Work above the masthead without leaving the chair
The ATN Mastclimber is the only single-handed bosun's chair on the market that allows you to work at the masthead. Other systems get you to the top of the spar; the Mastclimber lets you stand up at the very top and look down at the masthead block, anchor light, and wind instrument with both hands free. While mastclimbing is an inherently dangerous activity, the fact is that it is often safer to climb on your own than to rely on someone else operating a winch (particularly so if they are not experienced). One note, if you do go up a mast using a powered winch it is vital that you verify the switch is in excellent condition, there have been some bad situations caused by a stuck winch button not letting a winch turn off as the person going up nears the top.
Single-handed operation is the supporting feature: the ATN Ascender (part of the Mastclimber) self-locks under load, so you can climb, sit, stand, and work without a deck crew managing the halyard. Estelle Cockcroft, writing on The Catamaran Gurus in 2016, summed it up: "The ATN Mastclimber makes a scary, tough task a lot easier and safer - and a whole lot less scary. It is the only single-handed bosun's chair on the market that allows the climber to work above the masthead without leaving the chair." Read on The Catamaran Gurus.
There are myriad climbing systems that use rope ascenders. Cavers, Rock Climbers, Tree Trimmers, Emergency services, and many more. The ATN Mast Climber is the result of Etienne studying all of these and refining from them the ideal solo mast climbing tool. To these refinements, Etienne commissioned a custom built solid Stainless body ascender that only ATN offers. He then paired this with a comfortable bosun chair / harness to create the ATN Mastclimber. If you're climbing a mast, you need a toolbag, and Etienne designed the Mastclimber bag to double as a toolbag.
How it works
The Mastclimber consists of two parts: a bosun's chair with back rest and the ATN Ascender, and a leg strap with foot loops and its own ATN Ascender. The ATN Ascender can be fitted to any rope halyard from 3/8 inch to 5/8 inch. Operation is an inch-worm cycle: stand up on the leg straps, which lets you slide the bosun chair Ascender up the halyard; sit down onto the chair, which lets you slide the leg-strap Ascender; stand up again, repeat. To descend, the procedure is reversed.
Halyard compatibility: 3/8 inch to 5/8 inch
With skill, one can achieve 16-18" of height per stroke. There is a definite learning curve, and technique matters, but with many thousands of happy customers we are certain you can find this to be one of the most useful tools on your boat. It is HIGHLY advised that you practice with it before you need it. You will want to practice both going up and coming down to be comfortable with it...many owners report that it is more cumbersome to come down than to go up, so focus on practice coming down early.
The Mastclimber fits over any rope halyard from 3/8 inch (10 mm) up to 5/8 inch (16 mm). That covers the standard halyard range on essentially every cruising sailboat from 25 ft to 65 ft. The spinnaker halyard is usually the best line to climb as it is a low-stretch line and comes out of the highest point on the boat. For best efficiency, pick a low-stretch double braid with a DyneemaCore option providing the best overall performance.
Mastclimber vs traditional bosun chair vs DIY prussiks
| System | Single-handed | Requires deck crew | Time to set up | Max safe height | Working seat at masthead |
|---|---|---|---|---|---|
| ATN Mastclimber | Yes | No (spotter recommended) | ~5 minutes | 65 ft mast | Yes (above the masthead) |
| Traditional bosun chair (two-person) | No | Yes (1-2 crew) | ~10 minutes | Mast height | At masthead (not above) |
| DIY prussik loops | Yes (with climbing experience) | Spotter recommended | ~15 minutes | Limited by knot competence | No (hanging from line) |
Ready to Climb Solo?
or call +1 954-584-2477Product specifications
| Halyard diameter | 3/8 inch to 5/8 inch (10 mm to 16 mm) rope |
|---|---|
| Max boat / mast | 25 ft to 65 ft monohulls and multihulls |
| Ascenders | Proprietary Stainless body ascenders built by CMI in the USA |
| Chair | Bosun's chair with back rest and firm seat. Includes shortening loop to allow for work above masthead |
| Foot Straps | On a separate ascender, these are used to push yourself up as you climb the mast |
| Designed by | Etienne Giroire |
| Made in | Made in the USA |
| Shipping | Ships USA & Worldwide |
| Warranty | 30-day return in original packaging. Component replacement supported. |
Mid-ocean: Vendee Globe footage
Alessandro Di Benedetto of Team Plastique in the Vendee Globe 2012-2013 going up the mast with the ATN Mastclimber, mid-ocean. Three video parts below. Helpful video of a Vendee Globe solo skipper using the product in conditions you will never face on your weekend climb.
