Anchor Scope Illustrated

Good link from Compass Marine to help visualize (for those of us that need it) what's going on way down there in the briny deep whilst anchoring;

Anchor Scope Illustrated Photo Gallery by Compass Marine at pbase.com

MurrayM said:

Good link from Compass Marine to help visualize (for those of us that need it) what's going on way down there in the briny deep whilst anchoring;

Anchor Scope Illustrated Photo Gallery by Compass Marine at pbase.com

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Thanks for the link BUT I hope its does not start another long ANCHOR DISCUSSION!

Phil Fill said:

Thanks for the link BUT I hope its does not start another long ANCHOR DISCUSSION!

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Why, the possibility never once entered my mind

MurrayM said:

Good link from Compass Marine to help visualize (for those of us that need it) whDt's going on way down there in the briny deep whilst anchoring;

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Damn good post! It really illustrates the folly of too short a scope.

I thought a 5-1 scope was a 10' depth (bow roller to the bottom) and 50' horizontally from directly below the bow roller to the anchor. I'll bet Chapman spells that out.

Also I thought somebody established that under extreme conditions a chain rode would loose all the catenary. I tend to agree w the OP here. I think Marin got that straight out chain rode stuff from that Rocna guy Smith. That should discredit it right off the bow for me. Wouldn't be hard to prove or disprove though.

Phil Fill said:

Thanks for the link BUT I hope its does not start another long ANCHOR DISCUSSION!

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Ooohhh...don't be a party pooper Phil. We haven't had a rigorous anchor stousch for ages.

manyboats said:

I thought a 5-1 scope was a 10' depth (bow roller to the bottom) and 50' horizontally from directly below the bow roller to the anchor. I'll bet Chapman spells that out.

Also I thought somebody established that under extreme conditions a chain rode would loose all the catenary. I tend to agree w the OP here. I think Marin got that straight out chain rode stuff from that Rocna guy Smith. That should discredit it right off the bow for me. Wouldn't be hard to prove or disprove though.

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My Chapman's...pretty old now...shows scope as a ratio between rode length against water depth plus height to attachment point. That's because you can't really measure the distance from the anchor to a vertical under your bow along the bottom....

As far as the chain going "bar" tight...there are some reasonable thoughts on that...but none ever seem to stay above the roar of the "mindless internet crowd"...some of us "add" our own anchoring adaptations that never seem to get heard and absorbed into "others" thoughts on the subject.

I'm an all chain guy like many experienced cruisers. I have my reasons and "tweaks" to make it work for me.

About the OP and link...great job in showing "disbelievers" in living color the effects of scope. Granted, in the dynamic world that doesn't exist in his pictures, there are many more concerns with anchoring that hopefully cruisers study and overcome them through experience and sound judgement.

"My Chapman's...pretty old now...shows scope as a ratio between rode length against water depth plus height to attachment point. That's because you can't really measure the distance from the anchor to a vertical under your bow along the bottom...."

Chapman is good enough for me and like you say much easier to deal with. The difference is fly stuff anyway. Not the substance of a decent argument.

Excess chain (more than 25-40') is better spent on the anchor .. go figure.

Experience probably tells one how much they need or don't need.

And if experience = chain I'd probably have quite a chunk of it and my experience is that I've never dragged an anchor. Hmmmmmm

The majority of all chain cruisers don't think the weight of the chain is all that big of a deal in deciding for all chain...it's been said thousands of times.

Most cruisers have a size, two sizes or even bigger anchors than recommended so arguing the chain is best placed elsewhere pretty much explains the point I made in my last post...here it is again...

"there are some reasonable thoughts on that...but none ever seem to stay above the roar of the "mindless internet crowd"...some of us "add" our own anchoring adaptations that never seem to get heard and absorbed into "others" thoughts on the subject."

We can all argue the deatails of the perfect anchoring system until the cows come home. There are so many variables in the sea bottom, anchor design, weather conditions, etc.

But if someone needs an internet link with pictures to understand the fundamental concept of why more scope is better, then it makes me wonder........

HaHa and there's no sign of cows on the horizon.

