Boat anchoring tips

Mark Rothfield | Volume 29, Issue 6
There's more to anchoring than dropping the pick and hoping for the best - a few simple measures can help your pride and joy stay put at anchor.

In the annals of human achievement, the black art of anchoring remains almost universally ignored and unloved. Google the term and you're inundated with pages of psychobabble before an online dictionary finally bothers to give the bland interpretation: a heavy object cast overboard to keep a vessel in place.

The Star Treks of this world, and the Boy's Own Annuals of early maritime exploration, speak of Man boldly going places, with barely a mention of ever having to stop and boldly go nowhere. For Cook and Co, though, it was a lump of pig iron that commonly saved their bacon.

Today... not so much. In our perfect white-shoe world, a modern-day boatie need never drop anchor - they simply flit from berth to courtesy mooring, to restaurant wharf and back, and it's not uncommon to find new runabouts, particularly imports, devoid of deck hardware or even the most rudimentary anchor well.

But anchors live in the imperfect world, like a gale-blown lee shore with a recalcitrant motor or a raging tide that renders sails impotent. In such circumstances, the ill-forgotten discipline of anchoring becomes the last, desperate, defensive handbrake turn before oblivion.

Not so many years ago, there was a rendezvous of a certain cruiser brand on a NSW waterway, with a sumptuous luncheon awaiting. These prim and polished craft had motored from far and wide, yet upon arrival their owners simply plonked down the pick before hitting the plonk themselves. As the sea-breeze gained vigour, no fewer than half a dozen vessels began dragging. The knowing folk ashore allowed themselves a private chuckle and another spoonful of dessert as tenders were frantically scrambled.

Similar stories abound from the Whitsundays bareboat charter world. In one case, a honeymooning couple anchored in three metres of water at high tide, disregarding the tidal variation and, upon return from a bushwalk, found the boat firmly aground. A cold, soggy and unromantic night on the beach ensued.

Another famous case involved a charterer radioing the base to ask: "Can you send more anchors out?" It transpired that the novice skipper had cast the main and reserve anchors adrift on the first two mornings.

Rocket science it ain't, so let's drop the pick and consider the basics.

Where an ant earns respect for carrying 100 times its body weight, an anchor can hold a hull weighing 1000 times its weight or more. To put that into context, a five-tonne vessel can have an anchor that weighs less than 5kg... albeit throwing hydrodynamics, windage and anchor design into the equation.

Throw a rock overboard, as they did in the Bronze Age, and it will have minimal effect - it's the anchor's flukes penetrating the seabed that generates the resistance, unless they happen to snag a protrusion.

Ingeniously, as the boat pulls on the rode (the rope and/or chain) the anchor digs in and grips tighter. To do so, it needs a length of chain and sufficient scope (rope length) to create a horizontal force and serve as a shock absorber. If the pull is too vertical, the anchor's suction will break.

To calculate scope, take the maximum possible depth (current depth plus tidal variation) and multiply that number by at least three. For longer stays in exposed anchorages a ratio of 5:1, and up to 7:1, is recommended.

Obviously, an all-chain rode must be used around reefs because of the chafing risk, but a combination of chain and rope is a reasonable weight- and cost-saving compromise. Precisely how much chain is debatable, with some experts recommending that the minimum amount be anywhere from a half to a full boat length. For KISS's sake, a rule of thumb says 2.5m of chain for craft under 6m, and a minimum of 10m of chain beyond that.

Chain linkage size is another consideration. On smaller vessels, 5mm to 6mm will generally suffice, whereas larger craft are looking at 8mm to 10mm and beyond. With shackles, go for a slightly larger diameter again.

The formula for determining anchor line load is also convoluted, but around 3mm of line diameter for every three metres of LOA is a general rule. High windage boats can go heavier, sporty boats lighter. Your ship chandler or boat dealer can provide more specific advice.

When entering an anchorage most of us become fixated on the destination - the palm-fringed beach - rather than the voyage's all-important conclusion. The factors that really need to be contemplated at this critical phase are water depth, bottom type, potential underwater hazards, exposure to wind and current, and swing room.

Charts and cruising guides often provide advice on the preferred location, or the presence of similar boats is another good sign.

Knowing your vessel's draft, as well as both the timing and range of tides, is a major consideration. Worst scenario for non-trailable boats is a clear metre under the keel at dead low, but nor should you want to anchor in more than 15m at high tide.

Look ashore for signs warning of submarine cables, and never anchor on coral, seagrass or among rocks if possible.

A pair of polarised sunglasses is invaluable in this situation, as is circling the intended anchor spot for further reassurance.

Always make your final approach against the dominant wind or tide, noting the direction other boats are facing. Come in slow and steady, with the dinghy tied alongside so that its painter won't foul the prop.

Have the anchor ready to go as you monitor the depth gauge or lead line.

When you've chosen the location, don't just dump a pile of chain. Rather, proceed a boat length or two upwind before lowering the anchor to the bottom, then engage reverse while progressively paying out chain/rope to a sufficient scope.

The desired effect is to lay a neat, straight line, not a tangled trail.

Remember, it's a risky time for your crew's hands, feet, hair and clothing so make sure they stand well clear. And with hearing impaired by the rattle of chain and engine revs, use hand signals to issue orders - a thumbs-up to start lowering and a clenched fist to stop.

For length, digital rode counters are available or you can mark your chain and rope at five-metre intervals as a manual guide.

Once the line is secured, bury the anchor with a short burst of reverse power. Your boat should rebound forward when you ease the throttle.

Check for any vibration on the chain while it's taut, vibration being a likely warning of dragging. Conversely, propwash eddies moving from stern to bow are a good sign, and you can get absolute confirmation by lining up trees or posts ashore (as with lead markers).

