How to Anchor your Sailboat
Anchoring a sailboat is not that difficult provided you can answer the following questions:
- How deep is the water?
- What is the bottom like?
- Which way is the wind blowing?
- Is the area sheltered?
- Is there sufficient swing area?
- What is the tidal range?
- How much anchor rode is needed?
- Where is the traffic and where are other boats anchored in relation to your boat?
Water Depth and Anchor Rode Scope
You will want to anchor in water that is about 10 to 15 feet deep so that you will be able to pay out enough anchor rode to give you the proper scope for your particular situation.
Depth for the purposes of determining anchor scope is determined by adding the bow height above the waterline plus the actual water depth.
If the actual water depth is 10 feet and the bow or windlass is 4 feet above the water then to have a 5:1 ratio you would need to let out 70 feet on anchor rode. ( 14ft. X 5 = 70 ft.) For a 7:1 ratio you would need to let out 98 ft. of anchor rode.
You can see that anchoring in water deeper greater than 15 feet soon becomes impractical.
How much scope is needed? The Canadian Yachting Assoc. and the American Sailing Assoc. recommend a scope of 3:1 for quick stops (on a 3:1 scope, never leave the boat unattended); a scope of 5:1 for overnight anchoring where there are light winds and a scope of 7:1 or greater in windy conditions.
Bottom Conditions and Anchor Choice
Bottom conditions will help you determine where to anchor, what anchor to use and the quality of the holding conditions.
Never anchor on coral – it is illegal and seriously damages the coral and the surrounding eco system.
The preferred anchoring bottom would be sand or mud where the flukes on the anchor can did in for a good hold. Clay can also provide a good holding ground if the clay is not too hard.
A rocky bottom will provide a good hold if the anchor sets properly but rocky bottoms also increase the chance of fouling your anchor (i.e. anchor gets stuck between the rocks and cannot be freed)
Grass or weed bottoms do not provide a good holding ground. Lighter anchors like a Danford will skid along the top of the weeds and grass and never set. A plow, CNQ or Bruce style anchor has a better chance of digging into a grass or weed bottom given it’s shape and additional weight. Avoid anchoring in grass or weeds if at all possible.
Danforth Anchor: If anchoring on a sandy or muddy bottom you will want to use a Danforth anchor. The flanges on a Danforth anchor can dig well into a sand or mud bottom providing a secure hold. The Danforth is not effective in weed or rock bottoms.
Plow Anchor: The plow anchor is a good all purpose anchor. It is best for mud or clay bottoms but still has good holding qualities in sand. In weed it holds reasonably well but is not good in rock.
Bruce Anchor: The Bruce anchor is another good all purpose anchor. It works well in silt bottoms, may hold in rock but is not good in weed.
Grapnel Anchor: The grapnel anchor is good in rock and is generally onboard as a secondary anchor. It is not good in mud, clay or sand bottoms.
Fisherman Anchor: The traditional looking fisherman anchor is good in rock and weed. Again, this anchor is kept on board as a secondary anchor.
It would be unreasonable to carry onboard all the anchors mentioned. Generally most sailors will have two anchors on board and depending on the area they are sailing, most opt for the Danforth plus either the Plow or the Bruce anchor.
A change in wind direction will alter you anchor’s holding ability. If you have an 180 degree wind shift you will drift over your anchor and likely dislodge it.
When you anchor, always make note of the wind direction. If there is a significant shift, you may have to reset your anchor or you may want to set two anchors to account for any anticipated wind shift.
If you are setting two anchors, also factor in your swing area and other vessels anchored nearby. There will be less swing when two anchors are set so another vessel anchored nearby on one hook may potentially swing into you.
Sheltered Anchor Location
You always want to anchor in a sheltered location. Shelter means protection from wind and waves and any incoming weather. More shelter means less stress on the anchor rode and the anchor set. The constant jarring of the boat pulling against the anchor will eventually dislodge even the best set anchor.
Anchor in a bay on the leeward side. If conditions change, you may have to change your location. Avoid anchoring on a windward shoreline (shore becomes a lee shore), if you start dragging your anchor or snap your rode, you could quickly find yourself washed against the rocks.
When anchored from a single anchor, there is the potential for a360 degree swing.
If you have 100 feet of anchor rode you could swing out 100 feet from your anchor in any direction. Make sure that the shoreline, shallows, rocks and other boats or obstructions are well outside the area of your anchor swing.
Never assume the boat anchored next to you is also on a single anchor and therefore, the two of you will swing in unison. If the other boat is bow and stern anchored they will have much less swing.
The water depth will vary with the phases of the tide. A 7:1 scope at low tide will not be a 7:1 scope at high tide.
