The Offshore Voyaging Reference Site

Going Up The Mast—Fundamentals

This article should not be acted on without reading the entire series.

Matt did an excellent job of bringing building site safety procedures and his engineering training to bear on safe mast climbing.

Now I will cover things I have learned in some 50 years of going up masts, as well as highlight several important things I learned from Matt’s post and the comments thereto.

Yes, that’s right, despite climbing masts since before Matt was born, I learned from him (and others), and I’m thinking that might be the most important point I will make in these articles, particularly since I noticed a disturbing note of complacency in some of the comments to Matt’s article.

Let’s dig into my present beliefs about mast climbing.

Login to continue reading (scroll down)

Inline Feedbacks
View all comments
Kevin Towers

The video you linked was VERY enlightening. I don’t think they mentioned in the video, but the slings they were breaking were both rated for 22kN (4945 lbs). This reenforces your recommendation for doubling the minimum breaking force to 10,000 lbs.


Hi John,
Thanks for the climbing article. Yours and Matt’s are very informative and will probably prevent some accidents!
I whole-heartedly agree with your advice to not try specialized climbing equipment without training. Many years ago I tried that and fell, fortunately not far enough to prevent this sentence from being typed. (I did have to get a few stitches though.)  As I wanted to be able to maintain my rig, I needed to learn to climb the rig alone and safely. I engaged a local rigger who climbed masts solo for a living and he taught me several important things which you and Matt have described including: use a knot (doubled figure 8, halyard shackle to lazy loop) not the shackle to connect, and have an independent backup that you take with you up and down (short line tied between harness and a fixed 2nd halyard with prussik or climbheist). He wore a climbing harness inside the bosun chair. I did that too for several years. I tried just the climbing harness and agree about how uncomfortable it becomes within minutes. A friend who did SAR suggested I try a cushy harness like they use, and I got one of these:  I have hung in mine for more than an hour for several mast jobs and, while not as comfy as a padded bosun chair, doable. And the harness offers plenty of ways to hang a bucket or tools from the harness. I learned quickly to never wear shorts when climbing, and always wear shoes (I like leather moccasins, like the old topsiders). 
The only big difference between what is described in these articles and what I was taught is the means to ascend and descend: I use what the rigger showed me which is a block and tackle system. In my 30’s, I used a 3:1, but now in my 60’s, I use a 4:1 (and even with that I have to stop and rest before the 2nd spreaders). The upper block is a double (with becket for 4:1). The lower block is a ratcheting single (double for 4:1) with a ratchet release. I ascend with the ratchet engaged and when I’m where I need to be I tie the hoisting line to my harness with a doubled half hitch. To descend, I disengage the ratchet and feed the hoist line thru the carabiner attaching the tackle to my harness, using the carabiner as a descender. For mast head work, I added two steps a few feet below the top, and, after tying off to the mast, stand up in them while working up there. Here’s pix of my old 3:1 block and tackle:
I’ve felt safe using this type system for 30+ years, but I’m not an expert in these matters and in no way am advocating my way versus the means described here. The main disadvantages of the block and tackle system that I see are: it depends solely on upper body strength, and once 2-blocked at the top, you are a bit further from the top. I’d welcome your and others thoughts on the block and tackle method, at least for the benefit of anyone else who sees people using that technique. I’m motivated by the knowledge that the ~”it’s always worked” argument was used against adopting seat belts and air bags which turned out to have saved many lives.

thanks gain,


Steven Hodder

Plus one for the “sit harness”. A friend of mine who is a timber framer and has spent many eight hour days suspended on the side of historic train trestles uses them daily in his job. I’ve also used it to go work up the mast and they’re quite comfortable to work in.

Pete Running Bear

Hi Steve,
Just checking I understand currently, do you hoist the top block to the top of the mast before ascending and have the 4 long lines hanging down to the bottom block?
Guessing you need mast height X 4 of rope? I’m just wondering what happens if the rope gets snagged around something at deck level while you’re on the way down, would you then be stuck up the mast?
If I had 100 odd meters of rope in a pile on the deck it feels like it would almost certainly get tangled or snagged.

Dick Stevenson

Hi Peter,
I know at least one rigger, who works alone, and a couple of cruisers who use this method without problems. The line just lies down on deck well behaved. My experience is that a pile of line, not messed with, always comes off the pile as easily as it lays down: it is when we crew try to “straighten” up the “mess” that tangles emerge.
My best, Dick Stevenson, s/v Alchemy

Pete Running Bear

Ok, I guess that stands to reason. It would be a great system if it worked, I’d need to try it to believe it though (with someone on standby). Rope doesn’t like me, I only have to look at it the wrong way and it gets itself in a tangle. Especially 3mm mousing lines, they’re the work of the devil.

James Evans

Steve’s system is very similar to the one I used singlehanded for years, except that I left the ratchet engaged for descending ( why disengage? The rope still runs easily enough and it provides an extra measure of control). The addition of a carabiner is a good one. And John’s recommendation never to use climbing gear on which you haven’t been trained is a VERY good one.


James, you are correct, with a ratchet block, there is no need to disengage for descent. Thanks for pointing that out. My example of the 3:1 above actually uses a jammer, which works like a clutch, and must be disengaged for descent. My description above should’ve distinguished between ratchet and jammer blocks, and I should’ve used the term jammer in describing the 3:1. The jammer allows one to hang without tying off or holding onto the hoist line. With a ratchet block you have to always hang onto the hoist line, or tie it off. I actually use a ratchet block in my 4:1 system. Both work.

Barry Z.

I’m a climber. I was taught the following method by an IRATA -certified instructor and practiced from a tree branch under supervision with various simulated gear “failures”.

Key safety points in the method are redundancy and not falling any distance. I use two halyards (they are not dyneema). If a knot is used it is always the standard figure 8 used by climbers backed up by a simple knot. I climb up one halyard using a hand ascender, grigri and foot loop. This is a standard method. I am connected to the hand ascender by a 3 foot piece of line. I also have a shunt clipped into a second entirely separate halyard. The line from my climbing harness to the shunt is also about 3′ long. As I climb I slide the shunt up. As I descend I lower the hand ascender down to the grigri. I also lower the shunt about 2 feet. Then I lower myself using the grigri leaving some slack in the line connecting me to the shunt. Repeat until down. The process is time consuming! The maximum shock load arises from a fall of no more than 2 – 3 feet. I.e. the length of the line from my harness to the shunt. As is standard practice; I let myself “fall” when standing on the deck by simply dropping. I test both lines. That is about the extent of the distance I could ever fall.

For me to fall, I would have to lose the grigri and ascender on one line and the shunt on the other. Both halyards would have to fail following a drop of a 160lb person of two feet. It would be pretty sad to be sailing with halyards that could not take that strain.

If I absolutely had to go up the mast in heavy weather I would tie a line around the mast to keep me from swinging away from the mast. I would wear a helmet as well.

This is an outline only. You will want an instructor to demonstrate how to use carabiners properly and to back up the grigri and shunt. Line diameters should be within the specs for your hardware. All climbing gear should be stored to avoid UV. A serious fall means your gear should be replaced.


James Sarrett

Hi Barry,

You should be careful using a grigri on many halyards. The grigri is only suitable for a very small range of rope diameters, and even then it’s smooth release actin relies on the rope maintaining it’s cross section somewhat well. An easy solution is to haul a cheap static line up the halyard just to climb on. I’ve had problems trying it on various lines on my boat, and I won’t climb a mast on it, but it’s great for rocks! incidentally, check out for some jammers that are perfectly happy with double braid.

Arne Mogstad

I tried to find and link to the video you linked to from DMM in my comment for Matt’s part 1, it is a great and sobering video!

Regarding helmets: I usually recommend the “deforming-shell” type helmets (as the ones you two wearing in the pictures), as opposed to the “absorbing-styrofoam” type (like a bicycle helmet). The Styrofoam one is more sensitive about storage, and will only protect you from one blow. They work by being destroyed on impact. This means if you drop it, sit on it, or take a hit, you have no helmet anymore. The weight savings are negligible for this use anyway. Also, having hooks for a headlamp is nice. And choose one with a chinstrap that you can actually operate, as there are many interesting solutions out there.

Regarding harnesses: Big-wall harnesses are designed to hang and work in for days. They are pretty beefy and comfortable, and work pretty well for this use. Probably not the same as a bosuns chair (I have never tried the chair), but I have spent a lot of time hanging in those harnesses. SAR and work harnesses are often in the same category.


Arne Mogstad

They are excellent helmets! For those with limited space (and deep pockets), Edelrid makes a foldable helmet called “Madillo” that takes up much less space. However, a harness or something can be stored “inside” the helmet, so it is usually not wasted space anyway.

Dan Perrott

I wouldn’t want to work in my climbing harness for any length of time. I also would never feel a need to back it up with anything. (It may be a backup while climbing but it isn’t while abseiling or being lowered back down).
A note on choosing bosun’s chairs is to be careful with the width, Especially for women (often called for to be winches up due to lower weight) and larger gentleman (generally the last choice). Make sure they are wide enough. I can sit comfortably in ours but my girlfriends hips make it very uncomfortable for her.

William Murdoch

Dan Perrott said, “I wouldn’t want to work in my climbing harness for any length of time”.

I too found the couple of climbing harnesses I tried to be a bit uncomfortable to sit in motionless for any length of time. Back then there were tree sitters in the US Northwest protesting logging operations. They were hanging in trees for weeks or months at a time. I called, asked what they were using, and bought a New Tribe Saddle. It is now called the Basic Saddle and with stiff triangular pads in the leg straps is a sort of a cross between a bosuns chair and a climbing harness. It is made to sit in. I hang a canvas bucket on one side, hang a tool pouch on the other, and put a lanyard around the mast. I’ve had it for twenty or maybe twenty-five years now.

Eric Klem

Hi William,

It is funny that you mention a tree harness as reading Matt’s and John’s articles I keep wondering if arborist rigging is not more similar to our use case than climbing. My understanding is that they spend a lot of time hanging in their harnesses and are climbing things that move much more than a rock wall. I have seen a few of the local tree service trucks picking up line at the marine store although not recently and I know that at least Samson, Yale and Teufelberger all make products for both industries.

Of course, arborists might not be as niche as riggers but they must be a pretty small market.


Matt Marsh

Arborists and telecom tower workers are probably the two trades whose situations are closest to what we do up the mast.
People come in a lot of different shapes and sizes, so it’s very important to test-fit any harness, chair, saddle, etc. you’re considering for long duration work — and to do so under load. Comfortable on the ground is not the same thing as comfortable when hanging from the halyard.

Brian Russell

Glad to see someone else advocating for helmet use! Ditto on the Harken bosun chair-ours has served well and has nice deep pockets and lots of d-rings for tethered tools. I welded some simple tether rings onto various wrenches and vise-grips and drilled holes through screwdriver handles.

As a safety line I hoist an 11mm Static climbing line on a spare halyard and tie it tight to the mast base. Static lines have a much grippier surface texture than Dynamic lines.Then I wrap a short high modulus webbing climbing sling into a Klemheist sliding knot onto the static line.

When I’m ready to go aloft I sit in the chair, which is knotted to a dacron halyard, attach the Klemheist sling to my Black Diamond climbing harness with a locking carabiner and away I go up as Helen hoists me up with the mast winch-assisted by our cordless Milwaukkee drill motor. With one hand I slide the short Klemheist sling up the static line as I go. It’s very easy to slide in either direction, but when loaded in the down direction (Unlike the Prusik, the Klemheist is assymmetrical) it grips the static line instantly. I can remove my hand from the Klemheist at any time and it will instantly grip should I begin an unplanned descent. The potential fall distance is only about 16″/400mm.

