Re: Anchor sizing
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.toggle quoted messageShow quoted text
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
S/Y Amelia AML 54-019