Powerboat Lessons and Powerboat Course


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:

Types of Anchors: