driven hull, to a maxium of 33tonnes for the UNEW-DVC waterjet-driven hull. Subsequently, the design candidates


opted for the propeller-driven UNEW-DVC hullform, in order to save power and because this propulsive methodology would best serve the vessel’s target service and top speeds, as well as ensuring a bollard pull rating of 3tonnes. A pair of 0.8m diameter, five-bladed fixed pitch propellers was deemed the best choice for the vessel.


ASB development Te next step was to optimise the hull lines, to improve the calm water performance of the hullform as well as the performance in waves. Serner’s anti-slamming bow principle was combined with a novel and optimised, MAST-pioneered bulb form, titled an ‘anti-slamming bulb’ (ASB), which was intended to not only reduce bow waves and dynamic trim but to also provide the hullform with increased damping in the vertical plane, subsequently improving the vessel’s vertical motions and accelerations in waves. While the PLA vessels had been operating


in sheltered waters, the new research vessel would not have this luxury and the ASB was deemed to go some way in addressing concerns regarding liſting activities in open waters. Although the main hull was to be constructed from aluminium, it was decided that the ASB bow section would be built from a composite. Te aſter-body part of the replacement


research vessel had to be prammed by a cut-up angle of 14degs, to accommodate the propellers and stern gear to prevent their extension below the keel line. It was then decided to introduce a shallow tunnel (or propeller pocket) to enable the fitting of a relatively large diameter propeller with reduced tip losses and reduced shaſt inclination. Such a shallow tunnel would also help to smooth the sharp wake peak at the bottom of the V-shape hull in the propeller plane, as well as provide more flexibility for relaxed tip clearances. Te selection process for the best aſter body configuration was conducted using potential and RANS-based viscous solvers to compare their efficiencies in terms of resistance, wave making, form factors and wake flow characteristics, until the team could decide on the after body section that created the least form drag, least stern wave height and least vertical motion


Ship & Boat International May/June 2013


at the tunnel exit, as well as well-ordered streamlines at the buttock of each demi-hull. Te main appendages of the vessel were


specified as conventional rudders, I-shaſts, bow thruster openings and initially a partial central box keel in front of the hull rising at the aſt to support the hull for beaching and drydocking purposes, as successfully demonstrated by the PLA boats. However, this latter appendage was converted to a skeg by extending it all the way from the rising point to the rudder stock to provide more protection to the propeller and stern gear from possible grounding and tanging with nets, and so on, as requested by the skipper of the vessel.


Heave and pitch Te above water hullform was dictated by the maximum air draught, which imposed a height limit to the wheelhouse on the main deck. A reasonable wet deck clearance was allowed so as to avoid frequent wet deck slamming, as production costs ruled out the introduction of a deadrise or jaw to the wet deck to lessen the impact of such slamming. A shelter area was also introduced at the starboard side of the vessel, to enable the staff and students to work in safe and dry zones. Based on the preliminary weight


estimation and distribution, the natural heave and pitch period of the vessel were recorded at around 7seconds for heave and 3seconds for pitch at zero speed. Te results of strip theory- based seekeeping analyses indicated that the vessel would be operable in conditions of up to sea state 4, whilst maintaining her 15knots service speed. Te vessel’s twin rudders, each with a minimum liſting area of 0.04 long tonnes, were maintained to keep the vessel directionally stable with a projected area of 0.96m² and aspect ratio of 1.2.


Tank testing With these decisions made, two sets of separate but complementary model tests were conducted to validate and verify the designed hullform. Tese tests were made in different towing tanks and with different sizes of model; a


3.5m model in the


160m-long Ata Nutku Towing Tank housed at Istanbul Technical University (ITU), and a 1.5m model in a 40m-long towing tank at UNEW. Te model tests at ITU included calm water resistance tests, paint tests for the bare hull and appended hull in fully


loaded / ballast conditions, a wake survey and self-propulsion tests with five-bladed stock propellers. Tese were complemented by further flow observations around the bow and aſter-body of the vessel using tuſts in the ITU Circulation Channel facility. Meanwhile, experiments at the UNEW


towing tank, commonly used by third year undergraduates, involved bare hull calm water resistance tests and seakeeping tests for a wide range of wave frequencies in head and following at zero speed and service speed for the latter. Separate wind tunnel tests were also conducted with a specially constructed wooden above water model, to predict the wind resistance characteristics of the above water hullform with two different wheelhouse structures in the UNEW combined wind, wave and current tank facility. The large model tests confirmed an


efficient calm water performance of the designed hullform except for a slight spray observed from the upper foremost point of the bulbous bow at the corresponding full speed of 17knots and above. However, this was eliminated by transforming the bulb cross section to an oval shape, with a slight elongation of the bulb. Te flow streamlines around the ASB and stern were recorded as favourable and without concern. Meanwhile, the smaller model tests


conducted at UNEW, with the original bulb, presented comparable resistance curves to the ITU tank test results, while the form factor analysis with the smalle model indicated a value of (1+k)=1.5. Comparison of the model test-based resistance curves with the CFD predictions for three different separations validated the CFD predictions and indicated that the lowest resistance occurred with the largest hull separation. Aſter testing was completed, the tender for


Princess Royal was scooped by Alnmaritec, which, alongside its subcontractor BMT-Nigel Gee, commenced the building process in April 2010. First preliminary sea trials were conducted in September 2011, when she achieved speeds in excess of 20knots in her light condition. Te vessel features a wide array of marine scientific equipment, as well as a 1.5m x 1.5m moon pool, facilitating ROV deployment; a series of pot and net haulers; a wave radar; and two propeller observation windows per demi-hull. SBI


23


In-depth


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