Why Do Anchors Drag? 7 Causes and How to Prevent Each One

How Anchors Work (The Basics)

Before we look at why anchors fail, it helps to understand how they work. An anchor holds your boat by digging into the seabed and resisting the horizontal pull of the rode (chain or rope). The key word is horizontal — an anchor's holding power depends on the angle of pull. The more horizontal the pull, the better the anchor holds. The more vertical the pull, the more likely the anchor is to break free.

This is why scope — the ratio of rode length to water depth — is the single most important factor in anchoring. More chain out means a more horizontal pull angle at the anchor.

Cause #1: Insufficient Scope

This is the number one cause of anchor dragging, and it's entirely preventable. Scope is the ratio of the total length of rode deployed to the total depth (water depth + freeboard + tidal rise).

With a 3:1 scope ratio, the pull angle at the anchor is roughly 18 degrees from horizontal. At 7:1, it drops to about 8 degrees. That difference dramatically changes the anchor's holding power — a lower angle means the force pushes the anchor deeper into the seabed rather than pulling it out.

How to Prevent It

• Use a minimum of 7:1 scope for overnight anchoring
• Increase to 10:1 in heavy weather or deteriorating conditions
• Always calculate total depth including freeboard and maximum tidal rise — not just current water depth
• Use our anchor scope calculator to get the exact chain length for your conditions

Cause #2: Anchor Not Set Properly

Many sailors drop the anchor, let out chain, and assume it's holding. But an anchor sitting on top of the seabed hasn't engaged yet — it needs to be driven into the bottom under load. Without proper setting, even a moderate wind change can pull the anchor free.

How to Prevent It

• After paying out your full scope, put the engine in gentle reverse and slowly increase throttle
• Watch your GPS or take shore bearings — the boat should stop moving backward once the anchor bites
• Hold moderate reverse power for 30-60 seconds to drive the anchor deep into the seabed
• If the boat keeps drifting backward under power, the anchor is not setting — retrieve and try again

Cause #3: Poor Holding Ground

Not all seabeds are created equal. The type of bottom has a massive impact on whether your anchor will hold. Rock provides almost no holding for conventional anchors. Thick weed or Posidonia grass prevents the anchor from reaching the actual seabed. Hard-packed sand can resist anchor penetration.

How to Prevent It

• Check your chart for bottom type before anchoring (S = sand, M = mud, R = rock, Wd = weed)
• Choose anchorages with sand or firm mud when possible
• If anchoring on marginal ground, use extra scope and set the anchor carefully with sustained reverse power
• Consider carrying different anchor types for different bottoms (e.g., a CQR for mud, a Rocna for sand)

Cause #4: Wind Shifts

Wind shifts are one of the most dangerous causes of anchor dragging because they often happen while the crew is asleep. When the wind changes direction significantly (especially 90-180 degrees), the boat swings around to a new position. This reverses the pull on the anchor, potentially levering it out of the seabed.

The anchor must then re-set in a new direction — which may not happen, especially if the new direction pulls the anchor through its own hole in the seabed.

How to Prevent It

• Check the weather forecast carefully for predicted wind shifts
• Use extra scope if a significant shift is expected — this gives the anchor more chain weight to help it reset
• Choose anchorages that provide protection from multiple wind directions
• Use a GPS anchor alarm app to wake you if the boat moves outside its expected swing circle

Cause #5: Increasing Wind and Wave Action

Every anchor has a maximum holding capacity. As wind increases, the load on the anchor increases exponentially — doubling wind speed roughly quadruples the force on the anchor. Add waves to the mix and the anchor faces not just a steady pull but repeated shock loads as the boat surges forward and snaps the chain taut.

How to Prevent It

• Check the forecast before anchoring and choose a spot sheltered from expected wind direction
• Increase scope ratio in deteriorating conditions (10:1 for heavy weather)
• Use a snubber or bridle to absorb shock loads from waves
• If conditions deteriorate beyond what the anchorage can handle, leave early rather than risk dragging
• Consider deploying a second anchor at 45 degrees if heavy weather is imminent

Cause #6: Tidal Changes Reducing Scope

This is a subtle but dangerous cause. If you anchor at low tide with a 7:1 scope ratio, rising water effectively increases the depth and reduces your scope. In areas with large tidal ranges (3-5 meters or more), this can drop your effective scope to dangerously low levels.

For example: you anchor in 4m of water with 1.5m freeboard (5.5m total) and let out 38.5m of chain — a comfortable 7:1. The tide rises 3m, making total depth 8.5m. Your scope is now 4.5:1 — borderline insufficient.

How to Prevent It

• Always calculate scope based on the maximum expected depth — that means high tide, not current depth
• In high tidal range areas, let out significantly more chain than you think you need
• Check your tide tables and know when high water occurs during the night
• Our scope calculator includes a tidal rise field for exactly this purpose

Cause #7: Wrong Anchor Type for the Conditions

Different anchor designs perform very differently on different seabeds. A plow-style anchor (like a CQR) excels in mud but struggles on hard sand. A Danforth-type holds brilliantly in sand but can't penetrate rock or thick weed. Modern new-generation anchors (Rocna, Mantus, Ultra) are more versatile but still have limitations.

How to Prevent It

• Know your anchor's strengths and weaknesses — read the manufacturer's recommendations
• If you cruise in diverse conditions, consider carrying two different anchor types
• Make sure your anchor is appropriately sized for your boat — going one size up is always a good idea
• New-generation anchors (concave blade designs) generally offer the best all-around performance

The Ultimate Safety Net: Anchor Monitoring

Even with perfect technique and ideal conditions, unexpected things happen. A freak gust, an unusual current, a passing wash from a large vessel — any of these can cause a well-set anchor to break free.

That's why continuous GPS monitoring is the most important safety layer you can add. Safety Anchor Alarm watches your position around the clock and sounds an alarm the instant your boat moves beyond your safe zone. It's the one piece of equipment that protects you from all seven causes of anchor dragging — because no matter what the cause, the result is the same: your boat moves, and you need to know about it immediately.

Quick Reference: 7 Causes at a Glance

1. Insufficient scope — let out more chain (7:1 minimum)
2. Anchor not set — always reverse to set under load
3. Poor holding ground — check the chart, choose sand or mud
4. Wind shifts — check the forecast, use extra scope
5. Increasing wind/waves — use a snubber, increase scope
6. Tidal changes — calculate scope for high water
7. Wrong anchor type — match your anchor to the seabed