Definitions of Swivel

A swivel joint is a connection that allows a connected object, such as a gun, chair, swivel caster, or anchor, to rotate horizontally or vertically.

Rotary design

A common design for a swivel is a cylindrical rod that can rotate freely within a support structure.The rod is usually prevented from slipping out by a nut, washer or thickened rod.The unit can be attached to the end or center of the rod.Another common design is a sphere capable of rotating within a support structure.The device is attached to the sphere.A third design is a hollow cylindrical rod with a rod inside it that is slightly smaller than its inner diameter.They are secured against separation by flanges. The device can be connected to either end.Swivels for pipes are usually threaded connections where at least one of the pipes is bent, usually at a 45 or 90 degree angle.The connection is tightened enough to be watertight or airtight, then tightened further to get it in place.

Anchor riding rotation 

Swivels are also used in the nautical sector as an element of anchor bolts and boat mooring systems.For yachts, swivels are most often used between the anchor and the chain.There is an opinion that the anchor swivel should not be attached to the anchor itself but should be located somewhere in the chain.

The anchor swivel is expected to serve two purposes:

• If the boat swings in a circle, the chain may twist, and the swivel may alleviate this problem.

• If the anchor is turned around, some swivels may straighten it.

• Follow.

• The biggest concern with anchor swivels is that they may introduce a weak link with the ride.

• With most swivels, the shaft fits nicely and neatly into the other half of the swivel, such as the stainless steel anchored swivel example shown here.When used in marine applications, and worse in tropical climates, this is a cause of corrosion, even with stainless steel.

• The chromium in stainless steel forms a passivating layer on the surface that prevents the steel from rusting.In low oxygen conditions and/or warm water,this passive layer breaks down and begins to corrode.Hypoxia can occur in wet cracks (cracks, welds, shackle threads, keel bolts, etc.) or confined spaces (rotating shafts, etc.).Corrosion can also occur inside.Welding can cause chromium to bond with carbon, indirectly causing corrosion.

• In some cases, the shaft is threaded and has a nut welded on to hold the two bits together.First, threaded rods are inherently weaker than solid rods of the same diameter.Then there is the problem of the weld not being fixed.

• As the boat swings on a well-seated anchor, this creates strong side loads on the swivel, causing its jaws to pry open thereby disconnecting the chain from the swivel.Therefore,Rocna proposes the above. 

• Some rowing schools teach that the anchor should be winched tight against the bow roller.When a boat hits in a wave, this puts stress on the weakest link (rotation),accelerating failure.