Arborist Gear for Solo Mast Ascents

Hybrid ascenders offer singlehanders another route up.


My introduction to rope walking ascent was caving back in the 1970s. Each trip started with 75-200 drop straight into a sink hole, followed by hours of cold crawling and scrambling in the dark. Tired and muddy, you then faced a rope climb without a whole lot of energy left.  Fifty-some years later, new equipment has moved the technique into the 21st century and given it some really cool advantages for sailors. Anyone who has seen the acrobatics in this year’s Vendée Globe could recognize how these devices would be beneficial to the single-handed sailor.

There are a half a dozen basic methods for climbing a fixed rope using ascenders. Most involve using the feet to lift the weight and the hands to move the ascenders up between steps. The ATN Mast Climber system (see “PS reviews of the ATN Topclimber,” January 2001 and August 2005), uses one ascender attached to the feet with a sling, and one attached to the waist harness. Rope-walking systems, on the other hand, fix one ascender directly to your dominant foot with a compact harness.

Another ascender, often referred to as a knee ascender, floats at about knee height, suspended between a harness to the other foot by a length of bungee cord that is routed up through a carabiner or small block on your waist harness, and back down to the foot ascender. Both of these ascenders are completely self-tending. You march up the rope, hardly thinking about what your feet are doing, with your hands free to grab the rope, mast, or anything else that will help your progress and prevent swinging—a real nuisance in the harbor, and a serious danger underway.

Rate of climb

At the local climbing crag, we found we could easily maintain an easy 30-foot-per-minute pace for hundreds of feet. Just keep marching at one easy step per second, hands gripping either the rope or rock. Some of our test climbing was banging against rock, and some was free-hanging under overhangs.

It was never strenuous or difficult to stay in balance and we never felt the need to take a break, even on climbs up to 100 feet. Our arms and legs were not tired at all, because the lean back, pull forward, and stand up cycle of the frog-type climbers is eliminated. You stay in-balance and in-column the entire time. With any of these systems, if you want to rest, you can just sit back on the chest ascender.

Arborist Gear for Solo Mast Ascents
Hybrid ascenders like the Unicender, or the combination Zigzag/Chicane, allow the climber to both ascend and control their descent. Some of the Vendée Globe sailors used a variation of this system to climb their mast.

The rigging is a little fussy to adjust. Expect to spend 30 minutes settling on the right lengths for the knee ascender strap, bungee cord, and flip line.

The flip line deserves a little explanation. Arborists and construction workers carry an adjustable length line that they “flip” around the tree or structure so that they can lean against it to work. Think of the old leather strap that line workers use to use on telephone poles. Likewise, the mast climbing sailor uses a length of rope or a sewn climbing sling with a clip on each end to wrap around the mast and keep from swinging. Industrial harnesses have special D-rings on each hip to attach these. Climbing harnesses, on the other hand, have only one strong point, the center waist tie-in (accessory loops on the hips are not designed for use with flip lines.) I like to carry two climbing slings to use as flip lines, and at least 4 carabiners, for maximum flexibility in securing myself off to work.

Chest harness or not? If you are thinking of using your sailing harness  for this … forget it. The tie-in point for the chest ascender is mid-to-upper sternum and most sailing harnesses cross below the sternum. Instead of a chest harness, most arborists use a flip line connected to an eye in  the chest ascender. The line is rigged from one hip, over the shoulder, and down to  the chest ascender at sternum-level.

We tried both a climbing-specific chest harness and the flip line/chest ascender method, and decided the flip line method was simpler and more versatile (as illustrated on page 17).

Mast Climbing Gear Details

Arborist Gear for Solo Mast Ascents

Designed for arborists, cavers, and climbers rely on single line ascents and descents, the climbing gear described in this report is specialized equipment that requires training, and applying it to mast-climbing requires an added level of risk.

