Thursday, May 23, 2013

Anchor Bridle Rattle

Have you ever anchored in a nice little inlet only to be awakened in the middle of the night by the anchor bridle rattling? The current running past the bridle causes it to vibrate at a 2-3 hertz frequency. The thimbles and shackles on the bow rattle in their fittings as a result. I don't know about you, but I find that incredibly annoying. I'm very sensitive to noise on board and I like to minimize it as much as possible, so that anything out of the ordinary will alert me to something that's amiss.

Tonight, we're anchored in Lincoln Creek, near St. Catherine's Sound in Georgia and there's a 3 Kn current running. I could tell that the noise was going to keep me from sleeping soundly. So I set out to find a way to stop it. My task was complicated by the wind vs current. The wind was blowing towards the mouth of the creek while the current was incoming. LUX was facing the current, but the bridle was facing aft because the wind blew us back towards the mouth of the creek.

Tying a line to the bridle back and belaying it to the bow strut isn't a good solution because the angles will change when the current and wind changes the angle of the bridle with respect to the bow strut. I found that if I tied a piece of line between the two bridle legs, it performed two things. First, it changed the resonant frequency slightly, reducing the tendency to vibrate. Second, it stopped the shackles from rocking and the noise stopped. Here's a photo of the resulting arrangement. Now I can sleep and yet be awakened by any errant noise. The ends of the line are brought aboard so that if the knots loosen, we won't lose the line. I used clove hitches for this experiment. We'll see if they hold all night long. A rolling hitch would also be useful if the clove hitches don't work.


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