The Offshore Voyaging Reference Site

Going Up The Mast—Our System

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

Let’s take a look at the gear and techniques that Phyllis and I use for mast climbing now, improvements we are planning for next season and, most important of all, a list of mistakes I have made over 50 years of mast climbing that you definitely want to avoid.

Despite that, what follows will at least help you think critically about what you are doing and how to improve it.

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Alastair Currie

Great article in the series, all of which have now made me reconsider what I am doing. The Petzl ASAP device looks very good and I am going to look into this for my own boat. When I climb Derrick ladders, many are fitted with 3M DBI Sala LadSaf systems. They work similarly to the Petlz system but on wire. Which brings me to my point, Rescue At Height Plan. Basically if at height and an incident happens which requires the Petzl device to work, you need a rescue plan to get you down, if you can’t help yourself. That may mean, the halyard that the Petzl device arrests the fall on, may have to be lowered to get the suspended person down, unaided, which means the halyard may have to have a long tail, if the incident is at the top of the mast. Having been up the mast in the Atlantic, it took all my strength to hold on in the rolling boat (main halyard had jumped a sheave). Rescue plans need to be thought through and practised for the situation where the at height party can’t help themselves. It easy.

Alastair Currie

At the end of my comment, “It easy” should have been written as “It’s not easy” to sort out rescue on the day with a half thought through, unpractised rescue plan.

Drew Frye

A few more things.

  • Fall arrest tethers are call Screamers because that is a Yates Mountaineering trademark (John Yates invented them).
  • No, a 6500-pound test nylon rope is not compromised by a knot. The UIAA drop test is based on a knotted rope and the they never fail at the knot. The stretch of nylon rope attenuates the force below the knotted breaking strength of the rope. I seriously doubt you could exceed 400 pounds force on a mast fall unless you have massive slick, using a nylon rope. Taking a fall on Dyneema is different (nightmare). A cautious person would not climb on a Dyneema halyard; they would pull up a polyester or nylon climbing line.
  • A savvy climber always carries several carabiners and several slings for getting his weight off the rope and securing himself in place. For example, if you tie a Prusik around the mast you can unload all of the safety ropes. This is what the gear loops on harnesses are for. You will never be stuck if something fails. You could even rig an anchor to the mast and rap down a line hauled up. Contingency planning.
  • Arrest devises can be very fussy regarding rope diameter. Do a test jump on each new rope.
  • Using a chest harness for any purpose is just nuts. Punctured lung. Suffocation. OSHA and UIAA do not allow them for any fall arrest purpose. It would be safer to tie ~ 5 turns of rope tightly around the waist, under the ribs, assuming the climber has a well defined waist. If he does not … perhaps he shouldn’t be climbing.

Good articles with lots of good advise. Perhaps the best was the speach about a false sense of security. Climbers call bad gear “psychological protection.” Climbing the mast can be safe, and there are many ways, but no shortcuts.

The worst accident I have witnessed resulted from buckling a harrness incorrectly. The harness remained on the rope and the climber landed 40 feet from me (he fell about 250 feet). The other bad accident in involved a long time climbing partner (I was not there–he was climbing with someone I did not think was a safe climber). When time came to lower off, the wrong rope was belayed, resulting in a 50-foot fall and about 20 fractures.

Check your rigging and train your belayers. Belay errors are the greatest danger.

Drew Frye

I don’t understand why slings are a serious risk, or perhaps it comes down to knowing how to use them correctly. Climbers do this at every single belay, and very, very few climbers carry Screamers. They are a one trick pony that lacks versatility. Like rubber snubber for anchoring, it is simpler to just add a little stretch to the rope system. They were invented when ropes were less elastic and have become obsolete in the climbing community, except for some aid climbing applications.They have been adopted in industry, but the application is different from both rock climbing and mast climbing. I will not climb without a pair of long slings and a handfull of carabiners, based on long experience. I might need them for something, and I can rig them many ways. They are the most versatile gear I own and the bit I would be least likely to climb without. I have several Screamers and have not used them in decades, other than for testing something.

