Determining the leeway drift characteristics of tropical Pacific island craft

Abstract

An accurate understanding of the leeway drift characteristics of drifting objects is required to effectively forecast the drift of persons, vessels or objects lost at sea, and to generate efficient search areas to maximise the probability of successfully locating those missing. Presently, the most effective method for calculating the leeway drift characteristics of an object or vessel is to empirically derive the leeway coefficients of that object through field studies. The main goal of the studies is to measure how the object drifts in relation to the surface currents due to the wind and wave action upon it. This paper outlines the determination of downwind and crosswind leeway coefficients for three small craft common to Pacific island communities for which no accurate leeway coefficients exist. These craft were: a 19 foot (5.8m) fibreglass skiff (known locally as pangas, fibres, or banana boats); a 20 foot (5.97m) fibreglass outrigger canoe; and a 2-person sit down personal water craft (PWC). Due to the vast distances between pacific islands and the remoteness of these locations it can be several days until a search can be mounted to rescue those lost at sea, hence it is paramount that an accurate description of the drift of these tropical pacific craft is available for use in search and rescue (SAR) drift models, to define appropriate search areas. This study successfully derived the leeway coefficients required for each of these three craft. The leeway speed of the outrigger canoe and PWC, both with one person on board (POB) equivalent loading, were calculated to be 2.40% and 4.24% of the wind speed respectively. The leeway speed of the skiff was found to range between 7.71% and 4.40% of the wind speed for equivalent loading between 1 POB and 13 POB. The results of these field tests have subsequently been implemented into search and rescue models by several SAR organisations worldwide. These results show that the findings herein have the potential to both increase the likelihood of finding persons adrift at sea alive, as well as reducing search costs through more effective drift prediction and efficient search area formulation.

Designing an Automatic Beacon Ejection System for Aircraft

“…In 2014 [11] there was a study which determined the leeway drift characteristics of tropical Pacific island craft. The paper determined the downwind and crosswind coefficients for three small craft common to Pacific communities.…”

Search Path Planning Algorithm Based on the Probability of Containment Model

“…en, the POC model at time t + T is established, so as to realize the adaptive update of the POC model. Due to the update of the POC of the distress target p t C(i,j) corresponding to the search subarea g t (i,j) is not only related to itself but also related to the probability of detection of the distress target p t D(i,j) , the general updated formula of the POC matrix is shown in equation ( 9), and the updated formula of the number of particles in each search subarea is shown in equation (10).…”

“…Besides being related to the meteorological and hydrological environment, the geometric characteristics of the distress target should be considered further [9]. Brushett et al [10] carried out field tests in the accident-prone waters of the Pacific Ocean to complete the determination of the downwind and crosswind drift coefficients of three small vessels of different sizes for determining the search area. In [11], based on the information such as the debris location obtained during the search, a drift inverse model was established to predict the base position of the distress target, so as to predict the search area.…”

Search and Rescue Applications: On the Need to Improve Ocean Observing Data Systems in Offshore or Remote Locations

“…The leeway of an object does not just represent wind forcing on a drifting object. As detailed in Brushett et al (2014) and Hodgins and Hodgins (1998), the total drift of an object is the sum of the drift caused by the currents and the drift caused by leeway. However, inside both of these sources of drift are subcategories.…”

“…Many of these regions are isolated and lack observational current data for model validation. In addition, the island regime creates unique issues that are not common in mainland region cases such as the large ocean distance between population centers, crossing between islands can cover deep, exposed waters and may be done in small craft (Brushett et al, 2014). Here, we review the literature on SAR in maritime environments and examine SAR statistics in the USCG's fourteenth district to identify gaps in our current oceanographic data coverage.…”