Propeller Wash Research Articles

Modeling Sediment Resuspension and Transport Processes Induced by Propeller Wash from Ship Traffic

Resuspension and redistribution of sediments induced by propeller wash may significantly influence aquatic ecosystems at contaminated sediment sites. This study describes a numerical modeling method developed to predict the sediment resuspension and subsequent transport processes resulting from ship traffic, with a fully coupled simulation of hydrodynamics, sediment transport, and propeller wash. By including propeller momentum effects in the flow field computation, the advection and dispersion of resuspended sediments are better represented than in previously available methods. To achieve this improvement, a computational algorithm was first developed to calculate the propeller wash effects from one or more ships (e.g., erosion rate and momentum flux); these results were then dynamically linked to a hydrodynamic and sediment transport computation using Environmental Fluid Dynamics Code Plus (EFDC+). This modeling framework was evaluated using a field experiment conducted by the US Navy. The model was calibrated with flow velocities and sediment erosion depths, and then validated with resuspended sediment concentrations in the water column. The model results reproduced the horizontal and vertical distributions of resuspended sediments better when the propeller-induced momentum was incorporated into the flow field computation. The sensitivity test indicated that the increased flow energy from propeller momentum resulted in significant dispersion of resuspended sediments in both longitudinal and lateral directions. The maximum scour was dependent on the propeller revolution speed, the ship engine power, and the distance between the propellers and the sediment bed.

Autonomous Flight Test of a Novel Nonconventional Biplane Micro Air Vehicle

This paper presents detailed mathematical modeling, controller design, and flight test results for the autonomous mission of a nonconventional fixed-wing biplane micro air vehicle (MAV) called Skylark having span and chord length within 150 mm. Although numerous fixed-wing MAV designs are reported in the open literature, an MAV’s reliable autonomous flight is still a challenge. The primary difficulties in performing the autonomous mission of fixed-wing MAV are system integration within the weight and power budget, center of gravity (CG) management, and flight controller design for fast dynamics. In this paper, the key challenges are addressed by using the higher payload capacity of Skylark, suitable selection and design of avionics components, and design of controller after detailed development of the mathematical model, including the additional effect of propeller wash and motor countertorque. An autonomous flight test is successfully demonstrated after the validation of algorithms and software architecture through nonlinear six-degrees-of-freedom simulation. The detailed design and development approach will increase the MAV’s performance and reliability in civil and military applications.

Slow sink rate in floated-demersal longline and implications for seabird bycatch risk.

Bycatch of birds in longline fisheries is a global conservation issue, with between 160,000-320,000 seabirds killed each year, primarily through being caught and drowned as they attempt to snatch baits off hooks as they are set. This conservation issue has received significant recognition in southern hemisphere longline fisheries over the past several decades, largely due to the impact on highly charismatic and highly threatened birds, notably Albatrosses. As a result, the use of effective mitigation measures has been subject to fisheries regulations to reduce seabird bycatch from longliners in a number of national jurisdictions and in several Regional Fisheries Management Organisations (RMFOs). While mitigation measures have been mandated in a number of north Pacific longline fisheries, this is largely not the case in north Atlantic longline fisheries. This includes vessels using floated-demersal longlines in the North-East Atlantic longline fishery targeting European Hake Merluccius merluccius, in which high levels of seabird bycatch are estimated. In this paper, we analysed the sinking speed of a floated-demersal longline used to target European Hake in the offshore waters of Scotland, to determine potential bycatch risks to seabirds. We deployed Time Depth Recorder devices at different points of the gear. We assessed how this gear performed in comparison to the best practice minimum sink rate of 0.3 m/s recommended by the Agreement on the Conservation of Albatrosses and Petrels (ACAP) to limit bird access to baited hooks. We found that the average sinking speed of the floated-demersal longline was substantially slower than the ACAP recommendation, between two and nine times slower in non-weighted parts of the gear down to 10m water depth. Our work also found that the sink rate is particularly slow in the top 2m of the water column, increasing with depth and stabilizing at depths over 10m, presumably a consequence of propeller wash behind the vessel. We calculated that the distance astern of the vessel for hooks to sink beyond susceptible seabirds' reach largely exceeds optimum coverage of best practice design Bird Scaring Lines (100 m). Our results indicate that hooks from floated-demersal longlines are therefore readily open to seabird attacks, and as a result, present a clear bycatch risk. Research is needed to adapt existing mitigation measures to floated-longlines and to develop novel mitigation approaches to improve the sink rate of the gear without impacting target fish catch.