The only sling hazard is creating slack and falling directly on a sling (a VERY hard stop), but this will not happen unless you climb above the anchor (stupid). Another risk is attaching an extention sling to an ASAP or other arrest devise, but this is unnecessary climbing a mast–there is no need for any sling. I clip my Goblin direct to the harness. In industry there can be reasons you need an extension. They also have value on a non-strerch rope (Dyneema–polyester has enough stretch for this) halyard near the mast top, but I would hoist a climbing rope and eliminate the risk and halyard wear. To a climber, slings hanging from the gear loops are vital to contingency planning.

I agree you need to be careful taking advise from climbers. We may leave out important safety aspects that we thought were obvious. Less experienced climbers may not understand how all of the bits work together, particularly taken outside of their familiar practice. More expereinced climbers are relaxed at hight and know more contingency methods. You can’t imagine how many weird anchors and contingencies I’ve worked through up some crag. Rope frozen. Gear dropped. You learn all the tricks.

Matt makes some good points, but is off on the climbing vs. insurance issue, or rather it requires explanation. High altitude mountaineering (Himalayas) contains unavoidable risk. Avalanche and lack of oxygen, for example. But rock and ice climbing are considered much safer than, for example, riding a motorcycle. I know very few climbers who have been injured, and I know many, but practically every motorcycle rider has either scars or stories of dead friends. Climbing looks scary. Riding is scary.

Drew Frye

Does anyone actually use a seat harness for POB protection? That displays a distinct lack of common sense.

However as a counter, there are many sailors that use a sailing harness for fall protection climbing the mast. I suggest that they first try hanging in a sailing harness for 30 seconds–they probably won’t last that long. Stay for more than 2 minutes and permanent nerve damamge is common and documented. This is why OSHA and UIAA have banned them from all fall protection uses (other than in combination with a seat harness to keep you more vertical). And then consider what would happen if you fell on such a harness. Most likely a trip to the ER and some permanent damamge.

I’ve seen commercial bosun’s chairs that should never had a place in the market. Garbage. A case of a sailing manufacturer thinking he understands work at height. Then there are the Spinlock Race clips, that can unclip or bend under little more than bodyweight if loaded at an angle. They never investigated climbing gear testing standards, and then denied that they applied.

It’s not about sailing vs. climbing, it’s about quality and matching the gear to the application, which is not always obvious.

Matt Marsh

Be careful with screamers. They’ll absolutely save your ass if a window-washing scaffold falls out from under you. But they need some distance to work, and a lot of people who use them don’t think to add up the tether slack, plus the length of the *extended* screamer, plus the length of your body and legs, and then end up breaking their shins on something at 4–5 m/s when the screamer still has another metre to go.

I might mention that, if you talk to a life insurance underwriter, they charge a pretty fat premium, or sometimes refuse coverage entirely, for mountain climbers. And yet most of them don’t even care about whether you work at heights for your trade, as long as you’re in a trade that follows OSHA etc. regulations and requires proper training and approved/certified safety gear. 120 years of injury and fatality statistics have convinced them that proper industrial fall protection training and ANSI-certified equipment are sufficient to reduce the risk to statistically negligible.

Eric Klem

Hi John,

Looks like I am going to have to do my homework on non-knot based belay devices. I watched Petzls video on the ASAP and one thing that jumped out at me is how well does it stand up to the marine environment? Do you or anyone else have any experience with this? If the mechanism gets sticky, it may stop working reliably and I don’t know how you would tell that. I looked through their documentation and they say not to store in a salt or wet environment. They do provide an inspection procedure which is mostly high level but they do tell you to do a test actuation but what I don’t know is whether it could reach an intermittent stage. I know with the ascenders that I use for climbing only that they do get sticky and I have to inspect and sometimes lube them up before climbing despite them still looking cosmetically perfect and never having direct salt contact. This probably isn’t a big deal if you really focus on proper cleaning and storage and then do a few test actuations before using it.

Like you, we hoist a line (dynamic climbing rope in our case) to the masthead for the safety line for the exact reason you describe which is the ability to lower from deck if needed. If I am jumaring up, then I hoist a static line for that too but if I am grinding my wife up, then we just use the halyard directly.


