Roped Travel with Snowmobiles and Sleds in Crevassed Areas
Crevasses are dangerous, especially when traveling with machinery.
Avoid crevassed areas if possible, even if it entails making a considerable
To date, no one in the USAP has been killed as a result of a snowmobile
(skidoo) crevasse fall, but there have been numerous close calls. It's
only a matter of time before a death occurs if greater attention is not
given to safety. Personnel have been killed in a crevasse fall where snowmobiles
were not involved.
Limited field testing has been carried out on the actual effectiveness
of the methods described in this chapter. The results have been sobering
in regard to the difficulty of stopping a fall, especially at speeds higher
than 5 mph and/or with slack rope between the snowmobiles. The driver
of a machine that falls in a crevasse is virtually assured of severe injury.
This means that detection of crevasses and good route-finding to avoid
dangerous areas are essential to safe travel.
Always have the capability to rope snowmobiles and drivers when travelling
on a glacier. Be aware that glacial conditions vary enormously in Antarctica,
from one year to the next. Glacial conditions can change in a few weeks
in some areas of Antarctica.
In areas where there is any possibility of crevasses, roped travel should
be used. It is often very difficult to detect crevasses . Stop and probe
ahead if you're at all suspicious. Act conservatively and operate within
a wide margin of safety.
Roped travel with snowmobiles should be practiced with an experienced
person in a realistic area prior to beginning a trip. Make sure the Field
Safety Training staff knows that you'll be traveling in areas that may
be crevassed, and that you need to practice roped travel.
There are numerous systems for travelling through crevassed areas with
roped snowmobiles and sleds, and safer options are always being sought.
Please feel free to question the systems described in this chapter and
provide constructive comments. The information provided here does not
substitute for training or experience.
18.1 General Points for Roped Travel with Snowmobiles and Sleds in Crevassed
18.1a Aerial Reconnaissance
Aerial and satellite photographs provide an excellent source of information
regarding crevasse locations. Direct aerial reconnaissance from the flight
deck should include viewing proposed routes of travel from the air and
marking the positions of crevasses on a map. Crevasses are more easily
detected when the sun is at a low angle.
18.1b Tow Ropes
Tow ropes are used to connect the lead snowmobile to the sled(s) and/or
snowmobile(s) behind it. Tow ropes are separate from, and in addition
to, the safety ropes. Tow rope diameters of 3/4" to 1" (22-mm) nylon twisted
rope are recommended. Twin 1/2" ropes (or larger) are a good alternative.
In BFC field testing, Figure-8 knots tied every meter in the tow ropes,
dramatically increased the fall-catching ability of the roped-snowmobile
The length (distance between snowmobile and sled) should be 15- to 20-meters.
This length can be halved when you're not in a linked travel mode (i.e.,
when one snowmobile is pulling one sled and is not roped to another snowmobile).
The ends of the tow ropes should be tied with Figure-8 knots on a bight,
or spliced to 5-ton shackles or locking steel carabiners.
A 1.5-meter-long protective sheath (PVC or rubber tubing) should be
placed over the tow rope immediately ahead of where it secures to the
sled or snowmobile its pulling. Secure the sheath with a piece of cord
so that it can't move forward. This end of the tow rope will then be protected
by the sheath should a sled or snowmobile run over it.
Attach the tow ropes to the snowmobiles and sledges with either 5-ton
shackles or steel screwgate carabiners. (Don't use non-locking carabiners.)
Note: Engine vibration can unscrew the locking carabiners. Steel carabiners
have failed under very light tow loads when the gate is unscrewed. Two
steel carabiners with reversed gates will ensure a safer system. Secure
carabiner screw gates and shackle pins with wire, tape, or rubber washers,
etc. so that they won't unscrew.
18.1c Nansen Sled Back-up Rope
With Nansen sleds, it's necessary to loosely tie a back-up tow rope
on the underside of the bridges. This rope should be 3/4" or 1" nylon
twisted rope and should attach onto each end of the Nansen sled towing
rope with the same shackle or carabiner that is used for towing. This
back-up tow rope needs to be tensioned in such a way that it does not
bear the load unless a large impact occurs.
18.1d Snowmobile Cables
All snowmobiles used for travel in crevassed areas should be fitted
with a steel cable encircling the snowmobile. The 5-ton shackle on the
tow rope must be fitted over this cable when hitching the snowmobile,
to ensure that the snowmobile stays belayed to the tow rope in the event
a crevasse fall pulls out the snowmobile's hinge plate.
18.1e Tether Switches
The tether switch is a thin line that runs from the snowmobile's kill
switch to the driver's harness. This tether ensures that the snowmobile
will stop (the engine is killed) if a driver falls from the machine. If
the tether switch isn't used, the driver may end up hanging beside a spinning
snowmobile track, which could cut the driver's rope or result in serious
18.1f Driver Safety
When traveling linked, snowmobile drivers should kneel to one side,
rather then straddling the seat, so in the event of a crevasse fall there
is a better chance to jump or fall clear of the machine.
