Analysis of the Applicability of the Formulas the Calculation of the Loss of Ships Speed Due to Wind and Waves

Abstract

The article deals with the current issue of calculating ship speed loss due to wave and wind resistance. With this problem faced by all participants in the Maritime transport of cargo from navigators and engineers of ships, which the knowledge of the speed of the ship, it is necessary to calculate parameters of voyage and calculate fuel reserves to the transfer to the ship owners for solving problems of commercial effectiveness and logistics. The opening of Russia's traffic on the Northern sea route, full of winds and storm events increases the urgency of the problem of the forecast of speed of vessels in conditions of wind and sea waves.Wind and waves on the ocean surface caused by the wind are among those hydrometeorological factors navigators often come across when operating a vessel. The International Convention on Standards of Training, Certification and Watchkeeping for Seafarers (STCW) requires that hydrometeorological factors should be taken into account in navigation. Wind and wave effects cause wettability and slamming (wave impact on the ship bottom) which lead to ship speed loss. Slamming conditions can be calculated using Froude coefficient and wettability contours. Ship speed at which slamming is eliminated can be calculated on the basis of known parameters of wind driven wave length and height as well as vessel draft. Frequency of enforced speed loss increases with the increase of wind velocity and wave height and can be taken into consideration through repeatability factor. In case a ship is not forced to decrease her speed repeatability factor value is equal to zero. When it comes to 100 % cases that a ship is forced to decrease speed at gale and under rolling sea conditions repeatability factor value is equal to one. Speed loss due to wind and wave effect is the sum total of speed loss as a result of enforced deceleration and as a result of additional resistance to motion caused by wind and wave factors. Mathematical formalism to calculate total speed loss due to wind and wave effect varies greatly. There are numerous formulae to estimate ship speed reduction due to wind and wave effects. In the article the comparative analysis of the practical applicability of the most commonly used formulas for calculating wind and wave loss of speed of the marine vessel. The need for comparative analysis of the practical applicability of these formulas is because most of them were obtain quite long ago based on studies traditional for that time types and displacements of the vessels and some of them give unacceptable results in cases where weather parameters exceed set values. Based on the results of the study this article provides recommendations on the practical use of the considered formulae of wind and wave loss of speed of ships.