Journal Search Engine
Search Advanced Search Adode Reader(link)
Download PDF Export Citaion korean bibliography PMC previewer
ISSN : 2671-9940(Print)
ISSN : 2671-9924(Online)
Journal of the Korean Society of Fisheries and Ocean Technology Vol.51 No.1 pp.9-15
DOI : https://doi.org/10.3796/KSFT.2015.51.1.009

Structural analysis of a Korean-designed cruiser-class sailing yacht

Dong-Myung BAE*, Bo CAO, Dong-Jun KIM
Department of Naval Architecture and Marine Systems Engineering, Pukyong National University 45 Yongso-ro, Nam-Gu, Busan, 608-737, South Korea
Corresponding author: dmbae@pknu.ac.kr, Tel: +82-629-6613, Fax: +82-629-6608
January 1, 2015 January 27, 2015 February 10, 2015

Abstract

A Korean-designed cruiser class sailing yacht, based on the form of traditional yachts, has been developed. In this paper, structural design procedures for the yacht are studied. The scantling of structural members and loads is carried out based on the guidelines suggested by Australian Standard 4132-1993, the American Bureau of Shipping (ABS) and the International Organization for Standardization (ISO). Patran/Nastran finite element analysis is performed on models of the trial sailing boat, and from these results, the structural strength of the ship’s hull is verified.


초록


    Introduction

    Guidelines exist for the design of sailing yachts; however, internationally recognized standards dictating the design and structural strength of yachts are yet to be established. This research was performed as part of a systematic review of existing data to establish standard design techniques and rules, for cruiser-class sailing yachts.

    The hull form and other design information used in this paper was taken from a 31-foot trial ship due to be manufactured as a result of the project on ‘the development of the modern sailing boat of cruiser class for the Korean coastal sea based on the hull form of Korean traditional boat’ (Kim et al., 2006).

    Based on the approach of L. Larsson and R. E. Eliasson when discussing the design of the YD-40 (Larsson and Eliasson, 2000), we assessed the stability, structural strength, and stiffness of this trial ship, verifying results in accordance with elective ISO design standards (ISO/DIS, 2004). Using these resources, the design load, thickness, stiffness and scantling of the yacht’s panels were decided upon. Through stress calculations with finite element analysis, the authors verified the yacht’s structural design to estimate the strength of the completed ship.

    Structural design

    Design limitations

    The design restrictions in Australian standard 4132-1993 were applied to this ship, limiting the length of the hull bottom and side to 35 m as in Fig. 1.

    In accordance with design standard 4132-1993, the design pressure of the hull bottom and sides was determined by selecting the largest expected values according to equations (1) and (2).

    The design pressure for the hull bottom is defined as

    P bottom = max p 1 , p 2 , p 3
    (1)

    The design pressure for the hull sides is defined as

    P side = max p 1 , p 2
    (2)

    The following guidelines were applied to the design of this ship:

    • The scantling length of the yacht was less than 24 m, according to the ISO.

    • Design load calculations based on the panel size of the ship’s structural members (stiffness, bulkhead, web frame etc.), the related coefficient of position, the calculated load, and the moment of inertia were to be within the minimum values required by the ABS.

    • The thicknesses of the fiber-reinforced plastic (FRP) panels were calculated to ABS guidelines.

    • ISO-defined FRP properties were used as per Table 1.

    • Designs were based on the use of composite spray molding (CSM), with the weakest stiffness as shown in Table 2.

    Scantling of panel members

    Numerous panels must be constructed, including stiffeners, girders, bulkheads, the web frame, side and bottom shell plates, and the deck. Minimum values for the related coefficients of inertia and section modulus were calculated as follows:

    f k = 1.1 3 A / S 0.8 1.0
    (3)
    k 1 = 0.167
    (4)

    With the exception of the deck, the area reduction factor Kar was applied to each panel.

    K ar = 0.455 0.35 u 0.75 1.7 u 0.75 + 1.7 1.35 K ar 0.4
    (5)

    The longitudinal and transverse impact factors kL and kV, used in the calculation of pressure acting on the ship’s longitudinal panel were defined as

    K L = 0.13 1.4 x 10 v L wt + 0.76. v L wt + 0.64
    (6)

    for

    0.13 0.35 v Lwl + 4.14 K L 1.0

    and

    K V = z h z
    (7)

    where

    z = L H 12 f w m 20 L ml 1.7 B wl 1.5 1 / 2
    (8)

    where A = 1, B = 1, C = 0.9 and D = 0.8. A. The stability index was category four.