- Only one person should be on each snowmobile.
- Helmets should be worn in crevassed areas.
- No loose gear should be hanging from the driver's harness. Dangling
items can hang up and drag the driver into a crevasse.
- All drivers and sled riders should have either prussiks or mechanical
ascenders attached to their safety ropes.
A series of pre-arranged hand signals should be used for communication
between linked snowmobiles and sleds. Your field party should have signals
for stopping, slower, faster, ok/ready-to-go, crevasse, and any others
found to be necessary (i.e., "place flag here," etc.). The hand signals
shown on the following page have been used effectively by past field parties.
18.1h Travel Speed
Linked travel requires continuous concentration, and is not suited for
fast speeds. In BFC field tests, speeds over 5 mph dramatically increased
the distance a snowmobile fell, and stopping the fall proved very difficult.
When travelling in linked formation, it is vital that you don't allow
any slack to develop in the tow rope. Invariably this means that the lead
snowmobile will at times be slightly pulling the trailing machines. A
slack tow rope will continually be run over and will jam. If you drive
over the tow ropes and safety ropes, the system will be compromised. The
ropes may break under a load if one of the machines falls into a crevasse.
* [See figure ³ROPEDTR1²]
18.1i Crossing Crevasses
Stop and probe all crevasses to determine if they are safe to cross.
Probing should be done by the driver of the lead snowmobile. A ski pole,
without a basket, will suffice for a probe.
If you must cross a crevasse, always do it perpendicular to the line
of the crevasse. If a snowmobile or sled starts to break through a snowbridge,
experience and circumstances will dictate whether to brake and attempt
to hold the fall, or continue driving forward in hopes of getting across
before a catastrophic collapse of the snowbridge. In either case, a change
of underwear is recommended.
18.1j Stopping a Fall
When stopping a fall into a crevasse, apply the brakes and, if possible,
quickly kill the engine. The engine will be killed automatically if it's
your snowmobile that's falling and you fall off the machine, thereby pulling
the tether switch line.
In hard snow conditions, rope brakes on the sleds will increase friction
and braking ability.
If you're a rider on a Nansen sled, and the sled is rigged for it, stand
on the footbrake.
18.1k Travel on Foot between Snowmobiles and Sleds
In crevassed terrain, you must remain tied in when walking between your
snowmobile and the other machines and sleds. Many a crevasse has been
found by a driver stepping off their snowmobile (which has a lighter ground
pressure than a person on foot), and breaking through a snowbridge that
was crossed seconds before without incident by the snowmobile. To walk
forward or back to another snowmobile or sled, you can self-belay with
a prussik or ascender on your safety line or on a spare rope.
A good habit to get into when walking back and forth between machines
and sleds is to straddle the tow ropes.
18.2 Tying In
The prospect of falling into a crevasse on a snowmobile is extremely
frightening. No system presently exists that allows the driver a guaranteed
clearance from the snowmobile. There's a high probability of injury occurring
to a falling driver. However, the following roping procedures will keep
you as safe as possible in the event of a crevasse fall (see diagrams
on the following two pages).
18.2a Front Driver
Clip the bitter end of an 11-mm climbing rope to your harness with a
Figure-8 knot and locking carabiner. Use a prussik or ascender to fine
tune the tension.
Walk the rope back to the sled or second snowmobile, tie a Figure-8
on a bight, and clip it into the front towing thimble with a locking carabiner.
Coil the unused rope neatly and stow it on the sled.
If there's a rider on the sled, adjust the remaining portion of the
rope, clip it to either the front or rear towing thimble of the sled,
and then clip it into the rider's harness with a Figure-8 knot. Stow any
extra rope out of the way.
Roping up will be much easier and quicker if you cut your safety ropes
to the exact lengths needed before you go into the field. The BFC has
bulk spools of climbing rope, and can provide assistance on the lengths
* [See figures ³ROPEDTR2² and ³ROPEDTR3²]
Lead drivers should carry a 45-meter climbing rope in a stuff sack (throw-bag
style) neatly stowed on the snowmobile. This can be used for probing out
ahead of the machine, or to rescue others in the field party. Equip this
rope with prussiks or an ascender next to the carabiner (or Figure-8 knot)
used to hook onto the driver's harness.
18.2b Rear Driver
There are two recommended methods for tying in the second snowmobile.
Clipping In Behind: The easiest system to manage is to clip onto the
back hitch of the snowmobile you're riding on. Secure the end of a 45-meter
rope to your harness with a Figure-8 knot and a locking carabiner. Attach
this with a locking carabiner (on a Figure-8 on a bight) to the back hitch
of the snowmobile. Make sure the steel cable that encircles the snowmobile
runs through the carabiner.