Sediment Remediation Using Activated Carbon: Effects of Sorbent Particle Size and Resuspension on Sequestration of Metals and Organic Contaminants.

Thin‐layer capping using activated carbon has been described as a cost‐effective in situ sediment remediation method for organic contaminants. We compared the capping efficiency of powdered activated carbon (PAC) against granular activated carbon (GAC) using contaminated sediment from Oskarshamn harbor, Sweden. The effects of resuspension on contaminant retention and cap integrity were also studied. Intact sediment cores were collected from the outer harbor and brought to the laboratory. Three thin‐layer caps, consisting of PAC or GAC mixed with clay or clay only, were added to the sediment surface. Resuspension was created using a motor‐driven paddle to simulate propeller wash from ship traffic. Passive samplers were placed in the sediment and in the water column to measure the sediment‐to‐water release of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and metals. Our results show that a thin‐layer cap with PAC reduced sediment‐to‐water fluxes of PCBs by 57% under static conditions and 91% under resuspension. Thin‐layer capping with GAC was less effective than PAC but reduced fluxes of high–molecular weight PAHs. Thin‐layer capping with activated carbon was less effective at retaining metals, except for Cd, the release of which was significantly reduced by PAC. Resuspension generally decreased water concentrations of dissolved cationic metals, perhaps because of sorption to suspended sediment particles. Sediment resuspension in treatments without capping increased fluxes of PCBs with log octanol–water partitioning coefficient (K OW) > 7 and PAHs with log K OW of 5–6, but resuspension reduced PCB and PAH fluxes through the PAC thin‐layer cap. Overall, PAC performed better than GAC, but adverse effects on the benthic community and transport of PAC to nontarget areas are drawbacks that favor the use of GAC. Environ Toxicol Chem 2022;41:1096–1110. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Assessing the Risk of Contaminant Dispersion From Fibrous Sediments of Industrial Origin

Unregulated discharges of wastewater from pulp and paper factories resulted in the formation of relatively thick organic (cellulose) rich sediments in shallow waters along the Swedish coast. These deposits are known as fiberbanks and are contaminated by persistent organic pollutants (POPs), metals and methylmercury, which can be dispersed by diffusion and advective processes coupled to propeller wash, high river discharges, strong wind waves and submarine landslides. Based on a case study of polychlorinated biphenyls (PCBs), one group of prevalent POPs in the fiberbanks, we present a probabilistic approach to estimate the potential risk of dispersion of fiberbank contaminants. The approach allows for estimation of the dispersal pathways that dominates the risk within a given time and provides more insight about the significance of various dispersion processes. We show that it is highly likely that chemical diffusion and advection triggered by ship-induced resuspension will disperse PCBs (sum of seven congeners; Σ7PCB) above a threshold level for environmental impact, while the likelihood of river and wind-wave generated resuspension dispersion pathways are lower (∼20%, respectively). We further show that there is approximately 5% likelihood that a submarine landslide will disperse Σ7PCB above the threshold level. The study implies that the governing parameters for risk assessment specifically should include reliable data on contaminant concentration, water depth above the fiberbank, estimation of concerned fiberbank areas, time duration of erosive fluid flows and measured diffusion. The approach provides insight into the importance of various dispersion processes. We suggest that it can be applied to support risk assessment, especially when there are limited available data and/or knowledge about the system under study.

