BT ST-V- I 1.t5 - 1026
Reg. No.
B. Tech. Degree V Semester Examinstion in Navul Architecture and
Ship Building November 2015
ST 504 PROPULSION OF SHIPS
Time:3 Hours
Maximum Marks: 50
PART A
(AnswerlII questions)
(5 x 2: l0)
I.
(a) Define kinematic similarity in propeller model testing.
(b) Show that to achieve kinematic similarity the advance coefficient J must be same for
full scale propeller and rnodel.
(:) A 6 m dia propeller lras a pitch ratio of 0.9. Calculate the pitch angle at root and tip.
(d) A ship needs a thrust of 400 kN to achieve a speed of 5 knots. If wake fraction is 28%o,
1
calculate using axial momentuln theory the minimum propeller diameter to achieve an
ideal efficiency of 62a/o.
(e) Define dynarnic sirnilarity in propeller model testing.
t'
PART B
II.
(a)
A line segment AB translates along an axis with uniform axial velocity
(5 x 8:40)
of 1.6 m/s and sinrultaneously rotates about the axis with uniform angular
(b)
IIt.
velocity of 2.1 rad/s. Calculate the pitch and pitch angle of the helix geneiated
by a point C on lirre segment AB midway between A and B.
Show that the helix is traced out on an imaginary cylinder and using this, define
the pitch angle. Derive an expression for the pitch angle.
OR
'rhe expanded blade widtlrs in mm (chord) at different radii of a 4 bladed
propeller of 6 rn dia and Ap/A1y:0.6 are given below:
r/R
0.2
a(o/o\
46.90
29.18
b(%)
0.3
52.64
)-)-t.!-
0.4
56.32
37.3
0.5
57.60
44.78
0.6
56.08
43.92
0:7
s 1.40
46.68
0.8
41.6s
48.35
0.9
25.35
47.00
(4)
(4)
(8)
1.0
20.14
a = distance from G[- to l.l]. b'- distance from GL to TE (both expressed as o/o
of total blade widrh ar 0.6R given.by Co.o* : 2.1g7.D. (Auld,,)lz).
Calculate the expanded area ratio and check if it matches with the given value of
0.6. Hub radius:0.2R.
IV.
V.
Using axial monrentum theonv of screw propellers, derive an expression for
thrust and ideal efticicncy.
(8)
using blade element theory, derive u?t*p."rrion for efficiency of the blade
(8)
element.
(P.T.o.)
VI. (a) Define real slip, apparent slip, real slip ratio and apparent slip ratio.
(b) A propeller with dia:6 m and pitc{r ra{iq =,O.8, rotates.at 120 rym to give a
(4)
(4)
ship speed of 14 knots. Wake fractionis24o/o. Calculate realand apparent slip
ratios'
VII.
oR
Open water tests are conducted on a 4-bladed model propeller with 0.24 m dia
and P/D:0.8 at a constant rpm of 1780 over a range of velocity of advance.
The results are shown in the following table:
Vo (m/s)
Thrust CN)
Torque(N. m)
0.00
640.0
1.20
2.40
600.0
5s0.0
3.6
480.0
4.80
405.0
15.3
14.6
13.6
12.4
I 1.0
(a) Determine the corresponding rpm of a full scale 6 m dia propeller.
(b) Calculate the corresponding values of Va , thrust and torque for the full
Q)
(6)
scale propeller.
Vm. (a) Describe how cavitation occurs on a screw propeller.
(b) List the bad dffects of cavitation.
(c) List 3 methods to avoid cavitation.
IX.
x.
OR
A single screw ship has a main engine with brake power of 3000 kW at 120 rpm
with gear ratio : I:1. Calculate (i) delivered power (ii) thrust power
(iii) effective power (iv) shaft torque just ahead of propeller (v) QPC.
Data: wake fraction : 24o/o, thrust deduction fraction : 22%o, open water
efficiency : 650A, relative rotative efficiency ggYr, transmission
efficiency :96Yo.
Using kinematiac and dynamic similarities prove the following in relation to
propeller model tests
!r=:,n
Von
nM=+
J
!r: P, 7,
TM gu
Q, * -P;- 7a
(4)
(2)
(2)
(g)
(S)
ns
S"
Q, Pu
where 2 is the scale factor.
Xt. (a) Explain with a velocity diagram *try,n0.tp,imum pitch of a tug screw propeller (4)
is less for the towing condition than for the free running condition.
(b) Explain the advantages and disadvantages of a CPP.
,r
**
(4)