Anchor Types & Holding Power
The USCG exam tests anchor selection by bottom type and holding power. Know each anchor's strengths, weaknesses, and when to use it.
Plow / CQR / Delta
Exam Favorite★★★★☆Sand / Mud
Excellent
Rock
Poor
Grass / Weed
Good
Resets on Shift
Yes
Best all-around cruising anchor. Resets well on wind shifts. Delta is fixed; CQR pivots.
Danforth / Fluke
★★★★★Sand / Mud
Excellent
Rock
Poor
Grass / Weed
Poor
Resets on Shift
No
Highest holding power per pound in sand and soft mud. Does not reset reliably on direction change.
Bruce / Claw
★★★☆☆Sand / Mud
Good
Rock
Fair
Grass / Weed
Fair
Resets on Shift
Yes
Sets quickly and resets well. Lower holding power than plow or Danforth. Popular on powerboats.
Mushroom
★★☆☆☆Sand / Mud
Good (permanent)
Rock
None
Grass / Weed
None
Resets on Shift
No
Used only for permanent moorings. Builds holding power over time as it sinks in. Not for recreational anchoring.
Kedge / Fisherman
★★★☆☆Sand / Mud
Poor
Rock
Excellent
Grass / Weed
Good
Resets on Shift
No
Traditional anchor. Best in rock and kelp where modern anchors skip. Used as a kedge or secondary anchor.
Scope Calculation
Scope is the ratio of rode deployed to the total depth from your bow chock to the seabed. Correct scope is the single most important factor in whether your anchor holds.
Scope Formula
Total Depth = Water Depth + Bow Chock Height Above Waterline
Rode Required = Total Depth × Scope Ratio
Example: Water depth 15 ft · Bow chock 5 ft above water · Total depth = 20 ft
At 7:1 scope → 20 × 7 = 140 feet of rode
| Conditions | Rope Rode | All-Chain | Rope + Chain |
|---|---|---|---|
| Calm, protected anchorage | 5:1 | 3:1 | 4:1 |
| Normal overnight anchorage | 7:1 | 4:1 | 5:1 |
| Heavy weather / exposed | 10:1 | 5:1 | 7:1 |
| Storm conditions | 12:1+ | 7:1+ | 10:1+ |
Why Chain Needs Less Scope
- ▸Chain weight creates a catenary curve — a natural sag that keeps pull horizontal
- ▸Horizontal pull is the ideal load angle for anchor holding
- ▸Chain acts as a shock absorber — no jerking loads on the anchor
- ▸Chain is chafe-resistant on rocky or rough bottoms
- ▸At short scope, chain still holds because the catenary keeps the angle low
Rope Rode Considerations
- ▸Nylon rope has natural elasticity — absorbs shock loads better than chain alone
- ▸Requires longer scope to achieve horizontal pull at the anchor
- ▸Chafe is the enemy — protect the rode at the bow chock with a chafe guard
- ▸Add a 15–30 foot chain leader at the anchor end to improve catenary and chafe protection
- ▸Lighter, easier to handle than all-chain — preferred on smaller vessels
Swinging Room Calculation
Failing to calculate swinging room is one of the most common anchoring mistakes — and a frequent USCG exam topic.
Swinging Circle Formula
Swing Radius = Rode Deployed + Vessel Length
Swing Diameter = Radius × 2
Example: 140 ft rode + 40 ft vessel = 180 ft radius
Swing Diameter = 360 feet
Key Considerations
- ▸No other vessel, shoal, or obstruction within swing circle
- ▸Neighbors' swing circles must not overlap yours
- ▸Shoal water at any compass bearing within the radius
- ▸Vessels with different hull types (sailboat vs. powerboat) swing differently in wind vs. current
- ▸Depth at the edge of the swing circle, not just at anchor position
- ▸Tide rise changes depth — recheck at low water
Anchoring by Bottom Condition
Chart notation for bottom type: S = sand, M = mud, R = rock, G = gravel, Wd = weed/grass, Co = coral. Always check the chart before anchoring.
