Why does my boat swing so much at anchor?

Hi All

Very much a newbie here and to this form of boating. Seeking some advice on how to reduce the amount of swing when anchored. In most instances we anchor in relatively calm waters but while boats around me appear to move very little, mine swings back and forth. I don't know if its the bimini top on the flybridge or just the style of boat. I read a post somewhere that attaching a sea anchor to the anchor chain just below water level resolves the problem. Well it didn't...lol.

Thanks in advance.

Mike

Hi there & welcome aboard!

Search TF or Internet for ‘riding sail’

Welcome Mike.

My boat swings too. I only draw 3'6" and I thing this contributes to more swing when compared to full keel boats. You could also run a stern line to shore.

Check out this old thread : http://www.trawlerforum.com/forums/s42/sailing-anchor-38199.html#post658822

Our boat has a boom, so a small tarp/sail at the end serves the same function as the feathers on an arrow. There must be solutions out there for trawlers without booms...

My boat sails at anchor a fair bit as well. I think it is partly due to the high bow. using a bridle with attachment points part way back toward the middle of the hull helps a bit. But a lot of it arises from windage anyway.

Around Moreton Bay the anchorages can often be busy and some folks anchor closer than you would like. In that case you don't want to have a stern anchor or a shoreline! Also the tidal current reverse, so you definitely want to be able to swing around to the other direction when that occurs or there will be chaos with other boats nearby.

Next year I'm going to install some flopper stoppers for reducing roll when waves/wakes are at a different angle to wind/current. I think they might help reduce the sailing a bit as well.

This keeps coming up. The problem is usually a lot of windage forward. Solutions are many, as are opinions about which works best.

Some include: Set the rudder hard over. Run a snubber line to a midship cleat to force the boat to ride at an angle to the wind/current. Set a drogue, sea anchor or just drag a long line, or even trail a bucket aft. A steadying or riding sail has worked for some, but most report no luck with one. Some have gone as far as setting two anchors, but personally I find that more effort than it's worth.

As to why...

Do you have a nylon rode? If you do, then your boat would behave like ours.

In windy conditions, without the riding sail, our bow will fall off the wind presenting either the port or starboard side to the wind. The boat gets forced downwind and stretches the rode tight, then the boat springs back upwind when the rode releases it elasticity, and the bow falls off the other way for another ride downwind. Repeat.

The riding sail acts like the feathers on an arrow, reducing the yo-yo effect and the swinging. This also reduces shock loading the anchor every time the boat bounces on the rode.

Is this an issue? I mean mine swing when there is some wind, gently in light wind, more intense in heavy wind, however it has never been an issue. Look through windows it looks like cinemascope

L

What about a sea anchor off the stern. If you have any tide running it should help with the swing. Maybe would dampen it a bit. I use one when drift fishing to keep the bow into the current, seems to stabilize the boat.

A bridle might help. Sea Dog make a plate which fits on the chain,you attach 2 lines, one to each top corner drilled hole, through each hawse hole back to the bow cleat.
It`s as much a function of how much boat is under the water as anything else. Next time you are anchored look at the Rivs and "sports boats" with planing hulls, they really hunt around an anchor or mooring.

Mine swims pretty badly in some anchoring conditions. I've messed with various solutions, none worked very well and were generally a PITA. So now I just ignore it. Boat swims. Have a beer and go to bed.

Ski in NC said:

Mine swims pretty badly in some anchoring conditions. I've messed with various solutions, none worked very well and were generally a PITA. So now I just ignore it. Boat swims. Have a beer and go to bed.

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I’ll try your solution next time!

I’ve never tried it, but I’ve read that one can tie a line near the stern and tie a hitch on the bitter end of the line to your anchor rode. Tighten the line enough to pull the stern a few degrees to the side. Supposedly this will remove a lot of the “fish tailing”. I can also imagine that by doing this could create a recipe to increase fish tailing. I’ll go back to sleep now...

A drogue or sea anchor as far behind as practical. The further behind the sea anchor the more leverage it has in keeping you straight. Usually trailed behind with a buoy back about 2/3 of the line length. Never use chain, only line. The buoy helps get the sea anchor far behind you. Otherwise in shallow water the sea anchor ends up on the bottom right behind the boat. In the ocean in swells or a current you don't need the buoy.
Also a longer anchor line helps. A short scope makes the osculations worse.

Osculations? Why are we talking about smooching, when we were't?

A quick fix that only works sometimes is to tie off to a fwd. cleat that is NOT in the boats center line.

A stern tie can also work tho it screws up the boats natural ventilation.

Giving the boat a sheer looks funny to passing sailors , but sometimes quiets a dancing queen.

There is too much boat house fwd of the boats pivot point so you have a backwards weather vane..

An aft riding sail works well , if the vessel can rig it.

Easy to try, tho small, is a windsurfer mast and sail.

Think of it as a panoramic view of the anchorage

Hi,

I have noticed a shorter chain line out to reduce the sailing of 1: 2 up to 1: 3, but notice the Baltic Sea is not a tide and this is bosible.

NBs

Less windage forward or more aft is needed. try lowering the bimini and see what happens.
Any sort of sea anchor needs a current to work, slow movement of the boat will just take up the slack in its line.

Put some water toys on the side deck aft.

The key is to unbalance the wind effect on the boat

Too much swinging on a boat at anchor? Sounds like you guys are having some really good parties.

Casey6404 said:

Too much swinging on a boat at anchor? Sounds like you guys are having some really good parties.

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And we haven't even started winter yet!!

What you are experiencing is your vessels natural tendency to heave to when forward speed goes to zero. At anchor in light winds and no current boat’s are pretty much free to float forwards backwards and sideways whenever drag force induced by the vessels wind age is less than the forward pulling forces of the anchor rode. Rigging a riding sail aft with it’s clew forward might give enough reward force but hey in light wind who cares.

