anchoring - page 4

5.4 At anchor

Each anchored boat must be able to keep its position without drifting away, regardless of the weather conditions. To succeed, the boat must stay in place because of its anchor which has penetrated to the bottom but also by the chain that must be spread on the bottom (photo 5.4.1). Understandably, the effective anchoring of a boat requires a chain length significantly greater than the depth of the sea where the anchor is set.

Selecting a spot for the night or a shorter stay is pretty important and there are quite a few considerations.

Consider these:

  • Shelter from wind.

  • Shelter from swell and waves.

  • Out of the way of traffic.

  • Sufficient depth of water around the entire possible 360 degree swing of the vessel if wind direction changes.

  • The tide rise and fall.

  • Current changes due to tide change.

  • Bottom conditions - good or poor holding ability compared to type of anchor.

  • Not in a prohibited area.

  • Cables and lines across the bottom. These almost always exist in a marina. But also check the charts for subsurface electric and telephone lines to an island or peninsula.

  • Scope.

  • Make-up of your anchor line "rode". All chain or chain and rope?

The biggest failures to safely anchor and properly hold an anchor are lack of attention to wind and poor "setting" of the anchor in the first place.

Have in mind that: A very good guide for all the above is Greek Waters Pilot (or Italian etc. Waters Pilot). There is always one onboard, it is written in English and you will find all the necessary information for the bay or the marina that you would like to visit.

Scope

If you do not let out enough rode, and your scope is too small, your anchor will not set and will pull out. It takes an adequate amount of rope or chain for your anchor to hold properly. Scope is the ratio of the length of rode (R) to the depth of the water (H) (photo 5.4.1). Remember to take the tidal range and height of your bow into consideration.

The ratio of the length of rode to the depth of the water is called scope. The depth should be calculated to include the actual water depth at the time of anchoring plus the height of the bow of your boat above the water line. If it is two meters above the water it can make a big difference when you are anchoring in 4 meters of water.

The greater the scope, the smaller the angle at which the rode addresses the bottom. When calculating required scope, keep in mind that your depth sounder may be giving you the water depth under your keel, rather than from the true waterline, in which case you also need to add the difference from where it is measured to the waterline when calculating scope.

Greater scope also helps the anchor dig deep into the bottom, as the attack angle of the blade or fluke increases.

To help determine the correct amount of rode to let out to attain the optimal scope, you can mark your rode using colored whipping line at regular intervals, cable ties, plastic ribbons or even paint on a chain rode.

Photo 5.4.1

How much scope?

A 5/1 ratio (scope) rode/depth is considered to be the minimum scope for safe anchoring under moderate conditions by most people, though there are some who suggest less with certain newer gear. With an all chain rode, you may need less scope, but it is always better to err on the side of safety. We usually go for a 7:1 scope, more if we are expecting stronger winds.

In crowded anchorages, you may not be able to let out as much rode as you'd like. In this case you will need to weigh your options and see what is best for you and your vessel. Depending on your choice of tackle, you may get away with less scope in consistently moderate conditions. If there is a chance that the wind might pick up and you do not cherish the idea of playing bumper boats in the middle of the night, you may consider relocating elsewhere.

Setting

  • Use the proper amount of scope.

  • In general, do not try to anchor under sail, unless you are a very experienced sailor and conditions are ideal.

  • Motor into the area where you wish to anchor and select a potential spot.

  • Now survey the possible dangers throughout the potential spot's swing area.

  • Post a lookout at the bow to warn of any obstacles. This person may also be the one to lower the anchor, or give instructions to the helmsperson.

  • Keep an eye on the depth of water. Whenever anchoring near a shore, this depth can decrease in a hurry, risking running aground. Knowing the depth will also assist in determining rode. Review the chart first.

  • Remember to be courteous to other vessels anchored before you. They do have “right of stay” This includes respecting distances, keeping noise and commotion to a minimum. They will be watching you, often giving advice and encouragement.

  • Once at the "spot" ensure your boat is pointed into wind.

  • Lower the rode slowly so that it does not “pile up” on the bottom at the same time the boat is reversing away downwind.

  • Take care not to get your legs caught in the paying out rode. Proper communication between the person deploying the anchor and the helmsperson is essential.

  • Once the proper amount is paid out, continue with slowly backing the boat. This will give the anchor a chance to "set" into the bottom. If you are lucky it will set the first time, otherwise several attempts may be needed.

After the anchor has set and adequate rode has been played out, take time to ensure you are not drifting. Do this by sighting objects on shore and determining they stay put.

After completing the above procedure the boat should stay in position 4 (photo 5.4.2).

Photo 5.4.2

Swing

Very often wind will have your boat pointing in different directions over a period of time. This can be a gentle and eventual swing in the opposite direction, or it can have your boat pointing every which way. When planning where to set your anchor, you not only need to take your swing radius into consideration, but also that of the other boats in your vicinity. Remember that boats on moorings will swing in a tighter arc than those at anchor.

Swing radius of boats varies with a number of factors, including length of scope. Try to allow enough swing room to avoid overlapping swing arcs.

In an ideal situation, you would simply just stay away from everyone else (photo 5.4.3). However, that is rarely the case, and you will need to be able to tuck yourself a little closer in. As a rule of thumb, anchor nearest to other boats of the same type as yours. Powerboats, mono-hulled sailboats, and multi-hulls all swing differently.

Photo 5.4.3

Monitoring

It is important to monitor initially how well your anchor is set as well as periodically due to changing winds and tide. These methods can help you monitor:

  • Check the position on the chart plotter or mobile device.

  • Set an anchor alarm on the chart plotter or mobile device.

  • Take a  bearing on the beam of the vessel to a point on land. 

  • Observe the depth sounder. Set a depth alarm.

Note however that your boat will naturally swing and move with the length of the rode so some allowance must be made. But this swing and movement will be periodic. You can note the limits at the edge of each swing.

Weighing

When the time comes to leave an anchorage, “weighing anchor”, there are recommended procedures.

Step 1: Ensure all gear is properly stored. Crew and passengers need to be alerted about procedures that will be taken. Ensure you have an agreed upon set of hand signals between the crew member who is retrieving the anchor and the helmsperson.

Step 2: Start the engine and slowly motor towards the anchor, all the while pulling in the rode and placing it in the anchor locker. Do not let the rode drift under the vessel as it could become entangled in the propeller, creating some real problems.

Step 3: As the vessel moves over the spot where the anchor is - pull it up – if you can. Stop the vessel’s forward motion - as you continue pulling in the anchor. If you use an electric windlass to raise the anchor, be vigilant to ensure it is running freely.

 

If the anchor is set hard and you cannot pull it in, you may need to use the vessel’s forward motion to break the anchor loose. This means maintaining slight forward motion and cleating the rode as you pass over the spot. The theory is that the vessel’s momentum will break loose the anchor. Be very wary of the strength of the cleat on your boat.

 

If the anchor fails to break loose, due to rock formation, you can try to pull it out backwards by motoring to windward. The flatter the angle you pull the anchor out, the greater the chance of retrieval, so let out lots of rode when motoring to windward. Be conscious of the rode and propeller at all times. 

 

Try pulling the anchor out sideways. Let out lots of rode and motor across the wind on either side alternately.

 

A variety of other techniques can be used when anchoring in rocky bottoms. One is attaching a line and a float to the backside of the anchor making it possible to pull the anchor out backwards. However, this requires preplanning. If you're unsure of the bottom then this might be a safety precaution.