Sand
Best Anchors
Danforth, Plow, Delta
Avoid
Mushroom, Kedge
Notes
Ideal anchoring bottom. Flukes dig and lock. Set the anchor firmly with reverse power. Soft sand may need longer scope.
Mud
Best Anchors
Danforth, Plow
Avoid
Kedge
Notes
Good holding once embedded. Soft mud may require extra scope. Anchor may bring up mud when retrieved — have a bucket and hose ready.
Rock
Best Anchors
Kedge / Fisherman, Bruce
Avoid
Danforth, Plow
Notes
Difficult and unreliable. Risk of fouling — anchor can lodge between rocks. Use a trip line. If possible, choose a different anchorage.
Grass / Weed
Best Anchors
Plow (CQR/Delta), Kedge
Avoid
Danforth
Notes
Flukes skip on weed. Plow buries through grass. Grass can foul the anchor shank. Use extra scope and verify the anchor has set.
Coral
Best Anchors
Sand patch only — Danforth/Plow
Avoid
Anchoring on coral directly
Notes
Environmentally prohibited in many jurisdictions. Find a sand patch. Use a trip line to avoid damaging coral on retrieval. Consider a mooring ball.
Anchoring Procedure — Step by Step
The USCG exam tests both the correct sequence and the details of each step. Know the order cold.
Survey the anchorage
Identify depth on chart and sounder, bottom type (chart notation: S = sand, M = mud, R = rock, G = grass), wind direction and forecast, swinging room available, and nearby hazards.
Calculate scope and swinging room
Total depth = water depth + bow chock height. Multiply by your scope ratio. Calculate swing radius = rode length + vessel length. Mark the circle mentally or on chartplotter.
Approach into the wind or current
Head into the predominant force (wind or current, whichever is stronger). Reduce speed to bare steerageway. Stop the vessel at the chosen spot with zero headway.
Lower anchor to the bottom
Lower — do not throw or drop — the anchor until it touches the bottom. Confirm contact on the sounder or by feel on the rode. Allow the vessel to drift back or apply minimum astern power.
Pay out scope while backing
Ease rode at a controlled rate as the vessel moves astern. Keep the rode nearly horizontal as it is paid out — avoid piling rode on top of the anchor, which prevents it from biting.
Set the anchor
When full scope is deployed, snub the rode briefly. Apply reverse throttle — start at idle, increase to half-power — and hold for 20–30 seconds. Feel for dragging vs. firm resistance.
Take bearings on two fixed objects
Note compass bearings to two or more fixed landmarks, lights, or towers. Record bearings and time. This is your baseline for anchor watch. GPS anchor alarm as backup.
Verify rode angle and catenary
Look over the bow: the rode should angle gently down and forward, curving toward horizontal near the bow. A tight, steep rode angle means insufficient scope — pay out more.
Anchor Watch & Drag Detection
Bearing Method — Most Reliable
- ▸Take compass bearings to two fixed objects ashore immediately after anchoring
- ▸Record bearings, time, and conditions in the logbook
- ▸Retake bearings every 15–30 minutes
- ▸If bearings change beyond normal wind-induced sheering, the anchor is dragging
- ▸Use a hand bearing compass for accuracy — binnacle compass reads from helm, not ideal for this
GPS Anchor Alarm
- ▸Set the anchor position on the chartplotter as soon as anchored
- ▸Set the alarm radius to your swinging circle plus a small safety margin
- ▸GPS alarm is a backup — not a substitute for visual bearing checks
- ▸GPS accuracy can vary — a 10-meter error radius is common; account for this
Signs of Anchor Drag
- !Bearings to fixed objects are changing
- !Rode alternates between slack and jerking taut — anchor bouncing
- !Vessel's heading is wrong for the wind or current direction
- !Bottom scraping sounds or vibration through the hull
- !GPS anchor alarm sounds
- !Depth sounder shows unexpected depth change
- !Neighboring vessels' relative bearing is changing
What to Do If Dragging
- 1.Start the engine immediately — do not wait
- 2.Ease scope further if room permits — this may reset the anchor
- 3.If dragging continues, weigh anchor and re-anchor in a better spot
- 4.Consider anchoring in a different location or with a different anchor type
- 5.In an emergency, use engine power to hold position while sorting out rode
Two-Anchor Techniques
Two-anchor systems are used when a single anchor isn't enough — tight quarters, storm conditions, or reversing current. The USCG exam tests Bahamian moor in particular.