Nonlinear Flight Dynamics and Control of a Fixed-Wing Micro Air Vehicle: Numerical, System Identification and Experimental Investigations

The flight dynamics of Micro Air Vehicles (MAVs) exhibit significant nonlinear characteristics, which cannot be ignored in simulation or analysis. In this study, a full nonlinear simulation of the flight dynamics characteristics of a fixed-wing MAV is performed. To strengthen the developed nonlinear mathematical modeling, the MAV’s mass properties and propulsion characteristics are experimentally investigated. Moreover, the aerodynamic characteristics of the designed fixed-wing MAV are experimentally measured in a wind tunnel. The experimental aerodynamics investigation includes the propeller wash effect and the same flight conditions of the MAV. These measured data are fed to the nonlinear flight dynamics model to improve its accuracy and ensure the nonlinear aerodynamics effect on the flight dynamics. The enhanced model is then validated against response experimental measurements of the MAV in the wind tunnel that is free to pitch at different control inputs and initial conditions. Furthermore, it is compared to the response of the system identification model. The nonlinear simulation and dynamic testing investigations indicate many nonlinear phenomena, such as the appearance of the limit cycle in the longitudinal flight. This paper shows that the aerodynamic center of MAV with a low aspect ratio in the low Reynolds number regime of flow can move as a response to flap deflection. The validated nonlinear mathematical model was used to evaluate the MAV’s dynamics, design and evaluate a PID controller in flight conditions similar to the MAV’s actual flying mission. Moreover, the presented model can be used for flapping-wing MAVs using time-dependent experimental measurements.

Assessing iMET-XQ Performance and Optimal Placement on a Small Off-the-Shelf, Rotary-Wing UAV, as a Function of Atmospheric Conditions

The accuracy and precision of iMET-XQ (InterMET Inc., Grand Rapids, MI, USA) temperature measurements in ten different locations on an off-the shelf rotary-wing unmanned aerial vehicle (rw-UAV) were assessed, as a function of atmospheric conditions. The rw-UAV hovered near an instrumented South Alabama Mesonet tower. The mean ± standard deviation of all the temperature differences between the tower and the ten iMET-XQ sensors for all experiments are −0.23 °C ±0.24 °C. Both the UAV and the environment influence the accuracy and precision of the iMET-XQ temperature measurements. Heat generated by the electronic components within the UAV body has a significant influence on the iMET-XQ temperature measurements, regardless of solar radiation conditions, and is highly dependent on wind direction. Electronic components within the UAV body heat up and can cause sensors downwind from the UAV body to record temperatures that are too warm, even if the sensors are aspirated by propeller wash. iMET-XQ sensors placed on rotor arms not near UAV body heat sources, and properly aspirated by propeller wash, perform well. Measurements from iMET-XQ sensors suspended below the UAV are also accurate. When using an off-the-shelf UAV for atmospheric temperature sensing, the electronic components inside the body of the UAV must be properly located. It is recommended that multiple sensors are placed on the UAV. Sensor redundancy will mitigate data loss in case of malfunction during flight and the identification of poorly performing sensors.

Evaluating Temperature Measurements of the iMET-XQ, in the Field, under Varying Atmospheric Conditions

Temperature measurements of InterMET Inc. aluminum-coated iMET-XQ sensors were tested in an outdoor setting under a variety of solar radiation and wind speed conditions. Twelve unshielded sensors were mounted side-by-side on the tower of a South Alabama Mesonet weather station next to a reference sensor on the tower. The iMET-XQ temperatures were most precise and accurate in solar radiation values that were close to zero, regardless of wind speed. Under overcast conditions, wind speeds of 2 m s−1 were sufficient to obtain precise and accurate temperature measurements. During the day-time, aspiration of wind speeds higher than or equal to 3 m s−1 is sufficient. An iMET-XQ was placed in a radiation shield next to the tower reference sensor to test the need for a radiation shield. A second iMET-XQ was placed unshielded on the tower. The iMET-XQ sensors with aluminum coating do not need to be shielded, but they do need to be aspirated. It is recommended that, when taking temperature measurements using unmanned aerial vehicles (UAV) with iMET-XQ sensors, the UAV either fly at 3 m s−1, be embedded in winds of those speeds, or to use the propeller wash of the UAV to aspirate the sensors.