And I'll never argue that more scope is not better for maximizing holding power.

But if you had 300lbs of chain and a 40lb anchor isn't it obvious that a 100lb anchor and 200lbs of chain would deliver far better performance?

The illustration show that a rode more than 5 does not change the angle much. At 5 its 10 degrees and at 8 its 6 degrees. So if weight is a concern then having a bigger/heavier anchor might be better than more rode. However, the bottom type and condition are important factors which will be a factor as to the type and size of the anchor. The best illustration I have found is

Synthesis

So did I open the can or worms again!

manyboats said:

HaHa and there's no sign of cows on the horizon.

And I'll never argue that more scope is not better for maximizing holding power.

But if you had 300lbs of chain and a 40lb anchor isn't it obvious that a 100lb anchor and 200lbs of chain would deliver far better performance?

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Taken to an extreme...no...both would be overkill for a dingy...and especially for a dingy owner that watches the weather closely and ties to a secure dock when practical.

Thus the eternal discussion...no one is ever on the same sheet of music in these internet debates on anchoring.....so defend what you prefer ...but saying one setup is better than another (in principle not necessarily a side by side comparison for a specific vessel) is what it always is.....

manyboats said:

But if you had 300lbs of chain and a 40lb anchor isn't it obvious that a 100lb anchor and 200lbs of chain would deliver far better performance?

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Why must it be either or?

Take 300lbs of chain and 100lbs of anchor if it helps you sleep better at night. My little boat is perhaps the only boat on the forum that would feel the extra 100lbs of weight anyway.

Edit: Sorry, 60lbs.

AusCan said:

But if someone needs an internet link with pictures to understand the fundamental concept of why more scope is better, then it makes me wonder........

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Fundamental concept was understood...found it interesting to actually see the diminishing returns as scope was increased. Hard day at work or something?

CPseudonym said:

Why must it be either or?

Take 300lbs of chain and 100lbs of anchor if it helps you sleep better at night. My little boat is perhaps the only boat on the forum that would feel the extra 100lbs of weight anyway.

Edit: Sorry, 60lbs.

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My comment wasn't a recommendation but an example to prove my point. I have a friend w a Willard 30 that has a 65# Forfjord so a 100# anchor on a 40' trawler isn't "extreme". And it's doing some good.

The only reason for all chain is to reduce radius swinging at anchor, you don't trust the required splice for the combination rode or the REEL winch is not yachty enough for you.

manyboats said:

My comment wasn't a recommendation but an example to prove my point. I have a friend w a Willard 30 that has a 65# Forfjord so a 100# anchor on a 40' trawler isn't "extreme". And it's doing some good.

The only reason for all chain is to reduce radius swinging at anchor, you don't trust the required splice for the combination rode or the REEL winch is not yachty enough for you.

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If you feel that is THE ONLY REASON for all chain...WOW!!!!!

The main reason is probably just to help the anchor set. Once it's set and if the rode gets straightened out in a big blow loosing it's catenary there's not any reason or benefit for having chain in your rode as far as holding power is concerned. But of course there is swinging room, convenience ect ect.

Maybe benefits beyond just holdng? Like almost no chafe to worry about, easy retrieval (if that what you are set up for), short scope in moderate to light conditions, etc..etc...I bet people have posted dozens of advantages (at least to them)...that's what I mean when I say sometimes facts are lost in the din of internet posting.....

Sure FF has a point that having coiled nylon on deck is light and easy to take care of and doesn't smell...but if you are going to stow your gear in an anchor locker...I'll take chain every time...

I could go on forever...but that what these threads do anyway...so I'll make dinner instead.

But to say there's only one reason for chain is just an unbelievable statement.

Somebody has a lot of time on their hands!

manyboats said:

The main reason is probably just to help the anchor set. Once it's set and if the rode gets straightened out in a big blow loosing it's catenary there's not any reason or benefit for having chain in your rode as far as holding power is concerned. But of course there is swinging room, convenience ect ect.

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but but but even if the chain is straightened out gravity still sucks. The weight of the chain is still there , just no spring left.

