Section 3 Fixed and steering nozzles
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Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Ships, July 2022 - Part 3 Ship Structures (General) - Chapter 13 Ship Control Systems - Section 3 Fixed and steering nozzles

Section 3 Fixed and steering nozzles

Parent topic: Chapter 13 Ship Control Systems

3.1 General

3.1.1 The requirements given in this Section are applicable to fixed and steering nozzles with an inner diameter of not greater than 5 metres.

3.1.2 For nozzles with an inner diameter greater than 5 metres, the maximum pressure acting on the nozzle is to be submitted by the designer. This pressure is to be used to determine the nozzle scantlings in accordance with the requirements of Pt 3, Ch 13, 3.3 Nozzle scantlings to Pt 3, Ch 13, 3.5 Nozzle headbox.

3.1.3 Suitable arrangements are to be provided to prevent the steering nozzle from lifting.

3.1.4 Effective means are to be provided for supporting the weight of the nozzle. The hull structure, in way of the nozzle supports, is to be suitably strengthened.

3.1.5 Care is to be taken in the manufacture of the nozzle to ensure its internal preservation and watertightness. The preservation and testing are to be as required for rudders, see Pt 3, Ch 13, 2.11 Rudder blade, Table 1.9.1 Testing requirements and Table 1.8.1 Trial trip and operational tests.

3.2 Design pressure

3.2.1 The design pressure for propeller nozzles, in kN/m2, is to be determined as follows:
Pd = czPd0
Pd0 = 9+0,0025Nδp for NN ≤ 63
Pd0 = 13+0,002Nδp for 63 < NN ≤ 200
Pd0 = εcf for NN > 200

where

NN = is the nozzle numeral
= 0,01Nδp
N = is the maximum shaft power in kW
Ap = is the propeller disc area, in m2, taken equal to:
=
δp = is the propeller diameter in m
ε = is a factor obtained from the following formula:
cz = is a coefficient taken equal to:
= cz = 1,0 in Zone 2 (propeller zone)
= cz = 0,5 in Zone 1

See also Figure 13.3.1 Nozzle construction

cf = is a coefficient taken equal to:
= cf = 1,0 for fixed nozzles
= cf = 1,25 for steering nozzles

Figure 13.3.1 Nozzle construction

3.3 Nozzle scantlings

3.3.1 The scantlings of propeller nozzles are to be not less than required by Table 13.3.1 Nozzle construction.

Table 13.3.1 Nozzle construction

Item Requirement
(1) Nozzle plating but not less than 7,5 mm
(2) Ring webs and web stiffeners Not less than the attached nozzle plating in way of Zone 1
(3) Webs in way of headbox and pintle support structure mm
(4) Section modulus of nozzle profile about its neutral axis cm3
Symbols
Pd = nozzle design pressure, in kN/m2, see Pt 3, Ch 13, 3.2 Design pressure
t = thickness of nozzle plating, in mm
tw = thickness of web plating, in mm
s = spacing of web rings, in m
k = material factor, as defined in Pt 3, Ch 13, 1.2 General symbols
tk = corrosion thickness, to be taken as:
  • tk = 2,5 in general
  • tk = 1,5 for fresh water environments
  • tk = 0 for stainless steel
δ p = propeller diameter, in m
Ld = nozzle length, in m
n = coefficient taken equal to:
  • n = 1,0 for steering nozzles
  • n = 0,7 for fixed nozzles
V is as defined in Pt 3, Ch 1, 6.1 Principal particulars

3.3.2 The Zone 2 nozzle plating is to be carried well forward and aft of the propeller tips with due allowance being made on steering nozzles for the rotation of the nozzle in relation to the propeller, and is to extend at least 0,25Ld in length.

3.3.3 Fore and aft web stiffeners are to be fitted between the inner and outer skins of the nozzle. Both sides of the headbox and pintle support structure, are to be connected to fore and aft webs of increased thickness.

3.3.4 The adjacent ring webs fore and aft of those connected to the headbox and pintle support structure are to be of a similar thickness to the ring webs connected to the headbox and pintle support structure.

3.3.5 Local stiffening is to be fitted in way of the top and bottom supports which are to be integrated with the web stiffeners and ring webs. Continuity of bending strength is to be maintained in these regions.

3.3.6 The plating thickness of attached fins is to be not less than the Zone 1 nozzle plating thickness. Solid fins should be not less than 25 mm thick.

3.4 Nozzle stock

3.4.1 The requirements for the nozzle stock are to be derived, in accordance with Pt 3, Ch 13, 2.10 Rudder stock scantlings, using the lateral nozzle force and maximum nozzle torque obtained in this sub-Section.

3.4.2 The lateral nozzle force, CR, at the centre of pressure is to be determined as follows:
CR = PdAt103 N
where
Pd = nozzle design pressure in Zone 2, in kN/m2
At = total projected area of nozzle and supporting structure, in m2
At = An + Af + As
where
An = projected area of nozzle, in m2, to be taken as 1,57δpLd
Af = projected area of nozzle flap, in m2
As = projected area of support structure in the longitudinal plane, in m2

where δp and Ld are defined in Table 13.3.1 Nozzle construction.

3.4.3 The maximum nozzle torque,QR, is to be determined as follows:
QR = CR × r Nm

where

r = distance from the centre of pressure to the stock, in m, to be taken as:

c(ɑ-k1)

c = nozzle length plus the length of the nozzle flap if present
ɑ = relative centre of pressure along the nozzle length, to be taken as:
ɑ = 0,25 for fixed nozzles
ɑ = 0, 33 for steering nozzles
k1 = ratio of the nozzle area forward of the stock centreline to the combined area of the nozzle and flap

A1 is the portion of the projected nozzle area located forward of the stock centreline, see also Figure 13.3.2 Nozzle geometry

CR, An and Af are given in Pt 3, Ch 13, 3.4 Nozzle stock 3.4.2.

Figure 13.3.2 Nozzle geometry

3.5 Nozzle headbox

3.5.1 The section modulus of the headbox, Z, about the longitudinal axis is to be not less than:
Z = 0,143PdAtDh × 102 cm3
where
Pd = nozzle design pressure in Zone 2, in kN/m2
DH =
where
δh = depth of headbox, in m
δp = propeller diameter, in m
At = is given in Pt 3, Ch 13, 3.4 Nozzle stock 3.4.2.

3.5.2 Plans detailing the integration of the headbox into the sternframe are to be submitted.

3.6 Ancillary items

3.6.1 Requirements for ancillary items such as bearings, couplings, pintles, etc. are given in Pt 3, Ch 13, 2 Rudders.

3.7 Welding

3.7.1 Double continuous welds are to be used as far as practicable for the connection between the inner and outer nozzle plating and the internal stiffening rings and webs. Slot welding is not permitted for the inner nozzle plating.

3.7.2 Additional welding requirements are given in Pt 3, Ch 13, 2.4 Welding and design details.

3.8 Azimuth thrusters

3.8.1 In general, the scantlings of similar structures, such as azimuth thrusters, are to be calculated in accordance with the requirements of Pt 3, Ch 13, 3.3 Nozzle scantlings where the design pressure,Pd, is to be derived from loads specified by the designer. The stock may be assessed using these loads and the permissible design stresses given in Table 13.2.5 Rudder stock permissible stresses.

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