Design, experimental investigation, and nonlinear flight dynamics with atmospheric disturbances of a fixed-wing micro air vehicle

In this paper, the design process of a fixed-wing Micro Air Vehicle (MAV) is presented. The design cycle begins with mission requirements, followed by collecting statistical data from available MAVs. Next, MAV's sizing and weight estimation are conducted based on mission requirements. Finally, the aspect ratio, taper ratio, and airfoil selection are performed. As the MAV has a low aspect ratio and low Reynolds number airflow, the aerodynamics is not fully understood. The propeller wash increases the complexity of the aerodynamic flow; therefore, the MAV is manufactured for wind tunnel testing. The absent of actual flight performance and flight dynamics of fixed-wing MAVs are the main driven factors for this research. The wind tunnel experimental data are used in the flight performance equations to evaluate the MAV's actual flight performance and compare it with the estimated values. As MAV is very sensitive to the external disturbances which make the prediction of its dynamics a hard task, a nonlinear flight simulation model is created for the MAV's dynamics prediction. This model uses the experimentally measured data to predict the MAV's dynamics and its stability against wind disturbances. The results in this paper indicate that using aerodynamics historical data will give a huge error in estimating MAV's flight performance. The measured data in this research can be used to eliminate this error. Also, the flight dynamics of fixed-wing MAVs cannot be assumed linear, and the technique used in this paper gives a very accurate flight dynamics estimation.

Determining propeller scour near a quay wall

In recent years, seabed scouring caused by propeller jet flow impact, its resulting structural and environmental effects, and the increase in the use of powerful engines with the introduction of new types of ships with large-sized bows and main thrusters have become major issues. Consequently, there is a need for an accurate method to investigate scour formations and a protection method near berth structures caused by the propeller jet flow of a ship. The objective of this study was to examine the local scour caused by propeller wash in front of a quay wall as a closed-type berth structure. In the equilibrium (final) state, the maximum scour depth at the toe of the quay wall, as one of the primary dimensions of the scour, was investigated under different propeller gaps, propeller speeds, and distances from the propeller face. In addition, the time-dependent variation of the scour profiles was examined, and a new empirical equation was proposed for the determination of the scour depth at the toe of a quay wall.

PHYSICAL MODELLING OF PROPELLER SCOUR ON AN ARMOURED SLOPE

CITIC Pacific Mining (CPM) is proposing to increase throughput at their existing Sino Iron Terminal in Cape Preston, Western Australia, using self-propelled Handysize transshipment shuttle vessels (TSV) instead of dumb barges. Initial assessment using various desktop methods (PIANC, 2015) indicated that the armoured rock slope adjacent to the berth face would incur damage due to wash from the vessel side thrusters and the main propeller. Large scale (13.5:1) physical model tests were undertaken in a 6 m x 15 m x 1.4 m deep basin at UNSW to measure wash velocity and armour stability. The physical modelling demonstrated that the rock slope was more stable than expected, but that some armour was mobilized. Additional tests were also completed to investigate the efficacy of Articulated Concrete Block Mattresses (ACMs) to protect the rock slope from propeller wash.

