Re: Anchor sizing


ngtnewington Newington
 

There is an old rule of thumb. For every 9 to 10 ft of boat you need 1/8 inch of chain. So for a 53 ft boat that suggests say 5/8 of an inch chain. 

That rule of thumb was based on the old grade 30 chain. So it would be equivalent to 1/2 inch grade 40. This is the correct size grade 40 chain for a 53 ft sailing yacht. 

The MBL of 12mm galvanised grade 40 chain is 9.6 metric tons. 

The problem is we all want close to 100m of chain in the the locker and at least on my 54 it would not fit, it would also be pretty heavy in the bow. Just where you do not want it.

So most Amels cruise quite happily with 10mm chain, grade 40. This chain has a MBL of 6.7T. This is of course adequate and acceptable, but it certainly is not over engineering!!! It is what Amel specified.


I have chosen to upgrade to 10mm Grade 70 chain with a MBL of 11 Tons. It is slightly more expensive than grade 40 but twice as strong.

When thinking about the possible forces exerted on a yacht at anchor, it is not just the windage which is the surface area exposed to the wind and of course the square of the wind speed, but

there are sheering and snubbing shock loads to consider and also the action of waves. 

In addition we are all quite rightly moving towards these super high holding power anchors like the Ultra and the Spade, Mantus, Rocna etc. These anchors when well set do not budge even with several tons of load.

If anyone is interested there is a great web site coxeng.co.uk which is full of really useful technical information including tests of chain and connectors and shackles….formulas etc.

All the best 

Nick
S/Y Amelia AML 54-019

On 19 Sep 2020, at 01:28, Germain Jean-Pierre <jp.germain45@...> wrote:

Hello Victor,

As you own an SM, a 10 mm chain is vastly sufficient.. even a G70 grade 8 mm chain is overkill.

There are 3 grades of chain G30 (lowest grade), G40 and G70.  G40  is the grade installed by Amel.  As a suggestion, we have a 35KG Ultra with 100 meters of G40 grade 10 MM chain.  (We have been aboard 24/7 since July 15 and it never dragged. There is an additional 50 meters of 3/4 inch nylon line attached to the chain.  In the Pacific, you will encounter anchorages where the water is 35 meters....

Weight is also a factor in the choice.  Good luck and enjoy your Amel.

Jean-Pierre Germain, Eleuthera, SM007, Opua, NZ




On 18 Sep 2020, at 21:50, VICTOR MOLERO <victor.moleroxx@...> wrote:


This is a very enriching thread. Thank you all for such valuable information. I am also about to change my 30 kg. Wasi for either a Mantus 48 kg. or an Ultra in my SM. But I see no one talking about the size of the chain (not the length). Do you recommend 10 mm or 12 mm. My first idea was going for a 12 mm. but I fear it might be too heavy on the bow. The other option is to keep my current 70 m. 10 mm. Inox chain with a 30 meters line.
Any comments about this will be more than welcome.
Thanks in advance.
Victor 
Alendoy SM#314

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