Its a very important thing.
I look at the rules and laugh. ...reality is often different from consider advice.
whats the minimum chain you would put out for a 30ft most beloved yacht in good conditions.
I guess tbe deciding factor is the size the lagoon 
I have found that in shallower waters a scope ratio of 5:1 in 2 m depth, ie 10m is just not enough to cover higher than normal conditions as in more than 20 knots wind in a safe haven.
What worked for me in a poor holding sloppy mud bottom was 23 metres of chain on a 30 pound Manson Plough for a 30 foot, 4 ton yacht. That is around a 10:1 scope.
I guess the general rule is that you can never have too much scope out.
2 meters depth plus a couple of meters of tide plus a meter and a half height of the bow roller and even at 4 to 1 you need 22 meters of rode. A ten meter boat and your swinging circle is over 60 meters. There are some powerful arguments here for a high holding power anchor.
I would put out 8m of chain because that's all I have. The rode is mostly rope. So the answer to the question is 8m for my 30 foot yacht.
Select to expand quoteRamona said..
I would put out 8m of chain because that's all I have. The rode is mostly rope. So the answer to the question is 8m for my 30 foot yacht.
Nothing wrong with rope and a bit of chain - the catenary theory is a load of codswallop, when you need catenary the rode is bar tight in a blow and there is no catenary anyway. Just enough chain to clear the bommies is fine.
Select to expand quotePhoenixStar said..Ramona said..
I would put out 8m of chain because that's all I have. The rode is mostly rope. So the answer to the question is 8m for my 30 foot yacht.
Nothing wrong with rope and a bit of chain - the catenary theory is a load of codswallop, when you need catenary the rode is bar tight in a blow and there is no catenary anyway. Just enough chain to clear the bommies is fine.
+1
Primary is a CQR with 20m chain and 100 metres nylon. Secondary is a 30lb Manson with 12m chain. The nylon stretches and reduces the pull on the chain and anchor.
Never dragged but has been guitar string taut.
Extra rode is the way most of us use, but next day, quet morning extra low tide and rode is all around you.
Not only look silly but can easily get around the prop. or rudder.
When I anchor, I slide second much smaller anchor /no chain / along the main rode 3 to 8 meters depend on depth.
On low tide, sits on the bottom, on windy and choppy day, cushion the tension .
Depends too on how heavy your anchor actually is and how far you are willing to swing allowing for the tide.
In tight places and good conditions it can be handy to drop a minimum scope (2 or 3 x the depth). On Trek we get away with that quite often. But if you do that at low tide and the later high tide lifts up the anchor chain and you drag its a pain so it works best if you drop it at a high tide knowing that as the tide falls the scope will increase.
If one is determined not to drag at all so let out the lot and the tide/current/wind change then in the morning although the anchor didn't drag you can be floating a long way from where you were in the first place.
We have sometimes thrown a pick off the stern as well as bow both with 2 - 3 times the depth to keep the boat in the right place ie when surrounded by boats a the NYE fireworks in Sydney. That works but when all the neighbor boats swing and we don't it can be a pain too.
No wonder new recruits have a problem. Many times we've seen cruisers pull up near us, they let the anchor out until it touches the bottom then go to their beers. 15 minutes later they're half way down the bay 
Really appreciate that reply trek. Its all trial with hopefully minimum error. The idea of setting on the high tide makes a lot of sense
Select to expand quoteTrek said..
Depends too on how heavy your anchor actually is and how far you are willing to swing allowing for the tide.
In tight places and good conditions it can be handy to drop a minimum scope (2 or 3 x the depth). On Trek we get away with that quite often. But if you do that at low tide and the later high tide lifts up the anchor chain and you drag its a pain so it works best if you drop it at a high tide knowing that as the tide falls the scope will increase.
If one is determined not to drag at all so let out the lot and the tide/current/wind change then in the morning although the anchor didn't drag you can be floating a long way from where you were in the first place.
We have sometimes thrown a pick off the stern as well as bow both with 2 - 3 times the depth to keep the boat in the right place ie when surrounded by boats a the NYE fireworks in Sydney. That works but when all the neighbor boats swing and we don't it can be a pain too.
No wonder new recruits have a problem. Many times we've seen cruisers pull up near us, they let the anchor out until it touches the bottom then go to their beers. 15 minutes later they're half way down the bay
"On Trek we get away with that quite often"
That's scary.
Rocna recommend setting the Vulcan with 5 to 1 scope, then you can come up to 3 to 1. Their Vulcan seems impervious to all the anchoring glitches, wind against tide, veering, overrunning, coming up to the roller upside down, failing to self launch, failing to instantly set. But of course you can still pick up a crab pot so you take nothing for granted.
I have a 45lb Manson with 50m of 10mm chain for my S&S 36. She's 8 ton loaded. I always let out as much as I can as I see no point having chain in the boat. Of course that depends on how much space there is around you but I try always try to find lots of space. I find I sleep better if I'm confident I'm not going to drag 
Select to expand quotePhoenixStar said..Trek said..
Depends too on how heavy your anchor actually is and how far you are willing to swing allowing for the tide.
In tight places and good conditions it can be handy to drop a minimum scope (2 or 3 x the depth). On Trek we get away with that quite often. But if you do that at low tide and the later high tide lifts up the anchor chain and you drag its a pain so it works best if you drop it at a high tide knowing that as the tide falls the scope will increase.
If one is determined not to drag at all so let out the lot and the tide/current/wind change then in the morning although the anchor didn't drag you can be floating a long way from where you were in the first place.
We have sometimes thrown a pick off the stern as well as bow both with 2 - 3 times the depth to keep the boat in the right place ie when surrounded by boats a the NYE fireworks in Sydney. That works but when all the neighbor boats swing and we don't it can be a pain too.
No wonder new recruits have a problem. Many times we've seen cruisers pull up near us, they let the anchor out until it touches the bottom then go to their beers. 15 minutes later they're half way down the bay
"On Trek we get away with that quite often"
That's scary.
Rocna recommend setting the Vulcan with 5 to 1 scope, then you can come up to 3 to 1. Their Vulcan seems impervious to all the anchoring glitches, wind against tide, veering, overrunning, coming up to the roller upside down, failing to self launch, failing to instantly set. But of course you can still pick up a crab pot so you take nothing for granted.
Its not scary if you pay attention to where you are.
Select to expand quoteDexport said..
I have a 45lb Manson with 50m of 10mm chain for my S&S 36. She's 8 ton loaded. I always let out as much as I can as I see no point having chain in the boat. Of course that depends on how much space there is around you but I try always try to find lots of space. I find I sleep better if I'm confident I'm not going to drag
I've got 30m of chain and I do the same Dexport, means I sleep well at night also 
If one deploys tons of chain unnecessarily in good conditions its possible to wind up anchored by a ton of chain piled up on itself rather than the anchor.
One time off NZ on an RORC39 I had at the time my new crew dropped our anchor off the bow without paying it out (by accident) and the lot went out, probably 30m of chain.
He was astounded by how deep it was. Wow 30m straight down. Must be a big hole here! Actually the depth was 5m and we had created a pile of chain on the bottom
