USCG Masters Captains License 25/50/100 Ton Upgrade

SEAMANSHIP - Anchoring and towing

Seamanship - Module 1

Anchoring and Towing


To safely anchor a vessel, there must be sufficient scope in the anchor cable.  This is the ratio of the length of cable to the depth of the water.  When anchoring, it is a common rule of thumb to use a length of chain (rope) that is 5 – 7 times the depth of the water.  Paying out more anchor cable increases the holding power of your anchor.  Generally speaking, a mixture of mud and clay is the most favorable bottom for anchoring. The best method of determining if a vessel is dragging anchor is to note changes in bearings of fixed objects on shore.  The ground tackle is the anchor, rode (line and/or chain), and all of the shackles, thimble and gear used in anchoring.  The ground tackle should be inspected periodically to make sure that it is all in good working order.  Different fittings are used to attach the rode to the anchor.  A shackle binds the length of chafing chain to the shank of the anchor.  A swivel attaches the chafing chain to the detachable link.  The detachable link attaches the anchor and ground tackle to the anchor line.  The chafing chain lowers the angle of pull of the anchor and prevents chafing of the anchor line on the bottom.  The thimble protects the anchor line from chafing at the point of connection.  An eye splice is used around a thimble to connect it to a ring by a shackle on the anchor. The fluke is the part of the anchor that actually digs into the bottom.  A grapnel is an anchor with four hooks radiating from a common shank.  Lifting the anchor from the bottom is called weighing the anchor.

If an anchor is dragging the first step in trying to set it is to smoothly pay out more scope.  If you can’t handle the rode with your hands, try taking a turn around the bitt and try snubbing the line from time to time.  If that doesn’t work, use the engine to hold the bow up into the wind with just enough power to take the strain off the rode.  If you haven’t held when the scope is 10:1, retrieve the anchor and try again with a larger, storm anchor or in another spot.  For increased holding power in strong winds sometimes a second anchor is put out at a small angle (45 degrees) to the other (never in line). This is dangerous if the wind direction changes dramatically as both anchors may pull out and not reset.

A two anchor system can be used set at 180 degrees with the bow of the vessel mid-point (Bimini anchor) between them if the vessel is in a narrow channel where the current reverses or in an area where the wind is likely to reverse.  In this technique, set the upstream current first in the conventional way, and then back down until double the normal scope is out.  After the downstream anchor is set, adjust the scope of the lines at the bow chocks until they are both equal.


Anchoring and towing

A stern anchor can be used near a beach or up on a shore, but care needs to be taken to account for tidal fluctuation.

Rafting is a technique where one vessel anchors and other vessels tie up to that vessel.  This is a good technique in busy anchorage areas, but should only be used during light wind and calm water.

Two techniques can be used to assist in setting an anchor.  Using a sentinel or a sentinel and chain lowers the angle of pull on the anchor line.

Anchoring and towing

The second technique is to use a buoy, which lessens the shock load on the anchor or on the boat itself. The buoy would permit the vessel’s bow to ride up over a wave instead of being pulled down into them by the anchor.

When retrieving an anchor, an anchor ball system can make this job a lot easier.

When pulling an anchor be careful not to let the flukes hit the vessel.  Use the water to clean any debris from the anchor rather than bringing the debris into the vessel.  If a vessel is under sail alone, the mainsail should be up before the anchor is broken loose.

If the anchor fouls on rocky bottom, the first method to try to free it would be to reverse the original angle of pull.

Anchoring and towing

If that technique doesn’t work, snub the line around a bit and, under power, go a few feet ahead. Sometimes a wave will help break the anchor free by the lift of the vessel. Another technique is running in a slow wide circle on a taut line.

A buoyed trip line can be used to free a fouled anchor, but that must be rigged prior to setting an anchor. Use a light line, such as a 3/8” polypropylene, which floats. Attach this line to the crown of the anchor. The trip line should be just long enough to reach the surface where you normally anchor, adjusting for tidal changes. Attach the line through a float, and then end it with an eye splice that can be picked up by a boat hook. If the anchor is fouled, use the trip line to pick up the anchor crown first.

Anchoring and towing

Scowing an anchor is attaching the rode to the anchor crown and pulling it up by the crown after the sacrificial line break.

Anchoring and towing


Towing is covered in more detail in the Towing Endorsement Course.  It is important to understand some basic towing principals in the event of an emergency.  Towing is a dangerous undertaking.  In any towing situation, the most important concern is the safety of people on board.  The safety of the craft itself would be an important concern, but passenger and crew safety is always primary.  If you have any doubt that you can perform the tow safely, call the Coast Guard or private towing agency.  Stand by the disabled vessel until the professionals arrive.  You may be able to assist a vessel while waiting for help by putting a line across and keeping the other vessel’s bow at a proper angle to the seas.  You could also provide support in many other ways, especially when it comes to safety. 

On a calm day towing another vessel is fairly straightforward.  The towing vessel generally passes a tow line to the disabled vessel.   A lighter line that floats, such as a water ski towline, can be passed first and used to pull over the actual towing line.   Heaving lines can be used to pass towlines to a disabled vessel.

Anchoring and towing

When approaching a vessel that is dead in the water (drifting) do not run too close to the disabled vessel, especially if there is wind or current.  If you approach a burning vessel, always approach from the windward side so that the flames are blowing away from you.

Anchoring and towing

If you buoy a long line, towing it astern, take a turn around the stern of the disabled vessel, being very careful not to foul the line.  A person from the disabled vessel can use a gaff or boat hook to retrieve the line as it approaches.  You can use the wind and current to your advantage with this maneuver.  This method may be easier than using a heaving line and relying on throwing and catching. 

The towline can be attached to the towed vessel’s forward cleats or bitts, making sure that they are able to handle this load.  These bitts or cleats should be attached with adequate through bolts, washers and nuts.  These should be reinforced with a sufficient backing plate.  Wood or self-tapping screws should never be used.  Remember that bitts and cleats are found on deck whereas bollards are found on docks.  For a sailing vessel, wrap the towline around the mast, unless the mast is stepped on the deck.  If the mast is stepped then it will likely pull out.  Keep in mind that any item of hardware that fails could cause the towline to snap like a slingshot, putting anyone in its path in jeopardy.  A snapped towline can cause severe injury or even death.  If the towed vessel is trailered, it will have a bow eye that would be an excellent place to attach the towline.  However, be careful not to tow at sharp angles on a bow eye as it may snap under improper alignment of the tow.

Anchoring and towing

The towline needs to be secured so that it can be cast loose if need be.  Cutting tools, such as an axe or cutting torch, need to be ready for use near the towline.  Preventers can be used to overcome the whip of towlines when released (canvas, fire hose).  An anchor should be readied on the towed vessel in case the towline breaks or the tow is set free.  Bridles can be used to reduce the strain on the lines.  The lead of a tow bridle is redirected by a chock.  The legs of a tow bridle are joined together with a triangular plate with 3 holes called a fishplate (flounder plate).

Anchoring and towing

The hawser, or towline, needs to be attached to a secure fitting near the bow of the towed vessel.  The worst possible place to make the towline fast is to the stern of the towing vessel.  This causes the pull of the tow to prevent the stern from swinging properly in response to rudder action.  This limits the vessel’s maneuverability.  The towline should instead be made fast as far forward as possible. The most important point to remember is to start your tow gently.  Keep a steady pull at a reasonable speed to reduce strain.

Anchoring and towing
Anchoring and towing