G'day Carlo, Always nice to see someone with a similar morbid curiosity of anchoring and welcome to CF.
One quick thing, If Alain saw you drawing comparisons between a SARCA and Spade, he'd die... err or you would
They are very different and close to being on opposite ends of the holding power graph.
Basically the shorter the length of chain the quicker you straighten it out and once that's happened you have lost
all centenary (as used in anchoring discussions) effect. It is easy to lift
a very short length of even very big chain.
Easy example. Get a 20ft length of 3/8" chain and fix one end. Stand on a 10ft tall box and lift
the other end. You'll be able to straighten it easily. Now get a 57ft length of 1/4" and do the same. You'll find the load required to straighten this will be a lot higher. Both lengths of chain weigh the same. Numbers swapped from metric to that old imperial thing so 'close as'.
Increase the length of a chain by 50% and the load required to straighten it roughly doubles, not quiet but close. The load required to straighten say 100ft of 5/16" is big very big. Also with more scope
you have the loads increase over short scoping. Try the above example at say 3:1 and then again at 8:1 and you'll see what I mean.
So the longer the length the more load the boat has to apply to the chain before it starts throwing it's whole weight onto the anchor. Until you have maxed out the chain it will still be 'bending' so the anchor end will still be providing some horizontal pull on the anchor, all good.
People will argue against that and there is tht spreadsheet thingy drifting around suggesting all rope is best but sadly real life doesn't seem to agree with them/it.
We often get people in here with 'crap anchors' that are not holding only to find they are running short lengths of chain. Rather than swap anchors we add chain and suddenly the anchor is wonderful. The chain added is sometimes only another 20% sometimes more.
Actually SARCA owners are great for this as they actually believed the stupid SARCA recommendations, which are OK in the 10ft deep flat water they anchor in but not so once out of sheltered inland waterways. It's an Aussie thing.
Not to mention we have used heavy gear
and load cells to find out real numbers.
And of course you have the other chain bonus's being chafe resistance, drag thru the water which reduce shock loading and in some bottom types the drag co-efficient of the chain itself is surprisingly high so yet more added holding grunt.
The, mainly US, theory of tiny chains and massive anchors really just doesn't stack up well. By doing this you are basically taking the load off the rode and anchor and transferring it to the anchor. So your anchor is doing a pile more work and the rode's doing less. Why not make both work and reduce the stress's on both is my thoughts. And we are back to my favourite saying "Think System, not anchor only".
We run from a base of 1.5 to 2 times boat length and then tweak to suit the individual situation. Considerations we use are - the anchor, the boat shape style and windage, anchor winch
or not and the biggest wildcard of it all - 'the dick on the stick' known by some as the boat user
For you and the mighty Hartley I'd be starting at 10mts of 6mm and then adding to that if you or we think you should (sometimes we have to gently save the odd owner form them self). Behind that some 12mm warp. And a Stainless shackle to go on the SARCA. Don't use a galv one on the slot, they sometimes jamb up too easy.
The slot on the SARCA amongst many others, is a good idea. It has saved some anchors from spending eternity with the fishes. Not all of them but at least some of them.
ML1 - just work harder yourself. I'm paying for too many lazy bums now, there is 120 of the in Parliament alone
David M - I'd say the 200fter by quite a margin.
Just try the example I used above. Even use a bit rope. Tie one end off and grab it a little way back and pull straight. Then go further back and pull straight again. You should notice it takes a lot more the longer you are from the end. Then imagine the difference with something many times heavier. Maybe tie a brick in the middle to simulate the more weight you'd have with chain.
This whole this is very simple really, how the hell do you think I cope with it otherwise
I think many are just trying to over calculate or analyse it, which makes it look a lot more complex than it really is.