This method puts the climber in control of the safety and the winching crewmember is not responsible keeping 2 lines tailed. If I became incapacitated while aloft for some reason (not sure how since I am wering a helmet)they could lower me by simply lowering the static line’s hoisting halyard.
The likelihood of dropping anything on the winching crew while ascending or descending is slight-especially with the deep pocketed Harken. Of course, they are well clear when I am working. I feel the risks associated with rigging a block system to redirect is greater.

By the way, a Klemheist is much simpler and more trustworthy than a rolling hitch when, for example, unloading an overridden sheet winch. It cannot be shaken off the line. I also use very small ones wrapped on shrouds to support a temporary sun canopy- almost as useful as soft shackles!

Arne Mogstad

Hi. A prusik (or klemheist or which ever knot you use) are not a good idea to stop a dynamic fall. If it does not lock up immediately, it will start to generate heat, and weaken/melt. They also work by pulling a part of the rope tight over another part of the rope. This also generates heat and wear, which also weakens it. I would just simply not use a klemheist as a fall arrest system. And in the static use described here, it is as John points out, going to maim you. Or worse, break, and you fall down on deck, hitting a spreader and a boom on the way to “soften” the fall.

To not be all negative, I would highly recommend upgrading to a device specifically designed for this use, which also incorporates a “screamer” (shock absorbing sling). That is a sling that is sewn in a way that it will rip open to absorb the shock load. The Petzl “ASAP” with an “Absorbica” or “ASAP’sorber” is an example of a device that does this, and is designed for this exact usage on static rope systems. I suspect John have this covered in part 3.

Even 10cm falls on a static system is surprisingly painful, and the loads are incredible.

Hope this was helpful and not just negative.

Kindly, Arne

Dick Stevenson

Hi John and all,
I am not sure how relevant this is to belays and the knots being referred to used for belays, but I know I find HM lines impressively slippery. For example, with my Dacron line I had no trouble raising the main to pretty much full hoist. When I got a HM halyard, bare handed, my grip slipped ½ way up. With gloves on I can get most of the way.
This is a long way of saying that I would be very wary of any sliding/stopper knot over a HM line: perhaps a Starzinger icicle hitch, but even there. Much safer some kind of mechanical belay like a Petzl ASAP in my thinking.
My best, Dick Stevenson, s/v Alchemy

Brian Russell

I agree, Dick. A HM line, especially an uncovered one is totally inappropriate for a safety line used as I describe, which is why I only use the special Static climbing line, which features a special cover weave that has much more grip than any other cover weave.

Brian Russell

I wanted to clarify a detail about the Klemheist that I use: It is a Sterling ropes “Hollow Block”, specifically designed for the application of rappeling backup.

Matt Marsh

The slipperiness is a probably-unavoidable consequence of the chemistry that’s needed to make high-strength high-modulus fibres.

Hoisting a static line to the masthead, and clipping your rope-gripping gadgets onto that, is (I think) a far better idea than clipping those rope-gripping gadgets directly to the halyard.

James Sarrett

I second this, but I would like to hear what people think is the best method for attaching these two differnet ropes together.

Andrew Reddon

John: it’s a tiny point but i think you are talking about a bowline in a halyard, so presumably you did not mean “snap shackle”. What does one call those u-shaped halyard shackles?

Eric Klem

For what its worth, I tie a loop in the end of each line that are connected to each other. With the climbing rope, I throw a figure 8 in as that is super easy to do when you are not going around something but this is just my practice. Then I pass the halyard through the loop and do a bowline. Both knots do get backed up too. The advantage of this method is that both lines are independently knotted on themselves so you are not really relying on the 2 being compatible with each other. There is a sharp bend in them but as long as they are the same diameter, this should be an acceptable bend radius given there are also knots weakening things.

