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USnavy
Dec 16, 2013, 7:03 AM
Post #1 of 2
(8796 views)
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Registered: Nov 6, 2007
Posts: 2667
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Slackline Brothers (SB) sent me a set of their pulleys to play with in exchange for some testing and a review. So without hesitation, I will get straight to it. The first thing I noticed about the SB system is that it is compact and simple because it features an integrated brake. This means the user does not need a rigging plate, external brake or secondary sling to connect the brake to the anchor.
The next thing I noticed is how beefy the pulleys are. Since SB makes their pulleys out of 17-4PH stainless steel, they are incredibly strong (10,000 lbf.) The downside is that steel is heavier than aluminum. That brings us to the first examination: weight. Without rope or a multiplier, below is a listing of the SB system compared to some common alternatives.
SB system: 1,096g
CAMP ball-bearing system w/ GriGri2: 1,140g
SMC 3” PMP system w/ GriGri2: 1,340g
Next, I wanted to determine how efficient the SB system is relative to the CAMP ball-bearing system. Using 9.5mm rope for every test, Figure 1 demonstrates the efficiency of a single sheave. I included four trials for the SB system and an average of four trials for the CAMP ball-bearing system.
Considering the SB system uses friction bushings instead of a ball bearing, it was not surprising the sheaves on the CAMP system were more efficient. However, we are more concerned with the efficiency of the unit as a whole as opposed to the efficiency of a single sheave. The SB system does not use a traditional brake, so the efficiency of the brake is higher than a traditional brake.
Figure 2 examines the efficiency of the entire SB system relative to the CAMP system. It displays the basic 4:1 base SB system, a modified SB using a 5:1 embedded pulley and the 5:1 CAMP system using a GriGri one for a brake. I used a 2” Russ-Anderson SMC ball-bearing pulley for a multiplier.
Worth noting: after finishing the testing, I found I could increase slightly the efficiency of the SBs by applying Tri-Flow oil to the axle, which is easy to do.
Figure 3 uses the same data as Figure 2, but it demonstrates how much force a slackliner has to apply to the “pull strand” to reach a specific slackline tension. I conducted this test using a 2” Russ-Anderson SMC ball-bearing pulley for the multiplier.
One concern with any brake is that the brake could potentially slip. While this is not typically a problem with large diameter ropes, it can be a problem with smaller ropes. Figure 4 examines the maximum tension the 4:1 SB system can hold before the brake slips. Converting the SB system to a 5:1 would increase the values on the chart slightly.
The chart confirms what I noticed in the field: the SB system is best suited for large ropes.
Figure 5 demonstrates the maximum permissible slackline length with the 4:1 SB system using 11mm rope. It provides two sag values: 5.5’ and 7’. The chart assumes a maximum in-use tension of 2,500 lbf.
The last aspect to examine is the cost of the system, without shipping charges. Considering the variables associated with slackline accessories, we will examine only the cost of the base system—that is, only the pulleys and brake.
SB 4:1 set: $175
SB 5:1 set: $225
CAMP ball-bearing w/ Grigir2 set: $225
In summary, the key points are:
- Use thick rope with the SBs (11mm recommended)
- The CAMPs are more efficient, but the SB 4:1 set is less expensive, more compact and lighter
- The 5:1 SB system is as efficient as the CAMP system and costs the same, but is simpler
- A slackliner using the SBs with 11mm rope can expect to rig up to 300’ lines, unless the slackliner weighs more than 180 lbs or s/he is not willing to rig without at least 5.5’ of sag
Overall, the SB system is best suited for someone looking for an inexpensive way to rig moderately-long lines without having to deal with a large amount of gear or complicated systems. It is suitable also for those looking quickly rig tricklines, general slacklines, or waterlines.
(This post was edited by USnavy on Dec 21, 2013, 5:47 AM)
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sungam
Dec 16, 2013, 2:39 PM
Post #2 of 2
(8745 views)
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Registered: Jun 24, 2004
Posts: 26804
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This is a good poast.
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