None of the usual experts on seamanship seem to offer any specific information what weight an anchor sentinel should have. I own a Flicka—a 20-foot boat, which wanders quite a lot at anchor. I use a 17-pound sentinel, but the results aren't optimal. Can you offer any useful advice
Dan Dickison responds:
Thanks for your question. The object of a sentinel (sometimes called a kellet) is of course to increase the horizontal pull of the rode. In his tome, The Annapolis Book of Seamanship, John Rousmaniere recommends that a sentinel be weighted by something in the 20 to 50-pound category, so your 17-pound weight is a little on the light side. Prudence tells us to err on the heavier side, making sure of course that the sentinel is not chafing the main anchor line.
Rousmaniere also explains that choosing ground tackle—including the weight and placement of a sentinel—should be based not only the boat's displacement, but also on the amount of windage of the boat. In the case of a Flicka, you're dealing with a fair amount of windage for the boat's length, relative to say an Ultimate 20 or other more contemporary design of a comparable size. That partially explains your boat's propensity to wander at anchor.
According to the chart that Rousmaniere supplies in his book, a 30-foot boat with a nine-foot beam (I realize this is larger than your boat, but it's more applicable than the information given for a 20 footer) will produce 700 pounds of horizontal load on its anchoring gear in 30 knots of wind. Logic tells us that the stronger the wind, the larger the load on the rode. So it makes sense then that you'd need a slightly heavier sentinel in stronger winds in order for that device to properly deflect the rode.
You might also want to consider other ways of taming your boat at anchor in a blow. The simplest way to achieve greater horizontal pull on your anchor rode is to increase the amount of chain in the rode. This may not be a practical alternative for a boat the size of yours, so I'd also recommend the option of setting two anchors in such conditions. If you do this, try setting them 30 degrees apart, which should make the boat dance a lot less. Alternatively you could also try a Bahamian moor, with a stern anchor set. That too would limit the wandering you're experiencing at anchor.
Best of luck to you.