Anchor Rode Weight Bias

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manyboats said:
I'm just say'in those w all chain would be better off w a combination rode of the same weight.

This thread has turned into a forest of details 80% of which are off topic. This is not an accusational statement as I know how easy it is to do. The above sentence in this post is the subject. To bias the weight of an all chain rode well fwd toward the anchor to get a better rode angle. The operative word is BIAS.
Click to expand...


I think that's another broad brush that may or may not be true for a given boat/anchorage/anchor/wind/current/etc., may depend on specific implementation with all the variables just right...

If I had a 300' all-chain rode, let's say 300-lbs just for example... splitting that into a 150' chain segment and what -- 9000' of rope or whatever it takes to make up the other 150 lbs -- buys me what? If I'm anchored in 10' of water in that case, I'm using an all-chain rode, even at 7:1 scope.

Not arguing against a combo rode; that's what we use here, now, for a while. Just think the words "better off" are more specific to the individual circumstances one's trying to solve.

-Chris
 
Ye gods Ranger ... 9000' of ? ...

Put however many feet of line you like or need. By your example I'd leave 100' of chain taking off 200' of the stuff for a 200lb reduction in weight. Spend that 200lbs as a present. First get 200' of line and then you've got 170lbs about to spend on a heavier anchor (much heavier) or a lighter boat or something inbetween. Just limit the weight of all the equipment on board what you need. No more. And if you think the boat's too light then put a bit more ballast in the bilge. However you do it (using this idea) you'll wind up w a better boat.

Speaking of the whole idea it will have a cuttoff point in boat size where the all chain may be better. Or it's limited to gypsy size that is available for chain/ line combination. Either that or one would need to employ a reel winch. Then you could have as many different sizes of shackles, lines and chain as you wish. In one of these two anchor threads I posted fishing boats w reel winches.
 
The "Anchor Buddy"(AB) weight device is not really a catenary, it is designed to be lowered down the rode to a position just above seafloor at low tide. The effect is to cause the rode to lie along the seafloor from the anchor to the location of the AB, reducing upward pull on the anchor from the boat which might otherwise disengage the anchor.
 
Eric,

I have a program that calculates scope required to keep a selected amount of chain lying on the bottom under specified conditions. I ran an example of all chain and mixed chain/rode using heavy chain that weighed the same as all chain. Using the specific example the required scope was 6.4 for all chain and 4.0 for 50 ft. of very heavy chain. Settable below. Your intuition was right on.

Paul


Conditions:
Typical 40 ft .trawler
Wind 27 kts
Water depth 30 ft.
Anchor is set and does not drag. Weight or type does not enter into calculations
Total weight of chain + rode =145 lbs. in both cases
Chain weight is for HT
Scope is calculated so that 6 ft. of chain is lying on bottom. (0 deg. angle with bottom)

All chain 50 ft, chain +rode
Chain length 193 ft. 50 ft.
Chain size ¼ “ ½ in
Weight/ft. 0.74 lb./ft. 2.90 lb./ft.
Total weight 145 lb. 145 lb.
Nylon rode length 0 71 ft.
Scope 6.4 4.0
Tension at bow 370 lb. 370 lb.
 
Paul,
Very very good of you to prove my theory. Are you sure you're right and that there's no mistake?

waddenkruiser on the thread "Anchor Rode Poll" on page 4 offeren a great deal of data on post #69 and 76 that left me snowed in the forest. I tried but just couldn't wade through all his data. I sure appreciated his effort but it was over my head and no one seemed to respond so I thought everyone else was in the same state as I or it didn't add up.

I presented this theory on TF 5 or so years ago but got tired of the baugh humbug response and let it slide. I'm glad I raised the question again. With so many new members now there's a higher level of objectivity and a more receptive attitude toward things new. New ideas and objectivity is the essence of stimulating and interesting forums the world over. Don't go away Paul as I'm sure there's more things down the channel to de-bunk. You are now the official myth buster. Thanks.

I
 
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Clarity does have an advantage. Now explained clearly, I don't think people disagree with the bias theory, but that doesn't mean they think it is worth doing.
 
