Most seamen have experienced the pronounced yawing of a ship during high winds while riding to a single anchor with a maximum scope of chain. The ship seems actually to sail back and forth on opposite tacks through the wind, gathering appreciable momentum on each excursion. The anchor gear is then subjected to considerable strain in overcoming this momentum at the end of each reach, as the ship is pulled to a sudden stop and brought about to begin her travel in the opposite direction.
As the diagram on the next page shows, the pivot point of a ship at anchor with a long scope of chain in a high wind will move in a figure-eight path. When winds of hurricane force are encountered, the yaw may be increased to eighty degrees and the surging become violent.
Dropping a second anchor, with a short scope of chain in tandem with the riding anchor, will reduce the momentum and surging and halve the yaw, approximately. With a twin-screw ship the engines and rudder may be used to assist in holding her head into the wind, but the ship can be held steady only with the greatest difficulty. With a single screw ship, the problem is greatly increased; in fact, use of the engine may increase the yaw.
During hurricanes or typhoons, the violent winds impart so much momentum to the ship that she is likely to break loose her anchors and drag rapidly, broadside to the winds, trailing her practically useless anchors off on her windward beam. For this reason many commanding officers prefer to seek the open sea. Of course, at times it is necessary to anchor and ride one out.
By carefully placing the second anchor in what one may well call a Hammerlock moor, as described later, the ship can be held steady during severe storms. The Hammer- lock moor will prevent yaw and thus eliminate those violent excursions back and forth through the wind. With no yaw and no charging back and forth, there are then no sudden surges against the ground tackle. With the ship steady and heading continuously into the wind, it is then a relatively simple matter for a qualified conning officer to use his engines as necessary to offset the violent and variable force of the wind.
The Hammerlock moor can be used to tame a violent 75 degree uncontrolled yaw, with its associated violent charging and surging, into a mild five degree fluctuation of heading. The engines can then be used with precision to preclude dragging.
During the fall of 1954, while using the Hammerlock moor, the USS Muliphen (AKA 61), commanded by the author of this article, rode out hurricanes Carol, Edna, and Hazel, while anchored in lower Chesapeake Bay.
During the height of these three storms, the Hammerlock moor held the ship steady for a combined total of fourteen hours (four for Carol, four for Edna, and six for Hazel, the last being by far the most severe of the three). The rudder was not used. The Hammerlock moor held the bow and completely eliminated the yawing, charging, and surging. Our single screw could then be employed with ease to “station-keep” against the force of the wind. There was never any extreme strain on the anchor gear. There was a controlled balance of forces working on the ship, and it was just as feasible to station-keep against the force of the wind as it is to station-keep in our much employed maneuver of fueling at sea.
The conning officer utilizing the Hammerlock moor must adjust engine turns frequently to keep the proper strain on the anchor chains and must be prepared to adjust the scope of the underfoot anchor as the wind veers or backs with the passage of the eye of the storm. He can best observe these two items from the forecastle and accordingly a qualified conning officer must be stationed in the eyes of the ship with good communication set up to the bridge.
As Carol approached, the ship rode with a maximum scope out to the port anchor and we later dropped the second anchor underfoot. We were attempting to use the engine to reduce the strain on the anchor gear, but with the violent yawing and charging, the engine proved of little or no use and even seemed at times to increase the surge on the chain at the end of each yaw. Muliphen, a single screw ship, simply could not be held into the wind with her anchors in tandem.
The precise positioning of the two anchors in a Hammerlock moor occurred to Mnliphen’s anchors purely by chance as Carol roared by. We were anchored to westward of the storm track and as the winds backed counterclockwise the heading of the ship swung left. This caused the ship to swing across the starboard underfoot anchor, the chain to this anchor crossing under the port riding chain. The two chains became crossed at an angle of from 60 to 90 degrees and the yawing stopped. The boatswain wanted to heave in the underfoot anchor for fear of fouling his gear, but the ship was then under complete control and was no longer charging around like an iron monster. The engine could be used with ease and precision to offset the winds and reduce the strain on the anchor gear. I studied the situation and decided to ride out the storm since there seemed no real immediate danger of fouling the anchor gear.
