Course Pages

US POWERBOATING  Anchoring
 

The rode is the line and/or chain which goes to an anchor.  It is often composed of both chain and rope.   The chain is attached to the anchor and it helps the anchor to lie flat on the bottom.  This has three benefits: 

• The chain lies flat on the bottom and increases the horizontal pull on the anchor.  This will increase the anchor's purchase.

• The chain will not chafe as it lies on and is pulled across the bottom.

• The chain acts as a shock absorber as the boat intermittently pulls on the rode, lifting the chain off the bottom.  

One must be sure that the anchor has a good purchase on the water's bottom or it will drag and the boat will drift.  You can check the purchase by observing the tension on the rode and any change in position of the boat as the boat is placed in reverse.   While at anchor, intermittently check the tension on the rode as the boat's bow raises and lowers with the waves.  Also take several compass fixes and/or GPS positions to aid in determining if the boat is drifting and pulling the anchor.  A common predisposing factor of a dragging anchor is not letting out enough rode.  As a general guide, let out at least seven times the rode as the depth of the water plus the boat's freeboard (distance from the water surface to the deck)  This ratio is called the anchoring scope.  The scope may be decreased to 5:1 if an all chain rode is used or with someone on board in sheltered anchoring areas with a good holding bottom.    Scope may have to be increased in high wind or wave conditions.  Be sure to check the depth of the water where you anchor in relationship to the tide or you may inadvertently become grounded.  If a single anchor is placed, your boat will swing around the anchor as the direction of wind changes.  This is especially true on the coast where one encounters land and sea breezes.  The water must be deep enough for anchorage along the entire arch of this swing.  If less swing is desired, set two anchors at 180 degrees from each other. 

You  must also check the tide tables to make sure the water will be deep enough at low tide along the entire radius of swing, and that your scope will be sufficient at high tide.  For example, if you anchor with a 7:1 scope at low tide in six feet of water and a six foot tide comes in, your scope will be reduced to 3.5:1. 

NAOO Tides Online (You can view tide tables and graphs from various locations around the USA):   http://tidesonline.nos.noaa.gov/monitor.html

Go To: Swinging Radius at Anchor Calculator

In a crowded anchorage, always anchor in a similar fashion as the boat next to you or the two boats may drift into each other.  For example:  If your boat is fixed in place with two anchors and the other boat has a single anchor, the other boat may be blown into your boat.  In addition, look at the other boats in the anchorage and take note of the type and the angle of their rodes to the water.  This will help you judge the amount of rode let out and give an idea of the swing radius of the other boats.   Remember if a boat has an all chain rode, it may have a 5:1 or less scope and have a smaller swinging radius than a boat with a combination chain and rope line.  Boats that are anchored next to each other that have a different swing radius are also at greater risk to drift into each other if the current or wind changes.   ( Click on Picture to Enlarge !! )  

Sailor's Tip:  Place fathom or foot markers on the rode to help judge how much line has been let out.

A good anchorage has the following characteristics:

• Protected from wind and waves & swells.

• Enough depth at low tide along the full swing of the rode.

• Enough space along the full swing of the rode.

• Good bottom which will hold an anchor.
    

Types of Anchors: 

• Danforth - Holds well in soft surfaces, but may not hold on hard surfaces.
  
  
  
  
   

• Bruce - For both hard and soft surfaces
       
  
  
  
  
  
       

• Plow - A burying anchor for hard surfaces.  Notice the ring on the anchor's crown for attachment of a retrieval line (trip line) which is floated up to a buoy.

Tip:  One may place a second line (trip line) to the head of the anchor.  There is usually a metal loop to allow for the placement.  Bring the line up to the surface and attach to a flotation device.  Using this line the anchor can be pulled out by its head and will be easy to remove.  The length of the trip line is equal to the water depth at high tide plus 5 to 10 feet.

• Using Two Anchors:  Anchoring with two anchors is a difficult maneuver and is performed to reduce the swing radius of the sailboat or to increase the holding power in heavy weather.  In setting the anchors, one may maneuver the boat under power or even place the second anchor with a dinghy.  If one uses an engine, care must be taken not to foul the prop with the first anchor's rode while you are setting the second anchor.  To prevent this from happening, the first anchor's rode should always be close to the beam or forward while you are setting the second anchor.  To the right is an animated gif showing a method of setting two bow anchors under engine power which minimizes the chances of fouling the prop.   
  
  The tension on the anchor rodes is important especially when one is swinging up to set the second anchor.  Too much tension may cause the first anchor to break loose, too little tension on the rode may cause it to go astern and foul your prop.
  
  Setting Two Anchor Animated GIF.  Click On Picture To View Animation.
   
• Mediterranean Mooring:  This type of docking is commonly found in Europe, South and Central America..  It maximizes the number of boats which can be docked to a pier. 
  
  Each boat is docked with its stern to the pier with a rode and anchor going forward, away from the pier.  Boats are then docked next to each other.  During the maneuver the anchor is set and the boat is backed into position.  Prop-walk can create difficulty staying on course.  While backing towards the slip, one must be careful not to put too much tension on the rode to straighten the boat or the anchor may break loose.
  
   Mediterranean Mooring Animated GIF.  Click On Picture To View Animation.
    

Buy a CD version of the Powerboat Website !!!  

( Previous Page )    ( Comments: Contact US POWERBOATING^TM )    ( Site Map )

  Webpage Last Updated 04/20/2008    Number of hits as of  3/29/2003