CALCS PROC074
API2C Ed.7 Offshore Crane Loading

CONTENTS

INTRODUCTION
NOTATION
INPUT DATA
OUTPUT FROM PROCEDURE
PROJECT EXAMPLE INPUT
PROJECT EXAMPLE OUTPUT
PROJECT OUTPUT - SUMMARY TABLE

INTRODUCTION


The API method, as used in this procedure, is widely used for the loading analysis of cranes operating offshore. Characteristic (conservative) vessel motion results are provided and these lead to crane loadings that are relatively easy to obtain and should generally be fit for purpose.

Special vessel types, complex lifting operations, special cranes or operations in sea-states higehr than those for normal offshore lifting duties require vessel specific motion analysis and crane derating calculations. These arer outside the scope of the API general method.

See also: BAS020, PROC050, PROC052

NOTATION


UNITS L(SI) m (IMP) ft
UNITS M(SI) kg (IMP) lb
UNITS T(SI) s (IMP) min
UNITS(DERIVED) g KN
Av AhAccels Vertical & Horizontal (g) API2C T4 & T5
CvHoist Factor API2C (Fh)
GeomCrane geometric configuration assoc.with load case
heel(deg)
trim(deg)
KcCrane Stiffness
N_fallsNo.Hoist Rope Falls
N_geomNo.Crane Geometric Configurations for Analysis
N_SWHNo.Sig.Wave Heights
Pr1 Pr2Hoist Rope Forces for Vw1 Vw2
SWLHinc.Hoist Block
TABLE_D _R _W Define Read Write
UF_Vh Vh_min/VhUtilisation of available hoisting velocity
Vc Vd Vh VrVelocity of Crane_Boom_Tip Supply_Boat_Deck Hoist_Block Relative
Vh_minVelocity Hoist_Block Min (API2C Eqn.6)
Vw1 Vw2Rope Velocities at Winch Drum under Pr1 Pr2
vessel$FIXED TLP SPAR SS DRILL FPSO (API2C_Table3)
Output Data:Ah Av heel trim OL Cv - Output Data

INPUT DATA


Input data format is demonstrated by example: See Project Input for application of general description of data blocks described in the following.

UNITS. The API analysis is based on Imperial Units of measurement. Many projects (possibly with the exception of those managed by N.American organisations) now use SI Units and these are assumed for the input data. In the instance where Imperial Unit s are used for input, this can be accommodated by using unity conversion factors.

Vessel types are defined by API and the appropriate one should be chosen for the project.

Pr,Vw pairs. The Rope force relationship with hoisting speed is defined by pairs of sample values and linear inerpolation used for project operational values, these being needed for the API analysis.

TABLE T_Units. When input data with SI Units are used, this table may be used as presented in the project example.

TABLE T_Kc. The analysis requires the specification of Kc & Htip for the definition of project cases. Kc must be obtained by separate analysis. A geometric configuration i_geom will normally be associated with radius R (if for a crane) and this is in cluded for case identification and not is used.

TABLE T_SWH. This table presents the data for the crane boom tip velocity as related to the sea-state. Vc must be separately calculated.

TABLE T_SWLH. This table presents SWLH for the crane as related to i_geom (for example outreach R) and SWH.

OUTPUT FROM PROCEDURE


The description refers to the Project Output. The input data for this project provided nine cases for analysis. That is, three i_geom (configurations) times three SWH (sea-states). Output calculations, as presented on this webpage, have been edited ( for brevity of presentation) to include only i_geom=1 SWHi=1, i_geom=2 SWHi=2, i_geom=3 SWHi=3 combinations. The summary table is for all nine cases.

TABLE_R indicates case values read from tables. For example, TABLE_R T_Kc indicates reading from T_Kc.

TITLES. The cases are defined in the title lines. For example, the first title reads
'P3561535 - PROC074 OSC Loading API2C 150314 - G1SWH2').
G1SWH2 indicates i_geom=1 SWH=2(m).

