1/4"HT vs. 5/16" Proof Chain

[Cheechako]

I would go with the 5/16 for sure. It will last longer than HT which tends to rust quicker also, is heavier and easier to shckle etc.

[MidLandOne]

Originally Posted by Ancora Latina

...But this angle is given by SCOPE! not by the weight of the chain, if you are using a well adapted chain (not a very oversized one) and a « normal » scope, your chain is no longer lying on the sea bed for winds stronger than 25/30 knots...

This common mistake is due to the fact that very few (fortunately) sailors are experiencing winds stronger than 30 knots...

Like Emeraldsea 30 knots is pretty much just a days sailing for us and we expect to regularly anchor in much more.

I can tell you from experience that your claim is false. Furthermore your claim flies in the face of professional anchoring systems design. You have certainly put me off ever specifying for others or using myself one of your anchors.

[Ancora Latina]

Originally Posted by emeraldsea

I'm going with personal experience as well as what generations of fishermen would advise, and in my part of the world the advice is "bigger is better".

Well, different churches, different religions too,

My « gods » are « Mathematics » and not « what generations of fishermen would advise! » and the catenary formula says that the action of the weight of the chain can be considered (with strong winds) as negligible...

João

[MidLandOne]

Originally Posted by Ancora Latina

...and the catenary formula says that the action of the weight of the chain can be considered (with strong winds) as negligible...

In fact the catenary formula says nothing about strong winds, nor even anything about gentle breezes either.

[Ancora Latina]

[quote=MidLandOne;259123]In fact the catenary formula says nothing about strong winds, nor even anything about gentle breezes either.[/quote]

Not really, as the force pulling the chain is fully related to the force of the wind!

[MidLandOne]

The force at the end of a catenary is dependant on the width and depth of the catenary and the weight of that which forms the catenary - that force is nothing whatsoever to do with the wind. That force is there whether there is wind or not.

In the case of an anchoring system, whatever it is being anchored (whether, boat, buoy, etc) will range forward and back so that the depth and width of the catenary changes such that the force at the end of the catenary changes to resist in equilibrium the wind load on whatever is being anchored. It is ALWAYS possible to design a catenary to resist whatever force one wants.

So it is ALWAYS possible to design an anchoring system based on a catenary for the maximum wind load and the range of depths of water wanted to anchor in such that the part at the bottom does not lift beyond the pull out angle of the anchor for the load. So it is totally incorrect to say the chain has nothing to do with scope required as you claim.

You will find that those of us experienced in anchoring in deep water understand these things very well. We regularly anchor in 20m plus and unless a catenary is relied upon to shorten scope during heavy winds one will be swinging around within the likes of a close to one kilometre diameter circle much to the dismay of anyone else seeking shelter in the same anchorage. With a well designed anchoring system based on chain it is easily possible to anchor in 60-70 knots and a 3:1 scope in those depths, that even while relying on an older anchor design.

I hope others will give consideration to this before chucking their chain away. I have no more to say on the matter.

[Ancora Latina]

Originally Posted by MidLandOne

.

I fully agree with you when you said:

the depth and width of the catenary changes such that the force at the end of the catenary changes to resist in equilibrium the WIND LOAD on whatever is being anchored.

You can also point out that, with light winds, the chain is lying on the seabed by its own WEIGHT!.. (and there WEIGHT matters and catenary formula doesn’t apply!)

I also fully agree with you when you said:

So it is ALWAYS possible to design an anchoring system based on a catenary for the maximum wind load and the range of depths of water wanted to anchor in such that the part at the bottom does not lift beyond the pull out angle of the anchor for the load.

If you use a very long and very big chain, this is perfectly true... But (by experience ) I’m talking of “NORMAL” conditions of anchoring where you use a chain size and length adapted to your boat, and then it is totally correct to say that the WEIGHT of the chain has nearly NO influence..

You have certainly put me off ever specifying for others or using myself one of your anchors.

Sorry for that, but what do you prefer? A salesman who will accept all what you say to please you or somebody who is trying (hard) to explain the mathematic and physic laws related to anchoring to improve the safety??

João

[MidLandOne]

Originally Posted by Ancora Latina

..Sorry for that, but what do you prefer? A salesman who will accept all what you say to please you or somebody who is trying (hard) to explain the mathematic and physic laws related to anchoring to improve the safety??

Well, you have done the salesman bit, perhaps you should now go and get some advice about the physics.

[witzgall]

Back to the original question. check out this chain/rhode sizing table from West Marine's website:
West Marine: West Advisor

The table is at the end of the page. It seems that our boat would be quite well off with 1/4 ht chain, being 32' and weighing 10k lbs, perhaps 12k with all of ht stuff and people. So that I would think puts her as a medium displacement boat.

