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At 17:28 13 September 2016, BobW wrote:
On 9/13/2016 9:26 AM, Dave Nadler wrote: On Tuesday, September 13, 2016 at 10:34:20 AM UTC-4, BobW wrote: As for the report's claimed missing pawl spring...I must be getting dense in my old age, since I'm still puzzled by the intended function and line of force of that implicated piece of (missing?) hardware. Back to the hook design - what am I missing? Thanks! Bob W. If I understand correctly, the missing spring pushes the pawl in the direction opposite of pulling the release knob. Otherwise, the pawl is not secured in the "latched" position, except by a bit of friction with the hook plate (from the spring that is present and any rope tension). Do I understand correctly?? Quite possibly. I suppose such a spring fairly might be considered the "suspenders" to the hook-retract-spring's "belt." It's not obvious from the photos (Figure 1 shows it best), but installed-geometry, plus gravity, in the pawl's as-installed position/angle work "against" the pawl remaining detent-seated...i.e. the pawl pivoting by itself (no other physical contacts) would tend to flop its "business end" *away* from the detent due to the longer cable-attach arm's length compared to the detent-engagement arm's length (unequal length teeter-totter). Nonetheless, whether the absence of a compression spring between the pawl and receptacle/pawl-spring-housing was a crucial element in this accident is debatable; it would take very little force on the rope to rotate the cable hook from the barely-engaged position (Figures 9) to the fully engaged position (Figure 8). Once there, further testing definitely required to determine whether the design would be more or less prone to back-releasing in the absence of the pawl spring, in the presence of a rope bow... That said - and since a number of these hooks have been installed into the noses of German-built ships originally entering the USA with only a CG hook - owners of ships with these hooks SHOULD (and easily can) VERIFY the presence/absence of such a compression spring by checking to see if the pawl is positively forced against the rotating piece of the cable hook throughout its rotation range. Positive engagement = spring-present. (Note that the spring itself is hidden in the hook's assembled state...and might easily escape unnoticed in the event of the hook being disassembled for any reason.) Bob W. I am now confused by the "installed in German" part. Is the release you are talking about a TOST release? |
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