Matt Marsh

The pre-check procedure for the Petzl ASAP is pretty comprehensive. Indeed, the simple fact that such a procedure exists is one way to help tell good equipment from potentially sketchy equipment. (Linked from “Technical information” on the product page: )
Do note that virtually all devices of this type will include a certification warning that says something like:

Certification(s): CE EN 12841 type A, UKCA, when used with an OK TRIACT-LOCK carabiner and a 10-13 mm EN 1891 type A rope. An ASAP’SORBER or ASAP’SORBER AXESS energy absorber can be used when needed

In other words, the device is a component of a system and you need to follow the design and specification of the complete system in order for the thing to actually meet its safety certifications. You can’t just clip it to any old rope or carabiner that looks to be about the right size.

Arne Mogstad

These are all really great articles, and some good points on the comments too!

I just want to add, as I was mentioning in an earlier comment, that taking a fall, is serious stuff! A LOT can happen on the way down! And also, what happens to the ropes when they suddenly become loaded is sometimes hard to predict. It may very well pull you in unforeseen directions at an uncomfortable speed. Especially if you’re using a backup on the other side of the mast. Having taken countless falls while climbing, it never cease to amaze me how far you fall before all the slack is pulled out, and in which direction you go!

This goes for both fall arrest and fall prevention, since the primary and backup are rarely routed the exact same way with the exact same tension.

Ernest E Vogelsinger

I resorted to having mast steps as the main climbing device, no one needed to haul me up or down. Having a safety backup is a no-brainer, for me it is a Petzl climbing harness, combined with a Prusik knot over the main halyard that is snug tight when going up. I did some “test jumps”, and always had to get new underwear after that, but nothing more – the Prusik held, even after moving it up or down some steps.
I considered some device such as the ASAP, but the Prusik gives me a huge advantage – it is not only a safety backup, it also keeps me stable when I need to lean out to the spreaders, or the like, while the ASAP would start to brake a meter or so below. Not enough time to complete work planned, then.

At work height (the top being the most convenient, having two level steps), the Prusik is still attached, but an additional loop around the mast gives me a hands-free work area (and I always make sure to have some fresh underwear ready below…)

Ah, yes – the whole setup was trained and inspected with a friend who is an avid rock climber.

Drew Frye

My favorite method–and this is just me–is a MastMate. I have used pretty much every system, and this fits my individual needs best on my last tree boats. I was introduced to it by a solo-surveyor 35 years ago.

  • Not dependent on a belayer or hoister. Although I could and have used a human belayer, I can also use a mechanical tracking fall arrest devise (Camp Goblin is my favorite, in part because it is more compact than the ASAP, which is also very good). But primarily, as an experienced and active climber, I know in my heart that there is zero chance of me falling of a webbing ladder. That’s a big deal. The fall arrest system is very important and I rig it meticulously, but ultimately I know I will not be using it. I do not have to worry about belayer error.
  • Faster. I climb at about the pace you climb a ladder. Much faster than ascenders, much more efficient using legs than winching. If you pack it properly the foot loops fall right open, smooth deck shoes slide right in, and gloved hands hold the back side of the mast. This also means it is not tiring and multiple trips are not a big deal. I suppose a certain sense of balance and a certain strength to weight ratio help; perhaps not as safe or efficient for the portly.
  • Counter to the instructions, you can rig it outside the track. Just tension it hard and stay in balance when climbing.
  • I am very comfortable securing myself at height with slings, the result of long experience. That is not for everyone. You need to be cool-headed, meticulous, and understand the rules.
  • I use a climbing harness with additional padding for improved hang time. A regular harness is annoying at about 10 minutes. The modifications extend this to more like an hour. Within an hour I’m either finished or simply want to step back from it, because something has gotten complicated!
  • Self-rescue is more complicated. But you can still be lowered off if you have not tied off to the mast (you can tie off to the ladder). Simply lower both the belay and ladder lines. That is the compromise. The need is also exceptionally unlikely.

As I said, this is just me. Chairs are very well proven and have a few advantages, including increased mobility. But they are not very handy for the singlehander.

