[Seite 1]
Propeller-shaft earthing
and
potential monitoring
- maintenance
RJ. FETERIS B.V. Technische Handelmaatscha
[Seite 2]
HANDBOOK- & OPERATING INSTRUCTIONS
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Slioring assembly
A tuming propeller shaft on a ship becomes electrically insulated from the'hull by the lubricating oilfilm in the bearings and by the use of non-metallic bearingmaterials in the tail shaft. When the shafl is insulated in this way an electrical potential can be measured between the shaft and the hull and this can accelerate corrosion in the ship. If the ship has a system of cathodic protection, whether it is sacrificial anodes or an impressed-current system, the shaft-insulation will prevent the propeller and the boss from receiving protection.
An electncal potential between the shaft and the hull can also cause a heavy current to flow in bearings when the oilfilm breaks down or is contarninated withseawater. This current can cause deep pitting of the bearingsurface. Excessive wear on the shaftbearings can often be traced to this cause.
This potential trouble can be avoided and cathodic protection extended to the propeller if the shaft is properly earthed with a propeller-shaft slipring. The effectiveness of the shaftearthing system should ensure a contactresistance of less than 0.001 ohms for a waterfilled bearing and 0.01 ohms for an oilfilled bearing.
Tests indicate that only high-silver-content bmshes running on a silver track has the repeatable low conductivity needed to maintain these limits and to ensure a low resistance contact is maintained even under dirty conditions.
The shaftearthing assembly comprises a pair of high silver contentlgraphite compound bmshes mounted in a balanced bmshholder, mnning on a copper slipring with solid silver inlay track.
Each bnishholder has an adjustable springtensioner which is supplied preset to the rninimum and results in a pressure of approx. 790 grarns on each bmsh.
At this pressure the expected life of the bmshes is in excess of one year.
[Seite 4]
Shaftearthine - installation
Use a degreaser for cleaning the propellershaft 6om oil and grease before fitting the slipring.
The shaflslipring is supplied as two matched halves complete with band- and clamping- arrangement and can be readily installed by competent engineering personnel.
All sliprings are manufactured slightly oversize to allow some degree of tolerante for final fitting. All excess material should be removed by filing down at the joint faces before securing with the bandclamping to form a tight close fit around the shaft diameter.
NOTE: To prevent bmsh 'bounce' and ensure maximum utilisation of the silvert graphite bmshes, it is essential that the joints form a smooth and flush profile over the hll extent of the slipring Drawing no. SE 2100045 detail A refers.
The balanced bmshholder is supplied ready for fitting to a 20mm diameter rod which should lie with its center-line parallel to the shaft center-line. The bmshholder should then be clamped to this rod and aligned centrally over the silver track.
The rod and mountingbracket are supplied by the shipyard and can be mounted 6om either a
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suitable 6ame or bearing-pedestal.
It is essential that the complete assembly should provide a good electncal contact between the shaft and the hull, therefore the bmshholder-rod support should either be welded or bolted to
the ship's stmcture and a short length of 25 mm2 bondingcable should be comected between the bmshholder and ship's stmcture.
On completion of installation the complete assembly should be checked for trueness and smooth mnning of the bmshes in accordance with the attached checklist. Cover the possible gap between the edges of the slipring and shaft with a suitable compound preventing oil entering under the ring.
[Seite 5]
Proeiiershaft otentiami onitoring
The advantages and benefits of installing shaftbonding-assemblies with hull cathodic- protection are widely recognised and it is for this reason that many shipowners desire the additional facility to monitor the effectiveness of the shaftbonding-equipment.
Measurement of the potential between the shaft and hull is achieved by means of a separate monitoringbrush running on the main slipring but insulated ffom the hull. This brush is then connected to the impressed-current powerunit or to a remote millivolt- meter to display the shaftpotentiai with respect to the hull of the ship - drawing no. SE 2400084 refers.
Installation
The sh&-monitoring-brushholder should be mounted on a 12 mm steel rod mountingpost which should be positioned in a plane perpendicular to the center-line of the shaft.
The monitoring brushholder is insulatedfrom the mountingpost by means of the insulating bush provided - drawing no. SE 2200014 refers.
Before welding or finally fixing the mountingpost in position, the position of the brushholder should be checked to ensure that it aiigns centrally to the silver track and does not obstruct the slipring-securing-clamps.
Once the mountingpost is secured in position, the brushholder is insulated mounted on the rod and adjusted to ensure that the distance between the slipring and brushholder wnforms with the dimension shown on drawing no. SE 2200014.
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Adjustment of the brushholder is effected by releasing the clamp and sliding the brushholder to achieve the specified distance. The brushholder is then clamped firmly in position and the monitoringbrush inserted.