OFB said:

but but but even if the chain is straightened out gravity still sucks. The weight of the chain is still there , just no spring left.

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And that actually reduces holding power as it puts tension on the chain and your anchor is more likely to break out. You want that anchor to be resisting the pull of your boat in the wind not to hold up chain.

Once again...the bar tight argument...If you are anchoring in conditions where the chain is bar tight (which are conditions that are probably chaffing through your nylon at an alarming rate) without a long, adjustable snubber...or safe at some dock like I always seem to be...then you deserve to be dragging your anchor...

How can the same misguided argument persist forever....if your chain is bar tight...probably so would be a synthertic rode ....and most cruisers employ a snubber that takes the shock...the biggie is that a cheap snubber is chaffing and not your expensive synthetic rode.

Unless you are the one in a thousand cruisers that actually employ great chaffing gear.

Don't lecture me on how many DO employ good chaffing gear...remember I'm in the salvage business and profit from boaters who have chaffed through their "great" chaffing gear.

manyboats said:

And that actually reduces holding power as it puts tension on the chain and your anchor is more likely to break out. You want that anchor to be resisting the pull of your boat in the wind not to hold up chain.

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Are you implying that in this situation a nylon rode would be better than an all chain?
If so, I'm interested in learning why. I realize that it may be a long explanation and don't expect you to spend a lot of time explaining it to me, so is there somewhere on the internet that you know of that I can reference?

Well let's hear it. In a 50 knot blow does the catenary get pulled out or not. I thought we as a group decided it did. I personally don't think so but if it pulled straight enough so very little catenary was left one could call it "bar tight". If there was 1/16" of catenary the angle of pull would basically be straight so the 1/16" isn't worth talking about. As I said this whole "bar tight" thing came from the Rocna Smith guy so ????

psneeld,

I use a bridle and several people on the docks have said it's one of the best ones they've ever seen. This has given me a sense of confidence when anchored.

However, your comment about a long, adjustable snubber got my attention. Do you have a picture or a website I can refer to? I may be interested in changing my set-up

Also, I have chaffing gear, but I don't have any idea whether it's great or not. Can you give me reference on that also?

Nsail said:

psneeld,

I use a bridle and several people on the docks have said it's one of the best ones they've ever seen. This has given me a sense of confidence when anchored.

However, your comment about a long, adjustable snubber got my attention. Do you have a picture or a website I can refer to? I may be interested in changing my set-up

Also, I have chaffing gear, but I don't have any idea whether it's great or not. Can you give me reference on that also?

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No websites , just experience.

I use a single snubber and not a bridle...but that may change. The concept of adjustable is that the leg(s) are long enough that if you had to sit out a blow...you could keep letting out a few inches per hour(s) so the same part isn't working the same chaffing points...let out a few links of chain too.

For chafe I just use clear vinyl tubing that the line easily slides within...just use a tie wrap to secure it in the strands of 3 strand. They break but I just replace them...duct tape if they break in a blow and you need to secure the hose.

As a trawler guy who will probably never really sit out a blow at anchor (just too good enough WX info here on the East Coast) all this talk of bar tight and 100 pound anchors just makes me smile...now If I was back in Kodiak, AK and worried about Williwaw..then yes I would have a 120 pound anchor...still all chain...and rig several snubbers when expecting the worst...but even then I would be headed for safe harnor if Williwaw conditions were forecast.

Got it. And, thanks for the reply.

My bridle is pretty long, so I would be able to adjust it.

It's amazing how any aspect of anchoring can get peoples panties in such a knot. Must be because the variables are essentially infinite. Then again, heated debate is understandable when considering the advice I got from a fellow today who said, "Just let out 20% more line than how deep it is. So, if you're anchoring in 70 feet, let out about 90 feet of line. Also, clip a 10 pound weight near the end of your chain...that'll keep the anchor down".

Nsail said:

Got it. And, thanks for the reply.

My bridle is pretty long, so I would be able to adjust it.

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Most of the time chafe adjustments are in inches... so as long as you don't let chafe get out of hand...you can just keep feeding it out a couple inches hopefully every half hour to hour....