Anchoring is the skill that divides sailors who sleep well from sailors who do not. Not because good anchoring is difficult to learn, it is not, but because most sailors learn to anchor without learning to anchor well: they drop the hook in a position that seems reasonable, let out what feels like enough chain, and go below without the specific checks that confirm the anchor has set and the boat is where it will remain overnight. The anchor alarm, if they have set one, provides a false security: it tells you when the anchor has dragged, not when it is about to.
This article describes how I anchor and why each element of the process matters. It is not the only correct method and experienced sailors will have variations that work for them. But every element described here is the result of something going wrong when it was absent, and the complete process is what produces the consistent outcome: an anchor that holds through the night in the conditions that the night actually produces rather than the conditions that existed at anchor time.
Bottom Type
The holding of an anchor depends primarily on the bottom type. Sand is the best holding for most anchor designs: the flukes dig in easily and the grip increases as load is applied. Mud holds well in most conditions but can release suddenly if the load direction changes significantly. Rock provides no reliable holding for most anchor types. Coral is variable: some coral rubble holds like sand, living coral provides minimal grip and should not be anchored on both for holding reasons and for the damage the chain causes to the reef.
I assess the bottom type before anchoring from the satellite imagery studied before arrival, from the water colour (clear turquoise over white suggests sand, darker patches suggest coral or weed), and from the depth sounder’s bottom lock quality (a clean hard bottom return typically indicates sand or rock, a soft return suggests mud or weed). After anchoring, the anchor camera on the Eighty2 allows visual confirmation of the bottom type and the anchor’s orientation, which removes the uncertainty that most sailors are left with after letting out the chain without visibility of what is happening below. If needed, I take a dive tank and will take a look myself.
Scope
Scope is the ratio of the total length of chain deployed to the depth of water. The function of scope is to ensure that the anchor receives a horizontal rather than a vertical load: an anchor pulled horizontally sets deeper and holds better than one pulled vertically upward. The minimum scope for reliable holding in all-chain anchor gear is typically 3:1 in calm conditions and 5:1 or more in conditions with significant wind. In heavy weather or when overnight winds are forecast to be strong, I use 7:1 or more.
The calculation is simple: depth at anchor position plus the height of the bow above the water line, multiplied by the scope ratio, gives the chain length to deploy. In seven metres of water with a two-metre bow height, 5:1 scope requires 45 metres of chain. Most sailors who anchor in this depth deploy what looks like enough and what turns out, on calculation, to be 3:1 or less. The difference between 3:1 and 5:1 scope in developing conditions is the difference between a set anchor and a dragging one.
Setting the Anchor
Dropping the anchor and letting out the chain is not the same as setting the anchor. Setting requires applying a load to the anchor in the direction it will experience overnight: motor slowly astern after the chain is out to the correct scope, with the engine in reverse at a power level that approximates the overnight wind load. The anchor is set when the chain comes taut and the boat stops moving backward and holds its position against the engine load.
The confirmation of a set anchor is the chain angle: a correctly set anchor in adequate scope has a chain that lies nearly horizontal from the bow to the seabed, with a catenary curve that absorbs shock loads from the boat’s motion. A chain that rises steeply from the bow indicates insufficient scope or an anchor that has not set. The anchor alarm is set after the anchor is confirmed set, not before: the alarm marks the set position, not the desired position.
