Setting anchor is simple but to be successful its a good idea to be aware of the following factors that influence how an anchor sets.
Setting anchor Factors
Scope in ground tackle.
Thanks to Sailnet and Good Old Boat magazine for the image and link. All anchors are designed to dig in when pulled horizontally. If pulled vertically they break free, otherwise we would not get them back.
Anchor Scope and Catenary are important terms in anchoring.
Scope is the ratio of anchor line to the water depth. For example it its 10 feet deep and you pay out 30 feet of line or chain you have a scope of 3 to 1.
Catenary is a word which describes the curve of the ground tackle. In the diagram above you can see the curve as oppsed to the the horizontal line between anchor and boat.
Short scope (3:1) limits your swing in a crowded anchor, but is harder to get a good hold on the bottom. Longer scope increases the holding power of the anchor, but you will need more space and the likely hood of sailing around the anchor increases. The above image is 5:1 scope 100 ft in 20 ft water depth.
Problems with long scope
Long scope helps getting an anchor to dig in as the anchor line is more likely to pull horizontally. The problem with lying to a long scope is that you need lots of space which you might not get in a crowded anchorage.
Secondly you will find out about anchor sailing. This basically means that the wind will blow you side ways and when the anchor line goes taught you are pulled back. The momentum built up sends the boat to the other side. So you are essentiality sailing around the anchor which gets uncomfortable and the anchor line goes taught slack and taught again.
One way to prevent anchor sailing is to put up an anchor sail, another is to hang a large bucket from the bow. The bucket acts to dampen the swing as the bow has to tug on the bucket dragging it through the water.
Bahamian anchor method is another method we will be looking at in part 3. This involves setting two anchors.
Problems of short scope.
The problem with short scope is that the anchor shaft is not lying close enough to the seabed. Short scopes by nature means the anchor does not dig in with enough bite. The Fortress anchor has two settings for the fluke blades which allows you to set for different sea beds and scope.
Using an Anchor Kellet gives you some of the features of a short scope but with the holding power of a long scope.
Kellets are weights that are added to the anchor line or chain with a large shackle or loop which allows the weight to slide along the chain. The weight is lowered down the chain (see image). The effect is to lower the angle of the chain at the anchor bringing it closer to horizontal.
The anchor buddy is a kellet (also known as chums, angels, sentinels, anchor angels) which have been used for generations to anchor boats more securely. They can reduce the swing radius up to 50%.
How do you measure scope length
Mark the chain
Imtra have these markers you can press between the links at measured points like very 10ft or 3 meters. A different color for 20ft and 30ft will let you know how much scope you have let out.
For the anchor rode mark the line with magic marker or slip some leather strips in between the strands at intevals of say 20 feet whichever works best for you.
Measure scope length
Chain rode counter
Auto Anchor Remote chain counter telling you how much chain or line you have let out. The counter will work for either chain and rope/chain Rhodes. AA150 is Freeman K. Pittman award winner 2006.
This counting device can replace your anchor roller or be placed behind it. Designed for boats in the 25-45 ft range and rope dia 8-20mm and chain 6-10mm. Â£250 ex vat. The LED display on top of the unit counts the anchor rope or chain from the last reading or from zero if reset. The LED is solar powered so does not need wiring.
Books on Anchoring
Captains anchoring Quick Guide
What you need to know about anchoring–fast and easy! Anchoring is a necessary skill for any boater–power or sail–whether you are planning a picnic lunch in a secluded cove or an overnight visit in a distant anchorage. This 16-panel, foldout guide provides you with fast, easy-to-follow instructions for safe and efficient anchoring. Anchoring is in full color and is printed on hinged, heavily laminated, waterproof pages, so this tough resource will hold its own even when you are in rough weather.
by Peter Nielsen
The Complete Book of Anchoring and Mooring
This book has been cited in a few sites like www.boatsafe.com and other respected organizations.
Chapter One: Introduction Part I: The Technology of Ground Tackle Chapter Two: Loads at Anchor Chapter Three: Deck Gear for Anchors Chapter Four: Anchor Windlass Chapter Five: Anchor Rhodes Chapter Six: Anchor Options Chapter Seven: Anchor and Rode Selection Part II: The Art of Anchoring Chapter Eight: Human Factors in Anchoring Chapter Nine: Technique of Anchoring Chapter Ten: Anchoring Tricks Chapter Eleven: Rights and Responsibilities Chapter Twelve: Storm Anchoring Part III: The Mechanics of Mooring
The Complete anchoring handbook
A modern, authoritative anchoring guide for sailors and powerboaters A boat swinging safely at anchor can be a relaxing conclusion to a great day of boating or an essential emergency measure, while failure to anchor properly can be frustrating, inconvenient, or downright dangerous. The Complete Anchoring Handbook is your path to mastering this indispensable seamanship skill. Based on original engineering analysis–and with contributions from such international anchoring experts as Alain Fraysse and Chuck Hawley–The Complete Anchoring Handbook emphasizes the proven best gear and methods for anchoring safely in any situation with any boat, sail or power. Here’s everything you need to know, from the basics to the most advanced techniques
US Sailing Bareboat Cruising
One selection form this manual covers Anchoring Techniques 24. Select an anchorage and demonstrate appropriate helmsman and crew coordination and the skills necessary to anchor with two anchors under power using one of the following methods: bow and stern, two anchors off the bow at 60Â° , or two anchors off the bow at 180Â° (Bahamian Moor). 25. Pick up a mooring. 26. Demonstrate appropriate helmsman and crew coordination and the skills necessary to recover your anchor under power.