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Old 05-15-2010
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Anchoring with tidal currents

Had my first experience with anchoring in a place with stronger currents from the tides and I did not get much sleep. The tidal range is only 3 feet but that is still enough to get a good effect.

My question is this. When we got here and found a decent spot put out the anchor and set it our boat would dance around and ride up on the anchor and not turn around. So a couple of times the rode would wrap up on the keel and kind of hang there for awhile in an uncomfortable way before unwinding and repeating the process. Another boat similar to mine was riding up on the line as well but not spinning around. I looked and he had his rudder just a little bit turned.

I should clarify that I did not mean the boat was swinging with the tides. It would spin 180 to 360 degrees every 5 minutes or so.

Another bit is that the currents run north/south and the wind was from the east.

Turning my rudder a little bit seems to have helped but I have not been through a cycle yet so I don't really know.

Is it just my boat that acts goofy or am I probably in some kind of a eddy current?
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Old 05-15-2010
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I have experienced the running up to the anchor situation. The MC has a full keel so she did not spin around. I wonder if the water running by the hull creates lift and pushes/pulls the boat forward??? Dan S/V Marian Claire
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Old 05-15-2010
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The solution is to set two anchors - 120 to 180 degrees apart. When the current tries to run you up on the one anchor, the second one prevents it. I have to do this all time when anchoring behind Duck Island near the CT River.
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Old 05-15-2010
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or get a riding sail, which just basicly adds drag to the back of the boat. it run down the center line of the boat to help keep the boat in the wind. i set my rudder hard over when i anchor to stop if from sailing around.

if your in an area with massive currents and the wind is not inline with the currents you could also try a bucket thrown of the back with 30 feet of line. this will help keep the boat in line with the current instead of the wind.

another thing i do to slow the sailing is to throw my lunch hook out the back with 2 to 1 scope, it basicly just drags and keeps the boat from swinging as fast
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Old 05-15-2010
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I considered 2 anchors but no one else here is anchored that way.

Putting a little bit of rudder on seemed to keep it from dancing in circles so much. The extra drag must do about the same thing as a bucket. Hold it back just enough to keep from riding all the way around.

Were leaving here tomorrow so it will likely be awhile before I get to try it again. I could not find anything in the anchoring techniques searches I did on google to say if there was a reason for it dancing around or riding up on the anchor against the current. I just got the bottom cleaned so maybe it is so streamlined the little bit of wind overcomes the current. Not sure how a keel facing sideways to the current can be streamlined but I am not a naval architect.

Maybe I have a deformed keel and it generates lift on one side as MC suggests. Or maybe my boat is just happy and likes to dance jigs.

Thanks for the suggestions. Next time it happens I will give some of them a try and see if it works better.
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Old 05-15-2010
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Sometimes where you drop your anchor makes a big difference. If you try to get out of the strongest flow and put yourself in an eddy or a place that is really swirly, your boat can be all over the place. In most situations where there is a lot of current, I prefer to be right out in the main flow where it is at least steady. There are times though like a strong wind opposing the current that this can be the wrong thing to do.

The above advice about 2nd anchors, buckets and rudder position is all good.
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Old 05-15-2010
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Quote:
Originally Posted by marianclaire View Post
I wonder if the water running by the hull creates lift and pushes/pulls the boat forward???
That would be awesome if it were possible. Would that I could just point my bow into the current and the keel would generate lift and drive the boat forward! Don't forget that lift typically pushes boats sideways

What sort of ground tackle have you got? What scope? If there's a lot of tension on a nylon rode, the rode might stretch and then spring back if the current is not constant. I experience this pretty frequently when anchoring, though I have not had the misfortune of snagging my keel on the rode.

Are you downstream of another anchored boat? As the upstream boat swings it will throw little vortices off its submerged foils. When these foils hit your boat, the current might briefly drop in strength, allowing you to spring forward. Alternatively there could be some underwater object upstream similarly disturbing the flow.

What scope are you at? If there's a current pushing you back, it seems unlikely that you could spring all the way to your anchor with sufficient scope.

Finally, if "upwind" an "upstream" are more than 90° apart, it could be that your boat is sailing upwind against the current under her own windage.

When you're moving forward, is it directly upstream, or at an angle to the current? If directly, I would blame the rode for acting like a spring; if at an angle, I would blame wind-vs.-current.
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Old 05-16-2010
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Quote:
Originally Posted by AdamLein View Post
What sort of ground tackle have you got? What scope? If there's a lot of tension on a nylon rode, the rode might stretch and then spring back if the current is not constant. I experience this pretty frequently when anchoring, though I have not had the misfortune of snagging my keel on the rode.
I have a 20ish pound danforth with 10 feet of chain and nylon rode. Scope is about 5:1(don't want a lecture on 5:1 minimum). It is springy so you are probably right about it running forward and then getting pulled backwards by the rode.

Not that many boats around me but this is a spoil area and is pretty lumpy. I was thinking it must be some eddies but the rode pulling the boat backwards makes a certain amount of sense. When this started the wind was at 90 to the current now the wind has shifted a bit so windage may have amplified it.
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Old 05-16-2010
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Quote:
Originally Posted by AdamLein View Post
That would be awesome if it were possible. Would that I could just point my bow into the current and the keel would generate lift and drive the boat forward! Don't forget that lift typically pushes boats sideways


I think the fact that the boat is anchored makes a difference. Obviously a drifting boat will go with the current no matter how it is pointed. It just seems that on most boats the bow is narrower than amidships or the stern so the water has to move faster. Much like a wing. Just an idea. Dan S/V Marian Claire

Last edited by Faster; 05-16-2010 at 12:23 PM. Reason: fixed quote
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Old 05-16-2010
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Stream moor: With a Bow anchor and a Stern anchor out fore & aft. This way is the best. If you have two anchors out forward you may end up with a twist or more between the two rodes. And if that happens you then have fun getting the twists out.
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