Asleep at the wheel
Join Date: Sep 2011
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Re: 2 last minute questions
Scope should generally be 7-10 times the depth of the water. Add to that the length of the boat. Now double that, and you start to get an idea of how much the boat (or more correctly, the GPS) can move while you're at anchor, depending on exactly where/when you set the initial GPS location.
So, if you're like me and your anchor bounces for a bit, how do you determine the warning distance you want to set? I did the following (not sure if it's right, but it worked for me):
I stood at the bow with my phone over the bow cleat and marked that spot. I'm OK with the boat swinging around on its anchor, but I want to know when the anchor moves, so I based my calculations on an assumption that the boat was going to swing through at least 180 degrees. I decided that the most the phone/GPS will possibly move is 2x the scope plus the length of the boat. I then added 10 feet in case my calculations were wrong. So, for my purposes, my 31' boat was anchored in about 15' of water, so we had 150 feet of anchor rope deployed. That meant that I set the warning distance to (150x2) + 31 + 10 = 341', which I rounded to 345.
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