On completion of installation the monitoringbrush should be checked for tmeness and smooth running.
Connection to the required monitoringunit is made via ships intemal wiring in accordance with drawing no. SE 2400084.
Although the monitoring unit has been fitted-out with vibrationabsorbers it is essential that this unit is mounted on a place where a rninimum of vibration is to be expected.
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[Seite 7]
Sli~ringin staiiation checks
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Contirm slipring and brushgear are instailed as peI drawing no. SE 2100045.
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1s assembly clean and fiee fiom oil and grease?
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1s slipnng a tight fit to the shaft over its whole length?
Ensure no bumps or indentations can be felt over the whole of the workingsurface
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Are joints a good fit with no gap? YES/NO
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1s bmshholder secure on its rod? YES/NO
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Confirm that brushholder and its mounting are solid and that it YES/NO will not be afFected by vibration
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Confkm that bnishfaces are tangential to slipring YES/NO
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Confirm that brushes are fiee to move in their holders YES/NO
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1s there electncal continuity between tail shaft and hull? YES/NO
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Have the vibrationabsorbers been fitted between mV-meter-unit and its wall-mounting? YES/NO
[Seite 8]
SLiarine rnaintenance
The grounding assembly should be checked every seven days for cleanliness. If there has been a build-up of oil on the slipring face this should be removed with some degreaser. Inspect and clean the brushes and brushholder to prevent blocking from dirt. Inspect the bmsh- copper- leads (pigtails) to ensure they have not become loose or corroded. The brush- wear-down should be noted and the compression of the holddown-springs on the brushes should be adjusted to ensure good electncal contact.
[Seite 9]
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Drawinm Shaftearthing and Monitoring
PROPELLER-SHAFT EARTHING ASSY AND BRUSHHOLDER INSTALLATION
PROPELLER-SHAFT MONITORING BRUSHHOLDER INSTALLATION
SHAFTEARTHING & MONITORING
INTERCONNECTION DIAGRAM
Handbwk Br Op&g Inaiudms for Shafl Earthing and Monaoring Equiprnmt Page: 7
47
[Seite 10]
0 ! projeetion Tor cleamess not complete 0 dimensions in mm ! bandclamps partly omitted for cleaniess 1 !! make Sure th'at edges of
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! clean shaft under slipring with degreaser banddamp slots aG 40 mm apart in order to and close gap between ring and sh avoid brushholder hit witb compound (Li. Sicaflex) r=radius propeller-shaft . .
under bolt a and b
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25 mm' earthing cable (with cablelug) to ships structure
x=20,5 + V (13,s + r)' + 27l- 9,5n propeller-shaft monitoring I bnishholder installatlon I,
I
steel rod to be supplied and installed by sbipyard SE 2200014 ! . -~ I
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- rolled to suit 4 2 stainless steel badclamp ---_I shaft diameter 3 2 earthingbrusb ~~'2400081 bandclamps to be ti 2 1 brushholder assy
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1 1 silverlcopper slipring
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item no. qty. descnption part.no. da"Lm : 19-04-'o]g benaming/descnption ! silvEir/copper stri date : witb respect to sha prop'eller-sha - ft eartbing assy get. : % order to achieve fi and brushholder installatlon dm. : (detail A) schad : - scalc : P.J. FETERIS B.V. tck. no. : SE 2100045 - ! fill gap with soft solder and polish
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in order to obtain a smootb junction surface ,. eartbing brush: sllverlgraphite (80% Ag) l fomaat : A3 W. : . . formst : dat. :
[Seite 11]
I
/ steel rod to be supplied pr" %e ller - s baft earthing assy und !! make swe that edges of . .. and installed by shipyard brus holder instaiiatlon dmng SE 2100045 bandclamp siots are min. 40 mm apart in wder to , avoid brushbolder hit
SE 2400082
brushbolder clamp
1 I I I
item no. qty. . descriptih part no.
propellei-sbaft monitoring brusbholder installation " monitoring brushbolder assembly . . monitoring brush: silvedgraphite (80% Ag) dimensions in mm
[Seite 12]
propeller-shaft earthing ass!. 2nd
monitoring brush dsy
biushholder installation dnvng SE 2100045
see dnvg no. SE 2200014
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4 X anti-shock wallmount each T P . / , , J' to be fitted to a Corner of the 'shaft-eanhing potential monitor' - benamin.g /.d.e..s.c nption danim : V$ \ 'j 59 ,. date .:
- see note sbaftearthing & monitoring
- gcl. : @'. interconnection diagrnm dm. :
-note einhsonnection eartb-connection by means of dimensions in mm