Tuning an anchor rode
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Quiet sunset in Anse de Leoube (French Riviera)
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Most cruising yachts spend at least 80% of the time at anchor. The safety of the boat and its crew depends on a few pieces of metal and rope which hopefully will prevent the boat from running aground. When choosing a place to anchor, as well as sizing the anchoring gear, a wise skipper should not rely on luck to make sure that the anchor will hold if the weather conditions deteriorate: some physical sense and knowledge are invaluable.
Admittedly, although anchoring is based on longstanding physical laws, it cannot be completely mastered unless an in-depth (;-) analysis of the soil around the anchor is made, as oil platform engineers do.
Therefore, we will only skim the anchor problem, just stressing on the parameters that condition the performances of an anchor. We will focus on the rode behavior, with special emphasis on a generally underestimated problem: the dynamic behavior of various types of rode under wind gusts.
Finally, we will attempt the impossible: a synthetic spreadsheet to approximately size the anchor and the rode, given the anchorage conditions.
Note 1: Several downloadable spreadsheets are attached to the following pages, in order to allow yachtspeople to simulate their own rode configurations in various anchoring conditions. Those spreadsheets and their functionalities are summarized in the Synthesis page.
Note 2: If you feel allergic to formulae, tables, curves etc., you may skip them and directly go to the conclusions of each section!