Bill Harvey

The drop test video really got me concerned as I have a fraction rig my safety line is the jib halyard which is at least a 3 m drop with the loop

Matt Marsh

If your total distance to drop before the safety line catches is 3 m, then you’re already falling at 7.7 m/s (28 km/h) before it begins to do anything.
If your masthead is 3 m above your safety line exit point, then you have at least 6 m to fall, which means you’re doing over 11 m/s (40 km/h) when it snatches up.
To safely arrest a fall from that speed, you need lots of empty space below you. Probably more empty space than is available.

If you’re stuck with that situation and can’t get a safety line rigged from the masthead then I would be inclined to add a tether from your left hip, around the mast, to your right hip. That tether, plus your feet braced against the mast, should be sufficient to hold you in position and let you control your descent if the main halyard were to fail. Test it and work out the details at just above the level of the boom, before committing to climbing with such a setup.

Drew Frye

Actually, this common challenge has a simple, safe solution that I have used on a number of boats, a number of times.

Once you pass the hounds, wrap a 3/8-inch polyester rope loop around the mast, forming a Prusik hitch. Depending on the diameter of the mast this will take about 8′ of rope, tied with a double fisherman’s or other strong knot. Yes, the hitch will hold on a mast, over 1500 pounds, I’ve tested this with a winch and a load cell. The breaking strength of the Pruiskic should be over 5500 pounds (remember, it is a loop). Webbing can be used, but it is more difficult to move and reset. Dyneema offers no stretch and is not recommended for this. The method does add some complications, but it eliminates the slack and long fall potencial.

You will need to slack off your fall arrest rope as you ascend past the hounds (otherwise it would be pulling you down). You do not need to disconnect, though if climbing solo this may be the simpler way (I clip to the fall arrest device with a sling I can extend until I return to the hounds). Clip into the Prusik first. You will need to reset and dress the Prusik hitch each time you push it up. This is unavoidable. But you don’t have far to go and will probably only do this a few times. Repeat going down.

The trick to avoiding the risk of Prusiks not catching or heating when sliding is to dress the knots and manage the slack. Again, the polyester gives a little bit of stretch, reducing impacts, and the knots will slide/shift a bit when taking a hard load, absorbing more energy.

With no available halyard to the top of the mast, this is the only safe way.

This is one of the reasons, I suppose, that I am steadfast about carrying slings. My boat is fractionally rigged. I do this every time I climb, so commonly I take it for obvious. My last boat was masthead, but the others have been fractionally rigged sport boats.

Drew Frye

I don’t see why 8-9 mm climbing rope would not work well for the mast Prusik. Climbers just don’t think about it, because the rope is always the dynamic part. Same with a Prusik on the rode.

One downside is that knots in nylon are more prone to jamming than in polyester, because the rope gets skinny when it stretches, allowing the knot to over tighten and then jam when the rope recovers and expands. But I don’t think Prusiks are very prone to this, certainly not under body weight.

Climbers typically use Dyneema/polyester blends for Prusiks on climbing ropes in order the get the right blend of strength and friction in smaller sizes.

Eric Klem

Hi Drew,

It is good to see you write this. I have used this technique but never known whether it was really good.

One thing I have thought about when doing this is what you do if you ever end up using your safety. It could just be that the person grinding you up had a major whoopsie and can reset and continue but it could imply that something is really wrong and you are now stuck hanging from a prusik around the mast. I think a solution for people who are not able to freeclimb is simply to have a light tag line going from your chair/harness to the deck but there may be a better way. This would give you the ability to haul up what you need to set up a proper rappel and get yourself down, obviously requiring some skill for knowing how to execute this. You are going to want the tag line anyways for when invariably you need a different tool at the top of the mast. When it is available, I prefer to keep a bucket on a spare halyard with a tag line that is where most of my gear is instead of the chair pockets and then it can be hauled up and down quickly to restock ro whatever. When that spare halyard isn’t available, I just use a piece of light line and do the hauling from in the chair but then the bucket is lower and not as easy to get stuff in and out of.

One other thought is that most fractional rigged boats still have a topping lift. Even if it is deadended at the masthead, it potentially could be used as a safety with the same issues as a prusik around the mast. I have seen a lot of these be wire but these days there is no reason they couldn’t be a double braid allowing an asap or whatever to be put on them with appropriate shock absorption.


