Licensed 50 Ton Master
Join Date: Jan 2003
Location: Currently on Lake Ontario in New York
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There are simple formulas to calculate the windage a boat creates in steady wind-Bow-on with the perfect holding.
That is not what you buy an anchor for.
Your anchoring system has to hold during gusts, when the boat is sailing back and forth at anchor and increasing its windage considerably, and then you add the waves that shock load the anchoring system as they pass under your boat. All these things tremendously increase the load that your system has to sustain. Since waves also lift the bow as they pass they reduce your scope making the anchor work that much harder as well.
Different anchors work for different conditions and bottom types. Using the right anchor with its favorite bottom type makes it seem like the anchor can do anything. Then that same anchor in another situation seems like the worst anchor in the world. That is why most cruisers buy anchors considerably larger than any manufacturer suggests and have several different types aboard.
Remember that scope should be measured 1) from your bow, 2) at the top of the highest wave you may encounter 3) to the sea bottom 4) during the highest tide you may encounter.
5 to 1 is a lunch hook
7 to 1 is an overnight in a very protected anchorage
10 to one is the minimum for rough water high wind high current, etc.
Make sure you know the bottom your anchor is trying to hold onto
Make sure your swinging circle does not intercept anyone elses swinging circle
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Captain Don Quackenbush
SV HERMES, Pearson 33
East Coast, Great Lakes