Mast climbing techniques

Photo16 Climbing

I am the designated mast climber on Nine of Cups, if for no other reason than Marcie doesn’t like heights. This means, of course, that since there are only two of us aboard, Marcie gets stuck with the winch cranking duty. Hauling me up the mast gets old in a hurry, and when the project involves more than one trip up the mast, it can be downright tedious. We contemplated buying a powered winch or figuring out a fairlead from the aft side of the mast forward to the windlass, but in the end, we came up with a much simpler idea.

David Lynn demonstrates his mast climbing technique on his boat Nine of Cups.

I was raised in Colorado, and in my younger days I did a bit of rock climbing. I remember using friction knots such as the Prusik knot, as well as mechanical devices called ascenders, to climb vertical ropes. I could see no reason why this technique couldn’t be used to climb a halyard. After a little trial and error, I found a couple of quick, safe and easy systems for climbing the mast that you can make for yourself. The cost will range from about $20 dollars for the simplest system using a few simple knots to about $200 if you choose to use mechanical ascenders.

Friction knots
The simplest approach uses a friction knot. The Prusik knot, the most commonly known of the knots used for this purpose, was named for the Austrian climber, Dr. Karl Prusik, and was first shown in a 1930’s mountaineering manual on rope ascending. It is a friction knot that forms a loop around another tensioned line. When no weight or tension is applied to the Prusik knot, it will slide freely up or down. When you apply weight or tension to the Prusik knot, it locks in place and will not slide. There are several similar knots that are commonly used to ascend a rope. One of these, called the Klemheist or French Prusik knot, is the one I prefer, as it is less likely to jam, is easier to tie and is easier to use when descending the halyard.

Top: a Prusik knot. Bottom: a Klemheist knot. Both knots can be used to climb a halyard.

To make the Klemheist knot, I start with two five-foot lengths of quarter-inch quality double braid line formed into loops using a double fisherman’s knot. I keep these loops permanently made up and stowed in my “mast climbing kit.” The loops are attached to the halyard, one above the other, using a Klemheist knot. I then attach slings to the loops, described later, that are long enough to stand in.

Mechanical ascenders
The alternative to using Prusik-type knots is to use mechanical ascenders. The first commercially available ascender was manufactured by the Swiss company Jumar Pangit in the 1950s, and because of this, ascenders are sometimes referred to as Jumars, and the technique of climbing a rope with ascenders is sometimes referred to as “jumaring.” There are now several manufacturers and models to choose from, ranging from $30 to $80 apiece. I use a model made by Petzl that cost me $75 each several years ago. A slightly improved version of the same ascender is now available for $70 on the Internet. It works much the same way as a rope clutch on a sailboat in that it uses a cam with teeth that allows it to slide up the rope it is attached to, but locks in place if pulled downward. Two ascenders are attached to the halyard, one above the other. Foot slings are then attached to the ascenders.

These units can be used to descend as well. Ascenders have a release lever that opens the cam and allows it to be slid back down the line.

Friction knot vs. ascenders
I have used friction knots as well as ascenders to climb a halyard and both have pros and cons. Friction knots are less expensive, but it took me a bit more practice to become proficient in using them. I find ascenders easier to use and I can climb the mast faster with them. On the negative side, it is more difficult to descend with ascenders, and like a rope clutch, ascenders will sometimes chew up the halyard slightly, although this is unlikely to be a problem unless you are using them very frequently. Either will work, but my preference is to use my ascenders.

Foot slings
Marcie made foot slings for me using heavy webbing. We use webbing for our jacklines, and the last time we replaced them, we had enough left over to make the foot slings. Each foot sling is a length of webbing with a small loop sewn in one end and a large loop sewn in the other. The small loop is about three inches in diameter while the large loop is big enough for me to slide my foot into. Each loop is double stitched across the top and the bottom, with two extra diagonal lines of stitching for good measure. Since one ascender or friction knot will always be higher than the other, the two slings should be made slightly different lengths so the foot loops are at the same height. My preference is to have the upper ascender or friction knot at about mid-chest height when I am standing in the foot loop. The foot sling attached to the lower ascender or friction knot is short enough that my feet are even when I am standing in both loops.

1. 2.
3. 4.
5. 6.

The sequence of tying a double fisherman’s knot.

An alternative to making the slings is to buy something called etrier aiders, which is what climbers use. These look like short nylon ladders with four or five steps that can be clipped to the ascenders or friction knots. You put your feet in whichever “rung” of the aider is at the correct height and use them like the slings described above.