Anchor

Same problem with my single engine trawler. I replaced my nylon anchor line and anchor. I use all chain and anchor both oversized for my boat. I was able to reduce my rode and diminish my swings. I place a snubber from the chain to my Sampson post to reduce stress on my windlass. I carry two anchors for different bottoms. A danforth and a plough. On the biter end of my chain where it attaches to boat in anchor well I use nylon line. This I can cut the chain and anchor loose in an emergency. The end of the chain is attached to a large float and line for anchor retrevial. I know some will comment this is wrong but it works and anchor never dislodges when current or wind direction changes. I have weathered 60mph winds at anchor safely. It does add forward weight but in my boat this is a plus.

Our 41 foot full keel boat will swing at anchor (so it's not just a matter of a full/partial keel unless you happen to be in a current that keeps your pointy end upstream). Attaching a bridle to the chain and secured to the boat's side cleats (about five feet abaft the anchor platform) helps a lot in reducing the swing, but she still swings!

Giggitoni said:

I’ll try your solution next time!

I’ve never tried it, but I’ve read that one can tie a line near the stern and tie a hitch on the bitter end of the line to your anchor rode. Tighten the line enough to pull the stern a few degrees to the side. Supposedly this will remove a lot of the “fish tailing”. I can also imagine that by doing this could create a recipe to increase fish tailing. I’ll go back to sleep now...

Click to expand...

A great way to reduce the "fish tailing" is to shorten -by about a foot- one of the two snubber lines.

m/v ATHENA said:

A great way to reduce the "fish tailing" is to shorten -by about a foot- one of the two snubber lines.

Click to expand...

I utilize two snubber lines. I’ll try shortening one next time. Thanks!

The sides of your boat are curved, right?...like the surfaces of an airplane wing. In a perfect world after you anchor, the wind, even a tiny wind, should stay dead ahead and your boat should not swing. But that if perfect wind shifts even 5 degrees and now your curved sided boat is an airplane wing generating lift (call it suction) on one side and disrupted air flow on the other. The boat now swings or pulled to the side generating the lift. If it swings too far the anchor line going tight jerks it back the bow may go through the eye of the wing and the roles will be reversed, lift or suction will be generated on the opposite side and disrupted air flow on the other. This process repeats itself all night.

In additions to shifting winds the wake of a passing boat or a shifting swell can also upset the equilibrium in that perfect world.

The worst boats for this are like one of my boats, a fin-keel racing sloop. The only fix is to anchor stern to and lay in you bunk and listen to the slap, slap, slap of the waves under the transom.

My other boat is a large power cat that anchors with a bridle so no problem. If your boat has a wide beam pretty far forward you might try rigging a bridle fixed a little way aft of the bow. Boats with full length extended keels avoid most of this.


I

I’am on the upper Mississippi and anchor out fairly often. I’ve found that turning the wheel one way or the other cuts way down on swinging at anchor, stopping it completely at times.

We have always found that attaching your anchor Snub line to the front cleat near the anchor winch and the other end of the snub line on one of the cleats half or one third the way down the same side, works best. This will ensure that there is a positive drag down one side and the wind and current flow will create enough flow that will greatly minimize the swinging. This we found works the best.

Our last boat would swing quite a bit at anchor when the wind would pick up over about 15-18 kts. I've measured the swing angle as pushing 180 degrees.


I tried a bunch of tricks suggested here in a previous thread, and by others, including:


1) Use a two line snubber rather than a single line


2) Use an asymmetric snubber


3) Tie through the hawse pipe on only one side so the boat presents at an angle (extreme version of the symmetric snubber)


4) Hanging fenders off one side of the boat (yup, someone suggested that)


None of it made any difference.


I then found an article that seemed credible that explained what was happening. The basic dynamic is that the boat's natural center of rotation (the point around with it rotates if you pull sideways on one end) is BEHIND the center of force for wind hitting the boat. The result is unstable, like an arrow with feathers in the front rather than the back. Now this is all about the wind effect and doesn't take current into consideration. In my experience, current will almost always dominate wind.


So when a boat swings, here's what happens:


- As soon as the boat is anything other than perfectly into the wind, the point the wind force is acting on is forward of the boat's rotation center, so it wants to spin the boat around, and it does.


- But, as the boat rotates, more and more of it's side profile presents to the wind, and the center of windage shifts aft. The more house structure you have aft, the faster the center of windage will shift aft.


- As soon as the center of windage moves aft of the rotation center, it now wants to straighten the boat out, which it does. The anchor rode is also pulling from the bow, and that further encourages the boat to straighten out.


- As the boat straightens, momentum causes it to overshoot and the whole process repeats itself in the other direction.


The solutions offered were two fold, and you can find elements of them in all the remedies and tricks that people have suggested.


Remedy 1: Shift windage aft. This is why a small sail rigged aft helps, as does hanging fenders off the side (see, the person who suggested it wasn't crazy). Canvas "curtains" on aft railing, or enclosed aft decks could all help too. On some boats it might be possible to reduce forward windage, but I suspect that would be rare. Our last boat, with a high bow and forward pilot house, has lots of forward windage, so it makes sense that it would swing a lot.


Remedy 2: Move the anchor rode attachment point further forward. This has the effect of moving the boat's rotation point forward, and moving the relative location of windage aft. Unfortunately, this is impractical on most boats unless you want to make some permanent modification. At least I couldn't think of any practical way to rig a spar to move the anchor attachment point forward.



Hopefully this give everyone the basis for evaluating remedies. It helped me quite a bit, and was a significant factor is switching from a forward pilot house, to an aft pilot house boat.

a guess, put out a stern anchor to discourage movement.