It seems that most think I should go the 5/16 route - even if it is proof coil (which I cannot use on the windlass). I will admit that the bigger chain just feels better, but really?

Chris

[emeraldsea]

Originally Posted by Ancora Latina

Well, different churches, different religions too,

My « gods » are « Mathematics » and not « what generations of fishermen would advise! » and the catenary formula says that the action of the weight of the chain can be considered (with strong winds) as negligible...

João

Unfortunately your mathematics will be missing real world variables. Any experienced sailor on here will tell you, all kinds of things happen out there that you didn't add to your equation.

When your waiting out a blow thats stronger than forcast, in a hole with less room then you would like, and the only thing keeping you off the rocks is your ground tackle, you will wish you had the biggest anchor and chain you could have bought.

Find us a book on cruising, written by experienced cruisers that says "when it comes to ground tackle, just get the lightest gear you can, as long as its rated for your size vessel" ......or something to that effect.

I'm sure the original poster will be fine with the smaller chain, but that depends on the type of cruising, and the grounds he/she is sailing.
As was said though the heavier chain will give you alot more life after it starts to wear.

[Cheechako]

I am an engineer and I dont believe you can properly come up with all the variables to simply use your physics. (remember the americas cup boat that broke in half and sank in 15 seconds? I would guess that boat was very intensively "engineered") As I posted in another thread a while back, I have snorkeled the anchor alot in the Carribean. One morning in a steady 30 knots of wind in the tobago keys (42 ft catamaran, lots of windage, clear water and white sand) I had roughly 90 ft of 5/16 HT rode out in 13 ft of water. The chain seldom came out of the sand within 15 ft of the anchor, thus keeping the pull on the anchor very flat. However, this was a situation where the wind was high but the water was flat. Pitching and gusts of wind will snub the anchor up tight at times in other situations. I believe the key is having a rode that can take this shock loading and even more important, having a shackle that can take it.

[MidLandOne]

Originally Posted by Cheechako

...One morning in a steady 30 knots of wind in the tobago keys (42 ft catamaran, lots of windage, clear water and white sand) I had roughly 90 ft of 5/16 HT rode out in 13 ft of water. The chain seldom came out of the sand within 15 ft of the anchor, thus keeping the pull on the anchor very flat...

This has been my experience also with a monohull and several others on this forum have previously made similar observations. It also seems to take a surprisingly strong and sustained wind load to even pull the snakes out of the chain or drag it around in a wind shift. I think the basic problem is that people over estimate the wind load on the boat.

Proponents of no chain often quote Alain Fraysse's site where there is a wind load calculator for sail boats which he derives from a table of typical windloads from ABYC and uses as a basis for his calculations Forces. If one enters ones boat into that one comes up with forces greatly bigger than I and others I have discussed with find in practice. To be fair to Fraysee he does comment that it is difficult to model windload on a sail boat due to all the variables and unknown interactions but he then does go on to use the calculator.

For example, our own boat is a higher than average freeboard, 40 foot sloop with hard dodger and hard dinghy on foredeck. If I enter that into Fraysse's formula I get a wind load of 124daNewton (approx 126kgf) at 15 knots wind bow on. Now I know that I can hold our boat BEAM SIDE ON to the wind by myself while standing on the dock (only just but I only weigh 73kg). I am very sure that there is no way I can resist 126 kgf while standing so the beam on to the wind load is very much less than the calculator gives for bow on and the actual bow on windage is going to be very much less again.

As another example when relaunching a 13 meter sail boat of average freeboard and windage (it did have a hard dodger tho') in wind which was averaging over 25 knots 4 of us (2 on bow line and 2 on stern) could only just hold it BEAM ON to the wind. Now if I put a 13m boat into the calculator for 25 knots bow on I get 393daNewton (approx 400kgf) so for 4 men 100kgf each. Again I doubt if a man standing can resist that and the actual wind load for the boat bow on is going to be very much less again than the beam on case so the calulator seems to way, way over estimate the bow on wind loads.

So it would seem to me that the calculator gives bow on wind loads which are much greater than actual BEAM ON windloads are.

Many claim that chain will be pulled out straight (well almost straight because straight requires an infinite force) - again that is not what I have found in a well designed anchoring system nor have other experienced sailors I've discussed this with. In our own case if anchored in depth so 20m to the anchor roller and with a scope of 3:1 for the chain to be near straight it would enter the water 4m in front of the boat (in our case 1/3 of a boat length ahead of the bow roller). Now I have never seen it anything like that but I confess that I have never bothered to look in the several occasions we have been anchored in 60-70 knots as we seemed to be holding fine and was not very pleasant for going sightseeing .

