How Long Should Anchor Line Be?

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Anchoring is a skill that many boaters have trouble with. 

Knowing how much anchor line to let out is crucial to safely anchor your boat in every situation. If you don’t let out the proper amount of line, you risk having your anchor drag or pull, which can cause damage to your boat and other surrounding vessels. 

The basic rule of thumb for good anchoring is to let out 5-7 times the total depth that you will anchor in. If you are throwing a “lunch hook” and conditions are fair, 3 times is sufficient. If you are anchoring overnight or in rough conditions, you may need up to 10 times. 

This ratio is known as “scope” 

What is scope? 

Scope is the length of anchor line relative to the distance from your bow to the sea bed. It is crucial for anchoring safely and securely. 

As scope increases, the horizontal pull of the anchor will also increase which helps the anchor bury deeper into the sea bottom. As the scope decreases and the line becomes more vertical, the holding power decreases and you risk pulling or dragging the anchor. 

What is the proper scope for anchoring?

The ideal amount of scope depends on many factors such as depth, wind, tides, and location. 

It is important to know that scope is not just based on the depth of water, but the total depth from bow to the sea bottom. 

How do I calculate total depth? 

Here is a quick way to calculate the total depth. 

Total depth is the depth of the water plus the height from waterline to the bow. 

For example, if you want to anchor in 20 feet of water, and the distance from the bow to the water line is 5 feet, your total depth is 25 feet. 

In areas that have large tidal swings, you may also want to add in the difference between current tide and high tide if anchoring long term. 

Once you have your total depth, then you can determine how much anchor rode you should let out. 

Here is a quick chart to help you calculate how much rode you need to let out based on total depth and conditions. 

(Insert chart) 

How much anchor line to carry on board 

A good rule of thumb to follow is to carry 10 times the amount of the deepest water than you will anchor in. 

For example, if you mostly only anchor in a maximum of 20 feet of water, you will always have enough anchor rode for any situation if you carry 200 feet on board. 

Every situation is different, so it is important to have the right ground tackle on hand to adapt as conditions warrant. 

How to mark your anchor line 

So now you know how much anchor rode to let out, but how do you know when you let out the correct amount? 

Here’s a couple of ways I’ve used to measure the amount of anchor line that is let out. 

  1. Mark your line with a strip of electrical tape at every 20 ft. 
  2. Use these waterproof label tags to mark lengths 

Common Anchoring Mistakes 

  • Anchor too short 
  • Not setting the anchor 
  • Using the wrong anchor

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