Stabilizers are called to the bar - Naiad Dynamics for Benetti
The results of the analysis carried out by renowned USA company Naiad on the fins and interceptors foreseen for Benetti’s yacht “Spectre” which is scheduled for delivery by this coming summer.
Naiad Dynamics’s experience in stabiliser systems with active fins has few equals. The company is the result of a joint venture between Naiad Marine Systems and Maritime Dynamics, Vosper Motion Control, Vosper Stabiliser, VT Marine Products and Koop Nautic Holland. Naiad Dynamics has installed its systems into about 10,000 units of every kind: leisure craft , commercial and military ones as well.the companies research centre has carried out simulation trials for Benetti’s FB269, which is almost due for delivery July next. A series of complex trials have been carried out in compliance with Naiad Dynamics Monohull Seakeeping Program to test and foresee the yacht’s behaviour in different weather conditions at diverse speeds. In fact protocol established ship’s behaviour in wave trains moving steadily in one direction but at four different heights at three different speeds and at thirteen different angles within an arc of 180 degrees. As for the stabiliser system itself there are two possible options: the first
one consists in activating a pair of fins, the principal ones; the second entails exploiting “RCS” (Ride Control System) to its full potential by activating a further pair of fins installed in the bow area that are in fact smaller than the principal ones plus a pair of interceptors. In this mode further simulation provides data enough to gauge how much pitch and slamming effectively diminishes.
The controlling features The main fins are installed amidships to dampen roll at zero speed and underway. Their shape coefficient is equal to 0.47 for a surface area of 6,26 square metres.
The fins installed in the bow area in line with frame number 54 are deployed to dampen pitch with a shape coefficient equal to 1 for a surface area of 3.0 square metres. The interceptors are installed in the stern transom and when activated they control to what degree the stern sits back and/or heels to one side or the other, to what degree the yacht pitches and rolls.the interceptors are four metres long.
Simulation procedure This entails performing 5 separate trials for each of the following conditions: Hull with no stabilisers; Hull with principal fins only; Hull with principal fins, bow fins, and interceptor RCS (Ride Control System).
Pitch and roll The obtained results are presented as oscillatory deviations in relationship to reference point placed as “Zero”. Four graphs have been obtained for each speed and wave height selected:
1) Standard deviation of roll Without stabilisers; Only with principal fins; Total RCS.
2) Percentage of roll reduction in the same conditions expressed above
3) Excursion of pitch Without stabilisers; With RCS.
4) Percentage of pitch reduction in the same conditions expressed above; The graphs refer to roll/pitch at 16 knots with 1.1 metre high waves and 1.526 metre high waves with a cadence of 7.0 seconds. Emergence/slam are expressed in emergence/hour and slam/hour at the same speed of 16 knots with 2 metre high waves and 3,25 metre high waves with a cadence of 7.5 seconds. Finally, according to the simulation trials performed by Naiad Dynamics, the reduction of pitch in head seas was between 25 and 47 per cent accordingly; whereas roll in the worst condition examined with a wave train coming in at 75 degrees (almost broadside on edn.)was reduced between 79 and 88 per cent.
BENETTI FB 269 “SPECTRE” Designed for John Stalupi one of the shipyard’s most faithful clients who should be taking delivery of the Benetti FB 269 in July next. This yacht is the result of the most advanced technology available to large displacing units. Her hull lines have been drawn up by Dutch studio Mulder Design to deliver maximum efficiency underway within a considerable speed range while guaranteeing a remarkable range equal to 6,500 nautical miles at an econ speed of 12 knots with a top one of about 21. Among her main features: Naiad Dynamics stabiliser system which has been the object of the research work reported in this text.
TECHNICAL DATA Naval architecture: Mulder Design - Exterior design: Giorgio Maria Cassetta - Interior design: Benetti Shipyard - LOA: 69.30 m - Beam:11.70 m - LWL: 63.07 m - Beam at waterline:10.526 m - Draught at bow: 2.896 m - Draught at stern:3.034 m - Displacement: 900 t - Vertical centre of gravity: 5.00 m - Longitudinal centre of gravity: 30.125 m - GML: 147.2 m - GMT: 1.6 m - Fuel tank capacity: 120,000 litres - Water tank capacity: 18,000 litres - Engines: MTU 2 x 3.500 HP - Top speed declared: 21knots - Class: ABS Compliance LY3
Note: 13 diverse wave directions have been simulated ranging from 0 to 180 degrees at 15 degree intervals to represent the typical sea which forms in coastal waters or that is generated by a wind with little fetch by deploying Jonswap Spectrum, which derives from Pierson-moskowitz Spectrum multiplied by the ϒr. extra-peak factor.