The Frog Ascending System: A Detailed Description

Text and photos by Matt Oliphant

What is the basic concept of the "Frog" ascending system?

The Frog uses two ascenders: one at the waist, attached to the seat harness, and the second ascender above the first, with a safety line to the harness and a foot loop. You sit and stand to ascend the rope.

Frog_01.jpg (36354 bytes)

Icon_ArrowUp.gif (580 bytes) An example of the Frog ascending system. This Frog uses two small foot loops with vinyl tubing to hold them open and protect them from abrasion.

Like every ascending system, the Frog has many variations. Instead of discussing the pros and cons of each and every type of Frog, this article will address just one Frog setup and will outline most of the basic obstacles a vertical caver may encounter.

A detailed description of one type of Frog system

The harness is a low tie-in type, like the Fractio, Super Avanti, or Rapide, made by Petzl. The harness is held together by a 10mm aluminum, steel or stainless steel half-moon screw link. The screw link is important because everything will be attached to it at some point. Do not use any type of carabiner here: carabiners are designed to be loaded in one direction only, and this harness attachment will be loaded in several different directions.

A Petzl Croll ascender is attached directly to the screw link. A chest harness firmly holds up the Croll and keeps the caver upright when resting on rope, but the harness can be loosened when the caver is not on rope. There are many variations of chest harness, but a typical one is the Torse (by Petzl) made of 20mm flat webbing with a quick-adjusting buckle to allow tightening and loosening.

The cowstails are constructed of 10 - 11mm static or dynamic rope (the difference in energy absorption between a static and dynamic rope cowstail is minimal compared to that of a caver and the harness during a fall). The cowstails are made from one length of rope. The ends have figure-8 knots with small loops. The screw link attachment knot is a butterfly or figure-8 loop. The short cowstail has a strong, light-weight, non-locking carabiner clipped to its end and held oriented for use by a rubber band or tape wrapped around the 'biner and rope. The long cowstail is the same but uses a locking carabiner.

The initial cowstail lengths are determined by the size of the person. The length from the end of the butterfly loop to the end of the non-locking carabiner on the short cowstail should be approximately the same as the distance from the elbow to the middle of the palm of the hand.

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Icon_ArrowUp.gif (580 bytes) A properly configured Frog rig. The cowstails are on the closed side of the Croll. The descender is available on the right side. Knots ends are wrapped with duct tape.

The long cowstail is used as the safety to the upper ascender. It should measure approximately one and one-half times the length of the short cowstail including 'biner. It should be short enough so when you are hanging off it, you can still reach your upper ascender but long enough so that it does not restrict your ascending. Some people have a separate rope to permanently attach their upper ascender to the harness, in addition to both short and long cowstails.

The butterfly knot of the cowstail is attached to the screw link on the left side of the Croll (closed side). People who use a right-handed upper ascender (such as the Petzl basic) are tempted to place their cowstail on the right side (open side) of the Croll so the long cowstail won't get caught when ascending over rebelays. However, once you have half your weight on a cowstail and the other half on the Croll, the cowstail is jammed against the cam and safety of the Croll making it very difficult to open. It is better to always keep the cowstail on the left (closed) side of the Croll and not learn this lesson under a cold waterfall.

The upper ascender is a left-handed expedition style Petzl handled ascender. A right-handed ascender can be used (such as the Petzl handled, or basic) but it is more apt to get tangled at rebelays. The foot loop is made of 5.5 mm Spectra cord. (Spectra is very strong and static for its size; it is also abrasion resistant. Webbing and normal rope are bulky, and Kevlar is easily abraded.) One end has a figure-8 loop and is attached to the lower hole of the upper ascender using a 6-8 mm maillon rapide (screw link). The other end has a double figure-8 knot with its two loops each having plastic tubing around the Spectra to make the loops easier to get the feet in and out (the tubing also helps protect the foot loops from wear). The foot loop sizes are equal and are just big enough to place your feet into without the help of your hands. Chicken loops around the ankles are not needed, and in fact, are very annoying when crossing rebelays.

Frog_03.jpg (34551 bytes)

Icon_ArrowUp.gif (580 bytes) The short cowstail is in the right hand, the long cowstail is connected to the upper ascender in the left.

The length of the foot loop cord should be as short as possible but still allow you to easily straighten your legs entirely when ascending. One common variation is to have two cords attached to the upper ascender, with one foot loop tied at the end of each cord, although this may allow the legs to spread apart and cause less efficient climbing. Another common variation is to use one big loop that both feet can fit in, but if only one foot is used in this set up, the overall length of the foot loop changes, and the foot can easily slip through the big loop.

The descender should be as short as possible. A standard rappel rack is versatile, but it is heavy, and in the following procedures can be difficult to use because of its length. There are several rappel racks on the market that are smaller and shorter, and may be easier to use. A bobbin (made by Petzl, SRT, and other manufacturers) is a good choice, although it also has some disadvantages. For example. it is hard to lessen the friction of a bobbin once it is loaded, and it is difficult to use for a double rope descent. The figure-8 is small and lightweight, but without a tether it is easy to drop since it must be unclipped every time the rope is attached or detached.

