Bruce,
In review of a recent article (http://ussnautilus.org/blog/the-loss-of-uss-thresher-ssn-593/) concerning the anniversary of the sinking of the Thresher, I would greatly appreciate your evaluation of their findings. Secondly, could you clarify to me why an MCP would be considered part of a non-critical bus versus critical? Your insight would be greatly appreciated.
Response to Stephen Lechowicz's Two Questions About the Loss of THRESHER
FIRST QUESTION: What is the writer's evaluation of the cited 2014 SUBMARINE FORCE MUSEUM article that states flooding was the cause of the THRESHER disaster?
RESPONSE: There was not in 1963 – nor is there now – any evidence to support the Court of Inquiry (COI) conclusion - reprised by the article - that flooding occurred onboard THRESHER before collapse of the pressure-hull at great depth. As discussed in detail by the posting “WHY THE USS THRESHER (SSN 593) WAS LOST,” multiple, independent lines of evidence make it indisputable there was no flooding.
COMMENT: Attributing the loss to flooding allowed the COI to avoid the essential question which was then – and remains now: How did THRESHER arrive at test-depth significantly out-of-trim (heavy) if there was no flooding? The single answer to that question can be provided by anyone who qualified on submarines.
SECOND QUESTION: Why would Main Coolant Pumps (MCPs) “be considered part of a non-critical bus versus critical?”
RESPONSE: Under normal operating conditions for submarines with an S5W nuclear reactor, all ac electrical power requirements were produced by two steam-turbine-driven Ship's Service Turbo-Generators (SSTGs) which - operating in a twin-bus distribution configuration – could accommodate all loads including operation of MCPs in either SLOW (4-pole mode) or FAST (2-pole mode). MCPs in FAST were needed to support operation at speeds above about 20 knots and FAST required ac power several multiples of that required for SLOW. The SSTGs also drive Ship's Service Motor Generators (SSMGs) which are ac/dc machines that, when driven by the output of the SSTGs, function as dc generators. Basically, this is the non-vital bus.
If steam for propulsion and the SSTGs is lost for any reason, the SSMG flips function and becomes a dc motor powered by the battery to produce limited ac power, sufficient to operate the MCPs in SLOW – but NOT in FAST. This is the vital bus. For a limited period and under certain conditions, it can provide the ac power needed to retain propulsion. This is a critical back-up capability and is why the term “vital bus” is used.
One such condition is that if you are running the MCPs in FAST and there is a propulsion plant casualty, you MUST immediately shift the MCPs to SLOW so the vital bus can pick up the MCP electrical load. If the MCP speed is not shifted to SLOW, the SSMGs cannot accept the electrical load of the MCPs in FAST and the reactor will scram.
The SOSUS acoustic data previously discussed confirms a propulsion plant problem occurred during the minute prior to 0909R; however, the MCPs continued to operate in FAST - although powered by an unstable SSTG line-frequency - until the MCPs went off-line (strong signal abruptly lost) at 0911R. Thus the acoustic data confirms the MCPs were NOT shifted to SLOW when the propulsion plant problem occurred.
(Note: the strength of the MCP in FAST acoustic source relative to the known detectability of the MCP source in SLOW indicates that had the THRESHER MCPs been shifted to SLOW at 0911R, they would still have been detected at THRESHER's range to the nearest SOSUS hydrophone array: then 30 nautical miles.)
COMMENT: Attributing the loss to flooding allowed the COI to avoid another question which was: When the propulsion problem occurred, why were the MCPs not immediately shifted to SLOW? An ancillary issue is why were the MCPs operated in FAST during the deep-dive when operation in SLOW would have accommodated speeds up to about 20 knots and also would have provided the electrical system flexibility needed to possibly avoid a reactor shut-down?
Stephen: Thank you for your perceptive questions which strike at the two most basic issues involved in the loss of the USS THRESHER which - to date - have never been addressed by the Navy.
FINAL COMMENT: Much of the above information is already available on the internet. Example: scroll to the bottom of the linked site.