    Design pressure of bottom, side and deck

    The pressure distribution shown in Fig. 2 was used to find the design pressure of the ship’s bottom longitudinal.

    P b = P bs K ar K L
    (9)

    The pressure distribution shown in Fig. 3 was used to find the design pressure of the ship’s side.

    P s = P s min + K v P bsbase P s min f w K s K L
    (10)

    The design pressure of the yacht’s deck and bulkhead Pd was calculated as a function of their shortest dimension, independent of panel position.

    P d = f w P dbase K d
    (11)

    Scantling of panel members

    When the previously proposed design pressure was applied to a panel

    σ a 1 2 σ ut
    (12)

    The minimum section modulus and moment of inertia were calculated as follows:

    SM = b 2 f k 2 P k 2 6 10 5 σ d
    (13)
    I = b 3 f k 3 P k 3 6 10 6 k 1 E TC
    (14)

    The minimum thickness of sandwiched FRP material was calculated according to ABS guidelines:

    t f = 0.35 1.1 3.2 + 0.26 L H
    (15)
    I panel = 0.5 t f t c + t f 2
    (16)
    SM panel = I panel 0.5 t c + 2 t f = t f t c + t f 2 t c + 2 t f
    (17)

    where Ipanel is the moment of inertia, and SMpanel is the section modulus of each panel. The ultimate shear stress required of each panel was

    τ u = 2 v 0.0001 P b t f + t c
    (18)

    The stiffener scantling has a close relation to the design pressure acting on each panel.

    Yacht’s characteristics for analysis

    The ship studied in this research was a 31-foot cruiser- class yacht, capable of housing 4–6 men. The yacht (BBHH971) had a CR class keel type fin and a masthead rig mounted for efficient sailing.

    The principal dimensions of this yacht are as given in Table 3 and the finite element analysis modeling for each principal part (hull, deck, deckhouse, hull and keel) is shown in Fig. 4 (Ojeda et al., 2004).

    Only the principal components affecting the ship’s structural strength were modeled (hull, bulkhead, deckhouse etc.). FEM modeling of less significant parts was not considered, but their weights were included in the principal components where appropriate.

    Structural analysis

    In this work, the yacht’s performance was analyzed in six scenarios:

    1. Travelling at a speed of 12 knots with the ship in an upright position.

    2. Travelling through a wave to consider the impact of slamming on the hull model.

      • Heeling angle of 0° (upright)

      • Heeling angle of 30°

    3. Travelling through a wave to consider the impact of slamming on the hull and keel models.

      • Heeling angle of 0°

      • Heeling angle of 30°

    4. The ship’s carrying state (transverse slope of 90°), due to the weight of the keel.

    Structural analysis of the hull

    Structural analysis, using previously published design recommendations (Shin et al., 2006), was carried out in still water conditions with the ship’s speed set at 12 knots. Figure 5 shows the stress distribution for each part of the hull. The maximum stress at the deck opening was 32.7 MPa. It is thought that the peak stress occurs at this point due the lack of bulkhead. The maximum stress in the parts of the hull connected to the keel was 19.7 MPa.

    These stress values are, respectively, 28% and 17% of the tensile yield stress of FRP (115 MPa) meaning that there is no large impact on the hull.

    Impact of slamming on the hull

    In this section, we discuss the structural strength analysis of the hull and keel, and the effects of slamming. Two cases were considered: a Heeling angle of 0°, and a Heeling angle of 30°.

    The distribution of design pressure in the longitudinal and transverse directions is shown in Fig. 2 and 3. Values given in the ABS guidelines were used in this analysis. The stress distributions for each part of the hull as a result of slamming at heeling angles of 0° and 30° are shown in Fig. and 6.

    In Fig. 5, with a heeling angle of 0°, the maximum stresses in the deck and hull components were 47.8 and 25.3 MPa, respectively. In Fig. 6, with a heeling angle of 30°, the maximum stresses in the deck and hull components were 49.4 and 25.1 MPa, respectively. These stress values are 45% of the tensile yield stress of FRP.

    Impact of slamming on the hull and keel

    In case three, strength analysis was performed to assess the impact of slamming on the hull and keel, with heeling angles of 0° and 30°. Keel plates were modeled as solid elements.

