hi,, like many of you I singlehand and getting to the head of the mast has been an issue since i started on the circumnavigation, I was loathe to start adding weight aloft with metal steps of any description ( that and a perceived possibility of having halyard wraps or other issues with sails snagging etc) and not having a "spare" hand to winch myself up i toyed with mountaineering kit etc. I came across an idea, from a fellow yachtsman of advancing years , where the use of two "locking" multi sheaved blocks could allow you to hoist yourself up the mast safetly ( at least so far) in a bosuns chair arrangement.
The upper block, already fully reeved and lengthend to the height you want to attain , is hoisted aloft with a spare halyard and secured off, The lock on the upper block is set to the "locked" position prior to hoisting and prevents the falls sliding back as you rest between "pulls" as well as allowing you to rest and work or just take the pressure off your arms/muscles.
The lower block is also in the "locked' position on the hoist up as a "failsafe"security feature.
When you arrive at whatever working height you want to , its a matter of securing yourself to the mast and doing your work. The reason,as stated, for the double locking blocks is that if you have an extra safety feature although the system can work with one. When ready to descend , the upper "locked" block is switched to the "unlocked" position, (as is the bottom one) and you can then, by feeding the rope , descend smoothly and easily.
You can, of course,at any time apply the lock to the bottom block and "rest" or work at any point in the descent. There are a flaws I can see in the system, It does use a lot of rope as its a 4 fold purchase, there is no redundancy built in as a safetyline/halyard ,(so i use a sliding locking hitch attached to my safety harnees on the other halyard in case of catastrophic failure .)
Its all very time consuming and previous preparation and planning is a key factor.
Like some of the previous posts stated , going up in a quiet marina envoirnement and in a seaway are whole different ball games.
I would only use this in an emergency situation whilst underway. Long pants,and gripping knees seem to work but expect a few brusies and aching muscles. As i said at the beginning, really only one kind of system for use as a singlehander if you dont want or have the mast steps. I.m in the process of making a flexible ladder along the lines of the "mastclimber" I'll let you know how it goes .