Hollywood: "One of my pet peeves is a schmuck with a all rope rode that anchors in the middle of a group of all chain rode boats.. and deploys TWICE the length of rode.. then wonders why he plays bumper boats all night as his boat drifts around. All chain is used for a good reason. IT WORKS BETTER CONSISTENTLY! ... "

Here's a little different perspective: One of my pet peeves when deployed with my combination rode, is that an all chain rode boat will later anchor in my swing circle. After the wind switches, I am immediately accused of having a dragging anchor, and then have to re-anchor. This can get ugly at 0200.

I recognize the challenge of anchoring with a combo rode in the vicinity of all chain rodes, but most later-arriving chain rode boaters seem to be insensitive to this issue. And anchoring further from a bay full of chain rodes boats may mean anchoring in another bay. So, it's probably good for everyone.

Anchoring with all-chain rodes at short scopes only works better consistently when everyone else is doing the same, and when weather/current conditions do not cause the all-chain catenary to become minimized.

"Why can't we just get-along?" (Jack Nickelson, Mars Attack)
 
I think the whose right part of it rests on common sense, consideration and good seamanship.
Trollers in SE AK that anchor out every night don't like line roders. Some of them don't seem to move an inch after their ground tackle hits the bottom. They have their favorite anchorages and feel it's their turf.
 
manyboats said:
My talking about using a bigger anchor has always gone along w reducing the chain rode weight by eliminating 3/4 of the chain and using a some bit of the weight saved to increase the remaining chain weight and some to increase the anchor weight.
Click to expand...

I experimented a bit with my previous boat which was 60 tons. The primary was a big 100lb anchor with 400ft of chain.

However, I took the secondary 40lb Danforth-style, attached a fathom of really heavy chain (don't remember the size though) and the rest was nylon. It worked excellent. Never had really high winds to test it in, but I was often anchored just off Newport Beach in heavy swells and rollers.

So I'm following the same principle out here in the Gulf on my 20ft CC with a 22 lb anchor, 1 meter of 3/8" chain and the rest is polypropylene (too many sharp limestone rocks here). Never had a problem in gusty winds to 30 knots.
 
manyboats said:
I think the whose right part of it rests on common sense, consideration and good seamanship.
Trollers in SE AK that anchor out every night don't like line roders. Some of them don't seem to move an inch after their ground tackle hits the bottom. They have their favorite anchorages and feel it's their turf.
Click to expand...

Eric, all the research on this has ben done, and largely you are right. That's why the Anchor Buddy instructions advise running the kellet down the rode until it is about a metre above the bottom. Largely guessed, as you cannot see it, but doesn't really matter, as not that critical - just needs to be near the anchor, as you say.

The heavier anchor is better argument has a limitation which you yourself have advised us you suffer from - it's the hernia factor. That is, impractical. And so, (and you're gonna hate me for this), that is why the all chain rode - or a substantial length of chain on a combined rode - is the best compromise, because the weight in the chain, which, by and large, you never have to lift all at once, but the forces of nature plucking at your boat do, therefore allows lighter anchors to still work well.
__________________
Pete

PS. apologies, but also posted this on the rode type poll thread, but it is actually more relevant here... :D
 
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For the folks that worry about wind shifts and boats with long anchor lines , the use of a stern anchor (led to the bow) is easy to set , low cost and easy to retrieve.

A used sailboat sheet winch mounted astern on which ever side is usually dock side has many other uses.
 
manyboats said:
I'm just say'in those w all chain would be better off w a combination rode of the same weight.
Click to expand...

manyboats said:
Ye gods Ranger ... 9000' of ? ...
Click to expand...


:)

Just meant whatever length it takes to make up the remaining 150-lbs in the example.






manyboats said:
Put however many feet of line you like or need. By your example I'd leave 100' of chain taking off 200' of the stuff for a 200lb reduction in weight. Spend that 200lbs as a present. First get 200' of line and then you've got 170lbs about to spend on a heavier anchor (much heavier) or a lighter boat or something inbetween. Just limit the weight of all the equipment on board what you need. No more. And if you think the boat's too light then put a bit more ballast in the bilge. However you do it (using this idea) you'll wind up w a better boat.
Click to expand...



There are practical limits to anchor weight. Unlike chain, the whole weight of the anchor must be lifted at once. I can only lift X weight by hand, should the need arise, so X minus the weight of about 15' of chain is my practical limit.