Vendee Globe 2012-2013, Alessandro Di Benedetto, Team Plastique. Watch the series.
Pricing
The Mastclimber is offered in three configurations. The full Mastclimber includes the bosun chair, the foot strap, two ascenders, and a tool bag. The Kit is the same minus the chair, for owners who want to keep their existing bosun chair. The Bosun Chair alone is the chair-only purchase.
Order online or by phone
Hassle free ordering online using buttons below. You can of course also call +1 954-584-2477 during business hours or email info@atninc.com to order by phone or email.
ATN Mastclimber (Full)
Bosun chair + foot strap + two Ascenders + tool bag. Everything you need to climb solo.
ATN Mastclimber Kit
Two Ascenders + foot strap + tool bag. Bring your own bosun chair.
ATN Ascenders (pair)
Retrofit your old Topclimber, or replace worn ascenders. Open-design cam fits 3/8 inch to 5/8 inch halyards. See the ATN Ascender product page for full specs.
ATN Bosun Chair
Bosun Chair only. Firm seat bottom doesn't cut off circulation, stainless attachment points.
Florida customers pay state sales tax.
How to use the Mastclimber
West Marine put together a great instructional video on how to use the MastClimber, worth watching the video below.
Common Customer Concerns
As a one-of-one product the mastclimber does offer a few tradeoffs to allow for it offer the unique utility it has. The most common are addressed below. For more on technique and the working-aloft tradeoffs, see Best Way to Climb a Mast.
Will the ascenders damage my mast?
Frankly, the metal body of the ascender can put a mark on your mast. This can be mitigated (although not fully avoided) with some technique adjustments. The technique fix is to anchor the climbing halyard to a chainplate or fixed deck loop, then crank deck-winch tension on the halyard before the ascent. A pre-tensioned halyard keeps the climber's body and the cuff clear of the spar on the way up rather than swinging into contact. This will not completely reduce the risk of marking your mast, but will help. If you have a high dollar carbon mast you will want to be particularly careful using the MastClimber. We are in R&D on developing a softener to reduce this further so stay tuned. On the halyard line itself: the CMI ascender we ship is open-design so the cam clamps the line rather than crimping or bending it through 90 degrees which helps maintain halyard line quality. See our cross-link to Best Way to Climb a Mast for David Proctor's full write-up of the technique.
What are maximum weight recommendations?
While the MastClimber has been succesfully used by heavier sailors, we recommend it for sailors under 250lbs. The cam ascenders we ship have a working load several times the body weight of a fully equipped climber, so structural capacity is not the binding constraint. The binding constraints are the squat-to-stand cycle (each step is essentially a one-leg squat with your body weight on the strap) and the hip flexibility to bring your knees up high enough to advance the ascender. Practical guidance: if you can squat with your own body weight comfortably and bend at the hip without strain, the Mastclimber will work for you. If you are above 250 lb, have weight is concentrated in the abdomen, or you have limited hip flexibility the Mastclimber may not be a good fit for you.
Key safety points
The bow shackle pin must be installed left-to-right so the climbing motion tightens it rather than loosening it; we ship a printed install card stating this with every unit. Pre-flight inspection ritual: visually check every shackle pin, and every webbing seam before you put weight on the system. We strongly recommend giving the full rig a very solid set of "bounce tests" once set up by dropping a foot or so in the seat while still on deck. If there are any possible failure points in your halyard or rigging,
Where to use it
The single-hander on any cruising sailboat. The masthead-instrument installer (replacing wind instruments, anchor lights, VHF antennas, Windexes). The Vendee Globe and Global Solo Challenge offshore skipper. The rigging-cost-conscious owner who pays the product off in two climbs at $200-$400/yard-rigger climb.
Proven History
ATN Mastclimber units have shipped to thousands of sailors since 1990. The product has been featured in Yachting Monthly's Tried and Tested, reviewed on The Catamaran Gurus, and used by Alessandro Di Benedetto in the Vendee Globe 2012-2013 (mid-ocean footage above) and by Etienne Giroire's own offshore campaigns including Route du Rhum 2010. Cole Brauer carried one in the Global Solo Challenge.
Customer reviews Read Mastclimber owner testimonials
From the press
The ATN Mastclimber makes a scary, tough task a lot easier and safer...and a whole lot less scary. It is the only single-handed bosun's chair on the market that allows the climber to work above the masthead without leaving the chair.
Estelle Cockcroft, The Catamaran Gurus, 2016-01-20. Read on The Catamaran Gurus
From the sailing community (forums)
we purchased one and used it to do some mid-mast and masthead work at the dock last summer. We bought it to allow one person to go up on his/her own (short handed crew). It can also be used as a straight bosun's chair. There's definitely a technique to master, but you quickly get better with just a few climbs. I found it quite easy to ascend. Descending is actually harder (at least for me), but no big deal. Overall I like the climber.
