The History of the anchor dates back millennia. The most ancient anchors were probably rocks and many rock anchors have been found dating from at least the Bronze Age.
Many modern moorings still rely on a large rock as the primary element of their design. However, using pure mass to resist the forces of a storm only works well as a permanent mooring. They are so big you can’t pick them up easily and carry them around to use where you want.
Early anchors were rocks with holes in them for securing to a rope, these rocks can still occasionally be found on the shores of Cornwall and many other seafaring nations.
The difficulty is how big a rock can you carry around compared to how well you want it to hold you to the seabed.
To stop smaller stones skidding over the seabed various devices were made that dug prongs into the ground.
An early Roman design (third image below) is clearly an early prototype for a Fisherman’s style anchor. While often made with wood, the stock was often iron, and some examples have been found made entirely of iron.
The technology to produce iron anchors was not widespread for a very long time so alternatives were made with various combinations of wood, rope, stone, and anything heavy, like a bag of sand, lumps of lead. The second picture below shows a Killick anchor, which can be made on-the-spot using primitive tools and materials.
Anchor rope and chain
Tiny boats will attach the anchor with rope alone.
Small boats will use a combination of chain attached to the anchor and then rope attached to the chain and boat.
Yachts and bigger will use all chain… or NEARLY all chain. It is good practice to have at least a short length of rope attaching the bitter end of the chain to the boat, allowing you to cut the anchor and chain free in an emergency.
The chain has four very useful facilities.
- it is stronger than rope
- it is heavier than rope (more on this below)
- it does not get cut up by rock, coral, or deck fittings when in use
- it keeps the anchor head down ensuring maximum grip on the ground
What is a Catenary?
When a ship drops anchor, it deploys much more chain than the depth of the water (otherwise the anchor would just bounce meaninglessly along the bottom).
There is enough chain for the anchor to be pulled horizontally, giving optimum grip, but also the additional weight of the chain on the seabed adds to the holding power. The remainder of the chain then forms a catenary curve due to gravity. The heavier the chain, the more pronounced the catenary curve, keeping the angle of pull on the anchor low.
The curve allows the chain to store energy, acting as a shock-absorber. If the ship is pulled by a sudden gust of wind, the angle of the chain gets steeper, taking much of the energy out of the gust before it’s transferred to the anchor. This makes it less likely that the anchor will drag, and also makes things more comfortable for those on board!
How much chain to use?
Most people new to anchoring vastly underestimate the length (‘Scope’) of anchor chain to deploy.
First off, you need to know the maximum depth of water during your stay in the anchorage. Check your tidal calculations carefully.
The answer is 7 times your maximum depth. This ensures a good catenary and the best holding.
What is the best type of anchor?
One with a very long chain is the simplest answer!
The three most common types today are the Fisherman’s anchor, Danforth anchor and Bruce anchor. Here’s a quick look at their pros and cons…
Fisherman’s Anchor
These are ideal for rocky and weedy bottoms, as the narrow prongs can easily find purchase. The disadvantage of this is that they can snag easily. They fold flat for storage and reset pretty reliably on the turn of the tide. Holding power per kg is less than with more modern designs.
Danforth Style Anchor
These are ideal in sand and mud, providing excellent holding. They are also relatively lightweight and easy to handle. However their performance is very limited on rock and other types of seabed. Danforth anchors can also be trickier to set.
Bruce / Claw Anchor
These anchors are very versatile, with good holding on various kinds of seabed including sand, mud and rock. However, boats may require a larger anchor for the same holding power compared to other types. The hinged design can also make stowage a bit awkward.
Find Out More…
For a more detailed dive into the intricacies of anchoring, check out Brian Fagan’s excellent book, ‘Staying Put, the Art of Anchoring’.
For more on the various other ways to keep a ship still, check out our article When the Long Trick’s Over: How to Park a Tall Ship
