Saturday, March 31, 2012

Bolt Hangers--A Strong Point For Small Dollars

Cheap hardware via cross pollination from the rock climbing world. In the mountains these are used in combination with wedge bolts to create strong anchor points. On a boat...
  • 5,000-pound strength anywhere a single 3/8-inch bolt is handy. Of course, a good backing is required.
  • 316 stainless steel.
  • Cheap. About $2.95. (others brands may be 304 or other grades, some of which have been known to fail in marine environments.)
  • Designed for clipping carabiners, they easily accommodate 2 carabiners.  
  • Obvious purpose avoids confusion over acceptable strong points. Strength rating and certifications are stamped on hanger.


Countless potential uses. A few of mine....
  • Add an extra block to a sail track.
  • Add an anchor point at the stern for diverting mooring lines or attaching a dingy.
  • Tether anchors. Don't tie rope or webbing directly; though polished to eliminate sharp corners, the radius is really too short for acceptable strength.
  • Anchors to secure bicycles.

2 comments:

  1. Petzl has made warnings about bolt hangers in tropical marine environments. Failure at 1KN. Failure @ 9 months.

    http://www.petzl.com/en/outdoor/news-1/2009/12/16/planning-tropical-climbing-vacation-winter-beware-those-anchors

    Fair winds,

    Practical Pirate

    ReplyDelete
  2. True. I was a ware of this before posting.

    However, if it was completely true no stainless rigging equipped sailboat would keep its rig... and yet they do. The answer lies in rock chemistry, dissimilar metals, and intergranular corrosion. If we look at the failed samples they are all visibly corroded, showing signs of depassivation. The one on the right is attached to a galvanized quick-link, a VERY poor practice. In fact, I have seen 316 SS marine brackets become exactly as illustrated in the Petzel link if coupled to lower grade stainless (often the bolts are a different grade of stainless or non-stainless) or galvanized quicklinks or chain.

    The full answer is that the 316 SS Petzel bolt hangers perform exactly the same as stainless always performs; if properly installed, very well, if poorly installed, not so well. The example of SS chain plates is completely analogus.

    ReplyDelete