Mike OReilly, CruisersForum, 2012-09-01. Read on CruisersForum
The Mast Climber chair/harness has heavy duty leg restraints that keep your butt firmly in place on the seat. Best of all, the seat is so damned comfortable I spend way too much time when I climb the mast with Mast Climber seat enjoying the Zen moment.
roverhi, CruisersForum, 2026-05-11. Read on CruisersForum
I really think you should give the ATN climber another go eherlihy. It's a skill, like anything else, so the first few times will be challenging. But aside from working over top of the masthead, it really is a great way to work aloft. The built-in bosun's chair, with the stirrups, is very comfortable.
MikeOReilly, SailNet Community, 2024-07-30. Read on SailNet Community
I have the ATN Topclimber and it works very well for me. I would recommend it, my buddy bought one for his boat using my Topclimber. Great item that works as advertised.
Greg Riach, CruisersForum, 2007-02-20. Read on CruisersForum
I bought the ATN MastClimber and it works well and as described. As others have mentioned, it takes a bit of hand/feet coordination to move the ascenders up/down. Also, keep the line tight. I was able to make 2 trips to the mast in a single afternoon to repair my wind instrument. I did feel muscles in my legs that I didn't know I had for several days afterwards! Highly recommend.
Capt.Don, CruisersForum, 2012-09-01. Read on CruisersForum
In my group of friends we all have a ATN Mast Climber that we use and share. It's so much easier for the person going up the mast to use their legs to get up there. The Mast Climber is expensive, but building a self climbing system myself wasn't going to be that much cheaper (maybe saving $100).
Alex W, SailNet Community, 2013-06-20. Read on SailNet Community
The bosuns chair would be very difficult to fall out of if used as instructed and is far more comfortable than a harness. It does have leg straps. If you fall out of the chair than you have no business being up a mast. I used to use the harness for hunting; no go. Now with the ATN climber i can feel my toes again. You can hang out for hours. I bow hunt from it.
benesailor, SailNet Community, 2013-06-21. Read on SailNet Community
I am in my mid-60's and have been using a Top Climber for about 10 years. If you are able to do pull-ups and squawts without too much difficulty, the system works well but, with a tall mast, you will have sore legs unless you're in good shape.
svHyLyte, CruisersForum, 2012-09-01. Read on CruisersForum
Customer letters
I met you at the Miami boat show and purchased a Mastclimber and a Gale Sail. I have been up the mast twice in the last three days. The mast climber works very well (and impressed my neighbors!). Many thanks for your excellent products.
Sarah H., ATN MastClimber, 2026-05-10.
I wanted to thank you for your fine product the Mast Climber. I was up and down my mast 3 times last Sunday while replacing a wind vane on my Catalina 27. Your product has got to be one of the best investments that I have ever made for our boat. It was easy to use, and I felt very safe while working on top. Once again, thank you for a great product.
Bill, SV Loose Ends, ATN MastClimber, 2026-05-10.
Just to let you know I received the chair, and used it this weekend. Having the right equipment made all the difference I needed to work on top of the mast. Being able to stand up to work, and then sit down to rest worked perfectly. Thanks for a great solution.
Matt A., S/V Faith, New Bern NC, ATN MastClimber, 2026-05-10.
Frequently Asked Questions
Questions from real customer email and the public sailing community. We segregate by channel so you can scan the answers that match your buying stage.
How do I order the ATN Mastclimber, what does it cost, and how quickly can you ship it?
Is the ATN Mastclimber safe to use alone, and do I need a separate harness or safety line as backup?
Can I buy replacement parts for my ATN Mastclimber - ascenders, footstraps, pins, or the tool bag?
Do you ship the ATN Mastclimber internationally, and is there a dealer in my country?
How do I get all the way up above the masthead?
Can I order the Mastclimber over the phone or without setting up an online account?
From the sailing community
Questions answered by experienced owners on SailNet, SailboatOwners, CruisersForum, and the Ericson Yachts EY.o Information Exchange.
Should the halyard be tight or slack while climbing?
ATN markets it as a single-handed bosun's chair - should I actually use it alone?
Can I really reach above the masthead, and how do I set up halyard tension for different work positions?
Should I use a backup halyard as a safety line?
ATN Mastclimber vs Mastmate - which one for me?
Does the Mastclimber make noise grating against the mast?
From the press
Editorial and blog coverage of the Mastclimber from sailing publications.
