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-   -   Using Two Anchors (http://www.sailnet.com/forums/seamanship-articles/19166-using-two-anchors.html)

Tom Wood 01-19-2004 07:00 PM

Using Two Anchors
 
<HTML><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8>&nbsp;</TD><TD vAlign=top align=left width=222><IMG height=227 src="http://www.sailnet.com/images/content/authors/wood/060800tw_tropical_coveSN.jpg" width=222><BR><DIV class=captionheader align=left><B><FONT color=#000000>A wind shift could put the keel in the sand.</FONT></B></DIV></TD></TR><TR><TD colSpan=2 height=8>&nbsp;</TD></TR></TBODY></TABLE>The odds that anything will go wrong with a well-prepared ground tackle system are very remote. "Well prepared" means adequately sized with quality materials, professional-grade splicing, and attention to maintenance details such as seizing wire on all screw shackles. But if you anchor enough times, the odds eventually catch up with you. <P>In 30 years of cruising, we have had two complete rode failures on our boats, both occurring in light to moderate weather when such an event was the farthest thing from our minds. In the first case, a highly-polished stainless steel double-jaw swivel (read "expensive") simply broke in half. It was less than six months old and showed no signs of crevice corrosion. When we hauled up the chain, one half of the swivel was still wired to the end with a nice, round hole where the swivel pin had previously resided. We never found the anchor, the pin, or the other half of the swivel on the soft mud bottom. <P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8>&nbsp;</TD><TD vAlign=top align=left width=222><IMG height=247 src="http://www.sailnet.com/images/content/authors/wood/060800tw_anchoredDG.jpg" width=222><BR><DIV class=captionheader align=left><B><FONT color=#000000>A lee shore calls for two hooks and vigilance.</FONT></B></DIV></TD></TR><TR><TD colSpan=2 height=8>&nbsp;</TD></TR></TBODY></TABLE>The second failure was with a rope/chain rode. The rope came up looking like it had been cut with a surgeon's scalpel about three feet up from the splice around the thimble. We recovered this anchor and chain, complete with the other neatly cut end of rope, but never discovered what could have inflicted such a cut on a clean, sandy ocean floor. <P>Beyond these two inexplicable events, we've had several cases of anchors pulling out after as much as 12 days in the same spot. Usually, this comes with a fast wind switch or change of tidal current flow. Often, such a breakout is assisted by anomalies on the bottom, and we have pulled up tires, gallon paint pails, and once a six-foot length of picket fence on the tips of our anchors. <P>It is little wonder then that we feel more secure when we have two anchors down. It is simply the best insurance policy that can be bought with a little extra work. This is not to say that we always use two hooks. <TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD colSpan=2 height=8>&nbsp;</TD></TR><TR><TD width=8>&nbsp;</TD><TD vAlign=top align=left width=222><IMG height=189 src="http://www.sailnet.com/images/content/authors/wood/060800tw_sailboat1MH.jpg" width=222><BR><DIV class=captionheader align=left><B><FONT color=#000000>Limiting swing in a mooring field calls for multiple anchors.</FONT></B></DIV></TD></TR><TR><TD colSpan=2 height=8>&nbsp;</TD></TR></TBODY></TABLE>For light weather, where we know the holding is good, or when we can dive the anchor to visually check its set and the surrounding area, we normally use just our primary tackle. But if the slightest doubt exists, if the weather is unsettled, or we have a tight, lee-shore situation, at least two pieces of steel go into the briny. <P>In fact, it isn't terribly uncommon for us to set three anchors, or even four, especially when cruising Florida and the Bahamas in the winter. Cold fronts sweeping as far south as the Virgin Islands from December to April can pack nasty squalls with hurricane force gusts in their forward roll clouds, often accompanied by a wind shift of over 90 degrees. A nice, tight anchorage is the place to weather these fronts, but only if you can keep the keel off the beach by setting three or four hooks into terra firma. <P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8>&nbsp;</TD><TD vAlign=top align=left width=222><IMG height=184 src="http://www.sailnet.com/images/content/authors/wood/060800tw_anchorefig1.gif" width=222><BR><DIV class=captionheader align=left><B><FONT color=#000000>Two anchors limit swing radius to both sides.</FONT></B></DIV></TD></TR><TR><TD colSpan=2 height=8>&nbsp;</TD></TR></TBODY></TABLE>Beyond the issue of safety insurance or storm management, however, there are several other reasons to set two anchors. A relatively minor point is that two anchors set off the bow in a <I>V</I> formation helps keep the boat from sailing around the anchorage. Heavy, full-keeled boats generally lie fairly quietly on one anchor, but their lightweight, fin-keeled cousins are notorious for charging at the boats around them like a wild stallion. <P>The most typical uses of a two-anchor system off the bow is to place the two rodes anywhere from directly in line to a <I>V</I> formation of about 45 degrees. It is important to recognize that the width of the <I>V</I>, or the distance between the anchors in relationship to the scope, has a profound effect on how the boat behaves. If you play with the concept on a piece of paper, you will shortly see that the wider the <I>V</I>, the more the boat is limited from swinging either to port or starboard. In fact, there are several ways in which two anchors are set 180 degrees apart that are used specifically to limit swing to near zero in a crowded mooring field or a narrow stream. We will cover the techniques of the Bahamian moor and fore-and-aft anchoring in a future article. <P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8>&nbsp;</TD><TD vAlign=top align=left width=222><IMG height=209 src="http://www.sailnet.com/images/content/authors/wood/060800tw_anchorefig2.gif" width=222><BR><DIV class=captionheader align=left><B><FONT color=#000000>With the wind shift, the port anchor rode goes slack.