside the highway), and I sleep. And in the morning I have a windlass to pull the beast up and I wouldn't trade it for anything. (I also wouldn't add more chain - this works perfectly in 25 to 30 feet of water - you let all the chain out and you tie off nylon at the preferred scope and don't bother with snubbers and chain hooks and all that stuff...)

[Cadence]

Originally Posted by over40pirate

I cruised for 7 years, up and down the US east coast, spending 4 - 5 months each year in the Bahamas. Maybe 1 month total at a dock. A lot of anchoring. At least 1500 times.
I used 3 strand nylon, with 15' of 3/8" chain. 95% of the time used 2 anchors.

Anchored thru 2 hurricanes. Bob, in Block Island, and Andrew in Little Shark river, FL.

Ground tackle worked great.

If I did it again, I would do the same. I believe the stretch, shock absorbing of mostly nylon line (3 strand) is the best for anchoring.

The reason I used 15' of chain (used 20' before) was I got a seal of a deal on 2, 15' lengths of ss chain. Looked new after 4 years.

I guess ideally I might use 30' - 40' of chain.

35' sailboat/ 5/8" rodes

Just what worked for me

A winning combination for the east coast. The three strand hurts less when you need to cut loose a fowled anchor. Also don't need bolt cutters in a pinch. With a fin keel an anchor sally is a must with a rope rode. Even without a fin keel a sally take up shock and increases scope. JMHO

[Bulawayo]

When a regular sailor has an article published some people appear to believe thats it, so & so has said that is what they do and therefore it is now the only solution.
Caveats apply.
What Jim Cate says is also our philosophy; 60m of chain on our main supported by a further 50m of warp.
Number 2 has 30 meters of chain, whilst 3 & 4 have 20 meters each.
2, 3 & 4 are backed by 100m of warp each. Its a lot of weight but also a lot of security.

[adlib2]

Originally Posted by Jim Cate

Re all those responses from folks who say something like "I've anchored on rope for X years and it has always worked fine"...

We have seen a number of boats beached/wrecked when their rope rodes parted due to chafe, coral or rocks, or other debris on the seabed, or even on their own keels. Prior to those sad events, each and every one of their skippers would have made a similar comment to the above.

IMO (based on a lot of years of anchor-out cruising) if you plan to cruise to unfamiliar waters and anchor, an all chain rode is the only intelligent solution. The amount of chain required for general usage is, again IMO, a minimum of around 200 feet, and that with some additional rope rode for the occasional very deep anchorage. In such places (say 75 feet plus) if one gets most of that 200 feet on the bottom the rope portion will not be exposed to chafe (except on the bow of the boat), and thus be reasonably safe.

If you stick to familiar waters where you have local knowledge of bottom conditions, a shorter bit of chain may safely get you through... maybe!

Jim

My sentiments exactly; Having lost an anchor when rope rode parted and washed up on the beach I was lucky to just need to replace rudder, could have been whole boat. I purchased 400 ft chain and never had problem since.

[Lodesman]

Originally Posted by wsmurdoch

Earl R. Hinz, "The Complete Book of Anchoring and Mooring", 2nd Ed.

p 99, Fig 5-3 titled "Effect of scope on anchor holding power for the all-rope rode."

Rope anchor rode scope, Holding power efficiency-percent; 2:1, 17%; 4:1, 56%; 6:1, 72%; 8:1, 79%; 10:1, 86%; infinite, 100%.

p 97, Fig 5-1 titled "Anchor lead angle effects."

Rode lead angle, Relative holding power; 0 deg, mud 1, sand 1; 4 deg, mud .8, sand .6; 8 deg, mud .7, sand .45; 12 deg, mud .65, sand .4 .

Thanks for that. I found a PDF copy of the first book online and downloaded it - good reference, although I believe the data seem to relate to a palm and fluke (Danforth, Fortress) type anchor. I imagine different anchors would have different performance profiles.

