NormanS
Well-Known Member
The boatyard where my boat is kept in the winter, charges £140 each way, for masts. That would make it rather expensive to check both mast heads on my ketch. 
I use a climbing harness designed for big wall climbing. These have extra-wide leg straps so help to avoid blood being cut off to the legs. I combine that with a Petzl Kroll chest jammer and and Petzl ascender using the 'frog technique'. (Google for details.) This set-up is designed for climbing a single rope. It works better with a single static rope rather than a stretchy climbing rope so I don't hesitate to use it on a good condition 10mm halyard. My jammers are now 40 years old - are bombproof and never slip. I reverse down, which is a bit more of a faff, but perfectly safe. Cavers use them on ropes with no other safety line but, given the ease of setting up a safety line, I would generally have someone operate a lifeline or, if alone, use a prusik knot on another fixed line. It gives a fast and safe ascent and gets the head well above the top of the mast.
OP here...
So, after a lengthy delay while I re-thought things and waited for a weekend of no wind, Saturday morning dawned bright and calm. It was time to tackle the genoa halyard issue in particular, and run a new spinnaker halyard / attend to blown anchor light bulb, etc.
I had previously been up as far as the spreaders, but this time had a proper climbing harness.
On climbing to the very top, to my horror I discovered that the top of the forestay has started to unravel, I presume as a result of all the twisting / halyard wrapping that has been going on with the headsail furling problems.
Anyway, job abandoned... no point in re-routing halyards, etc., as there will clearly be no sailing getting done!
The plan now is to have the mast unstepped and replace all the standing rigging and running rigging in the yard. It's of an unknown vintage anyway and I had it on my plans for next year. I'm very glad that I did the climb, as the boat stays in all year round and I do sail in the winter, so some rough-ish weather wouldn't have been beyond a possibility.
The proprietary climbers get you to the top of the mast but not in a condition to perform two handed work safely. And they are expensive.
You need a length of climbing rope which you attach to the main halyard and haul to the top, then secure the halyard with clamp and knots. Take two ascenders (climbing gear) - the top one carries the bosun's chair and is clipped on to the climbing rope. The bottom one has a short length of timber attached with stout rope to act as a push bar for the feet. No bits of rope and prussic knots, swinging all over the place and unstable.
You sashay up the climbing rope pushing the ascenders ahead alternately, advancing your weight.
At the top you deploy a lanyard round your body (I use a galley strop) and the mast to steady yourself, whilst standing upright on the bar - this is stable and safe.
Usually best to assemble all work gear in a stout bag at the foot of the mast, trail an attached line up with you, and haul it up when in position..
Descent is the opposite of the above. You can also use a figure of 8 abseiler on a separate thick rope (12-14mm) hauled up at the same time as the climbing rope; stand on the wooden bar, transfer the bosums chair to the figure of 8 using a secure carabiner, step off the bar slowly placing your weight smoothly onto the abseiler and descend gracefully.
There is a warning, of course. It is not that the halyard or climbing rope will part, or the bosums chair disintegrate. No need to have a second carrying line - it gets in the way and endangers the ascent. The danger is from inversion in the bosums seat; so progress has to be steady.
I have used this arrangement for nearly 30 years and still do. When it's your life at stake you use only the best gear and check it all every time as if you were Chris Bonnington.
PWG
No need to have a second carrying line - it gets in the way
PWG

I was up my mizzen mast just the other day, to install an extra aerial. Shackled the halyard to the bosun's chair, and with my wife taking up the slack, I quickly climbed up using the mast steps to the required position. My wife then made fast, and using the spare halyard, pulled up the bucket with all the bits and bobs. What's not to like?