Project Brupegvideo
Diagnosing a PROBLEM & Fixing A Trawler Prop Shaft ALIGNMENT - Project Brupeg Ep. 376
October 6, 2024 · 41 min · 53K views · Bundaberg
What this video covers
Damien aboard the converted fishing trawler Brupeg diagnoses a propeller shaft misalignment at the Navy wharf in Bundaberg that caused a visible wobble in the rotating shaft assembly.0:04 The drivetrain uses an imperial-to-metric steel adapter between the propeller shaft coupling and the gearbox coupling, and the shaft had been aligned to within 0.25 mm before chock fast was poured — yet wobble persisted after final assembly.0:47
Three theories are investigated: a machining fault in the adapter's spigots, lateral engine movement, or an unknown cause.1:27 Using a dial gauge, Damien measures 0.27–0.28 mm of runout at the adapter spigot and confirms the two spigot centers are offset — meaning no amount of external alignment could correct the wobble once the flanges were bolted together.9:22 The spigots, not the bolts, perform all shaft-to-shaft alignment; the bolts only clamp.14:59
A machinist repairs the adapter for $560, roughly half the expected cost.15:16 The original high-tensile coupling bolts are replaced after TIG welding destroyed their heat treatment, and new 1-inch UNF and M20 fine-thread bolts are ground to length and chamfered.15:28 Post-repair dial gauge checks show residual 0.3 mm movement, attributed partly to slop in the stern tube's grease-packed flex bearing rather than the adapter.24:03
Machining error in an imperial-to-metric shaft adapter can mask perfect external alignment and must be verified with a dial gauge before chock fast is poured.
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