Witnessing a boat’s rocky death first hand is enough to make you rethink your anchor size.

How often has another car in the mall parking lot rolled into yours? Never, right? You don’t select your parking space based on some assessment of which direction the surrounding unattended cars are likely to roll. And as for your own car, when you park it and set the brake, you fully expect it to be exactly where you left it when you return.

So what’s up with boats? Why do so many sailors seem to hold boat "parking" to a much lower standard? Given the relative value of boats and cars, shouldn’t the opposite be true? Dinghying away from a $400,000 boat without absolute confidence in the ground tackle is unfathomable to me, yet that appears to be the norm. For the three years Olga and I have been cruising, rarely has a strong squall at anchor not been accompanied by the warning blare of horns and/or a VHF radio announcement that one or more boats was dragging through the fleet. We have fended off unattended boats, cringed at the crunch of collision, and witnessed six-figure boats drag to a rocky death. It doesn’t need to happen. It shouldn’t happen.

It is true that cars enjoy four-point contact with solid ground while we restrain a boat by hooking to a sea bottom of unknown consistency. Sometimes that bottom is too soupy, too weedy, or too hard for our hook to grip and hold, but where boats tend to gather, bad bottoms are the exception. The problem is bad anchoring. Here are two questions you should ask yourself: how big is your primary anchor, and why did you select that size? The answer to the second question is almost certainly because you consulted an anchor table—it doesn’t matter whose anchor table—and this was the size recommended for your boat. Too often that makes the answer to the first question not big enough.

Anchor selection is nearly always characterized as a numbers game. Anchor manufacturers publish selection tables based on boat length. If you have a 34-foot boat, you need a 20-pound Danforth or a 22-pound Delta or a 33-pound Bruce.

Baloney!

Old salts will eschew manufacturers' propaganda in favor of the Ground Tackle Loads table developed by the American Boat and Yacht Council. The widely-published ABYC table projects horizontal loads on the deck hardware of boats of a given length, beam, and profile (power or sail). The different load values the table provides for different wind conditions are calculated simply by squaring the increase in wind speed. When wind speed doubles, the force it exerts increases by a factor of four. So consulting the ABYC table for our 34-foot boat, we find that the cleat load on a 35-foot sailboat with a 10-foot beam should not exceed 225 pounds in 15 knots of wind, 900 pounds in 30 knots, or 3,600 pounds in 60 knot winds. If the beam of our 34-footer is closer to 11 feet, we move down to the next line on the table, giving 300, 1,200 and 4,800 pound loads respectively.

This is all well and good as far as it goes, but if you decide that you want your primary anchor to be capable of coping with 60 knots of wind, how do you determine what anchor can resist a 3,600 (or 4,800) pound pull? Funny that you ask. There have been some independent anchor tests, and not one of the three anchors recommended above for our 34-footer has shown itself capable of resisting a 3,600-pound pull in sand or mud. How far short do they fall? Around 3,000 pounds short.

What is going on here? For one thing, the ABYC chart is outrageously conservative. Pull tests conducted by naval architect and marine engineer Robert Smith yield actual rode loads that are less than 1/3 of those projected by ABYC. But even if we use Smith’s numbers, we still need an anchor than can resist a 1,200 pound pull. Our twenty-something anchors, despite representations made by the manufacturers, are not up to the task. Test results would suggest that we need an anchor of twice the recommended size if we want assurance that our boat will stay put in a strong squall.

Windage--the surface of the hull, cabin top, awnings, the dodger, and rigging--is yet another factor that varies from boat to boat and which empirical load tables don’t take into account.

So is a 40-pound anchor large enough for our example boat? I don’t know. Does this boat have a dodger? A radar arch? A stack-pack? All of these things create windage that is not accounted for in any of the tables. Worse still, does our example boat sail around the anchor? I see some modern designs that repeatedly sheer absolutely perpendicular to the anchor line. When that happens, the beam is effectively 34-feet, about what we would expect in a 100-foot monohull. No table recommends a 40-pound anchor for a 100-foot boat.

With the increasing popularity of catamarans, it is also worth noting that none of these length-based tables bears any relationship to the actual ground tackle loads induced by the extreme beam, tall freeboard, and even taller cabin height of these boats. As a result, virtually every catamaran in charter is outfitted with inadequate ground tackle. It is no surprise that these boats drag with depressing regularity.

Close consideration should make anyone wonder if a 20-pound anchor could really be capable of consistently resisting the determined pull of an 8-ton boat, but the tremendous holding power of properly designed lightweight anchors is so ingrained in boating literature that doubt is unthinkable. In fact, lightweight anchors are capable of impressive holding power—in ideal conditions. Unfortunately ideal conditions are not the rule. In marginal bottom conditions, bigger holds better than small, heavier better than light—period.

Where does this leave us? Tables or formulas are simply unreliable for determining appropriate anchor size. This is an empirical issue and the empirical evidence of epidemic dragging suggests that the majority of boats carry primary anchors that are too small. An additional 10 or 20 pounds of anchor weight makes little difference in ground tackle handling—none at all if the boat is windlass equipped—but the extra weight and surface area makes a huge difference in holding power.

Cognizant of the role cost plays in anchor selection, manufacturers are predisposed to recommend the smallest possible anchor. Given that the vast majority of day and weekend sailing is done in benign conditions, the capabilities of this minimal anchor are rarely exceeded. Everybody is happy. However, if you plan to sail beyond your home waters and beyond the two-day forecast, the smallest anchor you should consider is a size larger than the manufacturer’s recommendation. If you ever drag this anchor, even once, it is still too small. If you want to sleep soundly when the weather grows unsettled, go up two sizes from the start. It will be a choice you will come to think of as one of your best.