Common Causes of Failures in Stern TubesBlog | July 31st, 2020
The utilisation of low-submersion propellers on certain vessels with low-speed fixed-pitch installations isn’t new. All things considered, increasing incidences of stern tube harm brought about by incomplete propeller submersion may recommend that operational contemplations should be better tended to. Such propellers are utilized on a various scope of vessels, for example, mass transporters, container vessels and enormous big haulers, because of draft limitations at certain ports; they additionally become an integral factor when vessels are in a lightship condition.
Conditions in which stern tube failures happen differ and can be influenced by the general state of the propeller, rudder, stern tube and main engine. When looking into the elements that cause explicit failures, various issues must be thought of. The following are the absolute most common causes of failures in stern tubes.
Loss of Oil Film
A main thought is the unfavourable impact of wiping the bearing because of loss of the oil film, causing shaft and bearing contact. Hydrodynamic grease disappointment will prompt over the top temperatures and different side effects including diminished engine execution. In spite of the fact that this disappointment may not be an immediate after-effect of low inundation, the impact of cyclic loading and sheer weight on the stern tube bearings over the long run may prompt failures.
Pressure conditions within the bearing surfaces ought to likewise be thought of. The stern tube producer’s suggested oil provider ought to be counselled, as it will prompt the oil evaluation to be utilized with the right thickness during administration. It will likewise have information about help life reasonableness, yet standard sampling ought to be done to screen water contamination.
The propeller shaft width and weight determine the contact territory on the bearing, however shaft misalignment resiliencies will influence the general bearing burden dispersion. This will likewise be influenced by the propeller’s weight, which will cause bending minutes along the pole leading to limited weight varieties.
At the point when the propeller is just incompletely submerged, its presentation is typically another main contributory reason for stern tube issues. Since it isn’t operating to its ideal and structured push and force boundaries, the impacts of flighty push, cavitations and vibration will make lopsided burden appropriation and inadvertently lead to bending landmarks and confined pressure zones, particularly in the rearward piece of the bearing where edge loading may create and increase after some time. Aside from the stern tube being presented to harm, cavitations harm on the propeller may likewise happen because of operating the vessel in these conditions over an all-encompassing timeframe.
Enormous Rudder Angles
Enormous rudder edges when the propellers are in a low-inundation condition can likewise have an impact in increasing the danger of harm, as propeller wash proficiency is decreased causing the vessel to react to steerage arranges all the more drowsily. In certain instances, this can make the ace increase main engine force and speed, exacerbating the circumstance.
Outside materials on the water surface around the propeller territory can likewise add to stern tube bearing disappointment. Logs, ropes or other sizable items can contact the propeller sharp edges as they get through the water, leading to restricted harm and increased cavitations and vibration.
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