Expected load on anchor rode

[B4A]

Hi all,

I'm in the process of changing my anchor chain. I've looked everywhere for the formula used to calculate the expected load on anchor chain for given wind and boat weight, but I only found an old ABYC table where the load is based not on the weight of the vessel but on its length. And there is no mention of windage or Cat Vs Monos.



I have a 40 feet catamaran (light ship 10 tons, max 15 tons). I'm trying to determine what would be the Safe Working Load (SWL) for the new chain.

A G40 galvanized 10mm chain is only rated about 1.2 tons. That would be enough for my boat, according to the ABYC table. Is this chart accurate or am I missing something?

[thinwater]

Originally Posted by B4A

Hi all,

I'm in the process of changing my anchor chain. I've looked everywhere for the formula used to calculate the expected load on anchor chain for given wind and boat weight, but I only found an old ABYC table where the load is based not on the weight of the vessel but on its length. And there is no mention of windage or Cat Vs Monos.

Attachment 253330

I have a 40 feet catamaran (light ship 10 tons, max 15 tons). I'm trying to determine what would be the Safe Working Load (SWL) for the new chain.

A G40 galvanized 10mm chain is only rated about 1.2 tons. That would be enough for my boat, according to the ABYC table. Is this chart accurate or am I missing something?

Oh dear. An anchor thread. Yes, I have a cruising cat.

• The ABYC table is a working load recommendation, not a rode tension table.
• The table assumes no snubber, but you will be using a nylon bridle, reducing peak loads in worst case circumstances (shallow water) by about 50%.
• 10 mm G40 chain has a WLL of 2.4 tons.(About what ABYC H-40 table 1 says for a permanent mooring for 50 feet. Less is required for a storm anchor.)
• The windage on a cat moves you up about 5 feet in length.
• The table you posted is incorrect and out of date. The current tables does not reference wind speeds. The numbers are also incorrect.

(This is 1996, but I checked it against 2008. It has not changed, unless someone has a more recent copy. Where did the image come from?)



So you are more than good. Your actual peak tension at 60 knots is probably about 3/4- to 1-ton (I have measured this on a 34-foot cat or proportionate mass). What is the size of the windlass gypsy?

[piberman]

3/8 hi test US made chain will be sufficient for boats up to the 60 foot range. Smaller vessels can make do with 5/16”. It’s rare for hi-test US made chain kept from rusting to fail. Typically its the shackles/swivels that’s failure prone (China). Remember that’s the weight of the chain in the catenary as the boat rises and falls in the seas that’s important. Not how strange the chain when stretched out tight.

In 50 yrs sailing the globe in boats up to 60’ we’ve never had a chain failure. But we always carried 2 rides 400’ length either of 3/8” or 5/16” and survived more than a few hurricanes. Chain is the Blue Water’s sailor man’s best insurance !

Carrying sufficient chain in 2 rodes is more important than type of anchor. Once the anchor is well set its the changing catenary that holds the boat in place. We like Bruce and CQR’s and for the Islands the biggest Danforth you an easily carry. Remember during the War the 30 lb cast iron Danforths held the landing craft running full speed off the beaches. If the budget can afford it buy a 150 lb collapsible Luke storm anchor and stow it away. One day it will pay for itself. And always carry a spare anchor to help out a fellow sailor whose still learning the “ropes”.

[more]

Originally Posted by B4A

Hi all,

I'm in the process of changing my anchor chain. I've looked everywhere for the formula used to calculate the expected load on anchor chain for given wind and boat weight, but I only found an old ABYC table where the load is based not on the weight of the vessel but on its length. And there is no mention of windage or Cat Vs Monos.

Attachment 253330

I have a 40 feet catamaran (light ship 10 tons, max 15 tons). I'm trying to determine what would be the Safe Working Load (SWL) for the new chain.

A G40 galvanized 10mm chain is only rated about 1.2 tons. That would be enough for my boat, according to the ABYC table. Is this chart accurate or am I missing something?

https://jimmygreen.com/content/217-c...d-weight-guide

but for wind load is more important m2 of area in wind.
mass is important but not important in vave protected area and big wind.

but on wave mass of boat is important.

in reality all this calculation is so dynamic and complicate. but this table up is correct ,except for MED moring and croswind x3 is easy to calculate for mono. for CAT with flying bridge must be calculate how many m2 you have in wind,

[MicHughV]

This is a complicated topic that has been discussed ad infinitum on this forum.
Opinions, statistics, formula's, charts, etc, have been provided to support untold theories. This topic, together with " anchor" selection could generate a 100 pages of comments

There are too many loose ends to give a definitive answer to your question. Everybody has a way " they" like to do things, just as I do. I have my favorite setup, and am unlikely to change, as it works for me and has worked for as long as I've owned a boat.

The few posts above have already given you more than enough information. You need to adapt these to your own needs and wants. Some may require trial and error.

[B4A]

Thank you for posting that table. It's very informative.

I do have a 30kg Spade anchor, and in 3 years and 22K nautical miles across the Atlantic we've never dragged. Not once. Some times it took a couple of attempts to set in some places, but once set, it has never moved.

Most wind we've anchored with was 50 knots in Namibia.

We are considering replacing our 10 mm galvanized chain with Cromox Duplex, either 8 or 10mm. We know it's expensive, but we think it will pay down the road. You never know where you are when you need a new chain, and it's so darn difficult if you're not in US or EU to find good quality chain.

The Superduplex would be nice, but it's almost double the cost of the Duplex same size.

Our galvanized chain only lasted 3 years. The galvanization is gone, and it's starting to rust.

We are not sure what brand is it, it come with the boat.

