Holding Power - Primary Anchor

From the bow there will be two anchors.  The primary will be the hoss.... a Rocna Model 20 44 lb anchor on 60 ft (maybe 75) of 5/16" G4 HT chain spliced to 200 ft of 5/8" polyester eight-plaite line. The theory being there would typically be some rode out, thus eliminating the need to rig a separate snubber line. On a long scope, say 7 to 1 in 12 to 35 feet of water there would be enough rode out to absorb shock  but unlike nylon not so elastic as to behave like a bungee cord in a strong blow. The rode would be secured to the sampson posts not a chain stopper. On a short scope in 10 to 20 feet of water, the boat would lie to all chain, or almost all chain, with a nylon snubber. The chain will stow down low in the bottom of the sail locker (where many BCC owners install a holding tank) to keep as much of the weight off the bow as possible.


An all chain system excluding the anchor would weigh 300 lbs as opposed to 90 lbs for a 75 ft chain system. The 210 lb weight savings can be dedicated to the monster dual anchor roller assembly with Rocna extensions, Anchor rollers , an upsize from a 15 to a 20 kg model anchor and the bronze sampson posts. "The obvious item to benefit from this weight is the anchor itself – a large anchor upgrade could result in a massive performance improvement, including greater tolerance to short scope anchoring, and still represent a huge weight saving."

The Rocna knowledge base Optimal Rode offers some interesting info regarding anchor rode design, tandem anchor setting ( don't try it unless you have a black belt), cantenary effect (does little or nothing unless you are a deep water anchoring guy), kellets ( throw them overboard) and riding sails (get one). The topic of heavy chain and cantenary versus scope is currently being examined on the BCC owners site. Rocna has very specific views on the subject and even though their conclusions are self-serving they make a lot of sense and appear to be supported by recent tests:.  They say:

“We must examine the anchor's requirements, what it is capable of handling at any given angle of pull and for any given seabed, and how this compares to the forces that can be expected to eliminate most of the catenary curve from the rode.

In the West Marine testing in 2006, anchors around the 15 kg (33 lb) size were tested, with a rode consisting of 1" (25mm) nylon rope with a 20' (6m) leader of 5/16" (8mm) chain. The Rocna was the top performing anchor – Yachting Monthly reported "The Rocna was a powerful, impressive performer in our tests, recording instant sets at multiple 5,000 lb maximum (or near max) pulls at 5:1 scope." The behavior of the rode at these limits of performance were described by SAIL magazine, who commented that "the anchor's resistance produces whirlpools of turbulence [from the test vessel's propellers]... and a bar-tight cable."

So, it is clear that modern anchors are very efficient. Some, particularly the Rocna, also endure high pull angles fairly well, even in poor holding sea-beds. This means that the range of force vectors that the anchor can handle is quite wide, and it turns out that the majority of rode make-ups (at least those that are practical) lose most of their catenary curve well before the anchor is likely to be troubled. Beyond this point (once the rode is effectively straightened), the weight of the chain makes absolutely no difference to what the anchor will do, and the sole factor of import is the geometrical scope.

What does this mean?
The practical consequence of this is that it is not necessary to carry heavy chain merely for the sake of it. Rather, chain can and should be as light as possible, subject to strength requirements. Many boats could lose a large amount of weight by swapping to a lighter but stronger chain, and then investing part of that weight back into a larger anchor. Performance (holding power) of the system is thus substantially improved, while total weight is actually lowered.”