Technical
Vessel Performance Introduction
Operational parameters
Performance has become a buzzword in the Maritime Industry in recent years. Vessel performance is not only closely related to energy efficiency and environmental impact, both of which are becoming increasingly regulated, but it is also related to vessel safety, cost efficiency and profit optimization.
A vessel’s performance is greatly influenced by the By Konstantina weather. Wind, waves and current add resistance Fountouli to the vessel’s movement making it harder to achieve the desired speed and subsequently requiring more power output from the Main Engine. Of course, we cannot control the weather. What we can do, though, is to ensure the optimization of a vessel’s route based on the weather forecast. This often means avoiding bad weather conditions even by taking the longer route to reach the destination. Another important operational parameter of a vessel’s performance is the condition of the hull and propeller. While ships sail through the sea, the submerged part of the hull gets fouled, increasing the hull’s friction through the water and subsequently its resistance. Similarly, when the propeller is fouled, its performance is degraded. Hull fouling usually consists of slime, grass, barnacles and mussels, while the most common finding in propeller fouling is slime.
Performance Parameters A ship sailing through the sea is a complex process affected by many parameters that interact with each other. An easy way to categorize them is to distinguish between their design and operational parameters.
Design parameters Hull form and propulsion system performance optimization is thoroughly studied in the design stage of new vessels. Hull form optimization is one of the major ways to influence a vessel’s performance. Progress in this field has recently been accelerated by the introduction of CFD (Computational Fluid Dynamics) analysis and faster computer processors. In this way, multiple models can be examined in a fraction of the time and effort that would be required with the traditional way of testing scaled models in a towing tank.
Figure 3: Vessel's hull before and after hull cleaning
Figure 1: CFD analysis simulation
Figure 2: Model tests in a towing tank
Hull form optimization consists of first determining a vessel’s capacity, principal dimensions and service speed and then the detailed hull geometry (Lines Plan). Hydrodynamic performance varies significantly with changes in draft and ship speed, so different sailing conditions are often studied at this stage. Apart from hull form optimization, but closely linked to it, the propulsion system should also be optimized for the specific project. Propeller characteristics (diameter, number of blades, pitch, etc.) and Main Engine characteristics (RPM and power output at the MCR (maximum continuous rated power output)) are determined for a specific hull form. However, hull and propeller performance cannot be studied separately as they interact significantly with each other. Similarly, the propeller and Main Engine need to have the same operating points for the enhancement of propulsion efficiency. The vessel’s performance optimization at this stage is an iterative procedure aiming to optimize the whole hull-propellerengine system performance. Once the design parameters have been determined and a new vessel is built, performance evaluation is based on the operational parameters.
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Issue 84-June 2023
In order to delay hull fouling, the hull is painted with high performance anti-fouling paints. Anti-fouling paints affect a vessel’s performance in two major ways: first, they provide minimum friction resistance through the water and second, they act as a deterrent for marine organisms that usually get attached to the hull. When fouling appears, a vessel’s performance can be restored with propeller superpolishing and/or hull cleaning.
Figure 4: Propeller blade before and after superpolishing
Hull fouling is also influenced by the vessel’s operational profile. Long anchorage stays and sailing through tropical waters both facilitate the marine growth on the hull and propeller, while sailing at fast speeds and through cold waters can delay the appearance of fouling. Just as importantly, the condition of the Main Engine has a direct effect on the overall performance of a vessel. An evaluation of the Main Engine’s performance is made based on the Maker’s recommendations. The main parameters involved in the performance evaluation of the Main Engine are: