Trans RINA, Vol 152, Part B1, Intl J Small Craft Tech, 2010 Jan-Jun


helideck considers a number of including:


• Size, layout and marking. • Position of surrounding structures. • Aerodynamic environment.


The Helideck Certification Agency (HCA) assesses


helidecks on behalf of the MCA, and will not issue a certificate to permit operation as a commercial helideck in the event that a design does


not adhere to the


regulations. Without a certificate rotorcraft operations will not be permitted when the yacht is under charter. Such an outcome will adversely affect the owner’s investment and it will likely reduce the desirability and price of a weekly charter.


Given this, the design of a


super yacht to achieve commercial helideck operations may be stipulated by the owner as a requirement in the contract.


It is evident that one of the major risks facing the yacht designer is not achieving certification for helideck operation. One of the key aspects of achieving certification is ensuring that the influence of the superstructure on the airwake is understood at an early stage in the design. Modifications to the superstructure design late in the programme to meet airwake requirements will present significant additional costs and time delays. In the worst case scenario it may be impractical to modify the superstructure sufficiently to achieve certification.


This may result in contractual


financial penalties and/or certification of commercial helideck operation under a very limited set of benign atmospheric conditions.


Given these potential pitfalls, it is advisable for the designer to obtain an understanding of the implications of the superstructure design on airwake at the bid stage to de-risk the detailed design programme.


This will allow


modifications to be made at an early stage. In addition, a bid which demonstrates understanding of the airwake is likely to be highly attractive to the prospective buyer.


2.2


HELICOPTER LANDING AIRWAKE STANDARDS


Historically airwake have been assessed using the Civil Aviation Authority’s (CAA) CAP437 standard which provides guidance for the design of offshore helicopter landing areas [1]. The guidance covers the design of the helideck, airwake procedures.


characteristics and different factors


the sum of the wheel-to-rotor distance plus one rotor diameter plus 30ft (9.14m).


In the most recent edition of CAP437 (6th Edition 2008) there have been some notable revisions to the velocity requirement following two recent CAA research studies [2, 3]. In the previous edition (5th) two velocity criteria were stipulated, namely: a maximum mean velocity of ±0.9ms-1 at 25kt wind speed and a maximum standard deviation of the vertical velocity component of 2.4ms-1. In the current 6th edition, the mean velocity criterion has been removed following a recent study where no link was found between this


parameter and helicopter


performance or pilot workload, and the allowance for velocity fluctuations has been reduced to 1.75ms-1. The reduction in allowable velocity fluctuation recognises the possibility for reduced cueing conditions and less experienced pilots.


In 2007, the MCA updated Large Commercial Yacht Code (LY2) to include an annex (Annex 6) regarding technical standards for helicopter landing areas [4]. The LY2 code Edition 2 applies to motor or sailing vessels of 24 metres in length and over which are in commercial use for sport or pleasure with no more than 12 passengers and have a maximum gross tonnage of 3,000 tonnes. LY2 is currently considered to be the defining standard for acceptance for yachts of this kind.


Currently there is agreement between the current editions of CAP437 and LY2 with respect to airwake with the exception that LY2 does not stipulate a maximum hydrocarbon concentration in the landing zone. Table 1 summarises the airwake guidance given in CAP437 and LY2.


Velocity Requirement


Thermal Fluctuations


Hydrocarbon Concentration (CAP437)


Standard deviation of vertical velocity component


Average temperature rise over 3s period to be less than 2°C.





Table 1: Summary of maximum permitted airwake characteristics from CAP437 and LY2.


The current editions of both CAP437 and LY2 note that the certification may be supported by evidence from wind tunnel


testing and/or Computational helideck


In terms of airwake, the CAP437 standard provides guidance with regard to the permitted velocity and thermal fluctuations and maximum hydrocarbon concentration within the landing region.


The landing


region is defined as the volume of air of a basal area equal to that of the helideck and with a height equal to


Fluids


Dynamics (CFD). With specific reference to thermal fluctuations, the standards advise that an initial survey of plume behaviour is conducted using so-called Gaussian Dispersion techniques to identify where plumes may intersect the landing region. Under certain conditions thermal plumes may intersect the landing region and additional experimental testing or numerical analysis may be required to quantify the 3s averaged temperature rise.


B-22


©2010: The Royal Institution of Naval Architects


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60