When using an ascender, I use a carabiner to attach each foot sling to the ascender. If using a friction knot, I use either a carabiner or I can loop the foot loop through the small loop to attach each foot sling to its friction knot. The webbing is stiff enough that I can form a stirrup in the foot loop to make it easy to slide my feet in place. We contemplated stitching another few inches of webbing to the bottom of the foot loop to form a permanent stirrup shape, but it wasn’t necessary with the webbing we used. (To simplify things, from now on I will use the term ascenders to mean either a mechanical ascender or friction knot.)

Safety issues
Climbing the mast with nothing more than slings attached to ascenders would be very risky if not downright foolhardy. If I were to lose my grip for an instant, if either of my feet were to slip out of the slings, or if any number of other possibilities were to occur, my descent back down the mast might be a whole lot faster than I prefer. In addition, I most likely am going up the mast to work on something, and I want to have a bosun’s chair to sit in, carry tools and parts, and free up both hands. For all these reasons, I need more than just the two ascenders and slings.

To begin with, unless it is an emergency and no one else is around, I always have someone belay me. I attach the ascenders to the main halyard and attach the topping lift to my bosun’s chair. My bosun’s chair has a seat belt of sorts, also made by Marcie, to keep the seat attached to me. I also use a climbing harness with two safety lines, one attached to the bosun’s chair and the other attached to the upper ascender. On the rare occasion I have had to climb the mast at sea or in a very rolly anchorage, I also loop another line around the mast to limit the amount of swinging I do.

The technique I use when someone is there to belay me is quite straightforward. I attach the main halyard to the foot of the mast and tighten it as much as possible. The tighter you can get it the better. Once you start up the mast, any slack or stretch will make your ascent more difficult as you will have a tendency to swing out and away from the mast.

Steps in tying a Klemheist knot.

Then I attach the two ascenders and rig the foot slings. Next, I attach the topping lift to my bosun’s chair with a bowline, strap myself into the chair and clip my harness to the bosun’s chair and upper ascender.

Mechanical line ascenders (often generically called Jumars) are an alternative to using Prusik and Klemheist knots.

If the person who is belaying me understands the process, is paying attention and is in sync with me, climbing the halyard is quite easy. Marcie and I have done this enough times that we have the system pretty organized. I sit in the bosun’s chair and slide both ascenders up the halyard as high as I can. Then I stand in both foot slings. As soon as the topping lift goes slack, Marcie tugs on it to take up the slack. Then I sit back in the bosun’s chair, slide the ascenders up the halyard again and the process is repeated. Watching from below, it looks like I am climbing a ladder, and after a little practice, it is just about as fast.

If I am working at the masthead, it is usually necessary to disconnect the ascenders at the very top and have Marcie winch me up in the bosun’s chair the last foot or so to get high enough to see and work on the top of the mast. Once I reach the desired height, be it the masthead or elsewhere, I clip my harness to a secure fitting on the mast as a safeguard.

Occasionally, I have gone up the mast without someone to belay me and the technique is similar. I wear a climbing harness with a safety line clipped to the upper ascender. I attach myself to the bosun’s chair and attach it to the upper ascender as well. If the boat is rolling, I also clip a line around the mast to limit the amount of swing. To begin climbing, I put my weight on the sling attached to the lower ascender and raise the upper ascender. Then I shift my weight to the upper sling and raise the lower ascender.

When it is time to come back down, it is possible to descend with the ascenders. Even though it sounds like an oxymoron, they do work both directions, albeit a bit slower. If using mechanical ascenders, I put my weight on the sling attached to the upper ascender, then raise the lower ascender slightly, release the cam with the thumb lever and lower it. Then I put my weight on the lower sling, release the upper ascender and slide it down. Friction knots work similarly. Once the tension is removed from the knot, loosen it by pushing up on it, and then slide it down.

Since I normally have someone belaying me, descending is much easier than down-climbing with the ascenders. I just disconnect the ascenders and Marcie lowers me down in the bosun’s chair.

I have been using my ascenders for more than a decade now and have climbed the mast innumerable times in conditions ranging from calm anchorages to rather boisterous passages at sea. I definitely prefer the former, but the technique works at sea as well, and is faster than having someone winch you up the mast.

David and Marcie Lynn have lived aboard Nine of Cups, their 1986 Liberty 458 since purchasing her in 2000 in Kemah, Texas, and have sailed more than 70,000 nautical miles. Visit their website at

By Ocean Navigator