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Storrick Double Allp

Version A Version B
Version A Version B

Overview


Version A
(#1087)

Front View Rear View Side View
Front View Rear View Side View
 
Front View: Open for Rigging Rear View: Open for Rigging
Front View: Open for Rigging Rear View: Open for Rigging

Technical Details

I made this Double Allp in 2007, using the Troll Allp as a guide. The basic difference is that the bollards are longer so that the Double Allp will work on double ropes.

The Double Allp has three bollards mounted between two side plates. The plates pivot on a fourth attachment post near the bottom of the Double Allp. An adjustment screw assembly helps vary the friction in the device.

Each side plate is a roughly pentagonal piece of 1/8-in (3.3 mm.) 5052 aluminum. The plates are 138 mm. high with a curved top. The top half of each plate is 60 mm. wide at the top, and then starting about 60 mm. down, tapers to join a 22 mm. diameter circular arc at the bottom. The side plates are attached to a 16 mm. diameter steel attachment post at the center of the bottom circular arc. The front plate is tightly bolted to the post, while the rear plate is loosely bolted. Deviating from the Troll Allp design, I omitted the closure sprung. The top and bottom rope bollards are bolted to the front plate, while the center bollard is bolted to the rear plate. The bollards do not rotate, but there are no pins preventing the rotation. All bolts are hex socket round-head bolts.

The bollards are made of unfinished 6061-T6 aluminum. Each rope bollard has a groove that fits into a corresponding notch in the opposite plate. The bollards are 35 mm. wide, measured from between the insides of the side plates. The three bollards were made from 32.7 mm. diameter rod, with two shallow, 13.7 mm. wide rope grooves and a side plate clearance notch in each one. The three bollards are mounted 106.5 mm., 63.5 mm. and 43 mm. from the center of the pivot point. When the rope is inserted, this asymmetrical arrangement ensures that the rope is pinched between the center and bottom bollards only.

The rear plate has a small aluminum block bolted to the upper left inside of the plate. A 3/8"-16 left hand threaded rod passes through this plate and presses against the upper bollard. A cross piece is pinned to the other end of the rod, making it much like a wing nut.

Comments

I asked Dave Allport if he had ever made a double rope Allp. He had, but I haven't convinced him to part with it yet. In response, I decided to design and build my own.

One disadvantage of this design is that when rappelling on one rope, at least one bollard will experience a higher bending moment than on a single Allp. Even though the moments are probably small enough to be of no concern to the standard user (i.e., no double loads!), I developed a design change for Version B to address this issue.

The fit between the bollard and side plate notches is tight enough that I do not miss the spring.

Trivia question: How do you keep the seat carabiner from sliding to one side? Answer: use two, with gates facing opposite directions.


Version B
(#1121)

Front View Rear View Side View
Front View Rear View Side View
 
Front View: Open for Rigging Rear View: Open for Rigging
Front View: Open for Rigging Rear View: Open for Rigging

Technical Details

I made this Double Allp in 2007 as well.

The basic difference between Versions A and B is that Version B has a central plate in addition to the two side plates. The front and rear plates on Version B are plates are made of the same material and have the same dimensions as the Version A front plate, while the Version B center plate matches the Version A rear plate.

Version B also has three bollards, again made of unfinished 6061-T6 aluminum. The top and bottom bollards are rigidly bolted between the front and rear plates with hex socket round-head stainless steel bolts. Each of these bollards has a groove that fits into a corresponding notch in the center plate. These bollards do not rotate, but there are no pins preventing the rotation. The bollards are 41 mm. wide, measured from between the insides of the side plates. The middle bollard was made in two pieces that screw onto a hidden stainless steel axle. After assembly, I drilled a 4.2 mm. hole and inserted a stainless steel roll pin to keep the middle bollard pieces from rotating. All three bollards were made from 32.7 mm. diameter rod, with two shallow, 13.7 mm. wide rope grooves and a side plate clearance notch in each one.

The center plate has a small aluminum block bolted to the upper left rear of the plate. A 3/8"-16 left hand threaded rod passes through this plate and presses against the upper bollard. A cross piece is pinned to the other end of the rod, making it much like a wing nut. The result is

Comments

This design addresses the disadvantage of the Version A design, since the rope on a single-line rappel always passes over a bollard in a groove immediately adjacent to a plate supporting the bollard.

As in Version A, the fit between the bollard and side plate notches is tight enough that I do not miss the spring.

Trivia question: How do you keep the seat carabiner from sliding to one side? Answer: use two, with gates facing opposite directions.