If you have a tidal range of 5 feet and you are anchoring at low tide, you will need to add an extra 35 feet of anchor rode to allow for high tide situations.
It is important to know the tidal range, time of high and low water for any given anchoring location. You should always have onboard a Tide and Current Table and be familiar with the rule of 1/12ths to give a good approximation of the height of tide at any given time.
How to Anchor
Now that you have found your location, determined what anchor to use and how much anchor rode will be needed, made sure that you have allowed enough room for anchor swing, you are now ready to ‘drop anchor’.
With the sails stowed, slowly motor to the spot where you wish to lower your anchor. With the boat no longer moving, direct the crew to slowly lower the anchor (do not drop the anchor as the term ‘drop anchor’ suggests).
When the anchor has reached the bottom, slowly back downwind. (If the wind is strong, you may just want to drift.)
You do not want any tension on the anchor at this point otherwise you will start to drag the anchor making it more difficult to set.
The crew should keep track of how much anchor rode has been let out. (Usually there are measurement markings on the anchor rode.)
At a scope of 5:1, you will want to set the anchor. Have a crew member wrap the anchor rode around a bow cleat and then rev the motor in reverse to dig the flanges of the anchor into the bottom.
If the anchor does not set well, you will have to start from the beginning.
Assuming the anchor sets at a 5:1 scope, continue to drift or motor back slowly until the scope reaches 7:1. (Remember tide conditions.)
Once you have reached the appropriate scope, cleat the anchor rode off to the bow cleat.
If you are using a windlass (winch), you may be unable to cleat the anchor rode. In this situation you will want to rig a snubbing line. A snubbing line runs from a bow cleat to a point on the anchor rode. The tension of the anchor rode is taken up by the snubbing line so that no pressure is placed on the winch.
Once you feel that you are securely anchored, turn off the motor.
You will want to fix your position by eyeballing fixed objects nearby. If you find the position of those objects has changed, you could be dragging your anchor.
Most GPS systems have an anchor alarm. You can set your anchor alarm to give you what you feel will be your potential area of swing. If your boat moves outside that area it is likely that you are dragging your alarm. At the point you drop your anchor, set that as the anchor waypoint on your GPS. If you let our 100 feet of rode you could potentially swing 360 degrees but your distance from your anchor waypoint should remain relatively constant. You want to give some allowance for rode stretch and change in water height (lower water will mean you will be further away from your GPS anchor waypoint). Give yourself and extra 20 feet or 120 radius from your GPS anchor waypoint before the alarm will trigger.
If you grab hold of the anchor rode and feel a vibration, you are likely dragging your anchor. This can be corrected by increasing your scope. If this fails, you will have to recover your anchor and re-start the anchoring process.
You can also drop anchor under sail. Once you have found the spot where you want to drop your anchor, furl or drop your jib and sail under main alone. Stall the boat, head to wind, at the point where you want to drop the anchor. With main sail still raised but main sheet eased, lower the anchor. The waves and wind will move the boat backwards. With the main sheet eased, move the main sail from side to side to move the boat backwards in a straight line. If the boom is pushed out to the port side, the stern will swing to the starboard and vice versa. When you feel the anchor has been set, lower the mainsail and secure for the night. If you drop your mainsail before you have your anchor set, you could find yourself trying to quickly raise the mainsail to get out of the way of a rock or other hazard because you are dragging your anchor.
To raise your anchor, start your motor and slowly approach the anchor site. Be careful to not drive over the anchor location otherwise you could start to tear out fittings on your boat plus snag the propeller etc.
You can also sail off the anchor. Raise the mainsail, as the boat swings to one side of the wind, trim the mainsheet to get under way. Tacking back and forth you approach the anchor point at which time the boat is stalled head to wind until the anchor is freed and onboard.
When the anchor has been secured on deck, head out for a day of sailing.
Anchoring at Night
It is important to post an anchor watch, someone who monitors both the anchor and the anchorage. A secure anchorage can quickly go sour if bad weather and shifty winds put you on a lee shore.
Unfortunately most of us are shorthanded when it comes to having crew available to post for anchor watch duty. Accordingly a good approach is to check the weather, tide and current tables before turning in and then with your anchor alarms (good to have a secondary alarm as a backup), set your own personal alarm and get up a few times during the night to make sure that nothing has changed.
Prepare for the worst so have your flashlight and gear ready should you need to take immediate action.
It is good practice to anchor well before dusk to test your anchor hold and always make sure you have your anchor light on. You may want additional lights turned on (other than navigation lights) to make yourself more visible depending on conditions.