To determine if a propeller requires a design review, it is necessary to verify the performance of the boat, as well as the operation of the propulsion system installation components.



PROPULSION SYSTEM INSTALLATION COMPONENTS
They constitute 50% of the cases because of the engines not providing the expected power. This can happen because there is not adequate ventilation of the engine room or its admission; the exhaust gas discharge circuit is inadequate or the muffler may simply be clogged or excessively restricted.

In other cases, but with much less probability, it appears that the cooling system is defective; this may be because the complete decarburization has not been carried out during the integral repair or because the impellers of the pumps are worn or there is air in the seacock or it is blocked.

PROPULSION LINES ALIGNMENT
The alignment affects the performance of the propulsion system because with the whole system well configured, the excess temperature in the resting zones or bearings does not allow the system to operate properly. Another cause that can present heating in the resting zones or bearings is the excess deformation of the hull that affects the alignment of the propeller line.

REDUCTION RATIO
It is very often found that when designing a new propeller or by a re-motorization, the reliable information of the reduction ratio is not available, in some cases generating overload or simply that the propeller becomes light.

PARASITE CURRENTS OR ELECTROLYTIC CORROSION
A propulsion system must have the electrical system well grounded, maintaining the electrochemical valences, so that the propeller does not suffer premature wear that diminishes performance. Another possible effect is the poor distribution of galvanic protection anodes, which cause the same effect of premature wear or the bending of the tips of the blades. On barges, as they have a flat bottom, it can even be observed that it is important to have sufficient propeller clearance to avoid generating wear due to corrosion at the tips.

PROPELLERS WITH POOR PERFORMANCE
Given a suspicion that the propeller is performing poorly, it is recommended to measure the fuel consumption and compare it with the consumption curve proposed by the manufacturer. It is usual for the propeller to generate a variation of its consumption in a range of + -10% of that indicated by the manufacturer, due to the variation in the load conditions. If a greater variation is shown, it is recommended to review the propeller design. In addition, the following parameters can be reviewed that can help confirm the suspicion that a propeller should be redesigned:

• Comparison of speed between ships of similar dimensions and powers.
• The engine does not reach the working RPM and shows evidence of overload (heating, black smoke, etc.).
• The engine shows evidence of a light condition.
• When operating the ship, there is a knocking and / or buzzing sound in the sternpost area.
• The amount of incrustations on submerged surfaces.