The only variation that I can think of without going to splicing that could also make sense is to do 2 loops but strop hitch them together. It is a bunch more work and I don’t think it adds significant security. I would specifically not do a sheet bend or even a double sheet bend, I find they don’t work well with a lot of the types of lines you would use for a halyard as they take a really long time to tighten up enough to stop slipping. Things like a fishermans knot could potentially work but I don’t really see the point and haven’t tried it in those types of lines.


Brian Russell

Thanks, Arne, good information! I have several different ascender devices. I have found them clumsy to use and they severely scratch the anodizing on the mast. This ASAP device looks better in that it does not require a hand to move it along the rope, correct? I will also certainly investigate the “shock absorbing” sling as a component of the system. I have fallen several times, once doing tree work, the other installing a metal roof on my house-no fun, but both times a climbing harness kept me from going “splat”! For now, my klemheist will have to suffice, in fact I am going up today for pre-passage inspection. Next stop-St. Vincent!

Jorn Haga

Hi everyone,
Does anyone have a good recommendation on a cruising guide for brasil, an updated one.
Any help is highly apprevciated

Jorn Haga

Terence Thatcher

I had read some time ago that knots were better than mechanical fall arresters, which could break., I have always used a prussic on a static line, with no more than 12″ slack. I look forward to Part 3 to learn about the mechanical devices. I use a Brion Toss bosuns chair/harness. Expensive, but comfortable. I have never used a separate safety harness. Just made sure my safety line was attached to the bosuns chair. I guess I will need to revisit that. I take it that is to protect against the chair giving way?

Matt Marsh

Yes. Failure of the bosun’s chair itself is one of the cases we must protect against. In a “just clip the bosun’s chair to the halyard and winch away” system, the stitching of the chair’s webbing and seams is often the weakest mechanical link in the system, and is also among the hardest things to non-destructively verify.
The Brion Toss system, as I understand it, is compliant with the relevant OSHA standards, and is designed rather differently than a bosun’s chair. From what I can tell, it looks like the backup load paths are built into it; i.e. a failure of any single component of the system should cause the person’s weight to be transferred to a different load path within the same harness. But you should satisfy yourself that this is true for whatever system you use, rather than taking the word of someone on the internet.

Dick Stevenson

Hi Matt, John and all,
I have used a Brion Toss bosun’s chair/harness for 3+ decades or so.
I have spent many hours at a time in the harness waxing and cleaning the mast when we did not remove the mast for the winter as well as managing many other projects from the chair over the years and, while I would not say I was completely comfortable at the end of my time aloft, I was just fine. This may be, in part, as there is ample padding in the places that count and there are adjustments possible so that the leg supports can be lengthened or shortened to hit the leg in a good place. There are tool bags and ample places to fix tools and carabiners to facilitate the job at hand.
I give it inspection before every hoist and have never found any problem: stitching or otherwise.
I have always felt myself to be perfectly safe in the BT chair, even when fooling around hanging upside down which is probably not recommended, but was fun.
I was unaware that the design may incorporate a harness within a harness as an independent back-up as Matt suggests, but it makes sense as there are two independent rings one can tie onto: I always catch both.
My best, Dick Stevenson, s/v Alchemy

Pete Running Bear

Interesting stuff, as usual way more in-depth and informative than other sources. Looking forward to part 3, although I suspect that, as with a lot of your articles, it will prompt the purchasing of another piece of gear :/

On the subject of block loading (and I only know this because I was speccing a mast base block recently)

Harken have a handy table:

If this is to be trusted the load factor on the block increases at >60 degrees of line deflection.

Cyrille Rio

Glad we aren’t far of, while need to be extra careful with the fall prevention halyard slack…
one other tool we always use: the Sena SPH10 Bluetooth Stereo Headset. Makes communication on managing up and down much easier. Of course headset is secured/teathered to the harness…

On a side note, the plastimo chair isn’t too bad. A bit less bulky than the harken, and it goes back into a nice large pouch that doubles up as a tool box you can clip on. The attachment point is I think also lower than the harken, meaning it might be easier to get yourself higher at the mast top, if for example you need to drill the top mast flat head.

Drew Frye

Two comments on knots.

  1. The more compact the knot the higher you can get. It will also snag on less (important for rock climbers, and I’ve seen people get in trouble that forgot it). Remember this when you are tying it on the deck!
  2. Using the shackle on the halyard end as a backup clip is a good idea with Dyneema. Second that.
Drew Frye

About impact force. You might Google parachute opening force and harness impact force related to injuries. I recall that the military considered 1200-pounds in a full body harness the threshold beyond where chutes open diminish combat effectiveness due to injuries. Above 2000 pound serious internal injuries and broken bones are more likely than not, and above 3000 pounds it won’t actually matter if the rope broke. Most “serious” climbing falls are in the 500- to 800-pound range, since we have no trouble untying the ropes. Not once in 40 years of climbing have I had trouble getting a knot out or have known any of my close associates to. That includes many thousands of falls, from trivial to somewhat impressive (the longest fall I ever belayed was ~ 100 feet–and the knot was not very tight, through the climber was pretty shaky).

James Rosbe

Perhaps in Part 4 you may include Swi-Tec’s MastLift, which I found extremely practical and convenient. Basically it is a hoist-able chain-fall with 10-1 gear ratio, allowing one to easily hoist oneself aloft and lower back down again. I raise it to masthead with my genoa halyard that runs through a sheave within the mast, and hoist and lower myself with the Mastlift’s continuous line. For safety, a helper could simultaneously keep some tension on a second halyard secured to the bosun chair. An added bonus is how convenient it is for launching and retrieving the dinghy. Current pricing is 1050 euros.

Jim Rosbe
s/v Uncommon Loon

James Sarrett

Hi John and members,

I used to climb (many years, and a stronger back, ago) *only* on the double figure-8 knot and for that purpose it’s excellent. I have some extreme reservation using it on typical halyards though. In typical kernmanlte climbing ropes the cover of the rope is woven tight at a high bias angle (which makes it generally unspliceable). This means that under side loading it doesn’t ‘flatten-out’ nearly as much as double-braid. If you highly load a figure-8 in climbing rope it won’t cinch up nearly as tight as it will in double braid. In double braid it can much more easily become a “knife-knot” with even just moderate loading, not so with a bowline.

In lots of types of cordage it’s even less efficient as a knot vs a bowline, though in climbing rope it’s not a big difference. The real reason climbers don’t tie a bowline, is that there were some well publicized deaths on bowlines which were tied improperly in the early days of sport climbing. The figure 8 is MUCH easier to inspect by your climbing partner (2-2-2 rule), and this has dramatically improved it’s operational safety.

incidentally, this is the same reason I don’t recommend climbing ascenders for halyards. The special designed ones from Etienne Giroire ( don’t have the typical climbing style teeth and grips on the cams, and they close all the way down on double-braid. I’m typically singlehanded and I climb up on two of them.

Horses for courses. I recommend a bowline with a back-up for yacht braid, and keep those tails long!

Bob Hodges

Hi John,

All great information but here’s a curveball. How would you set up to do masthead work if your boat is a fractional rig and the only spare halyards exit the mast a couple of feet (or more) below where you need to go?

We have a Dragonfly 32 trimaran and the top of the fractional rig on it is 61 feet above the water (about 55 feet above the deck). If I have to go up on the mainsail halyard, I’ve thought about attaching the spinnaker halyard (the next highest halyard) to the bosun’s chair and once I am hoisted let it travel to the top with me and then have my wife pull out all of the slack. God forbid in the event of the main halyard failing, I would drop about 3′-4′ at the most before the spinnaker halyard would take the load. Seems like I would want to have a fall arrestor setup on the spinnaker halyard. Also, it might sling me out towards the upper diamond in that event also since the spinnaker halyard is on the front of the mast and I would be on the opposite side.



Bob Hodges
Covington, LA

Bob Hodges

Thanks John,

Good info there. The safety belt strategy makes a lot of sense and should be easy to implement.



Bob Hodges

And lots more to digest after reading parts 3 and 4!

Thanks again.