SUMMARY TABLES.

All nine cases contibute to the tables.

Vh_min & Vh.
Where Hoist velocity Vh < Vh_min then Vh is inadequate and brackets are used.
For example, if Vh_min=.8804 & Vh=.8 then table element is (.8)

These velocities are significant contributors to the principal result of the analysis,
Cv = f(Vr,Kc,SWLH) where Vr = f(Vh,Vc,Vd)

PROJECT EXAMPLE INPUT


PROCtitle("P3561535"," "," ")
P."UNITS 150317"
LET m=1:kg=1:s=1:REM SI
LET g=9.81*m/s^2:N=kg*m/s^2:kN=1000*N:t=1000*g*kg:REM Derived
LET ft=m/3.28:lb=kg/2.205:lbf=.225*N:min=60*s:gi=g*(m/ft)/(s^2/s^2):REM Imp
vessel$="FPSO"
LET N_falls=2:N_SWH=3:N_geom=3:TWNvar=10
LET Vw(1,0)=0:Vw(1,1)=50:Vw(2,0)=35:Vw(2,1)=25:REM Pr,Vw pairs

TABLE_D_1
T_Units
U_Htip(m/ft)
U_Kc(kN/lbf)/(m/ft)
U_SWLH(t/lbf)
U_SWH(m/ft)
U_Vc(m/ft)/(s/s)
U_Vd(m/ft)/(s/s)
U_Vh(m/ft)/(min/s)
U_Vr(m/ft)/(s/s)
TABLE_D_0

TABLE_D_1
T_Kc
i_geom_RKcHtip
162*32564.3
2302*32564.3
3402*32564.3
TABLE_D_0

TABLE_D_1
T_SWH
i_SWH_123
SWH22.53
Vc.05*2^2.05*2.5^2.5*3^2
TABLE_D_0

TABLE_D_1
T_SWLH
i_geom_SWLHSWLHSWLH
1343025
2252015
3151210
TABLE_D_0

PROC074

PROJECT EXAMPLE OUTPUT


P3561535 - PROC074 OSC Loading API2C 150604 -
TABLE_R T_Units:U_Htip=(m/ft):U_Kc=(kN/lbf)/(m/ft):U_SWLH=(t/lbf):U_SWH=(m/ft):U_Vc=(m/ft)/(s/s):U_Vd=(m/ft)/(s/s):U_Vh=(m/ft)/(min/s):U_Vr=(m/ft)/(s/s)

i_geom=1:SWH=2


--- i_geom=1 SWH=2.5 & i_geom=1 SWH=3 extracted ---

TABLE_R T_Kc:i_geom_=1:R=2:Kc=3:Htip=4
Kc= Kc*U_Kc= 8.808E5
Kc= 650*1355= 8.807E5
Htip= Htip*U_Htip= 210.9
Htip= 64.3*3.28= 210.9

TABLE_R T_SWH:SWH=2:Vc=.05*2^2
TABLE_R T_SWLH:i_geom_=1:SWLH=2:SWLH=3:SWLH=4
P3561535 - PROC074 OSC Loading API2C 150314 - G1SWH2
Pr= SWLH/N_falls= 17
Pr= 34/2= 17
LET Vh=FN_LIP(Pr,Vw())
Vh= Vh/N_falls*U_Vh= 1.035
Vh= 37.86/2*0.05467= 1.035
SWH= SWH*U_SWH= 6.56
SWH= 2*3.28= 6.56
Vh_min= .067*(SWH+3.3)= 0.6606
Vh_min= .067*(6.56+3.3)= 0.6606
Vc= Vc*U_Vc= 0.656
Vc= 0.2*3.28= 0.656
SWLH= SWLH*U_SWLH= 1.482E6
SWLH= 34*4.36E4= 1.482E6
Vd= .6*SWH= 3.936
Vd= .6*6.56= 3.936
LET Ah=.03:Av=1.07
LET Ah=0.03:Av=1.07
LET Vc=.05*SWH^2:heel=2.5:trim=1
LET Vc=2.152:heel=2.5:trim=1
Ah= .01*SWH^1.1= 0.07918
Ah= .01*6.56^1.1= 0.07918
Vr= Vh+SQR(Vd^2+Vc^2)= 5.52
Vr= 1.035+SQR(3.936^2+2.152^2)= 5.521
Cv= 1+Vr*SQR(Kc/(gi*SWLH))= 1.75
Cv= 1+5.52*SQR(8.808E5/(32.18*1.482E6))= 1.75
OL= (2.5+.457*SWH)/(.305*Htip)= 0.08547
OL= (2.5+.457*6.56)/(.305*210.9)= 0.08547
SL= .5*OL= 0.04274
SL= .5*0.08547= 0.04273