Within those kind of practical limits, the difference between the weight of an all-chain rode versus a combo rode is a minor detail for our boat; our hull will never notice.


Like I said, I'm not disparaging the idea of a combo rode, and that's what we use now... but I think your opinion that "those w all chain would be better off w a combination rode of the same weight." isn't true for everyone, every boat, every anchor, every holding ground, every weather situation, etc.


-Chris
 
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Ranger,
For most of our size boats I think the upper half of an all chain rode is a total waste .. as in excess baggage. And excess weight on any vehicle degrades performance and is usually a waste of money. And on lighter boats less than 25% chain has been doing the job for at least 80 years. But now it's a choice. One dosn't need to think he needs 100% chain. But like me you're having ground tackle handling problems so a small high performance anchor w 25' of chain and a combo winch may be in your future too.
 
manyboats said:
Paul,
Very very good of you to prove my theory. Are you sure you're right and that there's no mistake?

Eric,
Yes, the results of the program have been checked and agree with other peoples calculations so I am about 95 % certain that it gives correct results. i notice the table in the second section isn't come through very readable. It looked OK in the preview but got scrunched up in the final version.

I have attached a word file that shows the table more clearly. I can easily run any other example that you want.

Paul
Click to expand...
 

Attachments

  • anchor example.doc
    30.5 KB · Views: 32
manyboats said:
Ranger,
For most of our size boats I think the upper half of an all chain rode is a total waste .. as in excess baggage. And excess weight on any vehicle degrades performance and is usually a waste of money. And on lighter boats less than 25% chain has been doing the job for at least 80 years. But now it's a choice. One dosn't need to think he needs 100% chain. But like me you're having ground tackle handling problems so a small high performance anchor w 25' of chain and a combo winch may be in your future too.
Click to expand...


Might be a waste for some... unless some unexpected circumstance requires anchoring in much deeper water than usual. Given that I can't say that won't ever happen, I prefer the "more is maybe better, sometimes, just in case" approach. (Except for here in our mud.)

Sure, excess weight can be an issue for some boat performance. Reaching "excess" in our case would be a boatload of weight, though. A couple hundred pounds here or there, not so much.

I suspect many use 100% chain because they've thought out their situation and decided that's what's best for their expected circumstances.

Didn't meant to imply I haven't solved it -- for ourselves -- already. Just meant that my planned limit of anchor weight needs to (and does) take into account Plan B in case our windlass craps out... and before I can get it fixed if that were to happen.

So we already implemented all that. Already have a good anchor (~50-lbs worth, and I can lift it by hand if need be), already have a windlass, I can already deal with all-chain if I switch back to that. And I would, if circumstances dictate. Here, all-chain isn't so much required, and it's a pain in the ass to clean the mud out of it... so we've limited the amount of leading chain to about 25'.

But all that aside... I'm only quibbling a bit about the notion that one (combo?) or the other (all-chain?) is by definition always better for everyone, all the time, every instance... I can well imagine you're easily able to pick what would be best for you. Extending that same solution to everyone.... not so much.

-Chris
 
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Most people don't do everything in life that is better for them...they do what makes life best for them.

We have been told by a few...well maybe one...that we should get rid of our boats and buy smaller when we sweat a little fuel consumption....

Well here we are with the shoe on the other foot.

Just because I look for a way to save a bit of fuel should not result in me buying a different boat...neither should I change rodes because one pet theory that does hold a bit of water...even if immeasurable in most situations....mandate that I change my anchoring habits.

The most useful suggestion here would be a poll to see if everyone agrees with the pet theory...and let it go...it won't change 99% of the experienced cruisers habits anyway...they know better.
 
Thank goodness for the windlass. Regardless of the rode's construct, there are occasions in not-so-unusual strong winds and current where I couldn't pull in the rode by hand by myself. For the non-reel windlass, it's less troublesome when the rode is uniform its entire length.
 
That's a good point Mark. And if I ever used one that would be the reason. But w more challenging anchoring like Alaska you'd be better off adding quite a bit on line.
 
Scott you can do whatever you want.
 
Ranger,
Good points. For anybody w a trawler that's not huge the upper half of an all chain rode is better spent elsewhere .. so why not do it. There's no reason why not. Unless you don't think the splice is acceptable or if you want to be a member of the old salt traditionalists club. I ain't gonn'a change .. been doing it this way for eons and it says it's best in these here six books. And all the old salts on my dock use all chain. So one can have reasons to use all chain .. but none of them are objective.
 