Secure the extra rope in a stuff-sack (throw-bag style) and neatly stow
it on the rear of the snowmobile out of the way. The extra rope can be
used for self-belaying away from the machine using an ascender, and will
be handy for rescues. Clipping in behind the snowmobile makes rope management
easier, but in a crevasse fall, the driver will be hanging below the machine.
Self- rescue will be next to impossible.
Clipping In Ahead: Having the rear driver's safety line run ahead to
the Nansen sled is potentially a safer system, but is harder to manage.
Attach the end of the safety rope to the driver's harness (Figure-8 and
locking carabiner). Take the line forward and attach it to the rear towing
thimble on the Nansen sled with a locking carabiner. Use a prussik or
ascender on the driver's harness to "fine tune" the distance. Neatly coil
excess rope and stow it on the sled.
This system makes it possible for self-rescue by preventing the driver
from falling below the snowmobile, and providing an immediate safety line
for self-belaying up to the sled in front. However, it's very difficult
to keep from running over the rope, especially in rough terrain (sastrugi).
Note: An experienced USAP field mountaineer prefers to run the safety
rope from the rear driver to a 9-mm prussik wrapped on the tow rope just
ahead of the protective tubing. This helps to not run over the rope and
does not allow the driver to fall below the snowmobile.
Remember: It is highly probable that the secondary riders and/or drivers
will be the ones that will fall through a weakened snow bridge.
18.3 Travel Configurations
Just as in roped-mountaineering, three snowmobiles roped together are
safer than two. In BFC field testing, a roped-snowmobile train of three
dramatically increased the ability to stop a fall quickly (two snowmobiles
catching the third). Never travel with less than two snowmobiles and one
sledge linked together, when traveling in crevassed areas. Depending on
the size of your field party and the amount of cargo you're transporting,
there are various travel configurations, which are illustrated on the
following three pages.
* [See figures ³ROPEDTR4² and ³ROPEDTR5² and ³ROPEDTR7²]
18.4 Snowmobile Crevasse Extraction
- Rescue the driver. If necessary, the snowmobile can be tied off and
extracted on another day.
- Probe and mark off a safe working perimeter around the crevasse before
extracting the snowmobile.
- The crevasse edge must be thoroughly prepared before attempting a
snowmobile extraction. Dig a ramp the width of the machine and deep
enough to reach very hard snow. Place suitable edge protectors of wood
or metal on the lip of the crevasse; tie them off so they don't fall
in. These will minimize rope drag during the hauling.
- Your main anchor must be large deadman-style anchors equalized and
- A pulley system can be set up on the tow rope, but it is preferable
to set the pulley system on an alternate rope (static rope is best)
that can be belayed separately as a backup. The snowmobile tow rope
can also be secured to a separate anchor for a backup, if necessary.
Prussiks should be heavy duty (8-mm is the minimum).
- Before hauling, put the snowmobile in neutral gear, or cut the variator
belt so that the tracks can turn. Snow and ice may need to be cleared
from the tracks to free them.
- If possible, raise the snowmobile's back end first.
- Position a person on the crevasse edge for communication and observation.
If you have enough people, position another person in the crevasse.
This person can ensure that the ski is straight, and that the track
can spin. Secure this person to a safety rope anchored separately to
one side of the main anchor.
- se three people pulling on a 6:1 pulley system to extract the snowmobile.
Or, use snowmobiles to help pull it out. Snowmobile tracks should be
pre-packed, and the pull path must be free of anchors and ropes.
See the diagram on the following page.
* [See figure ³ROPEDTR6²]
18.5 Rescue Equipment
The following gear should be carried by each member of a field party
travelling in crevassed areas. Equipment carried in the crevasse rescue
bag is to be used in addition to the personal gear carried by each individual.
A listing of the equipment in a crevasse rescue bag appears in Appendix
Personal Equipment (Each Person)
4 Prussiks: 2 Long and 2 Short
2 Slings: 1 Long and 1 Short
1 Figure-8 Descender
2 Locking Carabiners
1 Ice Axe
18.6 How To Travel With A Nansen Sled
- When starting with a heavy sled load, have some slack in the tow-rope,
and have someone rock the sled and push to help break the runners free.
- Stop gradually so that the sled doesn't run into the back of the
- The driver should look back frequently to ensure that the sled is
tracking correctly, and those riding the sled are not being dragged
by their bootlaces like fools in a cheap spaghetti western.
- When not linked for crevasse travel, keep the tow ropes short to
prevent wandering sleds.
- Don't travel too fast. You'll damage equipment if your sled tips
- Travel together as a team -- don't get spread out too far.
- Use rope brakes on the sled runners when they're needed. A braking
snowmobile in the rear is a secure method for steep descents and for
traverses. At times, you may need to belay sleds down steep, difficult
- Sleds with handlebars and footbrakes are recommended on any trip
where personnel will be riding on a sled.
18.7 How To Load a Nansen Sled
The figures on the following two pages show a Nansen sled and how to
distribute the cargo load. Additional points on loading a Nansen sled
Chapter 19: Glacier travel with heavy machinery.