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Tool preparation : each tool has its own line and float attached, with the lines running
through a carabiner on the main float (attached to the stern). The smaller floats on the
tools are not intended to keep them on the surface, but to give us a better chance of
locating them on the bottom if we do drop them. After use, the tools were treated to a thorough fresh-water wash and liberal application of WD-40. |
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Diving off a raft for easy access in and out of the water - but not the most manoeuverable
of craft... For the sceptics, the photo on the right gives an idea of the visibility - see that dive equipment inches below the surface? No? Precisely. By the way - yes, my mask is on my forehead, but no, I am not in distress - some elements of certain dive training programs are less than useful. |
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Spectators always welcome... |
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The great white hunter proudly displays his catch; tying the line on and securing it
before attempting to remove the propellor was definitely a good idea. The pin and nut were removed easily; we used a gear/wheel puller on the prop. itself. Care was taken to align the shaft so that the locking key was on top and did not sink into the murk when the prop. came off. |
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Now the puller did not fare so well... Allegedly, this model can exert up to 4,000 lbs. of force, but those flimsy brackets look a damned silly design to me; still, what can one expect for US$7? Fortunately, it lasted just long enough to shift the prop., so major frustration was averted. |
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The prop after removal and before renewal - stamped as a Sailor 16x11 RH, made by Federal. Aside from some pitting at the edges of the blades (due to a combination of de-zincification and cavitation), it does not seem significantly out of whack... |
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...but here is the scientific analysis. Each pair of bars on the chart (one bar for each blade) represents the pitch of the prop. at set distances from the centre. The target is the 11" pitch, but blade symmetry is the critical objective. On the left is the "before" picture, with the other analysis coming after the prop. technician had worked his magic. The bad news is that the blades were only just outside Class I tolerance originally, echoing Menno's words when I expressed relief that the prop. removal had been easier than I had anticipated - "Well, you know what that means, don't you? This isn't going to fix the problem...". After rebalancing, the blades conform much more closely to the symmetrical ideal - just about within Class 0 tolerance. Even if this isn't the solution, at least there are several benefits : we have eliminated one more possible cause of reverberation, prop. performance should be significantly improved, and... |
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...I now have a lovely shiny prop - not bad for US$132. It is interesting to note the copperish tinge to the prop. colour, indicating de-zincification. The expert opinion is that this has not progressed far enough to compromise the structural strength of the prop., but I will keep an eye on the zinc. If you are interested in the rebalancing process, the Jacksonville chap did an excellent job (to my untutored eye at least) and is part of an informal professional group all using the same (Australian) technology - further details available on request. |
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