Anchoring is a method of using your boat’s anchor to secure the boat for a short time, such as lunch or perhaps overnight.
The objective is to lower the anchor to the bottom, lay out the anchor rode with slack and when you have the required amount of rode deployed secure the rode and let the anchor set into the bottom.
When choosing an anchorage there are four criteria you should observe.
1. Shelter from wind and waves – you want to be anchored in a protected area away from any other traffic.
2. Good holding bottom – composition of the sea bed that will give your anchor a firm hold. We are fortunate in the Pacific Northwest that many harbours have bottoms that are composed of mud, sand, shells and clay.
3. Adequate depth at low water – over the years I have seen a number of boaters who forgot to check the range of the tide overnight. It is a real shock to wake up falling out of your bunk because you have gone aground.
4. Swing room – refers to the requirement for your vessel to be able to swing 360 degrees around the anchor and not contact any hazards or other boats.
Scope is the ratio of the length of the anchor rode in use divided by the distance from the seabed to your anchor roller or chock. Always remember to allow for the height of the tide during your stay.
If you are using a line & chain combination the following ratios are considered the minimum for safety:
Lunch stop – 3:1
Overnight – 5:1
Open anchorage – 7:1
Let us look at a sample. The harbour chart indicates a depth of 20 feet at Lowest Normal Tide. When we arrive the tide has a height of 3′ and will be rising to a height of 7′ overnight. The anchor roller is located 3′ above waterline.
Therefore the maximum depth overnight will be
20′ charted depth + 7′ of tide = 27′
Height of anchor roller above water = 3′
Total distance= 30′
If we are stopping overnight and want a scope of 5:1 we will need to use 30′ x 5 = 150′ of rode.