Unless you're twisted in the head and enjoy the dizzying heights that are achieved through rock climbing or going aloft (such as myself), most sailors don't relish the idea of taking a trip up the stick, even when the boat is snugly hanging from her mooring pennants. Regardless of your ilk, the Spinlock Mast-Pro Harness should be a serious consideration for your "must-have" gear. Spinlock originally teamed up with Petzl (makers of fine LED headlamps and high-quality rock-climbing harnesses) to produce this extremely safe, very reliable piece of kit. Recognizing that racing bowmen often spend time sliding around on the bottoms, Spinlock wraps the leg loops with extra-tough Cordura material to protect this weight-bearing element of the harness from abrasion. The harness's buckles rely on two stainless plates that pinch down on the waistband's webbing, rather than a more complicated "thread-through" buckle that can be incorrectly set up (and thus render an unsafe harness), and Spinlock has incorporated special loops and holsters for carrying tag lines, tools, or a fid. Plus, it's comfy.
Many boats rely on cumbersome bosun's chairs for trips aloft. Yes, a wood-bottomed bosun's chair might be more comfortable if you are rewiring all of your masthead instruments while the mast is stepped and will be aloft for a long time, but in any other situation a rock-climbing grade harness is always your best bet, simply because these climbing-related companies need to consider that a climber doesn't always fall feet first. As a result, rock-climbing style harnesses are, in my humble opinion, far safer, as you will not fall out of the harness, no matter what (with the obvious exceptions of self-release or material failure). As a climber and a sailor who frequently goes up tall masts, I like this peace of mind. But I also like the fact that the Mast Pro is comfortable to hang around in for fairly long periods, without the dreaded "sleepy leg" kicking in.
Another safety note: Buckles. I was recently sailing aboard one of the world's premiere maxi yachts and none of the bowmen had properly laced their harness's webbing through their buckles. Having personally lost a friend to a climbing accident in which he didn't properly lace (double-back) his buckle, I was aghast. When I tried to point out this safety flaw, my concern was dismissed as that of a journalist who doesn't know much about moving around on vertical surfaces (very wrong impression, in fact). With the Spinlock Mast Pro, there is no complicated or confusing threading to be done; simply pull the waist belt straps tight, repeat with the leg straps, and you're good to go. No fussing, just safety. This is especially appreciated on cold, tired night watches where little mistakes can cost lives.
But Spinlock's attention to detail doesn't stop with its buckles (the newer versions even have padded covers over the buckles, ensuring that they can't accidentally come free or catch). By covering the leg loops with sturdy Cordura, there is little chance of accidentally chafing through these weight-bearing sections. The harness comes with two gear loops, which are stitched into the harness; these are great for hanging a boat bag full of tools (a climbing carabiner is the attachment tool of choice), tailing a spare halyard, or even ferrying up replacement gear. The harness has a dedicated slot for a fid (excellent), as well as a few other elasticized gear holsters that can store a variety of tools. At $175 the Mast Pro isn't the cheapest option around, but given its safety, utility, and reliability it is well worth the expense. www.spinlock.co.uk