Marine Stern Tube Bearings (Strut Bearings)
In 1977 the pilot vessel, RP Jackson was fitted with new A-frame propeller shaft bushes, the starboard one being Vesconite and the port one of the conventional rubber type.
The propeller shafts each transmit a maximum of 525Kw (700BHP) and have an average RPM of 400. The total length of the bush being 550mm (21.7"), it was made in two section, interference fitted into a brass sleeve and retained by the use of an end keeper and Loctite Retaining Compound.
Longitudinal U-shaped water groove, 11mm (0.43") wide by 2mm (0.08") deep were formed on the inside of the bush, each running the full length. The wall thickess of the bush was ±20mm (0.78").
The RP Jackson had been operating between 12 and 16 hours a day in and off Durban harbour under fairly abnormal and severe conditions. The waters contain a relatively high percentage of suspended sand particles arising mainly from propeller wash. The loads and speeds vary constantly.
During September 1982 the propeller shafts were drawn for the first time since 1977 and the following information noted. The bearing area of the shaft was highly polished and smooth and because of this aspect coupled with the very low wear rates, the shaft was reinstalled as it was drawn.
On installation the Vesconite bush had an inside diameter of 145.64mm (5.734"). After five years the inside diameter was measured at 147.14mm (5.793") which shows wear of only 1.50mm (0.059"). The outside diameter of the stainless steel shaft was 145.14mm (5.714"). After five years the outside diameter was measured at 144.91mm (5.705") – wear of only 0.23mm (0.009").
No accurate comparison could be made with those wear rates on the port side as initial dimensions were not recorded. Nor could very accurate dimensions be taken of the rubber bush after the period under consideration as its internal surface had worn unevenly.
Vesconite has now been fitted to both "A" Frame bearing housings carrying the propeller shafts on the pilot vessel RP Jackson and for this particular application, Vesconite will in future be favourably considered.
Last updated: Jul 20 2001
