Comments on: Anchor Swivels – Why They Are A Bad Idea

By: Colin Stone

Colin Stone — Wed, 21 Apr 2010 18:36:43 +0000

EC Directive 2007/87/EC (Technical Requirements for Inland Waterways Vessels (TRIWV)) requires swivels to be 20% stronger than the chain.

By: Nelson Lee

Nelson Lee — Wed, 16 Dec 2009 19:17:30 +0000

The other (and in my mind, the major) shortcoming with this arrangement is that the swivel is attached directly to the anchor. There have been some well-documented swivel failures in the last couple of years, leading to some testing by West Marine, as recounted in Latitude 38 earlier in 2009. The testing revealed particular problems with side/lateral loads on the swivel. When attached directly to the anchor, a load on the chain that is not in alignment with the anchor shank is going to put an enormous load on the swivel, potentially deforming it. Interetingly, West Marine suggested that for certain kinds of anchors (like a Delta or Bruce) with rigid one-piece contruction, the swivel should be separated from the anchor by a shackle. I don’t think that information is well known.

–Nelson Lee

By: Serge Roy

Serge Roy — Thu, 12 Nov 2009 00:59:05 +0000

Even though your conclusion is good, your proof is not totally accurate. The pin is working in DOUBLE shearing mode, that is there are 2 surfaces supporting the tension (the cross section on each side), so it matches the two legs of the link. But then, shearing strength is about 80% of tensile strength in steel, so for a same material, same diameter, we are 20% weaker. Then stainless steel being weaker too, we are looking at another lost of strength of about 30%, as you mention.

Great Blog! I truly enjoy reading you!

By: Craig Smith

Craig Smith — Wed, 28 Oct 2009 13:29:09 +0000

I believe this example would be best styled as “why this swivel is a bad idea”, as all the issues [correctly] highlighted may be dealt with by way of an appropriate design and material choice. That said, it is unfortunate that many (most?) swivels on the market quote SWL figures which work out to be a wildly different ratio to break as the ‘standard’ 4:1 of chain. Moreover, many are designed to be attached directly to the anchor shank (as shown in the picture), where their failure mode is typically not a straight line pull but rather a lateral load on a fouled anchor under which circumstances their effective strength is greatly reduced further still.

http://www.rocna.com/kb/Swivels

By: Steve Dashew

Steve Dashew — Tue, 27 Oct 2009 17:10:26 +0000

Bo:
To be safe the a swivel would need to equal the breaking strength (not working strength) of the chain and be proof tested.
The 3/8″ schedule seven chain on the FPB 64 has a break strength of 26,000+ pounds and we do not use swivels.
We have always avoided swivels and have not had problems with chain twist.

By: Bo Leonard

Bo Leonard — Tue, 27 Oct 2009 16:10:49 +0000

Steve

Are you totally againest swivels or just undersized ones. What do you use on the FPB series?