This may be a dumb question, but what do larger vessels do about snubbing an all-chain anchor rode? For a smaller boat, standard procedure after setting the anchor is to attach a nylon snubber to the chain and pull the chain up a few feet so the nylon takes the shock loads.
I have never seen a ship do anything like that and it probably isn’t even possible to do. So, what does absorb shock loading? Is the chain heavy enough that the catenary takes care of it? Is it all strong enough so it just doesn’t matter? Does the windlass have some function to absorb shock loading? Do ships just up-anchor and leave if an anchorage gets too rough?
I anchored a small coastal cargo boat once with no snubber, but it was flat calm and I totally forgot to look around to see if there even was one, it was not obvious if one could be rigged and the skipper didn’t mention it.
The weight of the chain acts as the shock absorber, if its rough, let more chain out. You will likely drag anchor before feeling any sort of shock.
Now, this next part varies based on the opinion of the captain, but from what I’ve read, the design theory for a ground tackle system is that the windlass brake is supposed to slip before you reach the breaking strength of the chain. Lots of folks like to put the paul down, which is a big bar that wedges up against the chain making a mechanical brake. This obviously will prevent the brake from slipping, and if you need to pay out more chain in a hurry you may not be able to if the chain is jammed, and there may not be enough torque to bring the chain up a little bit to clear it. This also prevents the anchor chain from running all the way out if the brake keeps slipping and no one notices. But even then, the bow fittings should be built with a safety factor to exceed the breaking strength of anchor chain.
A slipping windlass brake is definitely pucker factor 10 on the oh shit scale.
I have yet to see a commercial vessel anywhere use any kind of a snubber or shock-absorption system on their anchor chain, other than the catenary itself.
The weight of 76 mm stud link anchor chain is listed at 135 kgs / meter, it wouldn’t be practical to rig any kind of snubber.
The best option is to avoid anchoring if the forecast is for unfavorable weather. Second best is to heave up and leave the anchorage if weather deteriorates but before weather conditions make it difficult. Best to avoid having to heave up in unfavorable conditions, especially in an off-shore anchorage exposed to swell.
Ships loose anchors at the rate of around 1 case per 100 or 200 ships a year, traditionally a safety factor of 4 to 1 was recommended.
What is the most common cause of losing the anchor?
From a DNV article:
What about paying it all out to paint the chain? That’s gotta be at least one a year 
Ok, but what do those categories mean? What does “weather” mean? Something broke, even though weather was the root cause.
I don’t know. As chief mate we parted a chain off St Paul Island in the Bering Sea from overstrain in a swell, I was on the bridge at the time. I was on the bow when we parted a chain anchoring at the entrance to Chesapeake Bay. In that case the link that broke showed evidence of having partly failed previously.
It’s possible to do it with hydraulics, but considerably more expensive. The added complexity would outweigh (ha!) any benefit.
Weather in this context means excessive environmental loads, wind/waves/current.
I have dived on a few anchors on cruise ships and a few coasters just for interest.
The anchors where standing up with a huge pile of chain over them like in an anchor locker.
The cantenary effect put lots of chain on the bottom and slowly the chain led up to the ship although whipping around.
This is in 25kts of wind, sandy bottom.
Seen a few with where the 2 points on the anchor drag along and never set as the solid part at the rear prevents them from biting in. A big dump of chain further on is what was holding the vessel in each case.
Anchor does nothing, chain does everything. ( except in mud)
They dont anchor rigs with an anchor design used on ships do they???
There a thread here somewhere where we did the calculation. The holding power of a 8 ton AC anchor is approximately equivalent to 20 shackles of chain.
Sure but most times you anchor your sitting on the chain and the anchor is not pulled in.
I was gob smacked when I dived on a cruise ship in a breeze and it was only sitting on the chain.
Its was in about 30 metres of water.
No they don’t. Bruce anchors are used for oil rigs. They used to make scaled down ones, I snagged a Bruce for my boat and it works fantastic.
Mine is an earlier iteration and bit smaller, it fit in the back of my car. They got driven out of the small anchor business when cheap knockoffs showed up from China. They suck, but they’re cheap 
got a photo of a scaled down one with that design that would fit in yout boot?
I have a baby version of that anchor for my stand up paddleboard.
230gram Cooper Anchor no chain, just more than 7:1 scope and it hold decent in loose sand and mud. Not sure id anchor my paddleboard and take a nap on it, but good enough for fishing in the wind and current.
The truth of the matter is anchors are in fact designed to dig in, and just because you found a couple where the mate piled it all on the bottom instead of having it laid out across the bottom does not mean its the norm.
I dont have the book on hand to dazzle with formlas and vectors, but the Nautical Institute’s mooring and anchoring of ships has a lot of interesting anchor info.
At the end of the day there is no perfect anchor for every condition, the best angle for the flukes varies by about 10° between various bottom types, but your standard stockless anchor usualy compromises at like 37.5° i want to say.
agreed little anchors for pleasureboats work.
whole different story with bigger commercial vessels.
I have also seen where a typical stockless wouldnt dig in as the sand bottom was very hard and it just dug 2 furrows. Was maybe a 500kg anchor?
imho as pleasure boats rely on the anchor the designs are much more effective.
The poorly dropped anchor was a perfect example with the crusie ship in about 25kts was only anchored on the chain. Didnt need the anchor with only that load.
Guessing, in the US New Orleans has more lost anchors than any other place. Probably more than any port in the world. Recovering & untangling anchors thriving business there.
The yachties like to discuss this endlessly but in my experience which anchor to use comes down to choice of port or starboard.