[GordMay]

ABYC ‘H-40': ANCHORING, MOORING, AND STRONG POINTS, which is where the Appendix, containing those “Working Load Limit Tables” are located, and was last modified in July of 2019, but the tables have not been revised.
The Appendix contains some brief explanations.
Preview ➥ https://webstore.ansi.org/preview-pa...PUB%202019.pdf

A complete 2003 version is available here ➥ https://pdf4pro.com/amp/view/h-40-an...ng-24d459.html

➥ https://www.google.ca/url?sa=t&rct=j...DpC4FJlzB82D-J

[B4A]

Thanks!

[sailcrazy]

Following

[Paul Howard]

I have twice had anchor chain fail on my 39ft. catamaran, both times while in the Beagle Channel of Chile.
First time was with G4 10mm chain in a deep anchorage with a rocky bottom. Lowered the anchor in about 40ft. of depth, running out about 200ft and began to back down, feeling the chain rumble over the rocks. It suddenly jammed in the rocky bottom and whipped taught and snapped. Lost the 20kg anchor and about 50ft. of chain.
Second time was when anchored in Chile, about 20miles north of Cape Horn. Again 10mm G4, new chain and only about 3 months old. The wind blew hard for three days, the Chilean Naval Station on Isla Hornos was reporting winds of 90knots. We were anchored in about 10ft. at low tide, sandy bottom and good holding. When the wind was down to about 25knots we began to bring in the chain with the windlass, myself at the chain locker operating the windlass switch. I watched the chain come in round the gypsy and fall into the locker when I saw a link that that had opened up at the weld, forming a C, rather than a closed 0. As the chain fell into the locker the slack allowed the chain to un-hook from the opened link. We did not lose any chain or the anchor.
I emailed the manufacturer what had happened and they asked that I send them six links either side of the break as well as the opened link so they could test for breaking strength.
I did so and they reported back that the breaking strength was less that it should be, but close enough that it should have held.
They air freighted replacement chain at their expense from Europe to Chile. That chain has been in constant use and remained stable for another 20years in more 'normal' cruising areas and held us at anchor during Hurricane Sandy (2012, New Jersey shore) with winds reported in our area of about 95knots.

[malbert73]

Originally Posted by piberman

3/8 hi test US made chain will be sufficient for boats up to the 60 foot range. Smaller vessels can make do with 5/16”. It’s rare for hi-test US made chain kept from rusting to fail. Typically its the shackles/swivels that’s failure prone (China). Remember that’s the weight of the chain in the catenary as the boat rises and falls in the seas that’s important. Not how strange the chain when stretched out tight.

In 50 yrs sailing the globe in boats up to 60’ we’ve never had a chain failure. But we always carried 2 rides 400’ length either of 3/8” or 5/16” and survived more than a few hurricanes. Chain is the Blue Water’s sailor man’s best insurance !

Carrying sufficient chain in 2 rodes is more important than type of anchor. Once the anchor is well set its the changing catenary that holds the boat in place. We like Bruce and CQR’s and for the Islands the biggest Danforth you an easily carry. Remember during the War the 30 lb cast iron Danforths held the landing craft running full speed off the beaches. If the budget can afford it buy a 150 lb collapsible Luke storm anchor and stow it away. One day it will pay for itself. And always carry a spare anchor to help out a fellow sailor whose still learning the “ropes”.

Agree on importance of good chain. And sizing as you describe sounds right.

But… pretty sure the catenary effect has been well disproven by now.

(And, don’t want to start another new gen vs old gen anchor discussion but I think there are better choices now than what you cite)

[Benz]

There is a new company now making waterproof inline load cells that can sync to a phone or B&G display. Designed for tack line loads on racers, but it'd be interesting for someone to put one on their anchor tackle and experiment with different rode/snubber/boat size configurations for some real-time load experiments. It can graph the results, so one could see the load cycles during a blow.
Sadly, I don't have $3k to spare for one, and embarrassingly, I can't remember the name of the company, though I talked with the CEO just three days ago...
But it would be a neat thing to have for the anchoring nerds out there.

[MathiasW]

My son and I have recently developed a tool to calculate the anchor load stemming from wind and swell. It is based on energy calculations very much like a pendulum, where chain and snubber act as energy storage elements. As Thinwater said, it is not only the chain, but the snubber is a very important part of the system as well. In particular in very shallow water, when the chain does not absorb energy burst from gusts / swell well.

Here is my tool:

Anchor Chain Calculator

One or two parameters need further explaining - there is a document linked to.

You can also try Bjarne's tool, which includes even more effects than mine, but may be a bit more complicated to use:

http://svamanda.dk/anchor/intro

He uses the same model as me, but also includes effects like the actual elasticity of each metal link of the chain.

Cheers, Mathias

PS: If you have a lot of time to waste on this topic My long essay on the topic:
https://trimaran-san.de/die-kettenku...atiker-ankert/ (In English)

[MathiasW]

Further PS:

The extensive discussion on this forum that led to me creating the anchor chain calculator tool may be found here:

https://www.cruisersforum.com/forums...pe-235053.html

And an application of my tool to the shallow water scenario is found here:

https://www.cruisersforum.com/forums...hs-258009.html

Cheers, Mathias

[rgleason]

Mathias AnchorChain Calculator and his help and written information are a great start to understanding the loads and factors imvolvef, so a big thankyou is due to him.

Since I have decided to use largely rope with chain, I found that his app can be used for rope, but is somewhat cumbersome and involved as compared to BjarneK svamanda.ge on line rope and chain calculator which has some very nice features.
See this post
https://www.cruisersforum.com/forums....php?p=3557193

(I have chosen not to carry 170-200 lbs of chain around in my bow for various reasons, the main one being I don't think I need or want it, and it does not help much above 30kn, and our cruising does not merit this weight and expense.) (When we do need it and we are cruising such that it is merited I will add a new 60' piece.)