How to Anchor in Deep Waters

Ships generally prefer to anchor on depths of less than 50 meters. 

Beyond that can be considered deep and poses unique challenges that significantly differ from standard anchoring practices in shallow waters.

While anchoring is a common procedure to secure a vessel, deep waters require more precise planning and execution.

Here, let’s explore why anchoring in profound depths is discouraged, the situation that may necessitate it, and the correct procedure for doing so safely and accurately.

Why It’s Not Advisable to Anchor in Deep Waters

Anchoring in deep waters is typically not recommended due to several risks and operational limitations. These include:

1. Increased Anchor Line Length

It is generally recommended to use a scope of 5 to 8 times the water depth. In deep waters, the amount of anchor chain or cable required is significantly more. 

This can make it difficult to secure the vessel chain and creates problems for the windlass when heaving up.

2. Difficulty Retrieving the Anchor

The deeper the water, the more challenging it becomes to retrieve the anchor. 

The windlass is only designed for heaving a free handling anchor from a depth of 80-100m (max anchoring depth of 3 – 4 shackles).

Beyond that, it would be very difficult to pick up the anchor, especially in rough sea conditions.

3. Holding Power Issues

In deep waters, the anchor may not dig into the seabed as effectively, especially if the bottom conditions are less favorable, such as rocky or sandy seabeds.

This can lead to dragging, thereby putting the vessel at risk of drifting. And with a lengthier chain, it would take longer to heave up the anchor.

4. Dynamic Forces on the Vessel

Because of the long chain, the forces exerted on the anchor and the vessel due to wind, waves, and current are magnified in deep waters. 

This increases the risk of anchor failure and its fittings.

5. Risk for Equipment Damage

When anchoring in deep waters, the windlass becomes the weakest link within the ship’s anchor fittings.

The increased strain on the windlass and chain can damage equipment and even cause the loss of the anchor and chain as a whole.

6. Insufficient Scope

Since the perfect scope to use is 5 to 8 times the water depth, deepwater anchorage may provide insufficient scope. 

A water depth of 70 meters will make you pay out all of your 12 or 13 shackles just to have a scope of 5!

Why Would We Anchor in Deep Waters?

Despite the risks, there are situations where anchoring in deep waters becomes necessary:

1. Emergency Situations

In emergencies, such as engine failure or adverse weather conditions, anchoring might be required to prevent the vessel from drifting into dangerous areas like rocks or shallow waters.

2. Waiting for Berthing Space

In congested ports, vessels may need to wait in deeper anchorage zones until a berth becomes available.

Additionally, some ports have steep shorelines. Their water depth could easily reach over a hundred meters less than five miles from the shore.

3. Conducting Repairs

Some vessels might anchor in deep waters for repairs or maintenance, especially if maneuvering is restricted or drifting is unsafe.

4. Surveying or Research

Scientific vessels conducting oceanographic research or surveys may need to anchor in deep waters to maintain position for long durations.

Anchoring Procedures in Deep Waters

When anchoring in deep waters is unavoidable, these procedures must be executed carefully to ensure safety.

Here are the steps:

1. Pre-Anchoring Preparations

Survey the Area

Use charts and sonar to examine the seabed and ensure that it provides sufficient holding ground. Soft mud or sand is ideal, while rocks and coral should be avoided.

Check Depth and Tidal Conditions

Assess the water depth and the effect of tides, as deeper waters require more chain and attention to slack caused by rising tides. 

Checking the tidal flows will also give you an idea of the set and drift power.

Prepare Sufficient Scope

Ensure you have at least 5-8 times the depth of the water in the anchor chain or rope to provide proper holding power.

It is the master’s discretion if he should follow this rule or use a smaller scope if the anchor chain’s length is not enough.

2. Positioning the Vessel

Slow and Controlled Approach

Approach the intended anchoring spot slowly, considering the wind and current. Aim to be facing the wind or current to stabilize the vessel.

Correct Speed

Ensure the vessel approaches the spot at a very slow speed (ideally below 0.5 knots) to avoid stressing the chain and anchor gear.

3. Dropping the Anchor

Lower, Don’t Drop!

In deep waters, free-falling the anchor can create too much strain on the chain, destroy the brake, and damage the windlass. 

Lower the anchor slowly, using the windlass to control the descent.

Avoid Windlasses Taking Excessive Loads

If the paid-out speed of the windlass motor is 9 m/min, the vessel should not exceed 0.3 knots of speed. 

Otherwise, the vessel will pull the chain out, and the anchoring system will be placed under an excessive load, which may damage the motors.

4. Setting the Anchor

Allow the Anchor to Dig In

Once the anchor is on the seabed, allow the vessel to drift backward naturally. This helps the anchor to embed in the seabed, enhancing holding power.

Let the Drift Pull the Vessel

While the current pulls the ship, monitor the chain for signs that the anchor has caught the seabed.

5. Monitoring and Securing

Check for Dragging

Continuously monitor the vessel’s position using GPS or visual markers to detect anchor dragging. If dragging occurs, heave up the anchor immediately.

Maintain Anchor Watch

Assign crew to monitor the anchor’s position, weather conditions, and the tension on the anchor line throughout the stay.

Prepare for Heaving Up

When preparing to leave, heave up the anchor slowly to prevent damage to the windlass. The chain should be in an up-and-down position so the motors can pick it up smoothly.

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What are your special procedures when anchoring in deep waters? Would you rather do so or prefer to drift instead?

May the winds be in your favor.