A Performance Depowering Investigation for Wind Powered Cargo Ships Along a Route

Abstract

Abstract. For a sailing yacht, depowering is a set of strategies used to limit the sail force magnitude by intentionally moving away from the point of maximum forward driving force, potentially reducing the ship speed. The reasons for doing this includes among others; reduction of quasi-static heeling angle, structural integrity of masts and sails and crew comfort. For a wind powered cargo ship, time spent on a route is of utmost importance. This leads to the question whether there is a performance difference between different depowering strategies and if so, how large. In this research, a wind-powered cargo vessel with rigid wings is described in a Velocity Prediction Program (VPP) with four-degrees of freedom, namely surge, sway, roll and yaw, with a maximum heel angle constraint. The resulting ship speed performance for different depowering strategies are investigated and the implications in roll and pitch-moments are discussed. The wind conditions when depowering is needed are identified. A statistical analysis on the probability of occurrence of these conditions and the impact of the different depowering strategies on the required number of days for a round-trip on a Transatlantic route is performed.

A Review of Wind-Assisted Ship Propulsion for Sustainable Commercial Shipping: Latest Developments and Future Stakes

“…More recently, VPPs or performance prediction programs (PPPS) as they are more often referred to for wind-assisted ships, have been used to support the optimisation of sails [48], hulls [49] and hydrofoils [50,51], as well as maximise the performance of both wind-assisted ships [52,53] and fully wind-powered ships [54]. Similar performance optimisation strategies are employed; for instance, the established use of depowering in yachts [55] has now been applied to wind powered cargo ships [56], albeit with different constraints for the allowable heel angle, much smaller compared to yachts.…”

“…Establishing the constrains on the various degrees of freedom however remains a challenge. The most variation is seen in the critical value of the maximum heel angle, with values as low as 2° [39], recommendations for less than 4° [57], the use of 5° [56], 8° [11] and as high as 10° [58]. Guidelines for constraints applied to the performance prediction of wind-assisted ships are therefore suggested in Table 2.…”

Assessing the Impact of Membrane Deformations on Wing Sail Performance

“…Research has looked at assessing the overall performance of a wing-sailed vessel using Velocity Prediction Programs (VPPs). This has included predicting the steady state performance of a hydrofining catamaran with a wing sail (Hagemeister and Flay, 2019); investigating the control of a wing sail in order to complete successful manoeuvres of a foiling AC50 catamaran using a dynamic VPP (Hansen et al, 2019); understanding the impact of different depowering strategies for the use of wing sails on commercial ships (Olsson et al, 2020) and even coupling CFD optimisation of wing sail design with overall vessel performance (Viola et al, 2015).…”