Trans RINA, Vol 157, Part A3, Intl J Maritime Eng, Jul-Sep 2015
Table 1: Main parameters of different catamaran designs. Weight is relative to 130 m base line model. L Boa
L/d
[m] [m] 110 130 150 170 190
32 intensively
LIGHT 10.5 11.5 12.7 13.8 14.9
studied using 1/3 h
MEDIUM 9.8
10.8 11.9 13.0 14.1
HEAVY 9.2 9.9
11.2 12.2 13.2
both computational and
experimental approaches; principal examples include: [5], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16] and [17]. The outcomes can be summarised that increases in demihull slenderness and demihull separation both lead to a reduction in the total resistance of a vessel around hump speed,
although only few [2], [9], [10], [14]
investigated very slender hulls with slenderness ratios exceeding 10. Mostly demihull separation ratios of s/L > 0.2 were investigated, with some studies [11], [15], [17], [18] indicating there is a low sensitivity of drag force to changing demihull separation around hump speed for demihulls in very close proximity (s/L < 0.2).
In an earlier study [19] the authors showed that systematic hull form series data can be utilised to investigate hull form alterations for large medium-speed catamarans in terms of changing slenderness and demihull separation. Large gains in transport efficiency were achieved when compared to current high-speed catamarans. However, for the targeted speeds
of
approximately 30 knots, resistance data of sufficiently slender catamarans was unavailable to fully investigate the design space for an
energy-efficient design.
Therefore, this research aimed to provide resistance data for large catamarans with slender demihulls operating around hump speed to fully explore the design space.
L/1/3< 15 and the demihull separation from 0.135 < s/L < 2.33. Whilst he authors have previously shown that this tool is capable of correctly predicting the resistance of catamarans at medium speed [20], further validation was conducted. A base model was validated at model-scale using existing model test results and empirical ship- model correlation lines.
This paper investigated the resistance properties of large medium-speed catamarans using slender demihulls at a relatively low separation to meet
the zeitgeist of A-162
In the current study five different catamaran hulls of L = 110, 130, 150, 170, and 190 m were investigated for three different displacements at Froude numbers from 0.25 < Fr < 0.49 using computational fluid dynamics (CFD) at full-scale Reynolds numbers ranging from 8.9 < log(Re) < 9.6. The slenderness ratio was varied from 9 <
s/L [-]
0.233 0.197 0.171 0.151 0.135
LIGHT 0.85 1.00 1.07 1.06 0.96
relative deadweight MEDIUM
1.52 1.80 2.00 2.12 2.14
HEAVY 2.38 2.82 3.18 3.47 3.66
[-]
0.83 1.00 1.19 1.41 1.66
contemporary fast sea transportation. It aimed to provide a further insight into the hydrodynamic properties of these hulls as well as their performance in terms of transport efficiency when utilised as RoPax ferries.
Table 2: Parameters of catamaran demihulls that solely depend on loading conditions.
Displacement T [m] Bdh [m] AT/AX CB LIGHT 3.2 MEDIUM 3.6 HEAVY 4.1
3.2
0.21 0.25 0.28
2. METHODOLOGY
A hull form family was developed and drag prediction using RANSE-based CFD carried out
to study the
influence of the hull form on the total resistance of large medium-speed catamarans operating around hump. As reported earlier [20] this is an accurate method and superior to other methods such as potential flow solutions [21].
2.1 DESIGN RULES
A novel approach was chosen to study the influence of demihull slenderness on the drag force. The hulls under consideration differ in length (L = 110 – 190 m), but have equal dimensions of overall beam (Boa = 32 m), and demihull beam (Bdh = 6.4 m), draft (TLIGHT = 3.2 m) and identical hull form parameters such as block coefficient (CB = 0.50) and prismatic coefficient (CP = 0.63) in the light
loading condition. Constant demihull beam and
draft assured that operational requirements such as canal size and port infrastructure would not be violated. Each hull form was considered at three loading conditions, a light displacement corresponding to TLIGHT = 3.2 m, a medium displacement at a draft of TMEDIUM = 3.6 m and a heavy displacement analogous to a draft of THEAVY = 4.1 m. The displacement of each hull increased linearly with increasing length. It was assumed that the light weight of the aluminium ship consisted of the weight of the demihulls, components such as superstructure and outfitting, and machinery. While the hull weight was
©2015: The Royal Institution of Naval Architects CP
0.50 0.53 0.57
0.63 0.66 0.68
relative light- ship weight
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