Marking Anchor Chain

Story By Tim Murphy
Photos By Mark Corke

Here's how to make quick work of setting the right scope every time you anchor.

Anchor chain with colorful plastic markersPlastic "blocks" that snap into chain links are just one of many ways to mark anchor chain. Other boaters favor colored wire ties, rope, ribbon, or even paint.

"The cries of the leadsman began to rise out of the distance, and were gruffly repeated by the word-passers on the hurricane deck. ‘M-a-r-k three! ... M-a-r-k three! ... Quarter-less three! ... Half twain! ... Quarter twain! ... M-a-r-k twain!'"

On today's boats, electronic depth sounders have largely replaced leadsmen calling out the depth in fathoms, as related in Mark Twain's 1883 "Life on the Mississippi." But for anchoring, a traditional technology is still the best trick. That technology? Simply marking your boat's anchor rode at regular intervals.

Scope It Out

Successful anchoring heavily depends on scope: the ratio of anchor rode to water depth. A good baseline is to put out 5 feet of anchor rode for every foot of water depth. We'd call that a scope of 5-to-1.

Water depth for anchoring is calculated from the seafloor to the anchor roller or chock at the top of the bow, which is usually several feet more than the depth sounder's reading. More is always better, as a rule of thumb, providing there's room to allow for the boat to swing.

For a quick lunch stop in benign conditions, including a good-holding bottom, you can perhaps use a little less scope, say 3-to-1, if you're keeping watch. In rough conditions or for times you'll be away from the boat, you need more scope: perhaps 7-to-1, assuming the anchorage provides ample room for your boat to swing, considering shallow water, obstructions, and other boats. Many anchor-dragging incidents are caused by putting out too little scope, which doesn't allow the anchor chain and rode the best angle for digging in and staying in.

Mark It Up

Marking your rode is a quick way to see in real time just how much scope you're putting out. A typical marking system uses three colors three times each, first with one color used once, twice, then three times for each selected length, then the next color, etc. The colors may be from paint or dye, common on chain, or they may be made using ribbon or line, more common on rope. Voyagers Hal and Margaret Roth used ribbon (1-inch wide by 12-inches long in red, white, and blue) at increments of 5 fathoms, or 30 feet. This number works best for most boaters, as you'd almost always put out at least 30 feet of rode, even in shallow waters, so it's a good place to start your marks.

Colored wire ties

In the Canary Islands, I watched a transatlantic crew spray paint their chain with yellow, blue, and red marks at similar intervals. However, if you plan to regalvanize your anchor chain at some point, painted marks may make cleaning, or "pickling," the chain before regalvanizing more difficult.

Still another technique is to unlay colored three-strand line, then braid the strand through five or 10 links of chain at regular intervals. You can even use large colored zip ties, leaving the tails intact. If you're not into doing it yourself, chandleries sell color-coded markers in green, red, yellow for less than $6. These are marked with numerals for depth at 30-foot intervals.

No matter which method you choose, if you use a windlass, make sure your system passes over the gypsy.

Inside The Lines

What interval is best? That's something you can adapt to your type of boating. Some boaters prefer intervals of 25 feet between marks. I like 30 feet. Others prefer longer intervals, such as 50 feet. There is no set or prescribed interval; it depends in part on your boat and where you cruise. If you routinely boat in shallower waters, 10-foot intervals may work best. Use whatever works best for your needs. 

Tim Murphy, a BoatUS contributing editor and a longtime Cruising World Boat of the Year judge, is the co-author of Fundamentals of Marine Service Technology (ABYC, 2012).

— Published: June/July 2017


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