</FONT></B></DIV></TD></TR><TR><TD colSpan=2 height=8>&nbsp;</TD></TR></TBODY></TABLE>The best way we've found to visualize what happens to the boat on two anchors is to create an imaginary "anchoring baseline" that runs through both anchors. If the wind is from the north and the boat is anchored on a 45 degree <I>V</I> formation, the baseline is oriented east and west perpendicular to the wind. If the wind later switches to the east, both anchors will now be out in front of you in a straight line along this east-west baseline. <P>After such a wind switch has left you with the anchors out ahead, one rode will be completely slack (in this case it will be the port one). This gives rise to several choices. You can let out additional rode on the starboard anchor if you wish to continue sitting with equal tension on both hooks. Or you can leave the boat as it is, tied to the bottom with only the starboard anchor, leaving the port rode slack as a safety. This latter technique limits your swinging radius port and starboard. After all, one of the key reasons to use two anchors in the first place is to limit the swinging radius of the boat to the sides. <P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8>&nbsp;</TD><TD vAlign=top align=left width=222><IMG height=224 src="http://www.sailnet.com/images/content/authors/wood/060800tw_anchorefig3.gif" width=222><BR><DIV class=captionheader align=left><B><FONT color=#000000>Anticipating the shift puts the anchors on a baseline for the forecast wind.</FONT></B></DIV></TD></TR><TR><TD colSpan=2 height=8>&nbsp;</TD></TR></TBODY></TABLE>The beauty of envisioning an imaginary anchoring baseline is that you can use it to set the hooks in advance for an expected, future wind. Let's say that you have a moderate north wind, but you expect the wind to strengthen and gradually move to the east. You don't need two anchors now, but probably will want two down for tomorrow's stronger blow. If you anchor in a <I>V</I> formation to the current north wind, your anchors will be on an east/west baseline. After the wind switch occurs, the two anchors will both be out in front of you to the east with the boat lying on the starboard anchor and the port rode totally slack. You can let out extra rode on the starboard anchor until the port rode comes taught and riding on two hooks again. This is OK as long as you have the swing room, as discussed above. <P>But let's reverse the thinking process. If the north wind is going to clock to the east, this new east wind would leave you a north/south baseline for your anchors. If you put the two hooks straight out ahead of the boat along this north/south line in the first place, the port one directly in front of the starboard, the boat will swing just like all the other boats around her that are anchored on just one hook in the present north wind. But as the wind switches, the longer rode on the port (forward) anchor will go slack, and the boat will be sitting on only the shorter, starboard rode. At this point, all you need do is to saunter forward and pull in the slack port anchor rode, and you will neatly be anchored on a <I>V</I> formation, ready to weather the stronger breezes. Where a wind shift is expected, this technique can keep you from performing a firedrill in the dinghy after the wind changes and builds—you can relax and watch all the other cruisers perform these antics. <P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8>&nbsp;</TD><TD vAlign=top align=left width=222><IMG height=225 src="http://www.sailnet.com/images/content/authors/wood/060800tw_island_anchorSN.jpg" width=222><BR><DIV class=captionheader align=left><B><FONT color=#000000>Two hooks provide safety in close quarters and open anchorages.</FONT></B></DIV></TD></TR><TR><TD colSpan=2 height=8>&nbsp;</TD></TR></TBODY></TABLE>Another procedure that takes advantage of the baseline concept is directly connected with the worst of all the problems connected with the use of two anchors—the problem of twisting the rodes. Playing with your sketchpad again, it is easy to see that if you start in a north wind on a 45 degree <I>V</I> (east/west baseline) and the wind continues through the east and settles in the south, the boat will still be anchored on a 45 degree <I>V</I> on the original and proper east/west baseline. But the starboard anchor will now be out to port, and the port rode will be pulling out to starboard—in other words, they are crossed. If the wind was to continue to clock around to the north again, all would be just as in the beginning, except for one perfect and complete twist in the rodes at the stemhead. There is no immediate danger in this, but it does cause a good deal of premature chafing wear on the rodes. <P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8>&nbsp;</TD><TD vAlign=top align=left width=222><IMG height=227 src="http://www.sailnet.com/images/content/authors/wood/060800tw_anchorefig4.gif" width=222><BR><DIV class=captionheader align=left><B><FONT color=#000000>Preparing for a strong cold front involves initially crossing the rodes.</FONT></B></DIV></TD></TR><TR><TD colSpan=2 height=8>&nbsp;</TD></TR></TBODY></TABLE>The twist in the rodes is unavoidable, but because of its predictability, you can anticipate it when you are waiting for for the wind to switch. While we have personally never put a full twist in our rodes when we anchor, we often will cross the rodes in order to set the two hooks on a baseline for an anticipated wind shift. The most common scenario is our old friend, the cold front. In the winter cruising grounds, the wind associated with these usually builds out of the southwest, then shifts suddenly, sometimes with great violence, to the north. Since we are mostly interested in having both our anchors firmly planted and pulling equally during and immediately after the frontal passage, we want the anchors set on an east/west baseline to accommodate the new north wind. With a present south or southwest wind, this means taking the port rode out over the top of the starboard in a shallow cross, and setting it on a longer length of rode to the west. When the wind starts shifting, we simply pull in the slack on the port rode to keep even tension on the two anchors. <P>Using two anchors pays big dividends in how well you sleep at night and how hard you must work during changes in wind direction. With a little forethought and practice, you may find that you're the most relaxed crew in the anchorage.</P></HTML>


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