I work with ropes for a living and quite honestly, although the prussik will work, its not the answer. It becomes cumbersome to move up and down and after a while the moving of the knot becomes tiresome and one ends up removing it. Not to mention the safety aspects of working with rope on rope in wet weather
If you want the right tools for the job, then the Petzl ASAP fall arrester is what you need. It moves up and down the rope by itself but will lock off instantly should you fall.
A full body harness with a Petzl ASAP ($160)fitted with 11mm access braid (not dynamic rope) and you're in business.
Alternatively you can look at the Yates Rocker ($90)or the Petzl Shunt ($46). Petzl have stopped making the Shunt because of safety reasons, ie. it wasnt all that safe under certain conditions as you had to move it down by hand and when falling the usual reaction is to grab rather than release. The rocker moves up and down by itself but you have to move quite slowly.
Another reason to avoid the prussik for your application is the possibility of a high fall factor (>2 can be life threatening) due to having a longer length of rope attached to the harness. Ideally the prussik knot is used in access systems such as pulley rigs and only really used in direct harness applications in emergencies.
Go to
www.petzl.com and have a look around, theres tons of info. Alternatively, pop in at the local rope access store and speak to a specialist before making up your mind. Try and avoid buying from a climbing shop or similar outlet as they ask way over the top prices. Find an industrial rope access supplier if you can.
If you buy this kind of equipment and look after it, it will probably outlive us all.
Hope this helps