[Lodesman]

Originally Posted by noelex 77

I am not sure why 7:1 and 10:1 are specifically being discussed. The general principle of increasing an anchor's holding power as you let out more rope (or chain) rode, is true irrespective of scope.

I just picked a representative figure - 7:1 scope seems to be what many sailors use if they're expecting it to be a bit windy.

To answer your specific example, several anchor manufacturers suggest the holding power increase from 5:1 to 7:1 is about 15%. I have no way of verifying these numbers, but they seem a reasonable ball park figure to me.

Well the book seems to suggest it will go from about 73% to 81% of holding power. A bigger difference than I thought, but still fairly minor in the grand scheme.

I am curious to understand that while you believe "a few degrees difference between 7:1 and 10:1 scope has a negligible effect on the holding power of the anchor". You nevertheless feel that the very small change in angle from chain catenary seen in strong wind and moderate depths is so essential.

The catenary keeps the chain horizontal at the shank, so the anchor produces 100% of its holding power, vice roughly 80% with rode at 10:1, or 73% at 7:1.

If anchored at 10:1, which would be reasonable in strong wind, the maximum change in going from rope with zero weight to a hypothetical infinitely heavy chain would be only 5.7° and this theoretical maximium is independent of all factors apart from bottom slope.

But that 5.7º knocks nearly 20% off the anchor's holding power, doesn't it.

It would be nice to keep the chain on the bottom and the pull on the anchor at 0° relative to the seabed, unfortunately that is just not practically possible in strong wind. This can be shown by theoretical calculations or practical observation.

It is possible in light to moderate winds, but holding in these conditions with a good anchor is not normally an issue.

I'd like to know what theoretical calculations you use?
In my own observations, I've sat out at anchor in over 20-25G30 and never saw my chain go taut, with 160' of 3/8" chain in about 15' of water. When I checked out the anchor later, the 40' of chain at the bottom was still buried, and the next 60' was raking the sand.

[AlwaysFORSAIL]

Anchoring opinions are like ********, we all have one. When discussing anchors we all seem to swear by the one we use then after much discussion or a couple of cold ones will admit to a drag or two. Typically the drag or two is almost always related to limited scope. I try not to anchor in more than 15 feet because I am lazy. I also try not use less than 7:1 scope with chain. Anything left in the locker is a waste. An electric windlass can bring up several feet of 'spare' rode in no time. Comfort on the hook is directly related to scope. 10:1 is very relaxing.

[Orion Jim]

Originally Posted by over40pirate

I cruised for 7 years, up and down the US east coast, spending 4 - 5 months each year in the Bahamas. Maybe 1 month total at a dock. A lot of anchoring. At least 1500 times.
I used 3 strand nylon, with 15' of 3/8" chain. 95% of the time used 2 anchors.

Anchored thru 2 hurricanes. Bob, in Block Island, and Andrew in Little Shark river, FL.

Ground tackle worked great.

If I did it again, I would do the same. I believe the stretch, shock absorbing of mostly nylon line (3 strand) is the best for anchoring.

The reason I used 15' of chain (used 20' before) was I got a seal of a deal on 2, 15' lengths of ss chain. Looked new after 4 years.

I guess ideally I might use 30' - 40' of chain.

35' sailboat/ 5/8" rodes

Just what worked for me

Just wondering where you anchored at Block Island. I visited the cape a week after Bob hit and electricity was still out for the vast majority of the residents. I imagine Block suffered the same fate.

[noelex 77]

Originally Posted by Lodesman

I'd like to know what theoretical calculations you use?

This is a commonly used formula that indicates when the last link of chain will just lift off the bottom:

F= W(L^2 - D^2)/2D

F is the force in Kgf
W is the weight of the rode in water per unit metre
D is the depth + bow roller height (m)
L is the length of chain (m)
There is also an article here:
Scope vs catenary (Rocna Knowledge Base)
It includes this graph showing a graphical representation of the chain (note the horizontal and vertical scales are different). This visually shows there is very little sag or catenary.