Case Studies and Stories  

Hydra Main Propulsion Gearbox

Jason Tranter
Jason Tranter | Founder & CEO, Mobius Institute

Case Studies + Stories - Hydra Main Propulsion

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2 years ago

Dear Mr. Jason,

this is an interested case study than you for sharing.
I have a question. is it normal to see peak in spectrum for bearing frequencies ?

if it yes, when the peak exceed the limit. what I can see in this spectrum maximum peak was about 1 mm/s.
which is still low. will consider an problem even when the spectrum peak is low ?

2 years ago

Hello Murtdha, Thank you for your question – it is a good question. Under normal circumstances, when the bearing is in good condition it will not generate vibration at the defect frequencies. (However, SKF Carb bearings have been known to generate vibration at defect frequencies when they are in good condition.) So if you see a peak at a defect frequency, with harmonics, and possibly with sidebands (which indicates a defect on the inner race (1X sidebands) or a defect on the balls/rollers (<0.5X sidebands)) then there is a high probability of a bearing defect. Ideally, the bearing should be… Read more »

2 years ago
Reply to  Jason Tranter

Thank you for fast respond,

in our plant we are suffering high peak-peak acceleration Gs coming from gearboxes.
there is nothing in velocity spectrum in peakvue and acceleration spectrum all peak is less than 1 Gs.

maybe, we are not having a good setting for gearbox peakvue or acceleration spectrum. can you share setting guide line for gearboxes?

thank you again

2 years ago
Reply to  Jason Tranter

talking about oil sample,
we are facing iron contamination about every 8 months. I ask to replace the oil every time we face this issue.

what do you think the source of this iron .

2 years ago

Hi Murtadha, How are you testing the gearbox? How are you mounting the sensor? What is the size of the gearbox? And what is the frequency of the vibration you are observing (i.e. if you are seeing 1 g peaks, what is the time between them and how does that relate to your gearmesh frequencies and your bearing defect frequencies?). Also, how are you performing the oil analysis and wear particle tests? Are you seeing any other elements, like tin or lead? Is there water contamination (or other contamination)? Are you sure the viscosity of the oil is correct? Also,… Read more »

2 years ago
Reply to  Jason Tranter

if you don’t mind It is better to share with details with you by your Email

I will prepare all required information and data and send it to you

2 years ago

OK – with your permission, when this is resolved I will post any details back here if they add to the story at all.

1 year ago

Hi Jason,
i have a question about CBM on a Cascad mill(mill).
This mill has 2 lines drive. On each line there is a motor, a gearbox and a pinion. When i take vibration tests, i have every time dominant pic at 1xGMF of pinion and girth-gear but this high vibration value is located on the motor. My question is why the high value is on the motor and the high pic frequency indicate GMF issues between girth-gear and pion?
Those components are too far to the motor.

1 year ago
Reply to  jacques

Hello Jacques, It is a little tricky to answer this question without knowing more about the machine and circumstances, but I will make two comments that I hope will help: 1. Vibration at the gearmesh frequency GMF can be due to a number of reasons, including heavy loading on the gear and wear on the teeth. It is unlikely to result from damage to an individual tooth. 2. When you measure vibration it is a combination of the strength of the driving force (the GMF) and the response of the machine and structure. It is possible that the mechanical transmission… Read more »

About the Author

Jason Tranter
Jason Tranter Founder & CEO, Mobius Institute

Jason Tranter is the founder and CEO of Mobius Institute. Jason is the author of the majority of the Mobius Institute training courses and e-learning products covering reliability improvement, condition monitoring, and precision maintenance topics. Over 35,000 people (as of 2020) have been formally trained in these courses, and many thousands more have been educated via the elearning courses. Plus, thousands have read articles, attended conference presentations, and watched videos and webinars on many sites, including,, and YouTube (over 1.3 million views).