The effect of tides and vessel parameters of fishing boat generated waves

Ship generated waves (SGW) can cause bank erosion as well as disturbance to moored boats especially in the river at estuary due to the restricted area, very high boat traffic and shallow water. In this river, the dominant environmental effect is tidal, but unfortunately in-depth investigation of this effect has not been conducted before. Tidal effect may present the critical issues that are closely related to the different water depth, as well as current speed and direction of tide flow due to the boats movement at flooding and ebbing condition of the river. The aim of this research was to determine characteristic of SGW in the river that have tidal condition, also to obtain allowable speed of fishing boat while sailing in the river. Results of a full-scale field experimental work during rising and ebbing tides in the Mersing river are presented. The displacement hull fishing boat has dimension 14.05 x 4.35 x 1 m (length x breadth x draft) and the planing hull fishing boat has dimension 6.5 x 1.46 x 0.8 m (length x breadth x draft) and both were run at 6, 9 and 12 knots. Wave heights and wave spectral energy from SGW of the two fishing boats were analysed and the energy obtained are compared to one of the accepted river criteria known as Brisbane River Criteria. The effect of assessing the SGW beside the boats at different distances from the sailing line (SL) was also studied using Computational Fluid Dynamic (CFD) simulations. The results show that higher energy was created at the shallowest water depth (h=3.6 m). As SGW is propagated from 5 m to 13 m off SL with 12 knots, the wave energy density was reduced by 1687.6 kg/s2 (38 %) for the displacement hull fishing boat and 29.75 kg/s2 (83 %) for the planing hull fishing boat. During the field experiment, it was found that the SGW has the highest energy when the boat and tide condition are in opposite directions. The findings also indicate that in order to minimize river bank damage, the displacement hull fishing boat should not exceed a limiting speed of 4.8 knots during the flooding, slack and ebbing conditions. However, for planing hull fishing boat, the allowable speed is less than 9 knots. The findings can be useful for the fishing boats operators and local authorities to regulate fishing boat traffic in rivers

Speed limit determination of fishing boats in confined water based on ship generated waves

Ship generated waves (SGW) can cause bank erosion, disturbance to moored boats and bad impact on the environment especially in confined water. One of the important vessel parameters that will affect the SGW is the speed of the boat. The speed limit determination for fishing boats in confined water will be discussed which can be used as a reference to decide the maximum boat or ship speed. The confined water of Mersing River has been chosen for the current study. This river is a busy river located in Johor in the southeast area of Peninsular Malaysia. The limited speed is needed in this river because the river is restricted to many boat activities. The typical boat particulars in Mersing River are 14.05 m in length, 4.35 m in breadth and 1 m in draft. The field experiment has been conducted with several scenarios considering the speed and tidal conditions. The results of the experiment were used to determine the maximum energy of SGW in this area. By using trendline characteristics, the formula of maximum energy was generated by considering the speed of the boat. The Brisbane River Criteria in Australian River has been selected due to the same characteristic with Mersing River. Hence, the reference for allowable energy was defined in this study. By using this river criteria, the limit of the boat speed was provided for all tidal conditions (ebbing, slack and flooding), and it was found that the allowable speed as the speed limit in the Mersing River is 5 knots. This will reduce bank erosion, disturbance to moored boats, environmental impacts and energy consumption. Moreover, the generating process of the formula can be a reference to get the speed limit at particular area as the river in other areas

Field measurement of fishing boats generated waves

Ship generated waves can cause banks erosion as well as disturbance on stationary boats. Studies have shown that the boat generated waves are dependent on and affected by environmental factors and vessel parameters. The main environmental factors are tidal and current direction, and for vessel parameters are speeds and hullforms. This paper describes a full-scale experimental work to measure wave heights and wave angle direction on boat generated waves. The measurement method used in this paper is based on the analysis of digital video recordings and image processing techniques