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This is a general, informational posting meant to be of use to other jumpers. I am not a rigger, and not a particularly experienced BASE jumper either. Take this with a grain of salt, but I felt it would be best to share what I know in any case.
In the last 4 months I have broken two brake (i.e. control) lines while jumping slider down (one left, one right). The first break occurred after approximately 50 jumps on that set of brake lines. The second break, on new brake line sets ordered from the manufacturer and installed properly, occurred after less than 30 jumps. Nearly all of these jumps were slider down.
I set my toggles properly, and I am jumping properly-tuned brake settings as confirmed by several highly experienced jumpers. I set my tailgate on all jumps, and pack in a standard manner. In each break, the lines started to show fraying at the deep brake setting, but not enough fraying that myself or other jumpers felt that a break was iminent. Still, there was this warning in both cases.
Many of my jumps are slider down 2.5-3.8 second delays. Manufacturers recommend that one not exceed 3 seconds slider down, so a substantial minority of jumps on these brake lines were of a type that is specifically recommended against.
Finally, I am jumping a Mojo 280 with a custom container. The Mojo has about 125 jumps in total on it, with about 75 of those jumps during my ownership. The other lines on the canopy are not showing excess wear, nor are the tabs or reinforcements. The canopy has never been landed in water (trees and rocks and blackberries and talus aznd bushes, yes, but no water). The brake lines are standard, red Dacron.
My birthday suit weight is just over 220 pounds, an estimated exit weight of 245 pounds. I am NOT fat - I am just big-boned ;-)
Hypotheses:
1. Not many BASE jumpers weigh what I do and are routinely taking 3+ second slider-down delays. Thus, I am exposing a weak link in the gear chain through my jumping.
2. The standard rigging for brake settings creates an obvious stress point where the riser loop cuts into the "V" made by the finger-trapped (usually white) bit of line that creates the brake loop.
Solution:
I have now gone to what is sometimes called "captive loop" brake settings for my deep brake settings. These new brake lines were rigged by an experienced jumper for me (thanks DW!), and I now have 20+ jumps on them with no material signs of wear showing. Manufacturers will make these brake lines for you, either with your new canopy or as replacements, if you ask. There are no known material downsides to jumping this form of brake line, though they do take more time to construct initially and they involve eight separate finger-trapped loops and the required bar tacking of same. Some have speculated on a minor 'bumping' caused by these deep settings while steering and flaring slider-up. I have tested this and not found it to be material, or detrimental to slider-up canopy control. I do not know of anyone who has found otherwise based on firsthand experience, nor do I know of any incidents of steering line hangup slider-up caused by captive loop deep brake settings.
Blowing brake lines during deep (3-4 second) slider-down jumps is an. . . interesting experience. As soon as the line blows (which happens with an audible 'pop') the canopy loads highly asymmetrically during final pressurization, causing a rapid spinning malfunction. The response required to control the malfunction is immediate rear riser input and/or de-toggling of the non-broken toggle and then riser correction. With an unvented canopy, pure rear toggle input to correct a broken brake line will likely result in partial canopy collapse and inability to steer and fly until re-inflation occurrs. Minimum off-heading induced by a broken brake line in this type of scenario is 90 degrees with immediate correct response procedures, in my experience.
Landing is done via rear riser input.
If you are a heavier jumper and you are routinely taking deep slider down jumps, you will likely break your standard brake lines in due course. They will show initial wear and torn strands, and when you see this you are nearing the likely breaking point. If you ignore this, you will likely be faced with a serious malfunction that could kill you. Both of my breaks occurred on Es (cliffs, not pills), both moderately underhung at this delay. I was fortunate to respond quickly enough in order to avoid serious injury or death.
I do not view this as a gear inadequacy on the part of manufacturers - they specifically tell us not to take slider down jumps past 3 seconds. Rather, I feel that larger bodyweight jumpers taking deep slider down jumps are using standard gear in a non-approved manner. I now believe that the "captive loop" mod is a much safer setup for jumpers doing this type of jumping.
Since these incidents, I have heard of a number of experienced jumpers that routinely jump captive loop brake settings, simply as a precaution. This makes sense to me now!
As to the above, standard caveats apply: I don't know what I am doing, so don't do what I do. Some assembly required. Your mileage may vary. Objects in mirror are weirder than they appear. Do not remove this label under penalty of law.
Peace,
D-d0g
ddog@wrinko.com
www.wrinko.com
