Following the Treetools blog about friction hitch cords earlier in the month many climbers have asked about ratings and break strengths relative to the various hitch cords available and the prusik knot options associated with friction hitch based climbing systems eg Hitch Climber.
Very little research has been undertaken in this area, which is surprising given the popularity of friction hitches in tree climbing, but one report is well worth reading. Back in 2002 Paolo Bavaresco from Treevolution authored a UK Forestry Commission research reportinto knots and friction hitches used in tree climbing - it may sound a bit dated but the test results are still relevant today.Download the paper and put aside some time over the Christmas break to see how well your preferred prusik knot behaves under stressed conditions. The document is pretty comprehensive and it will probably require a couple of readings to get you head around all the details. It will be well worth the effort if you climb everyday for a living.
The best strength results were produced with an 8 mm friction cord using a 6-wrap Valdotain Tresse. Many of the 4-wrap prusiks apparently slipped at relatively low loadings - not very practical for the aerial rescue. Consider the friction hitch you use everyday and compare ratings with other versions of prusik knot - you might end up reconsidering the low base-friction V.T.