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Safe Boat Operations – Anchoring Techniques

by chet on January 14, 2012

Safe Boat Operations – Anchoring Techniques

 

An often-overlooked safety related operational procedure is the simple act of anchoring your boat in different sea and weather conditions. Anchoring must be performed correctly in order to be effective. In this Posting we will discuss the techniques necessary to properly anchor a boat.

 

The three basic elements of anchoring include having the proper equipment available; knowing how to use that equipment; and having the ability to select good area to anchor in.

 

Anchoring involves good communication between the boat operator and crew. With noise from the engine(s) and the wind, it is difficult to hear voice communication. The boat operator should ensure a pre-arranged set of hand signals that the crew understands. Keep the signals as simple as possible.

 

There are several important precautions that must be taken when considering an anchorage area:

•If possible choose a sheltered anchorage area in shallow water (40′ or less).

•Check charts to ensure that the anchorage area avoids any submerged cables or other obstructions.

•If other boats are in the same area, be careful not to anchor too close to another vessel.

•Never drop within the swing area of another boat.

•Always approach the anchorage into the wind or current.

 

Having selected a suitable spot, you should run in slowly, preferably on some range ashore selected from marks identified on the chart, or GPS data to aid in locating the chosen spot. Use of two ranges will give the most precise positioning. Later these aids will be helpful in determining whether the anchor is holding or dragging.

 

Bottom characteristics are of prime importance. The following characteristics of the bottom are normally shown on charts:

 

Firm Sand: Excellent holding quality and is consistent.

 

Clay: Excellent holding quality if quite dense, and sufficiently pliable to allow good anchor engagement.

 

Mud: Varies greatly from sticky, which holds well, to soft or silt that has questionable holding power.

 

Loose Sand: Fair, if the anchor engages deeply.

 

Rock and coral: Less desirable for holding an anchor unless the anchor becomes hooked in a crevice.

 

Grass: Often prevents the anchor from digging into the bottom, and so provides very questionable holding for most anchors.

 

As the anchor is lowered into the water, it is important to know how much rode is paid out when the anchor hits the bottom. It is advisable to take a working turn on the forward bitt or cleat to maintain control of the anchor rode. If anchoring in a strong wind or current, the anchor rode may not be held with hands alone. Never stand in the coils of line on deck and do not attempt to “heave” the anchor by casting it as far as possible from the side of the boat. Many an anchor has been lost for failure to attach the rode properly.

 

The scope is a ratio of the length of rode paid out to the depth of the water. Enough rode should be paid out so the lower end of the rode forms an angle of 8° (or less) with the bottom. This helps the anchor dig-in and give good holding power. Scope of the anchor rode should have a ratio range between 5:1 and 7:1. For heavy weather use a 10:1 scope. (Example: For the 5:1 ratio, anchoring in 20 feet of water would require 100 feet of rode.) Markers along the line, show the amount of rode that is out. It also helps to decide the scope necessary for good holding of the anchor.

 

An anchor must be set properly if it is to yield its full holding power. The best techniques for setting an anchor will vary from type to type; only general guidelines can be given here. Experimenting will help determine the best procedures for the boat, the anchors, and the cruising waters.

 

There are several ways to make a positive check to ensure the anchor is holding, and not dragging.

•If the water is clear enough to see the bottom, movement may be detected easily.

•If the anchor rode is jerking, or vibrating, the anchor is most likely not holding.

•Monitor bearings taken on at least two landmarks (if available) that are a minimum of 45° apart, or use radar ranges and bearings. Small changes usually mean that the wind, tide, or current has caused the boat to swing around the anchor. If the compass heading is constant, but the bearings change, the anchor is dragging.

•If using a buoyed trip line from the crown of the anchor, apply reverse power to test the anchor’s holding. The float on this line should continue to bob up and down in one spot unaffected by the pull on the anchor rode.

•Some electronic navigation units (GPS/DGPS) have anchoring features that will warn if the vessel has drifted out of its swing circle. These can be used, but should not replace visual and radar methods.

 

After the anchor has gotten a good bite and the proper scope has been paid out, the line should be made fast to the connection fitting (bitt, cleat, etc.). A check should be made to ensure the vessel is not dragging anchor before shutting off the motor.

 

Maintain a live watch whenever anchored to monitor the conditions and equipment. Things to watch for are:

•Dragging anchor.

•Changes in the weather.

•Other vessels dragging their anchor or anchoring near your vessel.

•Connection of the anchor rode to the fitting.

 

Stowage of ground tackle depends upon the size of your boat. In smaller boats, it may be on deck, with the anchor secured in chocks to prevent shifting as waves cause the boat to roll. Some boats have the working anchor attached to a pulpit and the rode in a forward locker. The ground tackle should always be ready for use when the boat is underway.

 

(thanks to CaptainBob for the article)

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