Ask any skipper who has dragged at 3am in a rising north-easterly, and they will tell you the same thing : the anchor was fine on paper. The problem was almost never a single component. It was a mismatch. Wrong anchor for the seabed, chain a size too light, rode too short for the depth, or a windlass drinking amps the house bank could not spare. Ground tackle is a system, and it fails as a system. Here is how to specify it properly for the boat you actually own, not the one in the catalogue photo.

Match the anchor to the seabed you actually see

The single biggest driver of holding power is not the anchor's weight. It is whether the fluke shape can set in the bottom under your keel. Mediterranean posidonia, Breton sand and rock, Baltic clay, and the soft mud of an estuary all reward different geometries. Before you shop, look at your logbook. Where do you actually spend nights at anchor ?

  • New-generation scoop anchors (concave fluke, roll bar or ballasted tip) set fast and reset quickly on a wind shift. They are the current default for sand, mud and mixed bottoms, and they have quietly displaced older plough-style designs on most cruising bows.
  • Plough anchors still work, especially the hinged types, but they are typically slower to set and less forgiving on a veering wind.
  • Fluke (Danforth-style) anchors hold well in soft mud and firm sand for their weight. They are poor in weed and rock, and they can trip on a 180° wind shift. Excellent as a kedge, questionable as a primary in the Med.
  • Claw anchors set in almost anything at modest holding power. Predictable but not remarkable.
  • Grapnels and specialist rock anchors are niche. Useful as a second anchor if you regularly overnight on rocky bottoms.

Rule of thumb : if you cruise a mixed coast (Atlantic France, Balearics, Adriatic), a modern scoop as your primary and a fluke as your kedge covers 95 % of nights. If you routinely anchor in dense posidonia, nothing sets reliably, and the responsible answer is to pick up a mooring buoy or move to a sandy patch you can see on the chart plotter.

Size by displacement and windage, not by boat length

Manufacturer sizing charts are conservative starting points, but they are calibrated on a "typical" boat of a given length. A 12 m aluminium catamaran with a flybridge and a hardtop presents a completely different load to a 12 m long-keel monohull with a low coachroof. Displacement and windage matter more than LOA.

The load on your ground tackle in a blow rises roughly with the square of the wind speed. Doubling the wind quadruples the load. Standard industry figures put horizontal loads on a 12 m cruising yacht at something in the order of 500 kg at 30 knots, and comfortably over 1 500 kg at 50 knots. Your chain, shackles, bow roller and cleats all need to survive the worst night, not the average one.

A practical approach :

  1. Take the manufacturer's recommended anchor weight for your length.
  2. Go up one size if you have significant windage (cat, trawler with flybridge, high freeboard sloop) or if you anchor in exposed bays.
  3. Match chain diameter to the anchor and to your bow roller. On most 10 to 14 m cruisers this is 8 mm or 10 mm high-tensile (grade 40/70) galvanised chain.
  4. Check that every shackle in the system has a working load limit above the chain's, and mouse them with monel wire.

Do not mix chain grades without knowing what you have. A grade 30 shackle upstream of a grade 70 chain is a hidden fuse. If you are refitting the bow, this is also a good moment to review the wider inventory of gear you carry, from tackle to safety kit ; our rundown of essential equipment on board pairs well with a ground tackle audit.

Rode length, scope and the snubber that saves your night

Chain length is where owners economise and regret it. For all-chain rode on a cruising boat, you want at minimum four times the deepest water you routinely anchor in, plus bow height above water, plus a safety margin. On the French Atlantic coast with 5 m of tidal range, that means carrying a lot more chain than the same boat needs in the Med.

A working baseline :

  • All-chain rode : 60 to 80 m for a 10 to 12 m cruiser working coastal waters. 100 m if you cruise Brittany, the Channel Islands or anywhere with real tide.
  • Mixed rode : at least 10 m of chain at the anchor (to keep the shank horizontal) with nylon three-strand behind. Cheaper and lighter, but you lose the catenary that dampens shock loads.
  • Scope : 5:1 is the honest minimum in settled weather. 7:1 when it pipes up. Measured from bow roller to seabed, not from the waterline.

