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Thread: Using GPS to see if anchor is set

  1. #1

    Default Using GPS to see if anchor is set

    I'd like some opinions on using a GPS to check to see if the anchor is set. After lowering the anchor, backing toward shore as rode is let out, then tying off to the cleat, I put the boat in reverse to see if the anchor is set. As the boat's in reverse, I'll look at the water (either something floating in the water, or maybe I'll just spit into the water) to see if the boat moves in relation to it. If not, then I know the anchor isn't dragging. I'll also watch the rode to see if it's steady or if it vibrates, and if it get tight, then slack, tight, then slack, etc. I know of others who look at their GPS as they are backing down to tell them if they're moving. What do you do, and what do you think about the GPS method?

  2. #2
    Member hoose35's Avatar
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    I pretty much do the same as you and I also use GPS as a reference. The problem with GPS is if the boat is swinging, it will show you are moving when the anchor is holding just fine

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    Between your posted speed on the plotter, if you are looking at a map you can also zoom in and see your breadcrumb moving. If it's side to side, you are solid, if it's a moving straight line.....you are not set. basically at some point your speed will post to zero even if you are on a slow swing. As long as I see zero at some point, I figure I am good to go.

  4. #4

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    I do like most and check the breadcrumb trail once I'm on the hook, but my question has more to do with using GPS to check to see that the anchor is set as you are setting it. So you're backing down on the anchor to set it and use the GPS while you're doing this, right before you turn off the engine.

  5. #5
    Moderator Paul H's Avatar
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    I check my gps to see if I'm holding ground while setting my anchor. I glance between the screen and shore. There are some anchorages with heavy kelp where I might have to set the anchor a few times before it will stay put. If the anchor is slipping you'll be able to tell on the gps screen.

    I'm a bit paranoid about the anchor staying put while sleeping on the boat.
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  6. #6

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    Depending on the GPS / Chartplotter you have, you can keep an eye on your Vector line to make sure it shrinks to near nothing and stops pointing directly away from the position you dropped the anchor while setting it (backing down). Due to swing, unless it's FAC and no wind, there will usually have some movement, but less then, say .3 knots, and the vector will point more to one side or another. Other option is most GPS / Chartplotters have anchor alarms that you can set when the anchor is at short-stay/up-and-down and/or determine your circle with known line let out and depth of water (pythagorean theorem- a2+b2=c2, with depth of line as a (or b), length of line as c)... but I believe you were looking more for the Vector determination.
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    Member JR2's Avatar
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    I back down on the anchor until the line gets tight and then let off the throttle and see what happens. Usually the line rebounds a bit and pulls me back over the anchor a bit. I just leave the plotter on zoomed in until bed time and as long as we have not moved I figure its good. This system has worked on all but one trip I have taken.... on that one I woke up in the middle of Blackstone bay drifting along with the tide. It was flat calm and I was about 1/4 mile from the anchor spot. I had set on top of a shelf and backed into the beach and set the anchor as usual. The light wind kept us stern to the beach until about 4 AM when the wind died and the boat drifted out over the bench into the deep water and the anchor fell off the cliff. Next time in that spot I will drop the anchor and back away from the beach to be sure it set good on the shelf.
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    Member JOAT's Avatar
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    An additional thing you can do with GPS is to mark the position you drop the anchor as you're right on top of it as a waypoint. Then go through your anchor set procedures. That waypoint should be roughly where the anchor is, so once you're set, look at the distance to the anchor waypoint. Scroll over to that waypoint and open the properties. Select the menu item "create proximity" and enter a proximity distance that is a tad larger than the distance you are from your set point to the anchor point. By a "tad" you'll need to take into account that the waypoint won't be exact for the position of the anchor and balance that with how far you are willing to drag before the GPS alerts you. The proximity function makes a circle around the anchor waypoint with a radius of the distance you enter. You can now swing on the tide in a full 360 around the anchor within the circle, but if you start to drag anchor you will break the proximity circle, which will set off the proximity alarm on the GPS. So, if something changes hours later and you start to drag, you'll know when the alarm goes off.
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  9. #9

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    Back down until the line draws tight, then shift to neutral to see if springs forward. Final and most important step, go forward and reach past the roller to grab the line and hold on for a minute or so. Vibrations you can't see, especially with lots of scope, are easily felt in your hand. After a few minutes, check your GPS for speed, then zoom and look at your track.

  10. #10

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    Quote Originally Posted by BrownBear View Post
    Back down until the line draws tight, then shift to neutral to see if springs forward. Final and most important step, go forward and reach past the roller to grab the line and hold on for a minute or so. Vibrations you can't see, especially with lots of scope, are easily felt in your hand. After a few minutes, check your GPS for speed, then zoom and look at your track.
    This exactly. If I don't put a hand on the line I don't trust it.


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