Paul,
Very good again but I was assuming your confidence would be closser to 100%.
A lot closser than my guess though.

Yes some pics look different after I post them and I always size them down to less that 1 kb. I'll PM you more.
 
I am far from a traditionalist...accept the fact while you have a good point...it doesn't trump what other people want out of their total ground tackle package.

Just like other pet ideas like what kind of boats people should own...the idea stops with the owner or any others that may accept it. Other with their OWN set of ideas and experience will make up their own minds.

It has nothing to do with good old boy traditionalists...it has to do with others having their own more than adequate brains to do what they have been doing well for a long time.

YES....weight at the anchor works better..... SO WHAT!!!!!!!!!!!!!!...it doesn't affect us in the slightest.

I am starting to wonder if these threads are serious or like the other so popular whimsical threads.
 
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Eric is correct as far as his physics is concerned. In the example I calculated for him, 193 ft. of ¼ “ HT and 50 ft. of ½ “ HT weigh the same. Using the 50 ft. of 1/2” with the rest nylon rode provided a significant reduction in scope over the all chain, while keeping the chain angle at the anchor at 0 deg. However, would I use this setup? I think I would not for the following reasons.

1- With the mixed rode-chain, adding a 55 lb. anchor to the 50 ft. of ½” chain gives a total weight of 200 lbs. This is a lot to lift if your windless dies.
2- You lose the shock absorber effect of all chain.
3- You lose the abrasion resistance from rocks and coral that all chain provides.
4- My windlass doesn’t easily transition from chain to line. Now I can do everything with a switch in the pilothouse.
5- The 200 lb. load and the requirement for a ½” chain wheel may require a new windlass.
6- (opinion) 1/2 “ chain is ugly.

Considering the above I will stay with my all chain system even though I agree with Eric.

Paul
 
psneeld,
"pet ideas" ... "adequate brains" .....
Why don't you say something that adds more than acid to a conversation?
 
Paul,
Interesting. Your standard anchor is 50lbs? What is wrong w using 100' of 1/4" chain and 100' of 1/2" line. Or 75' of 5/16" chain and 125' of line? What ever you think is best. The shock absorbing quality of the chain in catenary can be traded for the elasticity of nylon line.
Interesting that you use 1/4" chain. I only recently decided it was strong enough for my 30' boat. But I haven't contemplated a 50lb anchor at all.
A 25% chain rode should lay enough chain on the bottom to deal w typical abrasion .. but that may not extend to coral.
1/2" chain ... yup ugly. But it looks just like 1/4" chain .. only bigger. Still I agree.
If your windlass isn't up to lifting 250lbs I'd be think'in it's wimpy. There is probably a rating on your windlass.
 
manyboats said:
Ranger,
For most of our size boats I think the upper half of an all chain rode is a total waste .. as in excess baggage. .
Click to expand...

I think that"s a totally bogus assumption. Every ounce of weight along a length of a suspended chain contributes to the overall behavior of that length of chain. Every ounce of weight contributes to the curve and weight of the catenary, which in turn contributes to its effectiveness as a shock absorber and how it affects the angle of pull on the anchor.

The weight of the first few links of chain off the bow roller is as important as the weight of the links in the middle of the length with regards to the behavior of that length of chain. It's a combination of a couple of pesky little things called physics and gravity.

What that length of chain does in terms of anchoring effectiveness compared to some other setup is another matter. But to say the upper half of an all chain rode is a total waste is just flat out wrong. If it wasn't there, the chain wouldn't do what it does.

Hell, Eric, even my dog knows this.:)
 
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Ok, I don't know what I'm doing. Given. On a a sailboat in Magnalita Bay on the Pacific side of the Baja, on a 54' Aldin. 20' of water. 3/8" chain and "what I think is a Ronca anchor. I know the owner laid out 5:1 scope. Backed the boat up to set the anchor. Two days later I noticed the boat laying at the same heading, but, the anchor was under the boat! Sand & wind were beating the crap out of the boat along with the chain. A young lad dove & reset the anchor. From what I've picked up here & there, that is sometimes what one must due. Most of my friends in Mexico believe 2 X boat length in chain with added rode. That must be one of those conditions & location things. The common sense in me says "the least the better". So buy a heaver anchor; chain for all conditions; rode for depth beyond the chain; if you screw up, take everything back to the Broker & inform him/she (one must share the blame) that said person screwed up!!! It's more complicated to teach a colt to be tied than dropping a rock in the mud. Each environment & discipline must be mastered to make a top hand. Where's my hat?
 
