What makes a boat swing at anchor?

AusCan · Feb 19, 2014

I have tried to use reefed mainsail to position the boat so the bow is facing the swell.
One problem is the sail is too far forward; a mizzen sail would be much more effective.
Still, I can get it set to point the right way, and all is good.... for 10 minutes or so. Then the wind changes slightly, or the tidal flow increases/decreases, or the moon rises; changing the equilibrium ever so slightly.

So I just drop an aft anchor and all is good.

Nomad Willy · Feb 19, 2014

Ah yes Twistedtree that's the part I was missing .. CG. I see that now and that explains why Willy swings a lot even though she has a big long keel, plenty of weight and a bow that's only semi-high. Her CG is unusually far aft. Mystery solved.

A similar boat (Fisher) has a much further fwd CG (judging from her slack cheeks aft) and I'll bet swings much less. Better make a bridal. To be most effective it could tie off or attach to the gunn'l amidships ...... what think?

twistedtree · Feb 19, 2014

It's nice to have some science behind all this to guide our experiments to reduce swinging. Otherwise it's just poking in the dark, and guessing at the cause and effect. I'm too lazy for that.

FF · Feb 20, 2014

The cause is usually the owner demand for a roomeran ,

the cure is a second anchor out at about a 60 deg angle from the bow.

RickB · Feb 20, 2014

Perhaps a study of the "pivot point" would help illuminate this discussion ... or cloud it even further.

Hint: For the purpose of this discussion, CG is irrelevant.

Peter B · Feb 20, 2014

manyboats said:
I think design elements like a high bow and fwd cabin linked w little windage and keel aft. Not say'in that's the combo but consider a boat w a low bow and a huge cabin right at the stern. Probably make like an arrow and get stable ... especially if the boat is long.

Eric, I think you are right on the money there, and I'd wager the Nordhavn 62, rides very nicely and sedately at anchor, and probably without a bridle. There's one on our forum, who might chime in and corroborate this, but I suspect it is precisely because it is long, and has most of the windage aft. I noticed my Lotus sat much quieter at anchor, and sailed back and forth much less, after I had the extended flybridge and side deck canopy added, because it sort of acts like the fletching on an arrow.

What makes a boat swing at anchor?

AusCan

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Nomad Willy

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twistedtree

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FF

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RickB

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Peter B

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