  1. The Rock Exotica is an example of the hybrid uniscenders that the Vendée Globe sailors used.
  2. Adding foam padding to the climbing harnesses seat makes it more comfortable when working aloft for long periods.

Working aloft

Most systems place your nose just over the masthead. I like it closer to waist high, so I can look down on what I’m doing. To move up simply…

  1. Step up until the chest ascender is nearly out of rope.
  2. With one arm wrapped around the mast, lean in and wrap one of your flip lines around the mast, so you can’t fall back.
  3. Detach the upper carabiner of the chest ascender. Note that it is still attached to your waist harness.
  4. Wrap both arms around the mast, step up and lean forward, over the masthead. Cup the mast with your knees. You should be in a no-hands rest, leaning against the mast. Wrap the other flip line around the top of the mast, getting it snug and secure.
  5. You are now secure to work, supported by both the foot and by the knee ascenders, two flip lines, and you are backed up by the chest ascender. Safe.

The really cool part is that you don’t have to climb back down, step by step, as you do with other climbing systems. Hybrid ascenders convert to descender without removing them from the rope or re-rigging. You simply sit back in the harness, remove the foot and knee ascenders from the rope, and the hybrid device provides adjustable friction during the descent, just like the rappel devices rock climbers use. Going too fast? Just let go and the device locks up, stopping the descent. Each device has a specific procedure. Study it closely.

Because your hands are free to grab the rope, the mast, or standing rigging, it is surprisingly easy to maintain your balance on a stationary boat and control your motion on a moving one. Holding the rope or rigging, one of your hands will always be near full extension over your head, like climbing a steep ladder. It takes only light pressure, little more than the weight of your arm, to stay in balance. You can hug the mast if the boat is swaying; again, it takes little effort to stay in balance over your feet. And just keep chugging away with your feet. With a little practice, it’s just like climbing a ladder.

Single Rope Ascender Kits

CHEST ASCENDER Rock Exotica Unicender $375 Rock Exotica Unicender $375 Rock Exotica Unicender $375 Included Petzl Ascension $65 Mast Mate ladder $455
UPPER ASCENDER Petzl knee ascent system $176 Saka $140 Petzl Croll $75 Included Petzl Ascension $65 Camp Goblin $165
LOWER ASCENDER Petzl Pantin $80 Camp Turbofoot $60 Petzl Pantin $80 N/A N/A N/A
RIGGING A few extra carabiners $28 Chest harness and other components included Assorted gear $65 Bosun's chair and assorted gear is included Assorted gear $50 Assorted gear $30
HARNESS/BOSUN'S CHAIR Petzl Avao $300 Petzl Avao $300 Petzl Avao $80 ATN (included) Petzl Avao $80 Petzl Avao $80
COMMENTS Professional gear, Arborists and the Vendee Globe knee ascent system uses the Petzl croll. Petzl Zigzap ascender with the Chicane is another hoice, but it must be threaded onto the line from the end. Professiona arborist gear, less expensive with Petzl Adjama harness ($80)Additional harness padding neededComplete kitAdditional harness padding neededAdditional harness padding needed; fits masts to 50 ft.
TOTAL$959 $625-$845$600$450$240$730

Knee Pads and Helmets

While not needed at the dock, underway they are damn handy, as are gloves. A foam, Type III PFD  can be good for the ribs. The first time I climbed a mast, many years ago, we were sailing to windward. The boat was stable, all I had to do was retrieve a fly-away spinnaker halyard, and the ATN Top Climber system worked fine. The second trip, on the other hand, was a rolly downwind horror show climbing mast steps with a belay from a halyard. I was young and hung on tight, but the steps were a menace and a rope walking system or halyard hoist would have been safer.

Pros and Cons

Rock climbers dislike the method because there is more gear to carry, and it is prone to snagging when working around overhangs and through chimneys. But cavers, and arborists like it for its speed and energy conservation. The rigging is more complex, but once you work out the lengths, it’s ready to go in minutes.

