Rappel Racks and Spacers

By Bruce W. Smith

Spacers or collars of various lengths, with or without set screws, have proven to be the best spacers overall.

Spacers have remained a controversial ancillary piece of equipment that have received praise and at the same time rebuffed as a dangerous add-on device when used with a rappel rack. Some rappellers praise their virtues and testify that spacers eliminate the pinching that occasionally occurs between the top bar (bar #1) and the second bar. Excessive pinching could result in the bogging down and retardation of the smooth flow of rope through the device during a rappel. Spacers also maintain or guide the rope down the center of the rack frame keeping the rope away from the rack frame and causing unwanted frame friction. Some see this as a huge benefit.

Spacers move heat away from brake bars that normally get too hot.

While this may be true, the real reason spacers have virtue is that they change the angle the rope approaches and leaves brake bars as it moves through the rack. Reducing the actual amount of contact the rope makes with each bar as just described, maintains lower temperatures on the upper bars (specifically bars #1 and #2) during a rappel. This levels the playing field so that each bar shares more equally in providing the friction (and the heat) on the rope during a rappel. This in turn ensures that the top bars do not increase in temperature to dangerous levels. Realize that the sticky point of nylon is about 250o F. This is easily achieved during rappels as short as 100 feet.

There is very little formally written about spacers, rather a whole lot of opinions and experience has been recorded and shared over the years. Hopefully, it is here that we can draw some conclusions to the mounting evidence available about the benefits and problems of rappel rack spacers.

Fig. 2 Safe spacer use..

…Often requires 6 fully functional bars below your last spacer.

Spacers remove a rack’s friction producing ability to provide friction for a rappeller. Spacers establish a fixed distance between the top bar and 2nd bar. It becomes impossible to achieve the same amount of friction as the device can provide with spacers if the bars are configured the same. However, it will eliminate the possibility of the pinching mentioned earlier.

Fig. 3The best all-around configuration is four set-screw spacers: 2 positioning the top bar and 2 locking at the distance between the top bar and 2nd bar.

Typically, spacers are used on long racks (18”, 24” or 30”). Padgett and Smith agree conservatively that a safe approach to using spacers includes the use of 6 fully functional bars below the last spacer. It is important that the user maintain full control of their rappel for the entire distance of the drop. Several deaths have occurred because rappellers get caught up with the edge problems and rope weight at the top and do not think through the rappel to its final conclusion. “Will there be enough friction to control my descent all the way, especially at the bottom?”

Experienced people who use spacers all agree that the user must be (repeat: absolutely must be) an expert and know their craft to a high degree. There is no room for error and rappelling is perhaps the most dangerous thing we do on rope. Adding a device that actually reduces your friction must not be taken lightly.

Fig. 4 Floating spacers: Racks with only two set-screw spacers can be configured below floating (non-set-screw) spacers to keep them from sliding down the shorter snap-on rail so they won’t screw up the space between other bars.

There have been several deaths attributed to the use of spacers.

Most agree that spacers are only needed between bar #1 and bar #2. Spacers between bar # 2 and bar #3 have been successfully used but require substantially long rack frames (i.e.24”-30”) and still often follow the Padgett and Smith recommendation that there be 6 fully operational un-spacered bars below the last spacer.

Although it may not be absolutely necessary, there should be a matched set of spacers on both the long and short leg. This means that one set of spacers must be able to travel over the curve of the nose of the rack.

Fig 5 Springs as spacers: Long rack users have found two springs between the two top bars allows some compression and 2nd bar adjustment if the space between the bars needs reduction during a rappel.

Set-screw Spacers

There is a risk that a floating spacer may inadvertently become misplaced between the wrong bars connected to the short leg. Because of this, spacers that have a set-screw on them, allowing each spacer to be secured at a specific point, is best. There is another advantage to having set-screw spacers and that would be that the top bar becomes secured firmly in place making sure that it remains perpendicular to the legs of the rack and does not cant. (Fig #6) This also ensures that the rope runs true to the rack—right down the middle.

Set-screw spacers also have an available adjustment whereby the user can increase or decrease the distance between Bar #1 and Bar #2 without buying spacers of different lengths. Note: It would be difficult if not impossible to change spacer distances after a rappel has begun.

A full set of set-screw spacers would be 4. Two of them will have to have an ID large enough to go up over the nose (usually 7/16”) of a 3/8” frame. The other two need only be 3/8” ID as they do not have to go over the curved nose of the rack.

The question always arises, “What should the distance between bar #1 and bar #2 be?” There is no simple answer. Your expert experience must come into play here. Hypothetically, let’s look at some spacer lengths and what happens to our friction when different lengths are used.

To avoid pinching, it has been said that a minimum space between bar #1 and bar #2 should be ½” when 11mm rope is being used. Assuming the holes on the bars are center drilled and the spacer is increased to 1” this reduces the rope’s contact on bar #1 and on bar #2 about 40%. If a rack user had 6 brake bars as described above with a ½” space between them all, it would take about 10 brake bars spaced at 1” apart to achieve about the same friction. There are numerous variables that affect the friction so a hard number remains elusive.

Most spacer users do not feel any need for spacers below bar #2. Theoretically, with this much reduction in bar friction, the stopping friction will have to be made up in the lower bars on the rack, providing that level playing field between bars we spoke of earlier.

Long drop rappels (over 1000’)

Drops with such extreme rope weight as a 1000’ drop or longer will almost always require long racks with spacers.

Drops shorter than 1000’

There remains quite a debate as to whether rappellers really need spacers on a rack for distances below 1000’ There are some pretty good arguments for drops between 500-1000’. In the end the user needs to be an expert-- practiced in the skills of extreme rappels.

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Fig. 6 Set-screw spacers can secure and eliminate the canting of loose fitting bars. Sometimes loosely drilled holes, such as SMC or CMI “U” shaped bars, cant, forcing the rope to push into the crack, either at one or the other extreme sides of a rack. Two set-screw spacers can help to maintain the 90o degree orientation needed to prevent it.

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