Considerations for temperature sensor placement on rotary-wing unmanned aircraft systems

Abstract. Integrating sensors with a rotary-wing unmanned aircraft system (rwUAS) can introduce several sources of biases and uncertainties if not properly accounted for. To maximize the potential for rwUAS to provide reliable observations, it is imperative to have an understanding of their strengths and limitations under varying environmental conditions. This study focuses on the quality of measurements relative to sensor locations on board rwUAS. Typically, thermistors require aspiration and proper siting free of heat sources to make representative measurements of the atmosphere. In an effort to characterize ideal locations for sensor placement, a series of experiments were conducted in the homogeneous environment of an indoor chamber with a pedestal-mounted rwUAS. A suite of thermistors along with a wind probe were mounted inside of a solar shield, which was affixed to a linear actuator arm. The actuator arm was configured such that the sensors within the solar shield would travel underneath the platform into and out of the propeller wash. The actuator arm was displaced horizontally underneath the platform while the motors were throttled to 50 %, yielding a time series of temperature and wind speed that could be compared to temperatures being collected in the ambient environment. Results indicate that temperatures may be biased in the order of 0.5–1.0 ∘C and vary appreciably without aspiration, sensors placed close to the tips of the rotors may experience biases due to frictional and compressional heating as a result of turbulent fluctuations, and sensors in proximity to motors may experience biases approaching 1 ∘C. From these trials, it has been determined that sensor placement underneath a propeller on an rwUAS a distance of one quarter the length of the propeller from the tip is most likely to be minimally impacted from influences of turbulence and motor, compressional, and frictional heating while still maintaining adequate airflow. When opting to use rotor wash as a means for sensor aspiration, the user must be cognizant of these potential sources of platform-induced heating when determining sensor location.

Effect Method Evaluation of Forecasting Scour by Propeller in Harbours

The scour induced by a propeller wash is experimentally in uniform and non-uniform sand. A series of laboratory experiment with different experimental parameters was conducted in the current research. Moreover, the characteristics of scour hole were studied and compared including depth, length, and width between uniformly and non-uniformly distributed sand. Equations of predicting maximum scour depth, proposed by previous researchers, were evaluated using the current experimental data. Results revealed that there is a need to improve the study in propeller-induced seabed scour in non-uniform sand.

Experimental study on scouring of coarse sand and fine sand seabed caused by propeller washing in front of solid wharf

This paper presents the results of continuous scouring and intermittent scouring tests on two kinds of seabed soils (d50=0.7mm coarse sand and d50=0.162mm fine sand) induced by propeller washing at the front of the solid wharf. Three propellers with diameters of 70 mm, 130 mm and 150 mm were used for the test. The test results show that under the same test conditions, the maximum scouring depth of the coarse sand seabed is 8.2% to 58% deeper than that of the fine sand seabed under continuous test or intermittent scouring; compared with continuous scouring, intermittent scouring The maximum scouring depth increase caused by the coarse sand seabed is 2% to 4.8%, while it is increased to 5.1% to 37% for the fine sand seabed. The prediction formula of the maximum equilibrium scouring depth on the fine sand seabed caused by the front edge of the solid wharf during the intermittent washing of the propeller is established. This formula is a dimensionless formula, which can be applied to the intermittent scouring of the actual propeller wash.

Roto-Stabilizer for Superb Pitch-Related Post-Stall Maneuvers and STOL

Stabilizers and their control surfaces are vital components in maneuvering an airplane during flight. However, a shortcoming of stabilizers is that they require airstream or propeller wash for them to work properly. In this work, we propose the concept of roto-stabilizer as viable substitution for conventional horizontal stabilizer. A key benefit of the proposed technique is its ability to exert powerful moment in the absence of forward airspeed or propeller wash. Proof of principle is demonstrated via computer simulations. Results reveal that new aerobatic maneuvers are made possible. Furthermore, when implemented in canard configuration, it is possible to achieve ultra-STOL and VTOL.

