The Importance of Hydrodynamics in Ocean Research Vessels Ewan Baird Ria Bruenig Cameron Dinsdale James Duthie
To show how Marine Hydrodynamics can be applied to improve the performance of Ocean Research Vessels.
Performance of Equipment
Underwater Radiated Noise
Kongsberg Maritime , Aberdeen
David Shand – UK General Offshore Manager
National Oceanography Centre , Southampton
Edward Cooper - NERC Project Officer
Irish Marine Institute , Galway
Aodhán Fitzgerald - Research Vessel Operations
Echomaster Marine , Buckie, Aberdeenshire
Graeme Smith – Service & IT Manager
Bottom Animal Behaviour
Oil and Gas Exploration
Most people operate ships for commercial gain and therefore earn monies to pay for fuel, etc.
Fuel usage reflected in operating cost.
Design for minimal drag while giving a sea-kindly platform with adequate room and hull shapes to incorporate research-specific requirements, eg: drop keels, moon pools, etc
Research organisations have little earning capacity so increased fuel bills result in less days for science.
An efficient hull is needed for low running costs
Green – wave from hull Blue – wave from bulb Red – Resultant wave
Introduction of bulb reduces hull drag, improves fuel economy and range
Bulbous Bow relates to Boundary Layer position and thickness
An Un-hydrodynamic hull in turn leads to increased fuel usage again, and increased wear and tear on steering gear.
Towed specialist equipment requires high directional stability to obtain accurate data
Vessel control for straight course tracking with ease and without repeated correction.
Directional stability needed for straight course tracking for sampling acoustic data
Performance of equipment
Acoustic Instrumentation A poor hydrodynamic hull or one with appendages will result in under-hull aeration. These air bubbles can be microscopic, but they can also be sheet-like. For acoustics, they blank out the transducers from the ocean, either when transmitting, receiving or both. Hence no data, or poor data.
Water Sampling For water sampling, the air gets included within the pumped water sample which, when analysed by the on-board Chemist, masks or degrades the analysis, in some cases to the extent that the technique can not be used. Also, if there is too much air, the pumps can fail; sometimes catastrophically.
Underwater Radiated Noise
Modern science vessels tend to strive for a low acoustic presence in the water.
In oceanography: to get the best from the acoustic instrumentation.
In fisheries studies: to not scare away the fish and, therefore, get a more accurate population count.
Diesel Electric Propulsion installed to reduce noise levels and vibration.
Silent Mode of operation reduces the amount of power applied to propeller and reduce the onset of cavitation
Deck wetness – research ships tend to have a low freeboard on the working deck; best kept dry.
Scientists often experience motion sickness, leading to loss of valuable time.
A directionally-unstable vessel will roll heavily due to the rudder corrections and, in rough sea conditions, will possibly force water onto the deck.
Location of hull mounted equipment is critical, as is the reduction of pitching effects on equipment.
The ability to easily remove and repair hull-mounted equipment is a key requirement, i.e.: drop keels are extremely useful as equipment can be retracted from the water for repair/replacement.
Using gondolas, or other after-launch techniques, have a measurable impact in terms of vessel drag.
Acoustic equipment should not be placed near the turbulent flow
Laminar flow is acceptable
Below the any type of flow is recommended
Equipment is mounted in the vessel such that, when required, it can be lowered down away from the vessel. This keep it clear of the vessel noise that results from machinery vibration and turbulent flow from the hull. Specialist Equipment
Choice of propeller is critical for noise reduction but a trade will be made for efficiency and speed
Place transducers on particular side of vessel to keep clear of propeller noise
Drop keels are used to move equipment away from noise
The effect of hull shape and propeller noise on the operation of underwater hull-mounted equipment is perhaps the most critical aspect of hydrodynamics in relation to ocean research vessels.
Any outlet pipe of irregular shape on the hull will make noise giving inaccurate results.
Bow design can have a big impact on the creation of bubble sweep down effect, which can severely affect multibeams and other equipment.