The Petzl Zigzag was one of the first hybrid devices and has a faithful following. We saw one on a Vendée Globe boat.

Although it works very well, the Zigzag/Chicane combo is expensive, bulky, and must be threaded on from the end of the rope. This works for arborist, but darn inconvenient for climbing a halyard rigged through mast foot blocks and jammers. The Rock Exotica Unicender, on the other hand, can be installed midrope. We also find the descent friction adjustment smoother and more adjustable with the Unicender.

Ascenders and descenders are always sensitive to rope size and stiffness. Most are optimized for not too stiff 7/16- to 1/2-inch double braid rope and 9-11mm climbing rope. Too small they may not catch, too large and they may not feed. Check manufacture requirements.  We tested on a stiff 7/16-inch halyard and a well-used 10mm climbing rope; all the units worked perfectly on both.

Do add extra padding to the leg loops of common climbing harnesses. We’ve reported on this before, but it is one of the best, cheapest comfort steps you can take.

Lower Ascenders

BRAND Camp Climbing Technology ICS Petzl
MODEL Turbofoot Foot Ascender Stryder Foot Ascender Croll
MODEL Turbo Chest Anthron Chest Ascender Pantin


The big difference to us was having our hands free to hold on, balance, and maneuver. Around the crag and docks it was handy. Going aloft off-shore, this seems like a big deal. On the other hand, the increase in complexity and cost is a drag.

For a Vendée Globe guy, facing a 120-foot climb underway, we see the advantages, though we also see a lot of systems, all with their adherents. The frog style or Mastmate is probably the better value for climbing a 40- to 60-foot stick at the dock.


Drew Frye
Drew Frye, Practical Sailor’s technical editor, has used his background in chemistry and engineering to help guide Practical Sailor toward some of the most important topics covered during the past 10 years. His in-depth reporting on everything from anchors to safety tethers to fuel additives have netted multiple awards from Boating Writers International. With more than three decades of experience as a refinery engineer and a sailor, he has a knack for discovering money-saving “home-brew” products or “hacks” that make boating affordable for almost anyone. He has conducted dozens of tests for Practical Sailor and published over 200 articles on sailing equipment. His rigorous testing has prompted the improvement and introduction of several marine products that might not exist without his input. His book “Rigging Modern Anchors” has won wide praise for introducing the use of modern materials and novel techniques to solve an array of anchoring challenges. 


  1. Drew,
    From being a rock climber when I was younger, I did not want to use a foot ascender. My issue is that if you bang it against the mast or if it adjusts badly on your foot, its difficult to correct mid-climb. I have used this setup using a Grigri. The grigri is an amazing piece of kit. Its basically works like a Prusic but is much friendlier to use.

  2. Drew,
    I’m 64 years old, former rock climber. I live on a Bavaria 46 Cruiser. I bought the ATN mast climber, but found it difficult to use. After watching many YouTube videos of arborists using the Petzl Zigzag/Chicane with Croll knee ascender and foot ascender, I decided to give it a try.

    First impression: Difficult to set up. It’s really designed for professionals. Climbed and descended the mast easily. It works. Not for beginners.

    I’ve used a Grigri while rock climbing, which I really like. I’ll have to try the setup that Aongus Flood recommends.

  3. I agree with the commenters, that the rope walking systems are fussy to adjust. Very fast while climbing, but not the best choice for most users. Unless you are climbing often or far (big wall, industrial, or rigger) I would use a conventional ascender system or a mast ladder (fixed or webbing). I tested using both the Rock Exotica Unicender and a common ascender that I had on my rack, and they both knocked out 100-foot climbs in just minute or two with little effort. But fussy to set up just right.

    The foot ascender must be properly secured, and it can be uncomfortable if you don’t get it right. I tested on cliffs with overhangs and lots of banging. No problems. You also need a good harness, since it is difficult to get your weight onto your feet.

    (61-year old rock climber, still active)