Quote:
Originally Posted by dhays
I suppose accounting for the scope would work in shallow water. If I have 100' of rode out, I may be 75' away from the anchor. How big do you set your circle? I would have to set it at a minimum of 150' since current often reverses and I may end up on the other side of the anchor. That means that I could drag 150' before the alarm would sound.
To be honest, I've never had any problems with my cell phone gps not being as accurate as my plotter. The cell phone plugged into a 12v charger will take less of a batter drain than leaving my Nav package turned on all night.
Many ways to skin the proverbial cat however.
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First, if you do the math, the scope has much less of an effect than you imagine unless you are using a very short scope. At 4:1 or more, you could just use the rode length and be close enough. The larger the scope the less it matters. Doesn't sound right but do the calculation. subtract a foot or so if it really bothers you but for an anchor alarm it doesn't need to be exact. In the above example, the mistake is setting your alarm at some point of the swing radius rather than at the anchor position. You are correct that if you set it as stated you could drag 150' before it alarms. The alarm needs to be set at the anchor drop point then you can set your 75' radius (+ some allowable margin of error or drag, plus the distance your GPS is from the bow of the boat, etc). Some apps may allow you to offset from your current position to approximate the anchor position, I don't have a lot of experience with them. The point is not to be precise but to alarm you if your anchor has failed or you've dragged more than acceptable amount, especailly during a re-set. In some anchorages, maybe you don't care if you drag a few hundred feet. In others it might be critical.