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Boat Anchors

With their apparent simplicity, boat anchors are the least understood of sailing equipment. Everyone knows what they are intended to do but there is little scientific knowledge of how they perform in all circumstances because of the difficulty of observing their actions underwater. When they are buried in the seabed, their behaviour depends primarily on the consistency and strength of the seabed itself, factors which vary greatly.

The boat anchor does not actually 'hold', but its ability to penetrate the seabed and that seabed’s substantial consistency determines a good anchorage. Trials in artificial test tanks can be misleading and it is uncertain what type of boat anchor is best overall.

There will be a preference, due to experience for a certain type of anchor, in a particular locality. Classification Societies recommend weights of anchor in relation to size of boat, but avoid the controversy of specifying types. A large amount of weight and chain is a solution whatever the boat anchor, as the heavy chain absorbs much of the energy of a tossing boat before this force can reach the anchor. The need now is to save weight carried aboard, and many boats now carry nylon warp in preference to chain.

Nylon warp can absorb energy by its elasticity, but has little weight in the water with loads going direct to the anchor therefore putting more reliance on the anchor’s holding performance. Attach a few metres of chain, called the leader, between the warp and the boat anchor to absorb some of the effects of snatch loading.

Anchoring

An boat anchor's holding power is dependent on the amount of cable that is payed out; this, in turn, depends on the length the boat can carry and the depth of water. The minimum scope for chain is 3:1 and for rope 5:1 but it is much better to increase these ratios to 5:1 and 8:1 respectively if you have sufficient cable. In an exposed anchorage in rough conditions, paying out ten or more times the depth of water will avoid dragging, remembering to allow for the rise of tide if anchoring at low water. Anchors and Chain

Anchoring in light weather is less problematical and for this a kedge anchor is used. A kedge anchor is lighter than the bower (main) boat anchor. Heavy duty anchoring in heavier wind and

wave conditions requires as heavy an anchor that be handled and carried, particularly so for emergency anchoring where a sheltered anchorage is unavailable.

Fisherman Anchor

The universally-recognized type of boat anchor is the 'fisherman', and is still popular for many applications. Either way up it lands on the seabed, one of its flukes (points) will be in a downward position able to penetrate the ground. Keeping the flukes vertical is accomplished by the

Fishermans anchor stock (crossbar) at the opposite end of the shank lying horizontally on the seabed.

As most of the weight is felt at the tip of the fluke, this boat anchor design is good on rock, weed and firm soils but has its limitations in soft ground due to the small amount of fluke area able to resist dragging. The attributes of this boat anchor are its dependable performance in a variety of sea beds and its ability to reset quickly if dragged out.

Grapnel Anchor

The grapnel, which has four flukes on cruciform arm does not need a stock and are popular in areas of hard sand and rocks, but their disadvantage is that they are not easily stowed on yachts

Most other forms are classed as ‘high holding power’ or ‘stockless’. Having large fluke areas they bury deeply, achieving a much higher performance but on certain sea beds they are unpredictable in their holding power - the ratio of the force they can sustain compared to their weight.

Danforth Anchor

Tumbling fluke anchors, as the Danforth anchor, have a hinge allowing the flukes to ‘tumble' either side of the shank, pointing downward whichever side they land on the bed. The Danforth anchor's advantage is that this form stows flat on the deck ready for use. The Danforth anchor is usable on rock and soft ground where its large flukes are effective, but unsuitable on hard ground.

Big boat anchors are stowed easily by drawing them directly into a hawse pipe. At the limit of their holding power these designs tend to roll out of the ground and may not reset if they have collected a stone between the shank and the fluke.

Plough Anchor

The plough anchor, although being cumbersome, has a large fluke area and is popular. The best known is the CQR, which features a strongly forged hinge between the ploughshares and the shank. This causes the plough to ‘screw' its way into the ground assisting the digging-in phase. The plough anchor is a good all-round performer, especially in softer soils where they can penetrate deeply.

Bruce Anchor

A different form is the Bruce anchor, with its two curved horns which rotate the main fluke into the ground. The Bruce anchor is ideal on softer ground but is uncompetitive with other designs on harder ground as it cannot penetrate deeply. The Bruce anchor's advantage, on intermediate ground is even if it tends to roll out it retains some holding and a fair chance of digging in again.

Sailboat Mooring and Anchoring Techniques