No, that's not a bad questions at all. It is a very good question and a lack of undersatanding of anchoring causes more problems than anything else you can do sitting still. That being said:
No. The book is not wrong. In fact, 7:1 can be too little, depending on the winds, tide, seas, etc.
Let me also point out a very common mistake amongst new (and some old) sailors: That is 7:1 from where the anchor comes on deck, so to speak... not 7:1 from the waterline as most people use. Now, that extra 4 feet of freeboard may not make much of a difference when you are in 40 feet of water, but can make a difference when anchoring in 8.
That being said:
You can get by with 5:1 and sometimes even 3:1 on light days and slack tides. But I would not suggest it unless you are vigilantly watching the boat. I would never leave it unattended or go to sleep with that scope. I often call that a lunch hook... though others may have a different name. Much wind at all or current, and you will drag.
You can reduce your rhode by switching to all chain. The theory, as I understand it, is the chain is heavier and lays flatter on the surface which holds the anchor more parallel with the ocean floor. Still, even at all chain (which I typically use). I still run 7:1 unless I am just doing a lunch hook. I think you are based in the northwest? Rocky anchorages? If so, another good reason to switch to all chain.
You commented on swinging into other boats, so let me throuw out a few words of caution and some possible solutions.
1) I have always had the motto 'that the newest to arrive has to match to survive'. In other words, you have to anchor the way everyone else is anchored. This is especially true if you have chain and many others are using a rope rhode or are bahamian moored (explained later). If you let out 5:1 and they are letting out 7:1, you better watch that arc for the tide to switch. If it is tight, ask them what their scope is. I will. The only exception is if they are all anchored with too minimum of a scope for you boat. If you cannot anchor safely for swing, then as far as I am concerned, the anchorage is full.
2) Different boats swing differntly on anchor. In general, sailboats swing the same. Some will have more windage and are affected more by wind. Some will be more affected by currents. NOW, in general, motorboats will swing differently than sailboats are a much more affected by the wind versus tide. Thus, I always try and anchor clear of motor boats because (other than the genny's kicking on at night) they ride totally different on anchor. More than once I have seen a sailboat swing with the current and a motorboat stay still with the wind. Sounds that go BUMP in the night.
3) Good seamanship says it is the responsibility of the last boat not to bump into the others. If they were there first, they are right.
4) In crowded anchorages many people will use a bahamian moor. Annapolis and Chapmans have a better write-up on this than what I can explain, but basically: Drop and set one anchor and let out twice as much rode as needed. Drop a second hook (from the bow, again), and take back in the first rode to the correct amount. Effectively, you will swing in about two times your boat length. (The book shows it as inside you boat length, but that is not reality if you have much scope out).
Hope that helps. Again Chapmans and Annapolis are great gudes and have a place on every sailboat.
Last edited by Cruisingdad; 08-18-2006 at 12:10 PM.