Bahamian Moor
Exam FavoriteBest Used For
Reversing tidal current, tight anchorage, 180° wind shift expected
Swing Circle
Minimal — reduced to vessel length only
- 1Anchor normally; pay out twice your target scope
- 2Drop second anchor 180° from the first (directly astern)
- 3Motor back to midpoint between both anchors
- 4Take up slack on first rode; both rodes should be equal length
- 5Vessel pivots on the midpoint between anchors
Two Anchors — 45° Apart (Fore and Aft Spread)
Best Used For
Strong wind, limited swinging room, open anchorage
Swing Circle
Reduced — vessel held on two points of resistance
- 1Approach into the wind and drop the primary anchor
- 2Veer primary scope and fall off 45° to port or starboard
- 3Drop the secondary anchor
- 4Back down to set both anchors simultaneously
- 5Both rodes lead from the bow with a 45° spread
Tandem Anchors (In-Line)
Best Used For
Maximum holding power in soft bottom or storm conditions
Swing Circle
Normal — handles like a single anchor
- 1Shackle a second anchor (tandem/piggyback) to the crown of the primary anchor
- 2Connect with a short length of chain (5–10 feet) between the two
- 3Deploy both anchors together as a single unit
- 4The lead anchor acts as a deadweight, increasing downward load on the primary
Mediterranean Mooring (Stern-To)
Procedure
- 1Identify the quay and clear line of approach. Note water depth and any underwater hazards.
- 2Prepare anchor on the bow roller, ready to drop. Prepare stern lines and fenders on the stern.
- 3Approach the quay bow-first at slow speed. Stop the vessel at a distance equal to 2× water depth plus vessel length from the quay.
- 4Drop the anchor. Engage reverse to begin backing toward the quay, paying out anchor rode at a controlled rate.
- 5As the stern nears the quay (1–2 meters off), pass stern lines ashore to dock hands or tie to cleats.
- 6Tighten the anchor rode until it is taut and holding the bow off the quay. Adjust stern lines to hold the stern in position.
- 7Rig chafe protection on anchor rode at bow chock. Set anchor alarm or establish bearing watch.
When It Is Used
- ▸Mediterranean and European marinas with limited dock space
- ▸Commercial and naval quays worldwide where alongside is impractical
- ▸When the USCG exam asks about stern-to anchoring — this is the answer
Challenges
- ▸Requires precise engine and helm control — crosswinds make it difficult
- ▸Two crew minimum: one on helm, one managing anchor rode
- ▸Anchor must be set firmly before the stern reaches the quay
- ▸Stern gangplank or passerelle needed for safe boarding
- ▸Crowded anchorages — anchor rodes from neighboring boats may cross
Exam Note
The USCG exam may ask about Mediterranean mooring as a "stern-to" anchoring technique or describe the procedure without naming it. Recognize the description: anchor dropped from bow, vessel backed to dock, stern secured to dock with lines.
Anchoring in Current & Wind
Wind vs. Current — Which Dominates?
When wind and current oppose each other, the vessel will align with the stronger force. Deep-draft vessels are more influenced by current; shallow-draft, high-freeboard vessels are more influenced by wind. When anchored near vessels of different types, they may lie at different angles — plan for this in your swinging room calculation.
Approach Into the Strongest Force
Always approach the anchoring position heading into the dominant force — wind or current, whichever is stronger. This gives you maximum control at the slowest speed. Stop with zero headway before lowering the anchor. Never anchor with the boat moving forward — the anchor won't set, and rode will pile on top of it.
