MGDuff Propeller Shaft Earthing And Monitoring Systems

Product catalog summary

Shaft Bonding Overview
When steel, such as a ship's hull, is immersed in seawater, galvanic currents cause corrosion, particularly at the stern due to increased turbulence and differential metals. Cathodic Protection is used to suppress these corrosion cells by applying an opposing current from external anodes. For the propeller to benefit from this protection, a continuous electrical circuit between the propeller and the ship's structure is necessary.

Challenges and Solutions
While the propeller is at rest, metal-to-metal contact usually exists, but when the shaft is turning, lubrication creates high resistance, insulating the propeller from the hull. This can lead to spark erosion and damage. To minimize arcing effects, the potential across the shaft/hull interface should be less than 50 mV. Shaft Bonding equipment is installed to ensure cathodic protection extends to the propeller, applicable with both sacrificial anode schemes and Impressed Current techniques.

Shaft Bonding Equipment
The system includes a split slipring arrangement and ancillary brush gear, designed for easy assembly. The slipring is slightly oversized to accommodate shaft diameter variations and must be dressed to fit on site. Proper installation ensures long-term performance with minimal maintenance. The slipring should be installed on the intermediate shaft, away from contaminants.

Condition Monitoring
The condition monitoring system provides a continuous indication of the shaft bonding system's effectiveness. The Condition Monitor should display a shaft potential not exceeding 50 mV. Higher readings indicate worn brushes or poorly maintained equipment. Monitoring is achieved with a single brush on the main shaft bonding slipring, connected to the Condition Monitor Unit.

Components and Specifications

Slipring: Copper/Silver Track
Tension Bands & Clamps: Stainless Steel
Single Brush Holder: 80% Silver, Insulated Spindle
Double Brush Holder: 2 x 80% Silver, Mounting Spindle
Bonding Cable: 2M x 35mm²
Condition Meter

Ordering Information
When ordering, specify the shaft diameter and number of shafts.

Catalog excerpts

MGDuff Propeller Shaft Earthing And Monitoring Systems-1

1 Timberlaine Estate, Gravel Lane, Quarry Lane, Chichester, West Sussex. P019 8PP

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MGDuff Propeller Shaft Earthing And Monitoring Systems-2

When steel is immersed in sea water (e.g. a ships hull) small galvanic currents are initiated at anodic areas of the metal surface, causing Such corrosion predominates at the stern of a ship, where the combined effects of increased turbulence and differential metals results in accelerated corrosion rates. The application of Cathodic Protection effectively suppresses these corrosion cells by applying an opposing current from external anodes and if the propeller is to receive the benefits of cathodic protection then there must be a continuous electrical circuit between the propeller and the ships...

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MGDuff Propeller Shaft Earthing And Monitoring Systems-3

However, it is accepted that in practice, such a low value is outside the range of most commercial multimeters and is therefore difficult to determine. It is for this reason that many ship operators prefer a permanent visual indication in the form of a shaft condition monitor, which provides a constant display of shaft potential and confirmation that the bonding equipment is successfully maintaining this at a level not exceeding the optimum value of The M G DUFF system of shaft bonding comprises a split slipring arrangement and ancillary brush gear, which is designed to facilitate ease of assembly...

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MGDuff Propeller Shaft Earthing And Monitoring Systems-4

SHAFT BONDING CONDITION MONITORING The condition monitoring system provides a permanent and readily available indication on the condition and therefore, effectiveness of the shaft bonding system. To ensure a continuous cathode bond and freedom from shaft bearing damage the Condition Monitor should display shaft potential not exceeding 50 mV. Readings in excess of this value are indicative of worn bonding brushes or poorly maintained brushgear and/or sliprings. SLIPRING CONDITION VOLTMETER Monitoring Brush which runs on the main shaft bonding INSULATED spindle. This brushgear is connected Monitor...

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