Fully agree with that, the more packing's is more for the larger shafts, the smaller shafts are happy with 3-4 rings, it can also depend on how the rings are cut (square or taper cut),
These days with cheap laser temp guns it is a good idea to do a test run before tightening to much at all , then once happy with your results check with temp gun to be sure your running temp in the stuffing box is with in the "normal " range (which is approximately 30-40 f over the average sea temp) any more runs the risk of melting the lubricant out of the packing (dependent on type used),
As a side issue here I have been corresponding with Duramax company re an technical issue regarding their graphite packing, as many are aware ABYC recommend not using any thing Graphite in under water applications (packing/grease/ etc) as it's one of the most noble elements around ,Duramax's reply was is that the graphite is basically held in suspension and only in minor amounts therefore wont cause any issues,also noting the shaft zinc should take any negative effects away, They supplied technical data in way of an actual test report basically stating MINOR HEADLINE of whole report: Quote: the shafts were rotated at 25 RPM for eight hours each day and remained static for the remaining sixteen hours.?The samples were removed from the tank after 60 days and evaluated for corrosion. Under static and dynamic conditions, with zinc anode protection, both the Duramax Ultra-X® and the Flax packing exhibited the same degree of superficial corrosion «0.01 mm depth).
My only query would be the 25 RPM used as the test speed and was any stray electrical currents induced possibly inducing elevated Galvanic Corrosion issues, this has been a relevant issue for me as one of our 30 meter vessels using a graphite type packing developed a serious issue with in the Bronze stuffing box,TO BE CLEAR, I'm not saying it was Duramax how ever as our records are not that precise, Duramax them selves raised the point that there are numerous FAKE products out there trying to present them selves as the normally very respected Duramax products.
Just Saying, pays to be diligent!
Cheers Steve