| | | MOST of us worry about our anchors. I know I've crossed my fingers and hoped for the best on numerous occasions because anchoring is more an art than a science. I've heard all the old rules such as "never use a scope of less than three times the depth" and "if in doubt, let more out", but I decided to carry out a few experiments to see if they really held true. There are two aspects to this anchoring business. The first concerns the forces that act on an anchor, which I wrote about in PBO 386. I don't want to say more about that here. Instead, I'm going to look at how anchors behave when used to moor a yacht to the bottom. My experiences with Anchorwatch, a device that measures anchor cable tension, have led me to follow a simple routine. I tighten the cable until the reading matches the maximum figure it's likely to reach, given the local weather conditions. Then I | | set the Anchorwatch alarm to a slightly lower setting. By doing that, I'm assuming the anchor will hold to this tension regardless of how often stresses occur, whether the direction of pull changes, or because of any other factors. This is a big assumption. So, the main purpose of my experiments was to look at how anchors behaved when dragged through the seabed, and how badly they suffered from roll-out. (Roll-out occurs when an anchor is dragged and corkscrews through the seabed, losing its grip). I'm also interested in the behaviour of anchors when they're veered - and how holding depends on scope. Since a fair amount of folklore is attached to the subject of scope, I also decided to take a closer look at the effects of cable length. I've been unable to find much useful information on these topics. But, despite this, the results of my experiments are both unexpected and, dare I say it, even disturbing... | | |