Paul Swanson said:
manyboats said:
Paul,
Very very good of you to prove my theory. Are you sure you're right and that there's no mistake?

Eric,
Yes, the results of the program have been checked and agree with other peoples calculations so I am about 95 % certain that it gives correct results. i notice the table in the second section isn't come through very readable. It looked OK in the preview but got scrunched up in the final version.

I have attached a word file that shows the table more clearly. I can easily run any other example that you want.

Paul
Click to expand...

I‘ve finished my homework now. It was a nice engineers exercise and I will share the results although I realized that Paul has already given the answer. (Hope you will find additional input helpful.)
Recalculating Pauls data I’ve got exactly the same figures – thank you Paul, it gives me confidence in my calculation.

In the following tables you will find for 5 / 10 / 15 m water depth the maximum holding force and the potential energy stored in the rode, both for ultimate catenary situation (last chain link laying on the ground i.e. slope at anchor still horizontal) and for stiff i.e. straight rode situation (should be avoided).
It might be of interest to compare the data and the trends indicated:

100 m / 330 ft all chain 8 mm diameter, 0,9 lb/ft: High holding force and energy. Reasonable force margin between ultimate catenary and stiff rode, poor energy margin.
Ability to store energy is important if it comes to dynamic load situations! Ability to store energy increases with increasing water depth!

Chain 8 mm + 24 mm nylon rope combos (length 50+50 and 15+85 m): Both with reduced holding forces at same rode length and water depth, especially for the 15+85 m combo. Seems we have to pay penalty if we want to save weight which might not be of interest for typical “recreational trawler” but for sailing yachts.
Ability to store energy might be higher or lower compared to the all chain figures depending on the water depth. But the energy (safety) margin between ultimate catenary and stiff rode is increased significantly - the longer the rope portion the more the elasticity of the nylon is important with regard to energy!
Remark the reverse trend if we have a significant nylon part in our rope: ability to store energy increases in shallow water!

Chain 13 mm, 2,6 lb/ft + nylon, length 30 + 70 m (same weight as all chain above): Outperforming holding force and high energy figures. Reduced holding force margin, but reasonable energy margin.

Summary:
All chain vs. chain of same diameter + rope (reduced rode weight): the combos holding force is reduced at same rode length and water depth.
All chain vs. thicker chain + rope (same weight concentrated near anchor): the combo is outperforming with regard to holding force.
Will I change my all chain setup on our boat? No, …
Click to expand...
 

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  • TF-Combi-50-50-chain-8.pdf
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  • TF-Combi-chain-8-15-85.pdf
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  • TF-Combi-30-70-same-weight-as all-chain-8.pdf
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Just meant that my planned limit of anchor weight needs to (and does) take into account Plan B in case our windlass craps out... and before I can get it fixed if that were to happen.

Plan B could require a float that could hold the weight of chain not on the bottom , as you go have the windlass repaired ?

Or is plan be an emergency manual setup for the existing unit?
 
manyboats said:
So one can have reasons to use all chain .. but none of them are objective.
Click to expand...

I don't understand how you can say that. You mean everyone here who uses all chain does it for no good (aka objective) reason at all? Why would you think that?



Paul Swanson said:
1- With the mixed rode-chain, adding a 55 lb. anchor to the 50 ft. of ½” chain gives a total weight of 200 lbs. This is a lot to lift if your windless dies.
Click to expand...

Might only be that heavy of a dead lift if you're anchored in about 50' of water? Otherwise, some of the chain weight would be taken up gradually, rested on deck as it comes in, etc...

IOW, if you're anchored in 10' with a pulpit 5' off the water, it'd only be a dead lift of the anchor and about 15-17-ish feet of chain all at once... and then it'd get lighter as some of that chain comes in and lands on deck...

-Chris
 
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