i_geom=2:SWH=2.5


--- i_geom=2 SWH=2 & i_geom=2 SWH=3 extracted ---

TABLE_R T_Kc:i_geom_=1:R=2:Kc=3:Htip=4
Kc= Kc*U_Kc= 8.808E5
Kc= 650*1355= 8.807E5
Htip= Htip*U_Htip= 210.9
Htip= 64.3*3.28= 210.9

TABLE_R T_SWH:SWH=2.5:Vc=.05*2.5^2
TABLE_R T_SWLH:i_geom_=1:SWLH=2:SWLH=3:SWLH=4
P3561535 - PROC074 OSC Loading API2C 150314 - G2SWH2.5
Pr= SWLH/N_falls= 10
Pr= 20/2= 10
LET Vh=FN_LIP(Pr,Vw())
Vh= Vh/N_falls*U_Vh= 1.171
Vh= 42.86/2*0.05467= 1.172
SWH= SWH*U_SWH= 8.2
SWH= 2.5*3.28= 8.2
Vh_min= .067*(SWH+3.3)= 0.7705
Vh_min= .067*(8.2+3.3)= 0.7705
Vc= Vc*U_Vc= 1.025
Vc= 0.3125*3.28= 1.025
SWLH= SWLH*U_SWLH= 8.72E5
SWLH= 20*4.36E4= 8.72E5
Vd= .6*SWH= 4.92
Vd= .6*8.2= 4.92
LET Ah=.03:Av=1.07
LET Ah=0.03:Av=1.07
LET Vc=.05*SWH^2:heel=2.5:trim=1
LET Vc=3.362:heel=2.5:trim=1
Ah= .01*SWH^1.1= 0.1012
Ah= .01*8.2^1.1= 0.1012
Av= 1+.0012*SWH^2= 1.081
Av= 1+.0012*8.2^2= 1.081
Vr= Vh+SQR(Vd^2+Vc^2)= 7.13
Vr= 1.171+SQR(4.92^2+3.362^2)= 7.13
Cv= 1+Vr*SQR(Kc/(gi*SWLH))= 2.263
Cv= 1+7.13*SQR(8.808E5/(32.18*8.72E5))= 2.263
OL= (2.5+.457*SWH)/(.305*Htip)= 0.09712
OL= (2.5+.457*8.2)/(.305*210.9)= 0.09712
SL= .5*OL= 0.04856
SL= .5*0.09712= 0.04856

i_geom=3:SWH=3


--- i_geom=3 SWH=2 & i_geom=3 SWH=2.5 extracted ---

TABLE_R T_Kc:i_geom_=1:R=2:Kc=3:Htip=4
TABLE_R T_Kc:R=40
TABLE_R T_Kc:Kc=2*325
TABLE_R T_Kc:Htip=64.3
Kc= Kc*U_Kc= 8.808E5
Kc= 650*1355= 8.807E5
Htip= Htip*U_Htip= 210.9
Htip= 64.3*3.28= 210.9

