Preface: Some who read this posting may conclude the information provided is only ancillary to the analysis of acoustic data and has small practical application. Not so!! The more extensive the technical background analysts have, the higher the probability they will fully exploit the data under review in terms of the detail of the recovered information. It is of paramount importance to understand as much as possible about submarines, i.e., how they operate and under what constraints those operations are executed. It is never possible to know enough; there is always more to learn, and curiosity should not be age-limited.

- When nuclear submarines that employ geared-turbine propulsion systems - which can be up to 97-percent efficient - execute evolutions known as “crash backs,” which are about the noisiest evolution possible because of heavy cavitation, steam is redirected from the ahead stages of the turbine to the astern stages. The resulting maximum propeller shaft speed produced by the astern stages is approximately 50-percent of the maximum propeller shaft speed that can be produced using the ahead-stages.

- Crash-backs are used to “kill” forward speed and are almost never allowed to continue long enough to achieve “sternway,” i.e., forward speed is reduced to near zero knots. If forward speed is 30 knots, two to three minutes are required for a crash-back to kill all forward speed.

- Crash-backs usually are performed only during the initial acceptance trials of a submarine to determine if the propulsion shaft line can withstand the most extreme forces to which it is likely to be subjected during the service life of the submarine. ((Read SILENT STEEL (about the loss of SCORPION) by Stephen Johnson which discusses sea trials in PAC during which a 585/589 Class submarine operating at a depth of 300-feet lost its propeller (shaft broke external to the pressure-hull) while executing a crash-back in Dec 1961. The shaft had been altered to fit strain gauge wiring. The submarine (SNOOK/SCULPIN?) had to be towed in. Had the shaft broken internal to the pressure-hull, the submarine probably would have been lost.))

- When nuclear submarines execute course-reversals at speeds in excess of 30 knots using rudder angles of about five degrees, speed can be reduced by as much as 20-percent during the turn while propeller rpm is reduced by only about five-percent. This apparent anomaly occurs because of the increased drag produced when the rudder is not aligned with the longitudinal axis of the submarine and that axis is no longer aligned with the direction of motion because of side-slip; hence, the effective turns-per-knot value can increase by as much as about 20-percent during tight course reversals. Note following paragraph for a transient rpm exception.

- When nuclear submarines execute major course changes at high speed, the propeller rpm makes an extremely rapid transient speed increase of as much as two-percent for less than five-seconds before showing the usual drop in speed. Such very short duration speed increases may occur because, for a very brief period, the flow – and the resulting load – on the propeller is decreased. It is during the initial phase of such turns that side-slip velocity and roll angle are maximum. Maximum loss of speed occurs near the mid-point of the course change. The following article provides a useful discussion of these forces and the phenomenon known as “snap-roll:” http://archive.org/stream/investigationofs00libe#page/n25/mode/2up.

- Nuclear submarine propellers are designed to be most efficient at maximum speed. Accordingly, turns-per-knot values are lowest at flank speed and can be as much as 2-3 percent higher at half that speed. Note; however, that the horsepower requirements increase dramatically with speed as discussed elsewhere in these articles.

- Only when propeller cavitation becomes so advanced as to occur along a significant section of the leading edges of the blades is there a breakdown (loss) of thrust.

- The extreme forces associated with the hydrostatic collapse of submarine pressure-hulls are sufficient to cancel all pre-existing directions of motion. For example, if a submarine is operating at 20-plus knots when collapse occurs, the fragmented pressure-hull will sink nearly vertically from the point (position) of collapse; none of the wreckage will follow a trajectory in the direction of motion extant before collapse. All submarine collapse events for which information is available occurred as a result of the loss of propulsion power; hence, collapse while power is available is improbable.

- When nuclear submarines execute turns, a gyroscopic force is exerted on the propeller shaft. The longer the shaft and the greater the course change, the greater the force exerted on the shaft and the greater the resulting hull excitation. Had the writer known this on 20 June 1964, he would not, after two days of cogitation, have misclassified a Project BRIDGE target.

And finally, ZUI (you attention is invited to) the following website which discusses What is known about the character of noise created by submarines written circa 1995 by E. V. Miasnikov, a Russian expert in Arms Control and Submarine Strategic Nuclear Weapons: http://www.fas.org/spp/eprint/snf03221.htm

I love this stuff!!! Keep the keys clacking Bruce.