The anchors had been put down with the chains free as any seaman would prefer to see his gear. (Fig. 1.) However, as the wind backed the ship swung, thereby placing the anchors out of tandem, and soon the gear was as shown in Fig. 2. I know by later analysis that it is this out of tandem position of the two anchors which gave the ship a perfect balance of forces. The appearance of the crossed chains greatly resembled a hammerlock hold in wrestling, and certainly no hammerlock ever pinned an opponent more effectively than this moor was holding the bow of the Muliphen. For two hours the ship’s head was never more than five degrees out of the wind. That is better than an expert helmsman can steer at times in a following sea, and we were n6t using the rudder at all.
As the wind backed further around, the underfoot anchor took more of the strain, but fortunately its scope was neither too short nor too long. The short scope to the underfoot anchor permitted it to drag around as the wind backed, yet it was long enough to maintain a good out of tandem Hammerlock throughout. The winds backed a total of 135 degrees, while I was recording data during Carol. Fig. 3 shows the final position as the underfoot anchor had dragged from left to right.
During Carol, for a period of 1½ hours, while riding to one anchor, the maximum yaw was 56 degrees, the minimum yaw was 39 degrees, and the average was 50 degrees, charging and surging violent, winds 25 to 30 knots. For a period of one hour the ship rode with the underfoot anchor in tandem with the riding anchor. Maximum yaw 34 degrees, minimum yaw 21 degrees, average yaw 28 degrees, charging and surging moderate, winds 30 to 35 knots. Then the wind began to back and for thirty minutes, while the Hammerlock was being set and was tightening up, the maximum yaw was 22 degrees, the minimum was seven degrees, average 13 degrees, winds 35 to 40 knots. Then with the Hammerlock tightly set the ship rode for four hours. Maximum yaw 14 degrees, minimum yaw one degree, average five degrees, no charging and surging, winds 38 to 45 knots, with gusts to 55 knots.
During Edna I experimented with the anchors and demonstrated to my complete satisfaction that I could easily duplicate the position in which Carol had accidentally placed the anchor gear. For four hours during the height of the storm, with the Hammerlock set, the ship rode easily with no strain on the gear. No yawing, no charging, no surging. I was using the engines to counteract the force of the winds, but did not need the rudder. The ship was steady and under control, and remained under control. As Edna passed to the Eastward, the winds backed through 110 degrees, but again the underfoot anchor dragged around in an arc along the circumference of a circle, the riding anchor being the center of the circle and the scope to the riding anchor being the radius. The anchors remained out of tandem, and crossed at an angle of 60 to 90 degrees, maintaining throughout the same Hammerlock moor facing the wind.
During Edna I found essentially the same results:
1 anchor maximum scope—winds 35 to 45 knots |
|
Maximum yaw, 72 degrees |
Period of 1 hour—Charging and surging violent |
Minimum yaw, 35 degrees |
|
Average yaw, 55 degrees |
|
2 anchors in tandem, 1 underfoot, 1 maximum scope winds 35 to 50 knots |
|
Maximum yaw, 43 degrees |
Period of 1 hour—Charging and surging moderate |
Minimum yaw, 22 degrees |
|
Average yaw, 35 degrees |
|
2 anchors in a tight Hammerlock, winds 35 to 50 gusts to 65 |
|
Maximum yaw, 11 degrees |
Period of 4 hours—No charging and surging |
Minimum yaw, 1 degree |
|
Average yaw, 5 degrees |
When Hazel came along it was apparent that she would pass to» the westward. Accordingly, in order to duplicate my out of tandem moor, with crossed chains, I elected to put the starboard anchor down as the riding anchor. Then at the end of a large yaw to starboard I dropped the underfoot anchor, deliberately crossing the chains thereby, the riding chain being above the other. The winds from Hazel veered 135 degrees clockwise as she passed and again the underfoot anchor dragged around, maintaining a tight Hammerlock throughout. For six hours the ship rode beautifully, with the same good results experienced during Carol and Edna.