Current Affects Scope Requirements
Strong current adds load to the anchor system even in calm wind. In a fast-running current (2+ knots), increase scope as if the wind were blowing at similar velocity. The horizontal load on the anchor is proportional to velocity squared — double the current speed means four times the load.
Tidal Rivers and Reversing Current
In areas with reversing tidal current, the vessel will swing 180° twice per tide cycle. Use a Bahamian moor to minimize swing circle and prevent rode from wrapping around the keel. Check that the anchor resets cleanly each time the current reverses — a plow anchor resets better than a Danforth in these conditions.
Anchoring in Heavy Weather
Increase scope to 10:1 or more. Use the heaviest anchor available. Deploy a second anchor set 45° apart if space allows. Reduce windage — strike unnecessary sails, lower bimini. Chafe protection on all rode is critical in heavy weather — a chafed-through rode in a storm is a crisis. Check every hour minimum.
Night Anchoring
Display the correct anchor light: an all-round white light visible 360° at 2 nautical miles. Vessels under 7 meters may use a flashlight in the rigging. On a vessel 50 meters or more: forward white light (bow) at 6 meters, and aft white light lower. In known or suspected vessel traffic areas, use radar reflector and sound the required fog signal (one prolonged blast every 2 minutes in restricted visibility when at anchor).
Kedging Off a Shoal
Kedging is the technique of using an anchor — typically a secondary anchor carried in the dinghy — to pull a grounded vessel into deeper water. It is a core seamanship skill tested on the USCG exam.
Kedging Procedure
- 1Assess the grounding — determine which direction leads to deeper water. Check tide: if rising, you may float free without kedging.
- 2Launch the dinghy. Load the kedge anchor and its rode — coil the rode in the dinghy to avoid tangling as you row out.
- 3Row or motor the dinghy in the direction of deeper water, perpendicular to the shoal if possible, paying out rode behind you.
- 4Drop the kedge anchor at maximum distance — typically 150–200 feet from the grounded vessel.
- 5Return the free end of the kedge rode to the grounded vessel. Lead it to the anchor windlass or a sheet winch — maximum mechanical advantage.
- 6Haul in on the kedge rode with the winch or windlass while simultaneously applying reverse engine power. Shift crew weight aft.
- 7Rock the boat gently by shifting crew side-to-side — this can break the suction grip on a mud or sand bottom.
- 8Once free, retrieve the kedge anchor and motor immediately to deeper water before anchoring again.
Key Factors for Success
- ▸Rising tide is your best ally — time your effort with the rising water
- ▸Maximum mechanical advantage — use windlass or sheet winch, not brute strength
- ▸Engine must be in reverse while hauling on the kedge
- ▸Kedge anchor must be dropped far enough — too close and it will drag before the boat moves
- ▸Reduce weight — pump out tanks, move heavy gear forward or aft
Exam Tip: Kedge vs. Anchor
The term "kedge" refers to the act of using an anchor to move a vessel — not a specific anchor type. Any anchor can be used as a kedge. The fisherman/traditional anchor is also commonly called a "kedge anchor" because it was historically used for this purpose in rocky bottoms.
Fouled Anchors & Trip Lines
Fouled Anchor Procedures
An anchor is "fouled" when the rode wraps around the anchor, or the anchor is caught under rock, cable, or chain on the bottom and cannot be retrieved normally.
- ▸Motor over the anchor — approach from the opposite side of the foul. The change of angle may free it.
- ▸Motor in a circle — motoring around the anchor while hauling rode may unwind a wrapped chain.
- ▸Trip the anchor — pull on the trip line attached to the crown to invert the anchor and pull it free backwards.
- ▸Diver recovery — in clear water, send a diver to manually free the anchor.
- ▸Slip the rode — as a last resort, mark the rode with a buoy, slip it from the vessel, and return later or arrange for recovery.
Trip Line Setup
A trip line is a light line attached to the crown (bottom) of the anchor and buoyed at the surface. It allows the anchor to be retrieved from the crown end if normally fouled.
