A climber as asked why the DMM Aero HMS carabiner was used on the DB Rope Walker system we blogged about last week. The answer is simple: its the best carabiner for the job.Of course, you could use any of the HMS-style, triple-lock carabiners but the DMM Aero HMS is hard to beat. Its aero-dynamic shape, tight at the attachment end but wide at the rope end is perfect for the accommodation of multiple rope turns, webbing slings or hardware.
HMS is an abbreviation for the German word "Halbmastwurfsicherung" meaning 'half glove hitch belay' usually tied with a Munter hitch. The Munter requires enough room on the carabiner to take two turns of the rope without getting close to the gate, as pictured below.
Obviously there is not a Munter in sight on the DB Tree Rope Walker but the system does require a number of items to be attached to the same carabiner.
Therefore the ideal carabiner on the DB Tree Rope Walker system needed to be wide enough at one end to accommodate the footloop and 20mm webbing e2e cows tail on one carabiner and the Croll and the cows tail at the other - without the chance of side loading the carabiner.
The DMM Aero HMS was the best shape for the above requirement. For example, the DMM Ultra O would not be ideal for this purpose. The radius at each end of the Ultra O are too tight to take anything more than one turn of rope or narrow gauge hardware and a prussic (like the Hitch Climber and the Ocean Polyester e2e).
The 'aero' shape is an added bonus in making the DMM Aero HMS the right carabiner for the job. Its tapered, tear-drop shape and unique DMM I-beam section ensures the carabiner and other hardware are kept compact and tidy - all part of the DB Tree philosophy.