    The resulting stresses are shown in Fig. 79. The peak stress occurred near to the connection between the hull and keel, as shown in Fig. 9. The maximum equivalent stress was 50.5 MPa in the 0° case, and 54.8 MPa in the 30° case. All the resulting stresses were less than half the yield stress of FRP.

    Strength analysis due to the weight of the ballast keel and keel

    The carrying state of the yacht was then investigated in the case of severe loading.

    The total keel weight used in this analysis was 1500 kg. Strength analysis was performed by applying mass to the keel, to confirm the structural safety of the connection point with the hull.

    Fig. 10 shows the load distribution of the keel. Six loads, weighing 250 kg (2452.5 N) each, were evenly distributed about the center of the keel. Fig. 11 shows the resulting deformation of the keel shape, and Fig. 12 shows the Von-Mises stress distribution at the point of connection between the hull and keel.

    A peak stress of 50.3 MPa, which is 43.7% of the yield stress of FRP, was measured at the point of connection between the hull and keel. According to these results, no serious damage to the hull or keel is expected.

    Evaluation of analysis results

    The resulting Von-Mises stresses for all cases described above are summarized in Table 4. The maximum stress of 54.8 MPa occurred in case five where the effects of slamming pressure on the hull and keel were considered at a heeling angle of 30°. The total stresses were shown to be less than half of the yield stress of FRP. Consequently, no issues are expected with respect to the structural strength.

    Conclusion

    This work has investigated the strength of the hull and keel of sailing yacht BBHH971 for the “development of a cruise class sailing boat based on a traditional design” task as a part of the Local Innovation Project for Man-power Training.

    Patran (MSC Software Corp.) software was used to preand post-process data solved by Nastran. The initial conditions and example scenarios were based on ABS, ISO and Australian (4132-1993) standards. However, since there was no specific procedure for the structural analysis of yachts at the time of publication, the investigation was carried out with reference to other analysis examples. This study is therefore able to be used as yacht design reference material in the future.

    Further examination of the localized strength analysis for the joint between the hull and keel, in terms of condition and material, is required as the highest stresses were found in this region. Strength and stiffness analysis should also be carried out for materials such as FRP.

    Figure

    KSFT-51-9_F1.gif

    Delineation of bottom area for aft locations of 0.3L from the forward perpendicular

    KSFT-51-9_F2.gif

    Longitudinal hydrodynamic loads (ABS).

    KSFT-51-9_F3.gif

    Transverse pressure distribution (NBS).

    KSFT-51-9_F4.gif

    FEM model of the yacht.

    KSFT-51-9_F5.gif

    Stress contour of full hull model with 0° heeling angle, including slamming.

    KSFT-51-9_F6.gif

    Stress contour of full hull model with 30° heeling angle, including slamming.

    KSFT-51-9_F7.gif

    Stress contour of hull and keel model with 0° heeling angle, including slamming.

    KSFT-51-9_F9.gif

    Maximum stress region of hull and keel model with 30° heeling angle, including slamming.

    KSFT-51-9_F10.gif

    Loading of ballast keel.

    KSFT-51-9_F11.gif

    Deformed shape of ballast keel.

    KSFT-51-9_F12.gif

    Stress distribution on the ballast keel and hull.

    Table

    Material properties.

    Material properties of FRP.

    Principal dimensions of the yacht.

    Maximum stress for each load condition

    Reference

    1. Kim DJ , Park GO , Park JH , Kim YC , Shin SM (2006) Development of Cruiser/Racer Version Sailing Boat Based on the Traditional Fishing Boat , J SNAK, Vol.43 ; pp.504-511
    2. Larsson L , Eliasson RE (2000) Principles of Yacht Design, International Marine of McGrow-Hill Camden Marine,
    3. ISO/DIS 12215-5.3 and 12215-9 (2004) Hull Construction Scantling Part5 and Small Craft Hull Construction Scantling Part 9,
    4. American Bureau of Shipping (1994) Guide for Building and Classing Offshore Racing Yachts, ABS,
    5. Ojeda RB , Prusty G , Salas M (2004) Finite Element Investigation on the Static Response of a Composite Catamaran under Slamming Loads , Ocean Eng, Vol.31 ; pp.901-929
    6. Shin JG , Lee JY , Lee JH , Van SH , Lee SH , Yoo JH (2006) A Study on the Structural Design and Structural Analysis for Small Yacht , J SNAK, Vol.43 ; pp.75-86