No real drama

John Burns was to come up on Wednesday July 1st, which thing he did. But on the very day he was traveling we found pitting corrosion in the tail shaft, in the usual place, in way of the stuffing box. We should have inspected it earlier, but we didn't.

John Skipper Burns

So John took the opportunity to have a very good look around, and after making a few recommendations, satisfied himself that Orion was about ready (except for the corroded shaft) for the trip South. John has gone off now to sail a boat back from Bundaberg and will return to Orion in about two weeks, the time it should take to do the work on the shaft. All part of the fun when you own a boat.

The new shaft from Chatfield Marine

Additional detail for geeks:

It's crevice corrosion, and possibly occurred during the time she lay idle in Whangarei before Brian bought her. It's hard to really know how bad this kind of corrosion is just by looking at it. But there's significant loss of strength, and with the best part of 1000 Newton metres of torque made by the Gardner 8LXB and multiplied by the 3:1 reduction gear, there is the potential for even a 3-inch shaft to shear, and Simon Willis of Chatfield Marine confirmed this. Various courses of action were mooted, from doing nothing based on the premise that the corrosion was historical and Orion had been going around like that for years, to replacing the conventional stuffing box with a floating seal to prevent similar problems in the future. Sue and I felt that we couldn't live with a known (quite major) defect, and that equally we didn't need to fit (expensive) modern solutions that would involve disturbing the stern tube. So we took the middle road, and decided simply to replace what was there, but with SS2205 instead of the existing SS316. 316 would have been the standard of the day when the existing shaft went in, but 2205 is commonly used today. To quote Australian Stainless (ASSDA): "The grade has excellent corrosion resistance and is superior to grade 316, performing well in most environments where standard austenitic grades may fail. 2205's low carbon content gives the grade a high resistance to intergranular corrosion and has better resistance to uniform, pitting and crevice corrosion due to its high chromium and molybdenum content. As 2205 is a duplex stainless steel, the grade is also less sensitive to stress corrosion cracking in warm chloride environments, unlike austenitic stainless steels. The grade also has good resistance to stress corrosion cracking when exposed to hydrogen sulphide in chloride solutions. High mechanical strength combined with excellent corrosion resistance gives 2205 high corrosion fatigue resistance."