Check that you haven't lain across a nearby vessel's line, bearing in mind that the distance from the point you first dropped anchor is the radius of your swing. A stern anchor can reduce this swinging tendency in tight anchorages, but in some ways fights the natural forces.

Once completed, confirm that the rode is securely belayed because windlasses don't like load. With an all-chain rode, fit a snubbing rope and slacken the chain.

It's a good idea to grab a face mask and dive down to your anchor if possible, or peer over the side of the dinghy to check the anchor has set.

Your boat's electronics can then serve as sentry. If your GPS has an anchor alarm, set it to alert that the boat is swinging too far from the original position, the concern being that the anchor will have to reset itself. Electronic compasses and autopilots can also tell if the boat's heading changes radically, while a depth sounder should have an alarm for minimum depth.

At night, anchor lights must be switched on so other vessels can see you. It's an all-round white light with a visibility of at least two nautical miles. Remember too, it is illegal to anchor in shipping channels or tie up to navigational aids such as channel markers or buoys.

Too often there is a tendency for anchors to be undersized. Whether that's due to weight concerns, aesthetics or limited budget, an anchor that's fine for picnicking might be caught out by wind changes or sudden 'bullet' gusts overnight.

If you're dragging, first try letting out more scope or consider re-anchoring somewhere more protected. Limit the windage by tidying up sails or packing away the bimini.

A second anchor can be set off the bow, either at 90-degrees to form a vee, but as much as 180-degrees in exposed anchorages.

Among the cruising sailor's bag of tricks is a 'kellet', a weight lowered via a retrieval line to halfway along the rode, thereby dampening the shock. Some cruisers prefer a second anchor shackled to the primary as an alternative.

The so-called 'hammerlock moor' involves dropping a reserve anchor straight down after the primary anchor is set, to drag along the bottom and slow the horsing effect.

In more extreme conditions, you could consider the tandem anchoring technique where a second anchor is chained to the crown of the primary, increasing total holding power by as much as 30 per cent.

What goes down must come up, and this process needs a similar amount of preparation and forethought.

First, get the engine(s) idling in neutral for five minutes or so to ensure they're warm and to give the batteries a top-up charge - anchor windlasses draw a considerable amount of power.

Don't expect the winch to tow the boat towards the anchor. You can make its life easier by motoring forward with short bursts.

As the rode comes in, check that it doesn't pile up like a pyramid in the anchor locker or you're asking for a jam next time you drop it. A stick or gloves are needed if the chain comes in muddy. You can have buckets of water or a deck hose at the ready.

When the anchor breaks loose, stop the boat and retrieve the anchor fully so it can't drag or strike the hull. Be prepared for the bow to fall away with the wind at this point - it's a vulnerable time, for you have little steerage.

If the anchor catches, don't force it. A circuit-breaker - obligatory for most brands - is likely to trigger if you do. Snub the line and release the windlass clutch to reduce the pressure. Motor gently forward with the snubbing rope attached and the anchor should break out - if not, try steering at 45-degrees to one side or other.

A 'trip line' system can be deployed, comprising a ring that goes down over the crown of the anchor; you can then either pull from the dinghy or use a flotation buoy. If all else fails, cut the line at its lowest point and weight the bitter end to prevent other boats tangling with it.

When it comes to holding power it pays to know what you're dealing with.

Sand is relatively easy to penetrate and reliable, whereas mud has low sheer strength and can often be a thin veneer over rock. Pebbly and grassy bottoms are worse, having a high probability of false setting. Worst of all are rock and coral.

There are anchors for all occasions, but no single design is best in all conditions. It's for this reason you should always keep a minimum of two anchors aboard, one ideally for mud, the other sand... along with a grapnel if you're going near rock.

With the two-pronged Admiralty anchor (also known as a ketch) largely fading from use over the years due to inferior holding power, there are essentially four categories of anchor to choose from:


With flat, triangular-shaped pivoting flukes, the Danforth or sand anchor arguably has the greatest holding power per pound of any style of anchor. The lightweight and compact design also makes it easy to retrieve and store.

They don't like gravel or weeds, having a tendency to skate over the bottom, and on some occasions they might drag instead of resetting.


Also known as a CQR ('secure'), the plough-style design is a good all-rounder that generally sits neatly in a boat's bowroller, but can be a pain to store otherwise. They have a hinged shank that allows the anchor to turn with direction changes. Another style, known as a Delta, employs a rigid shank.

Thanks to their weight they tend to set easily, particularly in mud or weed. The addition of a rollbar prevents the anchor from lying upside-down.


You might know them as the Bruce, after designer Peter Bruce added three claws to the basic plough design to improve self-orientation and holding power when tide or wind changes were prevalent.

Being fairly blunt, the claws don't perform well on certain bottom types and are notorious for fouling.


These are your best option for rock and coral bottoms, but are lousy in other environments. The classic reef version has light prongs that can bend under strain to release or have a trip ring, whereas the grapnel is available with folding flutes for ease of storage (particularly in dinghies). They're also good for retrieving primary anchors that may become fouled.

As with most things marine, there are specialised versions of a basic theme. The SARCA (Sand and Rock Combination Anchor), for example, rolls over to allow its toe to penetrate like a fluke, and it incorporates a self-tripping mechanism to ensure recovery.

And as with most things maritime, all are only as good as the operator. Anchoring is a skill that can be improved with practice and performed perfectly when the appropriate hardware is at hand. The reward is peace of mind and a restful sleep.

At the very least boaties should always have the primary anchor ready to drop in an emergency, just as our maritime explorers boldly did. When all else fails, the cheapest part of the boating equation will suddenly become the most valuable.

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