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688 flight 3 ringed propellor

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Postby all ahead flank » Mon Aug 25, 2003 9:47 pm

For what reason did the USN decide to swap a normal screw (688 flight 2) with a ringed propellor(flight 3)? Did this help the 688(i) in any way during operations? ???

Perhaps the ring that is added reduces votex noise from the tips of the blades?
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John Petrucelli
all ahead flank
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Postby Dolphin » Tue Aug 26, 2003 2:19 am

Hello Flank (flank steak?) sorry. :D

The ringed prop seen on 688I's seem to have two main purposes. They are a 'poor mans' pump jet in one respect in that the ring helps to utilize some of the energy dissipated at the propeller blade tips and delaying some early cavitation. Cavitation is bad news to submerged submarines. Also it is useful in helping avoid blade damage when surfacing through ice polynas (thin polar ice). These blades are delicate things acoustically, any nick or such could change the submarines level of stealth. No two propellers fabricated in the casting and milling process are never ever exactly alike, even if they appear the same, much like church bell makers, they resonate subtilely in different ways. Often when returning to base for inspection by the shipyard either by divers or in dry dock, it is quite common for subs with the same propeller design to exchange props for inspection and maintenance, or even swap propellers for another in the base inventory to confuse the opposition's record of this boats acoustic finger print. Early ringed props were tried on 637 Sturgeons too I heard, but that the CNC milling technology then (1970's?) was not up to the level needed then. The 688I's designed with retractable bow planes among many other things was a design more dedicated to warfare under the polar ice caps. Since the end of the cold war, 668I's have distinguished themselves operating also in theatres that have been anything but cold. Whether the polar regions or the tropics, it is safe to model your 688I with this ringed prop, though there are other prop designs used too. Things are always being improved and redesigned. As the good Dr. McCoy 'Bones' of Star Trek was fond of saying, 'blast Engineers....the 're always changing things!'.

Steve Reichmuth
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Postby WL Upshaw/Scale Shipyard » Tue Aug 26, 2003 1:49 pm

Steve:

The USS Archerfish SSN-678 had the ringed prop in her final couple of deployments and decommed with it. According to her exec. Exact dates of it installation were not known by him.

W.L. Upshaw
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Postby all ahead flank » Tue Aug 26, 2003 6:02 pm

Thanks for the info :)
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John Petrucelli
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