Oil Droplet Surfacing Probabilities Under Realistic Low Turbulence in Arctic Ice

ABSTRACT 2017-081 Responders need to choose among oil spill response options to combat spills in ice covered waters as effectively as possible. A decision to apply dispersants in remote ice covered waters requires an estimation of whether or not the oil will initially disperse and then remain dispersed. A concern is that an effectively dispersed plume of oil will not remain dispersed under ice because the mixing energy required is insufficient. We are advancing the predictive capability to determine whether small oil droplets will rise in the calmer, more stable conditions that can occur in ice covered waters. The results will be presented as lookup tables that can be used to assess whether or not oil has been successfully dispersed in ice covered waters. Ice covered waters can have very low vertical turbulence (mixing) energy, so smaller droplets may rise to the surface in ice covered waters than in open water at lower latitudes. Laboratory studies with oil droplets and field experiments to measure the turbulence directly under ice are being used to provide input and validation data to numerically simulate an oil spill in ice. We assumed that oil slicks were effectively dispersed to form plumes in the water column. Dispersion was assumed to be from natural mixing energy or forced by applying the propeller wash from vessels. The numerical simulations will be performed to determine if these dispersed plumes could significantly resurface. The International Oil and Gas Producers (IOGP) funded the Joint Industry Project (JIP) “Fate of Dispersed Oil Under Ice”. Sintef led two field campaigns (2015 and 2016) with fast ice (ice attached to land) in Van Miljenfjorden in Svalbard. These data for realistic water currents and mixing energy (turbulence) were used in model development. In the second field experiment, dye was released and followed under the ice in order to measure dilution of the dye, as a check on our model. Neap tide periods were targeted in order to look at low mixing energy conditions. At the Plymouth University mesoscale laboratory, studies in a 30 m flume allowed oil droplets of known size to be released in water flowing under synthetic ice under controlled water velocity and under ice roughness conditions. In addition, an analytical model is being developed to estimate the magnitude and dissipation rate of prop wash turbulence. This was necessary to give the time zero basis for estimating how quickly droplets produced by prop wash would rise to the surface. Size classes of oil droplets that do not rise in low vertical turbulence will certainly not rise in higher turbulence. This will allow future research to target larger oil droplet size classes in the Marginal Ice Zone (MIZ). This project was led by SINTEF (Norway) with participation by McPhee Research (USA), University of Plymouth (UK), and Ben Gurion University (Israel).

Effectiveness of chemical dispersants used in broken ice conditions

ABSTRACT (no. 2017-095) In 2012, the International Association of Oil and Gas Producers initiated “The Arctic Oil Spill Response Technology Joint Industry Program (JIP)” with nine companies funding projects in a wide range of technical areas. This paper summarizes results from the project “Dispersant Testing under Realistic Conditions”, a collaboration between SINTEF (Norway) and SL Ross (Canada). The objective of the research was to build on current knowledge to increase understanding of the effect of oil type, degree of weathering, and environmental conditions on dispersant effectiveness in ice-covered waters. SINTEF and SL Ross performed approximately 70 tests using two identical recirculating flumes with variable parameters such as oil types, dispersant type, mixing energy, ice coverage, and water salinity. The oils were weathered in the flumes for 6 or 18 hours under simulated winds, waves, and cold temperatures to represent weathering that might occur at sea prior to dispersant application. The dispersed oil was exposed to various mixing energies, starting with low energy waves, followed by somewhat higher energy waves, and finally by applying propeller wash. Four crude oils were studied and the dispersant efficiency of three commercial oil spill dispersants were evaluated for the tested oils. Other test parameters were ice coverage (50% and 80%) and water salinity (35, 15, and 5 ppt). Dispersant effectiveness as a function of the different test variables were estimated using results from the flume-based experiments. As expected, shorter weathering times resulted in an increase in dispersant efficiency. The dispersant effectiveness varied with both oil type and dispersant type applied, and the effectiveness increased when higher mixing energy conditions were used. Varying the ice cover did not influence the results significantly, but water salinity did, with the lowest dispersant efficiencies found at 5 ppt salinity. The conclusions are based on the findings from testing performed under the controlled conditions and may not be directly transferable to all conditions that could be encountered in the Arctic. However, this study shows that dispersants can be considered as a response option for spills in ice, but effectiveness needs to be validated in the field during an actual event.