1 anchor maximum scope—winds 35 to 45 knots |
|
Maximum yaw, 73 degrees |
Period of 1 hour—Violent charging and surging |
Minimum yaw, 37 degrees |
|
Average yaw, 52 degrees |
|
2 anchors in tandem, 1 underfoot, 1 maximum scope winds 35 to 45 knots |
|
Maximum yaw, 49 degrees |
Period of 1 hour—Moderate charging and surging moderate |
Minimum yaw, 18 degrees |
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Average yaw, 39 degrees |
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2 anchors in a tight Hammerlock, winds 45 to 65—gusts to 80 |
|
Maximum yaw, 10 degrees |
Period of 6 hours—No charging and surging |
Minimum yaw, 1 degree |
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Average yaw, 4 degrees |
Later thought on the subject now makes me see rather clearly that the crossed anchor chains are unnecessary. It is the out of tandem anchors which do the trick.
Let us suppose we have a ship in a flooded drydock with two bow lines out to cleats and a stern line out to a winch as in Fig. 4 and Fig. 5. The resolution of forces in both cases will be essentially the same, (a) = (d) and (b) + (c) = (e)
Now with an out of tandem moor we may either cross the chains in an “X” or lay them out in a “V” Hammerlock with essentially the same results in preventing yaw.
In either Figure 6 or 7, force (a) balances force (d), while forces (b) and (c) combine to balance the wind force (e). Should the engines be used to offset the wind then forces (b) and (c) would be reduced accordingly.
Fortunately the anchor chains were accidentally crossed in an “X” Hammerlock for Carol, otherwise probably I would not have been willing to determine by experiment that such a position of the ground tackle is absolutely safe.
Even though the chains need not be crossed, I still prefer to call the moor the “Hammerlock” moor because, whether the “X” or “V” is used, the moor will hold the bow securely.
Having seen the Hammerlock perform so successfully for Muliphen during three hurricanes, I would be more than willing to try it during any high wind in any ship, of any size, even in one having only one anchor wildcat with which to handle her two anchor chains.
Now for the rules of how to set and maintain it. Like any precise maneuver it requires some degree of study, understanding, and preparation:
(1) Select an anchorage with a good holding ground, with about a mile of clear sea room around it.
(2) The anchorage should not be exposed to the open sea.
(3) Either anchor may be used as the riding anchor. However, in the northern hemisphere, if it is certain that the storm is going to pass to the east of the ship, then the starboard anchor should be used as the riding anchor so that a “V” Hammerlock, with an open hawse moor can be effected rather than an “X” Hammerlock with crossed chains. If the “V” moor is used, obviously the chains are less susceptible to becoming fouled in a round turn.
(4) Veer the riding anchor chain to maximum allowed scope.
(5) After you have anchored in anticipation of using a “V” Hammerlock, should the hurricane cross you up and pass on the wrong side, it is, in my opinion, perfectly safe to ride it out with an “X” Hammerlock and not change riding anchors. The winds at that time might be too high to permit re-anchoring with comfort.
(6) When the wind has reached sufficient force to cause yawing, the second anchor should be dropped at that extreme end of the yaw toward which the wind is expected to change direction. If the winds are expected to veer clockwise, then drop at the extreme end of a starboard yaw. If they are expected to back then drop at the extreme end of a port yaw. The final yaw can be increased by use of the engines to insure a good wide out of tandem moor. Use a scope of only five to eight fathoms more than the depth.
(7) Should the path of the hurricane still be in doubt, even when the second anchor must be dropped, and should you guess wrong and drop it at the wrong end of the yaw, it is suggested that you pick it up and drop it at the other extreme. Otherwise, the change in direction of the wind as the storm passes will first tend to unset the Hammerlock and then re-set it in the opposite direction. This might take an hour or more and during most of that time the two anchors would be forming only a tandem moor with a moderate yaw expected.
