Since time immemorial man has been wrapping rope around objects to create friction allowing the easy control of loads. Modern examples of this technique include the arborist’s “Bollard Friction Brake”, capstan winches on boats, the “tensionless hitch” used in rescue anchor rigging, etc. These examples rely on the common principal of the rope generating a frictional force with the object upon which it is wrapped in proportion to the load. The load can be easily controlled as long as the number of wraps is sufficient to generate enough friction to counteract the force generated by the load. All of this friction is generated at the contacting surfaces.
A very desirable further attribute of this principal is the ability of these systems to absorb large momentary increases in load forces. When the system is subjected to a sudden increase in force the rope grips the object harder creating a proportional increase in friction. This increase in friction effectively compensates for the sudden load increase and only a fraction of this force is transferred to the operator of the system.
The BMS Belay Spool works essentially on this principal with the additional advantage of the internal friction of the rope fibres created by the bending and straightening of the rope as it moves over it’s “lobed” surface under load. This same principal makes the brake bar rack an effective device given its relatively small contact surface with the rope.
Rope moves relatively easily through the Belay-Spool when not under load by virtue of the rope’s tendency to form a loose coil around the drum. This coil generally only makes contact with the top of the lobes so friction is low. This is especially advantageous when belaying a rescue load being raised, i.e. taking rope in through the device. When this is reversed, as in a lower, the belayer needs only to maintain a firm grip on the rope and allow the device to self feed.
Another advantage of the Belay-Spool is it’s ease of being rigged. The side plates are opened and the rope is wound around the drum filling the slots from one side to the other, the side plates closed, and the device secured to an anchor. Either end of the rope can be selected for attachment to the load with the remaining end being held by the belayer. It should be noted here when “on belay” that this end of the rope must be securely held by the belayer at all times. The only exception to this is after the device has been “locked off”. This is accomplished by tying a couple of half hitches on the load side rope with a bight of rope from the belayer side.
Since this device is so easily rigged and simple to operate, it is easy to train relatively inexperienced individuals in its safe and proper operation. Belay “lock-ups” are eliminated as well as the necessity for rigging load releasing hitches, both of which complicate and add time to an evolution.
Although not designed as such, the Belay-Spool can also function as an effective lowering device and thereby greatly simplify the rigging requirements of an operation. Personnel in industry who from time to time may be called on to accomplish rescues of their fellow workers can benefit from this added simplicity. This is also true for the fire service, especially when rope rescue scenarios are infrequent. In addition the speed of which they can be rigged can only be a benefit to the patient.
Carroll C. Bassett