Two devices for mitigating odontocete bycatch and depredation at the hook in tropical pelagic longline fisheries

AbstractOdontocete bycatch on and depredation from tropical pelagic longlines is globally widespread, having negative impacts on the economic viability of affected fisheries and on the conservation of affected odontocete populations. Reports by fishers that depredating odontocetes avoid gear tangles has underpinned the development of simulated structures to physically deter depredating odontocetes. This study assessed the efficacy of two such devices developed to mitigate odontocete depredation and associated bycatch. Of particular interest was their impact on (i) soak depth and (ii) sink rate using truncated trials, before determining their impact under full operational conditions on rates of (iii) catch of the five most economically important fish, and (iv) odontocete depredation and bycatch, on changes in (v) fish survival and size, and (vi) setting and hauling speed. The results indicated that the inclusion of devices on longlines had negligible impact on soak depth, thus were unlikely to impact on the suite of fish specifically targeted and caught. The sink rate was slowed, perhaps by drag, trapped air, or propeller wash, although the addition of weight might remedy this if the devices were to be used in areas where seabird bycatch could occur. Most importantly, trials conducted in Australian and in Fijian waters indicated that pooled fish catch rates (i.e. albacore, yellowfin, bigeye, mahi mahi, and wahoo) increased in the presence of the devices, possibly because more fish were attracted by them or because more depredators were deterred. Catch rates on control gear next to gear with devices attached were higher than more distant control gear, suggesting the influences of the devices may have extended to adjacent branchlines. The size of caught fish was mostly unaffected, although the survival of yellowfin and bigeye increased significantly in the presence of the devices. Hauling was slowed by the use of the devices and the need for an extra crewmember during setting and hauling, which could be cost prohibitive in some fisheries, especially if economic benefits from their use are not obvious. Despite the small sample size, odontocete bycatch only occurred on unprotected fishing gear and all individuals were released alive, although their fate was uncertain; there was evidence of injuries sustained from the event. The outcomes are positive and should motivate stakeholders to view such devices as a potentially effective tool for mitigating odontocete bycatch and depredation in this and similar longline fisheries. Future efforts should focus on improving operational integration and reducing implementation costs to encourage voluntary uptake and thus avoid non-compliance and the need for costly monitoring. The use of this technology could bring about marked improvements to the conservation situation for affected odontocete populations and to the economic situation for affected longline fisheries.

In situ measurement of sediment resuspension caused by propeller wash with an underwater particle image velocimetry and an acoustic doppler velocimeter

Flow induced by propellers of waterborne vessels can cause sediment resuspension in estuaries, bays and harbors, where sediments are usually contaminated. Bottom shear stress due to propeller wash is the key parameter that determines the initiation of sediment resuspension and the subsequent erosion. A novel self-contained underwater miniature particle image velocimetry (UWMPIV) system has been developed and deployed to study sediment resuspension under propeller wash in a US Navy harbor in San Diego, CA. Near bed profiles of mean velocity and Reynolds stresses were measured to evaluate the bottom shear stress, and to validate the shear stress measured with an acoustic Doppler velocimeter (ADV) that is simultaneously deployed with the PIV system. The critical shear stress was estimated by directly observing PIV images and identifying the moment when sediment resuspension started. PIV measurement became unfeasible as the propeller speed increased and the optical access was blocked by high level of suspended solids. However, the development of the bed erosion was able to be recorded in PIV images at several intervals when sediment concentration was relatively low and the sediment bed was visible. The observed time series of cumulative erosion depth agreed well with an erosion rate model that depends linearly on the bottom shear stress excess.

Seabed Condition from Single Beam Echo Sounder from Penang Port, Malaysia

Ship’s propeller wash induced scour is a well-known engineering problem for port structures along the shoreline. However, insufficient recorded data makes it difficult to justify that ship’s propeller wash induced scour is taking place in Malaysia’s major ports. This study reported the seabed condition of the two wharves in Penang Port using Single Beam Echo Sounder (SBES) data. The presence of seabed scour due to ship manoeuvring is investigated based on seabed data. The results showed that Penang Port is experiencing a severe siltation problem instead of ship’s propeller wash induced scour impacts.