(8) Use sufficient engine turns to relieve most of the strain on the riding chain. Keep the angle at which the riding chain enters the water at a figure between 45 to 60 degrees. If too much engine speed is used there will be danger of overriding the underfoot anchor and fouling the anchor gear. Also adequate strain on both chains is what holds the bow and prevents the yaw. If too little engine speed is used, too much steady strain will be placed on the underfoot anchor and it will be dragged into tandem with the riding anchor and the wind.
The Multiphen, after surviving two hurricanes and six hours of Hazel with excellent results, showed the effect of too little engine speed when the wind increased to eighty knots. At that time, turns for three knots were being used, instead of for six knots as the following table indicates necessary. Too much strain on the anchors caused the underfoot anchor to be dragged into tandem with the riding anchor. Without the Hammerlock violent yawing began immediately. The ship turned broadside to the wind, and both anchors dragged. After some difficulty the Multiphen was brought under control and reanchored with the Hammerlock moor. Increased engine speed was used, and then she rode out the last four hours of Hazel without further difficulty.
The following table of engine speeds versus wind speeds was made from a graph I kept during the three hurricanes. It has not been proven, but it is at least a guide for an AKA moored with a Hammerlock moor.
Wind Speed in knots |
30 |
45 |
60 |
75 |
90 |
100 |
Engine speed in knots |
1 |
3 |
4 |
6 |
7 |
8 |
It will be noted that these plot almost in a straight line graph. One should commence by making turns very slowly for only about one knot and then add turns gradually as indicated by strain on the riding chain to keep the chain entering the water at a 45 to 60 degree angle, always being careful not to override.
(9) Station a qualified deck watch officer on the forecastle. He should be thoroughly conversant with the effect of engine turns during accurate station-keeping. His duties are to observe and make recommendations with respect to the adjustment of engine turns required to maintain the correct strain on the chains.
(10) The riding chain should tend away from the ship at an angle of about 30 to 45 degrees to the ship’s head. Should this angle become too great as the direction of the wind changes, it means that the underfoot anchor is holding too well and is not dragging around with the wind as it should. Slow down some on the engine turns and if the underfoot anchor still does not drag around, it may be necessary to heave in some on that anchor chain until it does drag. Be careful, however, not to drag it into the tandem position.
(11) When anchored in tidal waters be alert for any indication that the ship will swing to the tide, instead of to the wind. The underfoot anchor with its short scope can be picked up very quickly to avoid danger of a round turn in the two chains.
(12) Should the eye of a hurricane pass directly overhead, be alert to stop engines for the expected calm and re-set the moor, if necessary, for the expected sudden reversal of the winds.
The Hammerlock moor may also be used in the following operations:
(a) To steady an anchored seaplane tender, yawing in high wind, so that a seaplane can approach and be hoisted.
(b) By an anchored tanker, tender, or supply ship to eliminate yawing in order to facilitate other ships mooring and clearing from alongside for fueling or services during a strong wind.
(c) By an APA or AKA, to eliminate yawing, to hold her head into the sea, and to prevent excessive rolling while lowering and hoisting her many boats during a strong wind.
(d) To steady any ship anchored in a current which is strong enough to produce figure-eight yawing.
(e) By a carrier at anchor, to hold her head steady into a strong wind, should it be necessary or desirable to catapult, or recover, several aircraft in rapid succession.
(f) By a ship secured to a mooring buoy during a severe storm, to ease the strain on the ship’s riding chain and the buoy’s anchor clump. It is, of course, necessary to veer sufficient chain so that the underfoot anchor will clear the buoy’s anchor clump.
Let us hope that you will never have to test out the Hammerlock moor during a hurricane, but, if you do, you should find it most effective. No special gear is required and there is really nothing new involved. It merely follows the ancient rule that many good pilots quote, “Always take maximum advantage of the wind. Let it work for you and not against you.” The Hammerlock most certainly does just that. It uses the force of the wind to stop the yaw and hold the ship steady so that the engines can then be used as needed to oppose the force of the wind.