If this "stuff" could have been taught or disseminated in some way back in the day, it's no doubt the system would have operated at a significantly higher level of efficiency. I think all that spent a career in the system and achieved some level of "gram experience" recognized that the more one understood about submarine operations the more the grams "made sense". When the grams made sense, analysis was easier and completed more accurately.

We're too old to read grams any longer but we're not too old to appreciate an education.

Keep it coming Bruce. It's good stuff!!!!!!!!!!!

JE

Yes sure Ellis, that is all we needed was more information for an oral board with: OTCM Widenor, OTC Peterson, OTC Williams. We could probably make SURTOPS like 3-4 Volumes.

Seriously, this would have been usual to know about.

Sandy

Postings by John and Sandy raise a point and a compelling memory about training.

First, does anyone know if this site – specifically this message board – is routinely accessed by active-duty System personnel?

Second, the memory which shaped the way I taught new personnel in Norway.

When I took the final exam at Fleet Sonar School (course 556?) in March 1959, I could not answer the following question: What is the rpm of an 80-Hz turbine? Pretty bad! I had not made the connection between seconds and minutes.

During the classes I gave to new Norwegian Intelligence Service personnel over a period of many years, the first thing I would do was to write 60s equals one minute on the blackboard. Then, whenever the speed of a machine came up, the students were asked to express that speed in revolutions per second, NOT revolutions by minute. It was a very simple approach but it got them thinking in the right terms. Of course, they were, almost without exception, very bright. After less than two weeks, they could handle almost any “translation” problems through gears and slip-rates. It was also nice to be able to check the all-source op-plot and then schedule specific lesson plans for days when the students could then actually observe the subject of that lesson plan which was very strong reinforcement. There was a lot to be said for on-site training.

Bruce,

Interesting and somwhat comical post with respect for the writer's status in the world today!!! I think all of us had that weak spot(s) that when we got older made us utter "How did I not know that"!! This brings to mind a training method that I saw employed that was ingenious by its simplicity.

Back in the late 70s, I had the ORI team from COSL. It was a transitional time in that for a few years, training and ORIs had somewhat been abandoned at some facilities. Well, I joined and later inherited an ORI team that had been charged by then Commodore Doug Simon to put some teeth into the ORIs(specifically the battle problem) in hopes that it would re-energize the training at individual sites.

The simple training method that I alluded to earlier was developed by then OTCS Dave Williams. He may have borrowed it from someone else or saw it used earlier but it was the first time I had seen it and it was a winner. Dave was an exceptionally sharp fellow so I give him credit for coming up with the idea.

Dave had the responsibility of developing the annual ORI readiness examination, one for the reader, plotter and supervisor levels. These exams were not new to ORIs but in the past, the emphasis had been put on a pass/fail basis. Dave was not remotely interested in individual scores. He would profile each examination with the question(s) missed and the incorrect responses the individuals made to the missed question. When he was finished with his profile, it was particularly easy to see trends where groups missed the same questions and, more often than not, the incorrect responses would be the same. So Dave, armed with that information, would look at records to determine who gave lectures or OJT in the area(s) of question. Then he would schedule those individuals to conduct the same training with senior ORI team members as well as senior on-site personnel in attendance. It was amazing how easily the real problem(s) were uncovered. In some cases, the questions on the exams were missed due to simply not knowing the answer. But, in more cases than one would think, the training was found to be misleading and as such led to consistently incorrect responses.

As I said earlier, it was a simple approach with very meaningful results. Sometimes, actually very often, simplicity wins out.

Just thought I'd share.

JE

Bruce,

I failed to address your priority question of the last post.

I don't think that, to date, sailors that currently man the facilities read this site as do the old timers. For obvious reasons, the current sailor is not as nostalgic about the days of old as are the plank owners and system sailors of the 50s, 60, and 70s.

However, posting such as you have made over the past couple of months are not only interesting to the old timer but equally interesting and relevant to any that are trying their best to analyze a gram.

Consequently, when the word gets out that one of our best is posting articles that are relevant to todays Ops as well as the past, then I think the "readership" will change.

i'm a big subscriber to "If you build it, they will come".

JE

John:

I hope you are correct. I have tried not to become Shoeless Joe Jackson by posting items that
would get the current generation concerned from a security standpoint. What I have posted
is small potatoes compared to what could be posted were there no constraints. It is the
possible loss of those techniques and findings or their non-availabiliy to current System
personnel that really concerns me.

Bruce