Safety At Sea Studies - 1995 Anchor Study Pg2
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The test objective was to evaluate the relative performance of anchors commonly used on sailing craft of the 40'-45' class in bottom conditions typical of the northwest. Performance characteristics included holding capacity, setting, stability and veering2. A visual underwater site investigation with divers was conducted prior to the tests but no detailed soil analysis was performed. The areas selected were chosen by the author based on extensive anchoring in Puget Sound and on the diver's opinion that the areas were typical of Puget Sound bottom conditions. It is also recognized that conditions will (and did) vary to some extent within each site. To make up for this, each anchor was tested at different locations within each site and different anchors were tested at approximately the same sites. A cautionary note should be mentioned at the outset. That is, this is not to be understood as the definitive anchor study but rather as one series of tests which we have compared with other tests. The tests did not focus on any special handling requirements of each anchor but effort was made to simulate an ordinary, careful setting procedure. The test collectively lead to only very general conclusions and do not account for anecdotal evidence. While there were controls applied to minimize variables, each attempted set was not on the exact location of other sets but rather in the same general area a short distance away. The boats used each had different horsepower which prevented some tests from recording the maximum resistance of the CQR, Delta and Performance 35 until they were placed on tugs the second day. Approximately 280 sets were accomplished in five areas in the two-day period of tests. The tests were conducted on a variety of bottom which ranged from good holding to foul. In general, than anchors with the largest surface or fluke area performed the best in good holding bottom and all anchors had trouble setting in rocky, kelp infested areas. The Davis and Luke anchors did not perform well in any area. The Bruce, which set virtually every time, had the least holding power of the remaining anchors. In the vast majority of anchoring situations in Puget Sound, resistance of 300-400 lbs. is probably more than adequate for summer cruising. Any anchor's best performance is probably optimized after some hours of soaking. Nevertheless, when the higher holding power is needed (storm conditions, lee shore, etc.), it is probably needed immediately and there may not be time to "soak." Getting underway can be difficult or dangerous. Two of the anchors that sustained the highest loads suffered damage, but the loads imposed were probably higher than would ever be imposed by weather except for shock loads caused by "bar tight" all chain rode. It also should be noted that the tests only recorded the static resistance in pounds given by the anchors, and dynamic shock loads, such as those caused by wave action or wind gusts, were not duplicated. Static holding power is nevertheless an important measure for anchor capability. Of the anchors tested, only five passed the threshold of 1,000 lbs. and only four could arguably pass as storm anchors. The holding power of those four - the MAX, CQR, Fortress and Performance 35 - exceeded storm anchor requirements, but failed to do so on a consistent basis. ANCHORS AND EQUIPMENT SELECTED AND PROCEDURES EMPLOYED The anchors selected3 were the Davis DXL 45, Luke 50, Delta 35, CQR 45, Fortress FX 37, MAX 17, West Marine Performance 35 and Bruce 44. Four identical rodes of 3/4" New England Ropes 3 Strand nylon line with 30' of 3/8" high test ACCO chain were supplied. The rodes were marked at 15' intervals and the distance from water line to where the rode led over the (bow/stern) of each boat was also measured to make sure a consistent 5:1 scope was selected. The 5:1 scope was chosen as a constant factor for all tests because it was the standard for the San Francisco 1990 tests and the most common standard used by Bob Smith in his Columbia River Tests. At 5:1 about 80% of each anchor's holding power should be achieved compared to 10:1 scope. Each boat had a strain gauge made fast to the rode. Three strain gauges had capacity up to 4,000 lbs. or more; the fourth gauge had a 2,000 lb. capacity. Two of the boats had insufficient horsepower to maximize the strain gauges but the anchors they worked with did not approach those limits. In theory a boat should be able to pull 30 lbs. per rated horsepower. However, two boats could only pull about 1/3 of this backing down.
Vessels 2. Portage Bay - The Seattle Yacht Club race committee boat, a 40' displacement trawler with a 120 H.P. Ford Lehman. Operator Denny Johnson. 3. Comfort - A 34' displacement trawler with a 120 H.P. Ford Lehman. Owner/operator Frank Shriver. 4. Reliable - A 45' commercial tug with a 225 H.P. 671 GMC rated at a bollard pull in excess of 6,000 lbs. Owner/operator Phil Shiveley. A maximum limit of 4,000 lbs. was imposed for all tests. This was well under the published breaking strength of the nylon rodes (16,000 lb.). Sometimes this limit was exceeded because of imprecise throttle setting. a. Straight Pulls. The procedure was to deploy the anchor, set it as gradually as possible to simulate normal anchoring, and observe the strain gauge and if it steadied at idle speed, gradually increase the rpms until the anchor dragged or until the strain gauge achieved the maximum predetermined limit. Dragging was ascertained to be any movement. It was usually indicated on the strain gauge first as a sudden drop in tension. Holding was determined to be steady tension for several seconds with no movement. Two people were assigned on each boat to take bearings and ascertain movement and one to monitor the strain gauge. When an anchor gave short periods of resistance or spikes, those were not recorded as holds. For instance, in foul ground anchors would apparently catch rocks and sometimes spike at 500-800 lbs., then let go and sometimes reload at equal stains. This was not regarded as holding. Slow consistent drag was not regarded as holding if the anchor did not stop although it might have been sustained for long periods. An exception to this procedure was with the Luke anchor which manifested some slow drag at the first series of tests and no numbers could otherwise be recorded. Sometimes it was difficult to assess dragging because it was very slow, perhaps one foot per minute was reported by the divers. b. Veering. If an anchor was initially pulled to drag, it was re-set at a minimum 300 lbs. then the boat maneuvered to 90-degrees from the original heading and power increased to drag or maximum strain. If the anchor did not drag initially a 90-degree veer was conducted without a reset. The same procedure was then repeated for a heading of 180-degrees from the 90-degree heading. Because of time constraint and anchor damage at the higher loads, the veering tests were primarily conducted only on the first day. c. Resetting. If an anchor dragged and did not reset immediately it was pulled to the surface and cleaned before reset. Only attempts with clean anchors were recorded. |