- ▸Attach trip line to the crown of the anchor — not the shank ring
- ▸Trip line length = water depth + 15% extra for tide rise
- ▸Attach a small buoy or plastic jug at the surface — marks anchor position and acts as a trip line float
- ▸Use a trip line in rocky bottoms, areas with known debris, or any time fouling is likely
- !In crowded anchorages, a buoyed trip line can be a hazard — other boats may foul it. Use with caution.
Exam Tips
Scope ratio — depth includes bow chock height
USCG exam scope questions require adding bow chock height to water depth for total depth. Miss this and you calculate insufficient scope. Example: 10 ft of water + 4 ft bow chock = 14 ft total. At 7:1 scope = 98 ft of rode.
Danforth for sand/mud; Plow for shifts
When the exam asks best anchor for pure sand or mud holding power — Danforth. When it asks which anchor resets best after a wind shift — plow (CQR/Delta). This distinction appears on many exam questions.
Bahamian moor — minimal swing circle
The Bahamian moor reduces swing to roughly the vessel's own length. Any exam question about minimal swing circle or tidal rivers with reversing current points to Bahamian moor.
Set the anchor with reverse power
Anchor setting requires applying reverse engine power — not just paying out rode and hoping. Half-throttle astern for 20–30 seconds is the standard exam answer for confirming the anchor is set.
Chain needs less scope due to catenary
All-chain rode achieves a horizontal pull on the anchor at shorter scope than rope because the weight of the chain creates a catenary curve. The exam tests this principle directly.
Anchor light — all-round white, 2nm
An anchored vessel displays an all-round white light visible at 2nm (for vessels under 50m). Two lights for vessels 50m+. This is a ColRegs question that often appears in the anchoring context.
Frequently Asked Questions
What is the minimum scope ratio tested on the USCG captain's exam?
The USCG exam typically expects a minimum scope of 5:1 for rope rode in calm conditions, and 7:1 to 10:1 in rough weather or exposed anchorages. For all-chain rode, a scope of 3:1 to 5:1 is acceptable because chain's weight provides a catenary curve that holds the anchor shank horizontal. Scope is calculated as the total length of rode paid out divided by the depth of water plus the height of the bow chock above the waterline. For example, in 10 feet of water with a bow chock 4 feet above the waterline, total depth is 14 feet. At 7:1 scope, you pay out 98 feet of rode.
Which anchor type has the best holding power in soft mud or sand bottoms?
The Danforth (fluke) anchor has excellent holding power in sand and soft mud — its broad flukes dig deep and lock into the bottom. The plow (CQR or Delta) anchor also performs well in sand and mud, and resets well if the wind shifts. For pure holding power per pound of anchor weight, the Danforth consistently outperforms other designs in sand and mud in controlled tests. The Fortress aluminum Danforth-style anchor can be adjusted for harder or softer bottoms by changing the fluke angle.
How do you calculate swinging room when anchoring?
Swinging room is the radius your vessel will sweep as the wind or current shifts around the anchor. Calculate it as: total rode deployed (scope × depth) plus the length of your vessel. For example, if you deploy 140 feet of rode and your boat is 40 feet long, the swinging circle has a radius of 180 feet — a diameter of 360 feet. You must ensure no other anchored vessels, shoal water, or obstructions lie within this circle. In a crowded anchorage, account for neighbors' swinging circles as well, and consider that different hull types respond differently to wind vs. current.
What is a Bahamian moor and when is it used?
A Bahamian moor uses two anchors set in opposite directions — typically 180° apart — on a single rode that runs through both anchor rodes to a central point at the bow. It restricts the vessel to a very small swing circle, making it ideal in restricted anchorages, areas with reversing current (tidal rivers), or when wind is expected to shift 180°. To set a Bahamian moor: anchor normally, then motor forward while paying out doubled scope of rode; drop the second anchor, then motor back to the midpoint between both anchors and take up the slack. The boat swings on a pivot between the two anchors.
How do you detect anchor drag on watch?
