Anchoring - Scope and its importance
It is very important to anchor with adequate "scope".
Scope is the ratio of the length of anchor chain or warp (rode) to the height of the bow roller above the seabed.
SCOPE = (LENGTH of RODE) / (DEPTH from BOW ROLLER to SEABED)
The chart opposite shows experimental data measuring the dependence of %-Hold upon Scope for the 9 kg Knox Anchor.
As the scope decreases the holding power of the anchor decreases more or less linearly with the angle a taut cable would make with the seabed.
What scope should be used?
3:1 for temporary anchoring in calm conditions – 70% of full hold
5:1 a good compromise for most conditions – 90% of full hold
8:1 or more for storm conditions – 95-100% of full hold