The descender is located on the screw link on the right (open) side of the Croll for right-handed people. It can either be attached directly into the screw link, or be attached with a locking carabiner. Whichever method is used (there are strong pros and cons for both methods), just make sure to check the connection often.

Ascending up rope

Clip and lock the long cowstail carabiner into the screw link on the upper ascender. Attach the Croll and upper ascender to the rope. Place one foot into a foot loop and pull the stretch out of the rope. Sit on the Croll, then cinch down the chest harness. Place the other foot into the foot loop, and put the rope in front of the foot loops and between your feet. When you stand, pinch the rope between your feet (this will take a little practice). If the rope keeps being pulled up by the Croll, point the toes on one foot down and point the other foot up so the rope is held firmly between the arches of your feet.

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Icon_ArrowUp.gif (580 bytes) Frog climbing sequence

The frog is a sit-stand, two-cycle system. First, you swing your feet underneath you and stand, pushing your upper body up and in towards the rope, using your arms to help you up. Next, you sit while the legs go up and out, and the arms push the upper ascender up. The motion should be a smooth rocking motion. For more efficient climbing, remember to keep your feet underneath you when standing. Each cycle should move you up the rope at least 1/4 your height unless you are very tired or carrying a heavy load.

Ascending against a wall

Take one foot out of the foot loop and keep it against the wall to stabilize yourself and keep the other foot in the loop and underneath you. If you are at the bottom of a drop and the rope is not feeding through the Croll, manually pull the rope through. Ten mm or smaller rope will pass through the ascenders more easily than 11mm rope.


Rebelays (or reanchors)--going up

Ascend up to the rebelay knot. Be careful not to jam the upper ascender into the knot because the ascender will be difficult to remove. Stand up in your foot loops to get the Croll as high as possible, and sit. Clip your short cowstail into the rebelay loop. Next, grab the upper rope and the anchor with one hand, stand in foot loops (one foot in foot loop and one against rock in overhanging rebelays), disconnect the Croll and place Croll on upper rope that will be hanging conveniently from your other hand. Pull slack through Croll. Sit on Croll, and remove your upper ascender and place above Croll on upper rope.

Be careful at this point that the long cowstail and foot loop don't get tangled around the rope. This can easily be avoided by always keeping your foot loops and your left-handed upper ascender to the left of the main rope. Check to make sure everything is neat and secure, then remove short cowstail. The first few steps up the rope can be made easier by placing one foot into the rebelay loop to help the rope run through the Croll.

Alternate way to cross: Ascend up to the rebelay. Place the short cowstail directly into the rebelay anchor if it will reach, and sit. Remove the upper ascender first, and place it on the upper rope. Pull the rope stretch out, then move the Croll over. Remove short cowstail, and ascend.

Rebelays--going down (using the safer two-cowstail technique)

Remove the upper ascender, wrap the foot loops around the ascender, clip the ascender onto the foot loops, and stow the ascender and loop on the side of your harness. Descend so your waist is level with the rebelay anchor and clip the short cowstail into the safest, uppermost part of the anchor (in order of preference: the hanger is the best, next screw link/carabiner).

Clip into the knot if it is the only safe option (for example, the rebelay is using a bad bolt, weak hanger, or non-locking carabiner). Once the knot is weighted, it is difficult to remove the cowstail. A locking carabiner on the end of the short cowstail can cause more problems here than it's worth (swinging over and trying to clip a rebelay and finding out the 'biner is locked).

Descend so your weight is hanging off your short cowstail. Next, clip your long cowstail into the rebelay loop. Then remove the descender from the upper rope and place on the lower rope just below the rebelay knot. Now you need to get your weight off your short cowstail. This can be done by placing your foot or knee into the rebelay loop and standing. Remove the short cowstail and sit, being careful that the descender and its attachment are all oriented correctly and are still secured to you. The next step after everything is double checked is to remove the long cowstail from the rebelay loop and descend.

Almost all books that describe this procedure use one cowstail. This procedure using two cowstails (the long cowstail as a backup) is MUCH safer and takes very little extra time. Be careful if you are tethering a pack that it does not get tangled up in the rebelay. Keep the pack to the outside of the rebelay loop when descending.

Alternate technique used by some people for getting your weight off the short cowstail: The upper ascender and foot loops are attached to your long cowstail. After clipping the short cowstail into the anchor, attach the upper ascender to the rope right below the rebelay knot (this is your backup). Move your descender to the rope below the rebelay. Now, use your foot loops to stand in to get your weight off of the short cowstail. After double checking your equipment, unclip the upper ascender.

In this method, the shorter the foot loops, the better. This alternate technique is useful in situations where the upper rope has a lot of stretch or comes into the anchor at an angle. It is also useful if there is a very small rebelay loop or you are tethering a heavy load. Some people don't like stepping in the rebelay loop because it gets the rope dirty.

Redirectionals--going up

Ascend up to the redirectional and push it as high as possible or until you are level with the redirectional anchor. Stand so both ascenders are close to each other and remove the redirectional from the rope. Place it below your Croll and continue up the rope. If there is a chance of dropping the redirectional and not being able to recover it, you can clip your short cowstail into it before removing it.

Redirectionals--going down

Descend so your waist is level with the redirectional, remove the redirectional from the rope and clip it back above your descender. Again, if there is a chance of dropping it, clip your long cowstail into the redirectional (this will give you a little more leeway in case you creep down the rope, so there is less of a chance of weighting the redirectional with a cowstail and possibly forcing you to ascend up to detach the cowstail).

Crossing knots--going up

Any knot tied midway up a drop should have an associated loop--these are ideal knots. Ascending over an ideal knot is simple, and similar to crossing a rebelay. Ascend up to the knot being careful not to jam the upper ascender into the knot. Stand up completely, moving the Croll as high as possible. Clip the short cowstail into the loop. Move the upper ascender above the knot first, allowing enough room for the Croll to be placed below it but above the knot. Next, stand in the foot loops and clip in the Croll above the knot. Check that both ascenders are secure. Unclip the short cowstail and continue climbing.

Unfortunately, the "ideal knot" is not the most common scenario. You can just hang off a single ascender for the few seconds it takes to move the other ascender, and there are some arguments in favor of this method. However, a safer method is to tie a loop in the rope below the Croll and clip the short cowstail into it, then cross the knot as in the above procedure. Don't forget to untie this safety loop once you are past the knot.

Crossing knots--going down

Crossing knots while descending can be one of the more challenging maneuvers. There are many different techniques to make this faster and "easier," but almost all of these techniques require unreasonable expectations of the tired caver who comes across the unexpected knot.

Descend to the knot, and remember not to jam the knot into the descender. Next, clip the long cowstail into the upper ascender, and attach the upper ascender above the descender leaving just enough room for the Croll. Stand in the foot loops and clip the Croll between the upper ascender and the descender. Sit on the Croll, remove the descender, reattach it just below the knot, and lock it off. Down ascend so both ascenders are as low as possible (just above the knot). Stand in the foot loops and remove the Croll, sit on the descender and check to make sure everything is secure ('biners oriented correctly and locked, etc), remove upper ascender and you are on your way.

This method is neither slow nor fast, but is more fool-proof and does not require a loop in the rope.


There are many different ways to rig a tyrolean, and many, many different techniques used to cross one, depending on how it is rigged. Tyroleans are not going to be covered because it would double the length of this article. Remember that all safely rigged tyroleans have two ropes across the traverse, with one rope at least one meter longer than the other. Because of the forces on the tyrolean anchors, you don't want to be clipped into only one rope--clip into the second rope as a safety.

Counterweight Pick-off

(added November 1997)

Ascend up to the patient, both of your ascenders just below their Croll. Put your short cowstail into their cowstail. Put your upper ascender above their Croll as high as your long cowstail safety will allow it to go and disconnect their upper ascender. Disconnect your Croll, and place it above their Croll (not always easy). Attach a 'biner to your upper ascender. Pass your long cowstail through the 'biner on the upper ascender, and attach it to their main screwlink on the closed side of their Croll. Ascend up as high as possible so that your long cowstail stops you. Disconnect your Croll, then sit and counterweight them up. (If they are a lot heavier, grab and pull them up as you counterweight.) Be sure they are as high as possible. Pull some rope slack up through their Croll (if you want to be really safe).

Take either their or your descender and attach it to them and the rope just below your upper ascender and above their Croll. No slack, and tie it off well, etc. Disconnect their Croll, and lower them on to the descender that is attached to them (make sure the descender is not twisted or weird in anyway). Remove your long cowstail (stand in your footloops) from the 'biner that is on your upper ascender, and clip your short cowstail into the descender 'biner (you can be safe and leave their cowstail clipped into your cowstail the whole time). Sit/hang on the short cowstail. Grab your upper ascender if you can, otherwise leave it, and carefully descend. This will put you below them--which is best for control.


The Frog system is very versatile. Although it may not be the fastest system to use when going up a long, free-hanging rope, it more than makes up for this disadvantage when it is used for just about any other maneuver. All of the described procedures require practice, practice, practice. It is highly recommended to practice these procedures with someone who is familiar with the Frog system and already knows how to use it safely.

I would like to thank the following people who have helped me with preparing this article: Mike Frazier, Roman Hapka, Peter Hartley, Joe Ivy, Pierre-Yves Jeannin, Patty Kambesis, Steve Kesler, Karlin Meyers, Nancy Pistole, Ian Roland, Bart Rowlett, Ursi Sommer, Bill Storage, and "Little" John Woods.

Version 1 appeared in the NSS News, May 1996.
Version 2, 14 October 2000, with revised discussion of pick-offs.


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