Join Date: Feb 2012
Location: New Orleans Louisiana
Thanked 78 Times in 74 Posts
Rep Power: 4
Re: Caternary & Chain...
This whole issue is one that has gotten some conversation on another forum, and I still stick by the fundamental premise I came to there which is that. "Pound for pound, additional weight in the anchor increases holding power faster than weight in the chain." Assuming this premise is true, and there is a lot of justification to believe that it is, then best practice would be to move as much weight from the chain to the anchor as possible.
In reality most cruisers carry anchoring systems that were designed decades ago when electric windlasses were expensive and very rare. With modern handling equipment the small anchor + lots of chain model, is incredibly inefficient requires carrying a huge amount of excess weight and provides minimal holding power. All in all this system is really due for a rethink.
Modern anchors generally create 40lbs of holding power or more for every pound of dead weight they have. While chain generates about 1lbs of holding power for every pound of weight. This massive difference is because modern anchors are incredibly efficient at converting their weight into holding power, while chain really adds nothing but dead weight.
So when we consider the 'average' anchoring system on a 40' cruiser what do we find? Typically a 60lbs primary anchor and 300' of 3/8BBB chain weighing in at 1.7lbs/foot. Then a secondary anchor of a slightly smaller size and the same amount of chain used to increase holding power in storms. A perfectly reasonable and reliable system... Until you consider that when it's all added up this system comes out to 1,070lbs of chain and 120lbs of anchor. Even while we know that anchor weight is much more important that chain weight.
Instead of this, my recommendation is to
1) get rid of the second anchor entirely, saving over 500lbs in weight alone
2) switch from 3/8BBB to 1/4 Grade 70 chain which will save 290lbs
3) Get rid of the 60lbs anchor and get a 120lbs one
All in all this saves 725lbs of weight from the bow of the boat, puts the weight where it matters the most, and puts an anchor on the boat that will hold thru anything. Heck it's heavy enough that it could work as a deadweight anchor in calm conditions. The only trick to this is that it pretty much requires an electric windlass, without one you would need to stick with a traditional system. But amazingly enough not a huge windlass, the Lewmar 1000 would easily handle this system.
Evan assuming you wanted to keep a completely separate anchor for some reason, switching to 1/4 G70 chain alone would save enough weight that you could switch to twin 120lbs anchors and still save weight.
Just as a btw, Steve Dashew on Windhorse (a 78' powerboat uses a 120lbs Ronca on 3/8 G70 chain).