Why one anchor rarely does it all

Every catamaran skipper eventually learns the same lesson: the anchor that held beautifully in the sandy shallows off the Solent can drag without warning across a muddy estuary or skate over a patch of weed. It is not that the anchor is faulty. It is simply that anchor designs are engineered for particular seabeds, and the seabed around the UK and near continent changes constantly. One mile you are over clean sand, the next you are over soft mud, gravel, or a thick mat of eelgrass.

For a cruising catamaran this matters more than for a monohull. Cats sit differently at anchor, they swing to wind and tide in their own way, and they present plenty of windage. Getting the anchor right is not just about holding power on paper — it is about sleeping soundly at anchor in a crowded anchorage or an exposed bay.

Matching anchor type to seabed

Most anchors fall into a handful of families, each with a preferred home. A plough or CQR-style anchor bites well into sand and mud but can struggle in weed. A Bruce or claw anchor sets quickly in sand and is forgiving on a weedy bottom, though it may not reset reliably after a wind shift. A scoop or spade design — often called a new-generation anchor — features a concave fluke that digs deep into sand and firm mud and holds with impressive consistency when sized correctly.

Flat, wing-like anchors such as Danforths are superb in sand and mud but fold under side load and hate weed. Grapnel anchors, useful on rocky ground, are a niche tool rather than a primary anchor. There is no perfect anchor, which is why the practical answer is to understand what your anchor does well and carry a second design that covers its weaknesses.

Reading the seabed before you drop

Long before the anchor leaves its roller, you should know what lies beneath you. A chart gives a clue — sand, mud, shingle, rock, weed — but charts are generalised and often out of date. The echo sounder and, on a catamaran with a transducer on each hull, the pattern of depth readings will hint at what is down there. Soft mud typically gives a faint, smudged bottom trace. Hard sand and gravel produce a crisp, strong return.

Look over the side. In clear water you can often see the seabed colour and texture. Bubbles or disturbed silt stirred up by your own wash can indicate soft mud. A quick cast with a weighted line and a smear of tallow or grease will bring up a sample on the lead, which is a trick still worth using. Finally, consider the anchorage's history: popular summer anchorages are often scoured to hard sand or packed mud, while sheltered backwaters accumulate soft, unconsolidated silt.

Sizing and technique for multihulls

Size matters, and catamarans need more anchor than many owners assume. High windage, a wide beam, and the tendency to snatch at the chain mean you should generally go one size above the manufacturer's recommendation for your length, or at least to the top of the range. Check that your windlass, bow roller, and chain locker can handle the upgrade.

Chain is your friend. A decent length of chain, ideally with a snubber or bridle to take the shock out of gusts, keeps the shank low and helps the anchor set at the right angle. A bridle from each bow to a single central chain also stops the boat sailing at anchor, which reduces the risk of unsettling a lightly set anchor overnight.

Setting technique is straightforward but demands patience. Lay out your scope — at least five to one in settled weather, seven to one or more when it is blowing — then motor gently astern in short bursts and watch two fixed points ashore to confirm you are holding, not dragging. Dive on the anchor if the water is clear and warm enough, or use a marker buoy on the tripping line, so you can see how the anchor has buried. A well-buried anchor with the chain lying along the seabed is worth more than any specification on a box.

Building a sensible anchor inventory

For coastal cruising around the UK, the Channel Islands, and Brittany, a practical kit looks like this:

• Primary anchor: a new-generation scoop or spade type, sized generously, on all-chain rode. It copes with the sand and firm mud you will meet most often.
• Backup anchor: a plough or claw in a different pattern, stowed ready to deploy. If your primary excels in sand, your backup should be the one that handles weed and softer ground better.
• Kedge or stern anchor: a lighter, easily handled anchor with a rope and chain rode, useful for Bahamian mooring, setting a stern line, or kedging off.
• Spare rode: plenty of nylon anchorplait with a chain leader, so you can extend scope or set a second anchor in a shifting breeze.

Carry spares of shackles, mousing wire, and a couple of swivels. It is surprising how often a small fitting, not the anchor itself, lets you down.

Practical habits that keep you secure

Whatever you carry, the habits around anchoring matter as much as the hardware. Use an anchor alarm and set it properly, bearing in mind that GPS drift and a catamaran's swinging circle need a sensible radius. Note transits, check your position before turning in, and if the wind is forecast to veer, consider whether your anchor will reset or whether you should move to a different patch of seabed.

Above all, practise. On a quiet afternoon, drop your anchor on sand, then mud, then weed, and feel how each one sets. Learn what a good set feels like through the chain and how the boat behaves. That instinct, built up over a season of short coastal hops, will serve you better than any single piece of gear. The right anchor is the one you understand, backed up by another that covers the ground you are most likely to meet.