The most reliable method is to take two or more compass bearings to fixed objects ashore — landmarks, towers, or lights. Note the bearings and watch times, then retake the bearings every 15–30 minutes. If the bearings change significantly, the anchor is dragging. On GPS-equipped vessels, use the anchor alarm function, which alerts when the vessel moves outside a preset radius from the anchored position. Other signs of drag include: the anchor rode becoming slack then taut in a jerking motion, the vessel sheering wildly, unusual sounds on the bow, or the boat taking a position inconsistent with wind and current direction.
What is Mediterranean mooring and how is it executed?
Mediterranean mooring (Med mooring or stern-to) involves anchoring off a quay or dock, then backing the stern in so it is secured to the dock with lines while the bow is held off by the anchor rode. It is common in European marinas and areas where dock space is limited. Procedure: Approach the quay bow-first, drop the anchor at a calculated distance (typically 2× the depth plus boat length), then back down while paying out the anchor rode, then secure the stern to the dock with breast and spring lines. The anchor rode must be taut enough to hold the bow off. Requires precise engine and helm control, especially in crosswinds.
How do you kedge off a shoal?
Kedging uses a secondary anchor (the kedge) to pull a grounded vessel into deeper water. Procedure: Deploy the dinghy or take a crew member and carry the kedge anchor with its rode into deeper water in the direction you want to move the vessel. Drop the kedge and return the rode end to the grounded vessel. Use a sheet winch or windlass to haul on the kedge rode with maximum tension. At the same time, shift crew weight aft or to one side to help break the hull free, and use engine power if available. The combination of winch tension and engine power working together is often enough to free a moderately grounded vessel. Success is more likely at rising tide.
What is the holding power advantage of chain over rope rode?
All-chain rode provides three advantages over rope rode: (1) Catenary effect — the weight of the chain creates a natural downward curve (catenary) that keeps the pull on the anchor horizontal even at shorter scope, which is the ideal load angle for anchor holding. (2) Chafe resistance — chain does not chafe on rocks, coral, or rough bottoms. (3) Weight and shock absorption — the chain's weight acts as a shock absorber, preventing jerking loads on the anchor when the vessel pitches. Rope (nylon) is lighter and easier to handle, but requires longer scope and is vulnerable to chafe. A common compromise is a chain leader (15–30 feet) at the anchor end of a rope rode.
How does a plow anchor (CQR or Delta) differ from a Danforth in holding performance?
The plow (CQR, Delta, Rocna) anchor uses a pivoting or fixed plow-shaped shank that digs into the bottom and buries the entire anchor head. Its key advantages: (1) It resets well if the wind or current shifts direction — the plow rolls and re-buries rather than breaking out. (2) It performs well in grass, weed, and mixed bottoms where flukes may skip across the surface. (3) It stows easily on a bow roller. The Danforth/fluke anchor provides higher holding power per pound in pure sand and soft mud, but is more likely to break out if the pull direction changes significantly. For cruising where overnight wind shifts are expected, the plow is generally preferred.
What are the steps to properly set an anchor?
To properly set an anchor: (1) Choose the spot — identify the depth, bottom type, swinging room, and wind/current direction. (2) Approach slowly into the wind or current and stop the vessel at the chosen spot with no headway. (3) Lower — do not throw — the anchor to the bottom while the vessel drifts back or is backed slowly. (4) Pay out scope at a 3:1 to 5:1 ratio while drifting back. (5) When full scope is deployed, snub the rode briefly to allow the anchor to bite. (6) Apply reverse engine power at idle to set the anchor — gradually increase to half-throttle astern for 20–30 seconds. (7) Take bearings on two fixed objects ashore to establish your position. (8) Verify the rode angle: it should be horizontal near the bow, indicating good catenary and proper scope.
Related Study Guides
Rules of the Road
ColRegs lights, shapes, and sound signals — including anchored vessel requirements.
Marlinspike Seamanship
Knots, splices, line types, and cleating — essential skills for anchoring and mooring.
Chart Navigation
Reading chart symbols, depth soundings, and bottom-type notations for safe anchoring.
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