So getting back onto the original question putting all that together with some of the things others have said (especially the comments as to where the boat will be sailed) I would recommend -

- not using HT as it has a reputation for poor performance against shock loads and poses problems when it comes to regalvanising it.

- if the boat is not required to be independant ie it will always be day sailed or sailed within a short distance of very sheltered refuges then the West table (ie 1/4in) would likely prove fine. Note that the West table states for winds under 30 knots. However, I would still go for 5/16in in order to get away from "toy" sized chain and so as I could use a reasonably sized shackle (the shackle normally being the weakest component).

- if the boat is required to be independant then I would suggest 5/16in is best. As others have said, one will sleep much better.

With respect to using little chain and mostly a rope part to the cable (and it seems the orig. poster doesn't have this in mind) then one has to keep in mind -

- that it is the experience of many experienced cruisers requiring independant sailing that this is a less secure system than all chain, and professional mooring design says the same (allowing for neutral bouyancy rope additions in the case of depth making all chain impractical or uneccessary - we carry 75m of chain and 100m rope, with 75m chain we have never yet had to use the rope in up to a little over 20m of water).

- much greater scopes are needed which means a big swinging radius which one may find is to the consternation of others in the anchorage. It also means that if finding need to anchor in the lee of land for shelter one has to anchor very much further out in case a wind shift has you swinging towards shore, towards other dangers or even towards other boats that have the comfort of anchoring closer in under on shorter chain scopes (having to anchor out often putting oneself in deeper water again and more exposed to the wind one is supposed to be sheltering from so even more cable and swinging clearance from shore needed).

All in my view and sure to be disputed by others, but I hope of some help .

[starfish62]

Formulas are fine. Until the squall comes through at 3:00 in the morning and the anchor pops out and you wake up groggy and wondering why the motion of the boat has changed. Then the chain is really important, as it slows your drag out of the anchorage (and maybe into other boats). Basically I agree with pretty much everything that S/V Faith has opined and disagree with most of what S/V Ancora has said. However, I do live in an area where squalls are very frequent and we get short-lived wind loads of over 50 for brief periods and then back to calms. There is nothing worse than waking up at 2-3 in the morning and having to crank the engine and running forward to get the anchor while wondering where the hell you are and what you are blowing into. I've seen chain wrapped around two coral heads like figure eights and short-scoping a boat that didn't realize it until a big wind came in and then bad things happened. I just know that I sleep better (which is what it's all about) when I have a long length of heavy chain down. 8:1 or better, all chain.

My two cents is to get the biggest chain you can accomodate, use a long snubber and use two hooks if the tide is an issue.

[Benny]

Here's some non mathematical and experience only data on wind force which i am sure some of you have discovered as well. With my then 6 ton 30 foot sloop tied normally to the dock - exposed to the full wind, a 70 knot gale came up and i was concerned about mooring lines so I went out in the blow to double them up. I was able to pull the boat forward easily against 70 knots of wind just standing on the dock to take the strain off the existing bowline while I rigged another to double up. This points to wind not being the problem so much as wave action and it's adherent pitching and yawing thereby causing the weight of the vessel and it's momemtum to be the real concern in the holding power of your ground tackle.

Any experienced sailor will tell you that heavier chain/tackle will slow these movements down thereby lessening the chance that a sudden sideways tortion on the tackle may pull out the anchor. The nylon rode will take up intial shock but when it has stretched under load, it is then that the heaveier chain will slow the motion more effectively than a lighter one. The heavier chain will also tend to help the anchor reset better if the wind and waves change direction and the anchor is dislodged.

Just my non mathematical experience talking.

[Ancora Latina]

Originally Posted by Benny

Just my non mathematical experience talking.

Galileo's championing of Copernicanism was controversial within his lifetime.

The geocentric view had been dominant since the time of Aristotle, and the controversy engendered by Galileo's presentation of heliocentrism as proven fact, resulted in the Catholic Church's prohibiting its advocacy as empirically proven fact, because it was not empirically proven at the time and was contrary to the literal meaning of Scripture.

Galileo was eventually forced to recant his heliocentrism and spent the last years of his life under house arrest on orders of the Roman Inquisition.

Today, they are still people who believe Aristotle theories...


About mooring lines and chain, they are still « conservative » people who are advocating « experience » against « mathematics », but this is just a question of time, Conservative people will disappear and mathematics will stay.

Although I have a HUGE experience in this field, my theories are different and I expect that conservative people will not make an inquision action against me...

João