Mark the chain every 10 m with coloured cable ties or paint. A chain counter on the windlass is useful, but every skipper has seen one miscount after a jammed link or a slipping gypsy.

Then, always, a snubber. A 3 to 5 m loop of nylon (12 to 16 mm on most cruisers), hooked to the chain forward of the bow roller and belayed to a strong cleat. It does three things : absorbs shock loads, quiets the boat, and takes the strain off the windlass gearbox, which is not designed to hold load at anchor. If your windlass is the only thing holding you overnight, you are one bad snatch away from a very expensive repair.

The windlass, the battery bank and the electrical reality

A 1 000 W windlass on a 12 V system draws around 80 A steady and can spike well over 100 A on the first metres of retrieval when the chain is at its longest. That is a serious load. Three things follow from this :

  • The windlass needs its own heavy-gauge feed from the battery bank, sized for the run length. Undersized cable is the most common cause of a slow, hot, unhappy windlass.
  • You should run the engine while retrieving, both to hold the alternator's charge on the bank and to give you steerage as the boat comes over the anchor.
  • A dedicated windlass isolator or battery switch protects the whole circuit and lets you kill power fast if a foot switch sticks. If yours is missing or corroded, our note on battery switches and their maintenance is worth ten minutes.

Windlass loads also make the case for honest energy accounting on board. If you anchor most nights and your alternator only sees an hour of engine time a day, you will feel it in the house bank. Sizing solar, alternator and battery capacity around anchoring habits is not optional on a modern cruiser ; we cover the trade-offs in on-board energy, batteries and solar.

If your windlass is networked (chain counter, load sensor, some newer units publish PGNs), it can share data with the rest of the boat over the bus. That is where the NMEA 2000 wiring guide becomes relevant : a properly terminated backbone lets a chain-out reading appear on the plotter, and lets an anchor-watch alarm cross-reference GPS drift with actual rode deployed.

Anchoring in company, and the rules that apply

Ground tackle choice does not end at your bow. In a crowded anchorage in August, the boat that swings differently is the boat that hits someone. All-chain rodes swing tighter than mixed rodes. Multihulls swing on the tide before monohulls do. A boat with a lot of windage yaws more. If you arrive last, you inherit the responsibility to leave enough room, and to move if you cannot.

The COLREGs still apply at anchor, including the requirement to show the right shapes and lights, and to keep a watch appropriate to conditions. Our summary of the right of way rules every skipper should know is a useful refresher, especially the sections on restricted visibility and vessels not under command, both of which apply if you drag.

The checks that make the difference at the end of the season

Ground tackle degrades slowly and then fails suddenly. A short annual inspection catches almost everything :

  • Lay out the full chain on the pontoon. Look for elongated links, deep pitting, and any link where the galvanising has gone through to red rust. Replace end-for-end if the working end is tired, or re-galvanise if the chain is otherwise sound.
  • Check the anchor's swivel and shackle. Swivels fail more often than chain does. If in doubt, replace.
  • Inspect the bow roller, its cheeks, and the bolts through the stem. A chain that has jumped the roller cuts fibreglass surprisingly quickly.
  • Open the windlass gearbox drain, check for water and grease condition, and grease the gypsy shaft.
  • Run the chain locker dry and check for corrosion at the bitter end fitting. The point where the chain is shackled to the boat is often the least inspected part of the whole system.

Ground tackle is one of those subjects where the boat tells you the truth in one bad night. The rest of the time it sits in the locker and you forget it exists. If your anchor system is instrumented, whether that means a chain counter on the plotter, an anchor-watch alarm, or a shore-side alert when the boat starts moving off its swing circle, you sleep better. That is really the question worth asking on the next fit-out : how would you know, from ashore or from the aft cabin, that your anchor had started to walk ?