Drew Frye

I don’t recall reading this in these threads, but a tag line is extremely handy for the tools and parts you have forgotten, or even the whole tool bag, if it is heavy. You avoid climbing with all that extra weight. I always take a tag line, unless climbing solo, typically an 8 mm climbing rope, just because that is multi-purpose and I have it. But anything ~ 5/16- to 3/8-inch would do.

Stan Blakey

I don’t see you suggesting having a proper climbing rope, especially with an ASAP. Where possible running a dedicated climbing line ensures you know the rope is good and is the correct type and diameter for the safety equipment. Especially if you are on someone else’s boat but even on your own knowing the rope is safe would be rule one in an industry setting rather than relying on what is there.

Andrew Wade

Hi John
I wonder if you are missing something from Stan’s comment. Or maybe I’ve misread your article, or mis-interpreted Stan’s comment, or both.
I’ll plunge in anyway.
In your article you’re talking about hoisting a dedicated climbing/high elongation rope on a halyard to the masthead as a back up line for your ASAP to run on (at least that’s how I understood it), whereas I thought Stan was suggesting running a halyard out entirely and replacing it with a climbing rope. This ensures you’re using a good, known rope; solves the problem of a tested splice (you don’t need one); and adds to the overall elongation available should a fall ever need to be arrested.
I’m curious as to whether this is what you meant, and if not, your thoughts on it.
It is our standard practice.
The ropes we use for going up the rig (we call them ‘person halyards’) are only ever used for this purpose.

All the best

Andrew Wade

Good point about the extra length needed to lower the climber if the primary system fails. I think your idea is a good one. It is more rope, but at least at 10mm or so diameter it’s not going to be too massive to stow. And that diameter is the same whether you’re going up a 30ft or 100ft rig.
We have a couple more halyards free, at least potentially if we’re dockside, so I’ve just thought I’d use one of those. It does, however, rely on the climber being in a fit state to transfer on to a new halyard. Being able to lower the backup halyard is better because that should work in the event that the climber was unconscious too.

Terence Thatcher

THANK YOU. My rigger, amazing guy, walks up the mast on a halyard, but with a fall arrest system in place. I will never try that. We too use the anchor capstan. He did urge me, in the strongest terms, never to use a spinnaker block hanging from a crane. Best to use, as you do now, an in-mast sheave.Worst that happens is your line hangs up on the mast if a sheave gives way. I have two main halyards to use. But your focus on the 5000 lb strength raises this concern: How much strength does a line lose going 180 degrees over a sheave? Do rope manufacturers tell us that?

Eric Klem

Hi Terence,

It is a function of the bend radius of the sheave and the radius of the line (for some reason I often see it as D/d in the sailing world but everywhere else it is R/r). Hampidjan has a graph you can find that is widely quoted. For an uncovered dyneema line, a sheave radius equal to the radius of the line would give a 50% strength reduction but this is a really small sheave. That same line with a 5:1 ratio gives closer to 20% reduction. This is a more realistic sheave size and the strength reduction is significantly less than most knots we are discussing. One other safety factor built in is that most of us run covered, core dependent halyards so using the line radius as opposed to the core radius is overly conservative.


Eric Klem

Hi John,

I don’t have the original source for the graph but this US Sailing lifeline one includes it and should be reputable:

That is scary about Aramid. 20X gets pretty impractical on a lot of mastheads or just about anywhere.


Terence Thatcher

Other questions. I use big double screw shackles on my main halyards. Why do you urge tying the halyard to the chair/harness rather using a ROBUST shackle? Also, I use a Brion Toss harness, not a chair. I can’t see how I can wear another harness under the Toss thing. It is pretty bulky and has leg straps. Suggestions? Thanks.

martin johnson

Please be certain that your helmet is rated for side impact. Many climbing helmets are intended to protect from falling objects only.
I hoist a 10mm dynamic climbing rope attached via figure 8 to the main halyard. Hoist per normal and fix at mast winch. Ascend climbing rope with a Petzl Grigri and one ascender. No winching of me at all. If any crisis, crew can lower me down at the mast winch. When my tasks are complete, Grigri is already rigged for me to lower myself to the deck. Rigger bucket is tied to the bottom end of the climbing rope so I can hoist tools and equipment once I get to the masthead. a stopper knot can be added for backup once you get above deck level.
Good explanation here:

Ernest E Vogelsinger

Hi John, as I see it a mountain may throw stones at you, from above, but rather seldom would rock violently to the side, forcing your head crashing against it, as some sailboat masts might consider 😉

Roland Stockham

For anyone looking at safe mast climbing can I respectfully suggest not looking at industrial fall prevention equipment or climbing books. The specialists in fixed rope accents are cavers not climbers and all the specialist rope access techniques have been developed from caving practice.
In a past life I was a caving and climbing instructor and was involved in the development of equipment and techniques for static rope climbing. If it works on a 1000ft underground pitch through a waterfall it may be good for a 50ft mast! Since then I have worked as an industrial nurse and managed emergency evacuation on construction sites.
I have seen a number of articles on mast climbing and it always worries me when I see people using equipment that was not designed for that job, or worse mixing techniques and equipment designed for different jobs, and that they have not been trained to use and may not fully understand.
The first thing I will say is that the safety line should be a dynamic climbing rope used ONLY for that purpose. No lines that have been out in the elements on a mast should be used and it should be belayed by a competent person using a climbers belay break. This persons ONLY job is managing you safety line and acting as your backup if things go wrong. You should both have a hand held VHF for comm’s. Best place to learn this is you local climbing wall, they have instructors and a safe place to practice.
Second point is the difference between static and dynamic ropes. Dynamic ropes are rated by their fall factor not break load. Fall factor is the length of any possible fall divided by the length of rope. If you fall 10ft onto 10ft of rope that is a fall factor of 1. If you fall 100ft onto 100ft of rope that is still a fall factor of 1. Dynamic climbing rope is generally rated for 4 to 6 falls with a fall factor of 2. By comparison static ropes may have very high break loads but still have low fall factors. This can often be as low as 0.5 or less so even a short fall can break a static rope. The lower the stretch the lower the fall factor. That however is not the main point. Dynamic ropes are very carefully engineered to arrest a fall generating a maximum impact load during arrest that the human body can tollerate. Basically the question is not whether the rope will break it is weather you will!!! A falling body acquires a lot of energy and if you stop it too quickly that nice harness will act like cheese wire, you risk whip lash injury to neck and spine and tendon injuries or dislocations to hips. If you fall for 1 second you could be traveling at 22mph. Arresting yourself on a static rope is like hitting a wall, a dynamic rope is like landing on an air bag.
Can you use shock absorbing fall arrest devices? Generally not a good idea. Most of these devices are designed to clip directly into a strong point. So if you have a 6ft tether it is designed to safely arrest a fall of no more than 6ft, after that it has absorbed it maximum amount of energy and becomes a static link. If you use the device as part of a much longer system it may not have the capacity you need. Remember that kit was designed for someone working on a platform not free climbing a tower!
So now you have a proper safety line and safety back up person but how do you get up the mast. Pretty much how you like, how you climb will dictate how hard it is but it is the safety line system that will save you. You can have a third person to winch you up, mast step permanently attached or climb a static rope. If you want to climb a static rope I would strongly recommend doing a training course that covers rope ascent, decent and self rescue plus you need to practice before trying it on a mast especially at sea. The advantage is that you are in control and not relying on someone at the bottom with a winch. Also means you can do it safely with 2 people. PS. If you climb the mast at sea always have a strop around the mast, lowering off the mast head into the sea because the boat rolled at the wrong moment will definitely take the edge off your day!
If you must go up a mast on your own it can be done using static rope climbing technique and an emergency brake system but you have to have well practiced skills and accept a substantially higher risk level. On thing though is to NEVER use a rope climbing jammer on a safety line That is one with a toothed or ribbed cam, in even a moderate fall it will tear the sheath off the rope.
As a PS. If I need to access the mast my preferred way is to tie to a key and hire a hydraulic lift like you see people using to service street cables. If I can’t do that my mast has steps. I climb the steps while the crew belays me. If I am alone and absolutely have to get up the mast i.e. the alternative is a MAYDAY call, then I will use a self arrest system but then solo sailors have a different take on safety don’t they.