TABLE_R T_SWH:SWH=3:Vc=.5*3^2
TABLE_R T_SWLH:i_geom_=1:SWLH=2:SWLH=3:SWLH=4
TABLE_R T_SWLH:SWLH=10
P3561535 - PROC074 OSC Loading API2C 150314 - G3SWH3
Pr= SWLH/N_falls= 5
Pr= 10/2= 5
LET Vh=FN_LIP(Pr,Vw())
Vh= Vh/N_falls*U_Vh= 1.269
Vh= 46.43/2*0.05467= 1.269
SWH= SWH*U_SWH= 9.84
SWH= 3*3.28= 9.84
Vh_min= .067*(SWH+3.3)= 0.8804
Vh_min= .067*(9.84+3.3)= 0.8804
Vc= Vc*U_Vc= 14.76
Vc= 4.5*3.28= 14.76
SWLH= SWLH*U_SWLH= 4.36E5
SWLH= 10*4.36E4= 4.36E5
Vd= 5.9+.3*(SWH-9.8)= 5.912
Vd= 5.9+.3*(9.84-9.8)= 5.912
LET Ah=.03:Av=1.07
LET Ah=0.03:Av=1.07
LET Vc=.05*SWH^2:heel=2.5:trim=1
LET Vc=4.841:heel=2.5:trim=1
Ah= .01*SWH^1.1= 0.1237
Ah= .01*9.84^1.1= 0.1237
Av= 1+.0012*SWH^2= 1.116
Av= 1+.0012*9.84^2= 1.116
Vr= Vh+SQR(Vd^2+Vc^2)= 8.91
Vr= 1.269+SQR(5.912^2+4.841^2)= 8.91
Cv= 1+Vr*SQR(Kc/(gi*SWLH))= 3.233
Cv= 1+8.91*SQR(8.808E5/(32.18*4.36E5))= 3.232
OL= (2.5+.457*SWH)/(.305*Htip)= 0.1088
OL= (2.5+.457*9.84)/(.305*210.9)= 0.1088
SL= .5*OL= 0.05439
SL= .5*0.1088= 0.0544

PROJECT OUTPUT - SUMMARY TABLE


Vh_minHoist Velocity (Min Allowable)
(i_geom\i_SWH)(1)(2)(3)
(1)0.66060.77050.8804
(2)0.66060.77050.8804
(3)0.66060.77050.8804
VhHoist Velocity
(i_geom\i_SWH)(1)(2)(3)
(1)1.0351.0741.123
(2)1.1231.1711.22
(3)1.221.251.269
VcBoom Tip Velocity
(i_geom\i_SWH)(1)(2)(3)
(1)2.1523.3624.841
(2)2.1523.3624.841
(3)2.1523.3624.841
VdSupply Boat Deck Velocity
(i_geom\i_SWH)(1)(2)(3)
(1)3.9364.925.912
(2)3.9364.925.912
(3)3.9364.925.912
VrTotal Relative Velocity
(i_geom\i_SWH)(1)(2)(3)
(1)5.527.0338.764
(2)5.6087.138.862
(3)5.7067.2098.91
AvVertical Accel
(i_geom\i_SWH)(1)(2)(3)
(1)1.071.0811.116
(2)1.071.0811.116
(3)1.071.0811.116
AhHorizontal Accel
(i_geom\i_SWH)(1)(2)(3)
(1)0.079180.10120.1237
(2)0.079180.10120.1237
(3)0.079180.10120.1237
OLOff-Lead
(i_geom\i_SWH)(1)(2)(3)
(1)0.085470.097120.1088
(2)0.085470.097120.1088
(3)0.085470.097120.1088
SLSide-Lead
(i_geom\i_SWH)(1)(2)(3)
(1)0.042740.048560.05439
(2)0.042740.048560.05439
(3)0.042740.048560.05439
CvHoist Factor
(i_geom\i_SWH)(1)(2)(3)
(1)1.752.0172.389
(2)1.8892.2632.813
(3)2.1672.6493.233

END074

PROJECT END