Did you do any reversing testing, i.e. 180 degree change in direction of pull?
Unfortunately not. During the course of four full days, each anchor was tested 5x for a total of 60 pulls, which we felt was a required and respectable benchmark.
Since several of the anchors tested did not engage and develop much resistance in this soft mud during these straight line pulls, when they should have performed optimally, then as you might imagine their results would not have improved if we conducted off center load testing.
What surprises me about that data, which I think came from the SAIL article, is that we're challenged to find an anchor which provides holding greater than 1,500 lbs. and even over a 1,000 lbs. for the other anchors. I must not understand these numbers because posters on this forum have almost all remained anchored in conditions which would have created greater forces. In other words, on a 30 to 35 foot boat in 30+ knots of wind (I couldn't find the exact reference.) How is it that most of use have remained anchored at forces that must exceed the forces of this test - in less ideal circumstances? Is it the mud bottom? Is a power pull different than windage on a boat? Are there differences in the forces measured in a test vs. real life? I don't get it.
The data referenced in the Sail magazine article is from the Horizontal Loads Table (image below), which has been published by the American Boat & Yacht Council (ABYC).
Bob Taylor, a 45+ year retired US Navy anchor design and soil mechanics expert, who consulted for us on this project, had this to say about the ABYC tables:
"I checked on the basis of the ABYC table. It includes a factor of safety of 3 to account for waves and for current so the numbers are probably realistic. What this means is that the loads specified are high if all I have to deal with is wind but as soon as current and wind enter into the equation a boat may assume an orientation that results in a larger projected
wind and current drag areas.
Wind and current can come from different directions so the boat will assume an equilibrium position that resolves all the forces. If I presume that this load is realistic then I need to select an anchor that will safely hold this load so I need to provide a factor of safety to the anchor selection. If I do a full up dynamic analysis to determine loads then most regulatory agencies suggest sizing an anchor with a factor of safety of 1.5.
So, let's assume that the loads in the table reflect that of a dynamic analysis because they presume that wind, waves and current are considered. At a minimum an anchor should hold 50% more than that in the table (my suggestion). If I were being really safe I would suggest a factor of safety of 2 because of the uncertainties in bottom condition."
Shemandr, I know that you just asked me what time it is and I told you how to build a clock, but hopefully this answer, at least in part, will help. While many of us, including the boating media aboard, were surprised by some of the results, particularly for the "new generation" anchors, Bob was not, as he stated that anchors which are designed for harder soils will oftentimes have a holding ratio (holding capacity divided by anchor weight) of only 10-15 when used in a soft soil.
This is almost exactly what we found in the soft mud of the Chesapeake Bay, as almost all of the 44-46 lb anchors had averaged peak tensions of 450-700 lbs.
