Section 2 Rudders

2.1.1 The scantlings of the rudder stock are to be not less than those required by Table 3.2.6 Rudder stock diameter.

2.1.2 For rudders having an increased diameter of rudder stock, see Figure 3.2.1 Rudder types, the increased diameter is to be maintained to a point as far as practicable above the top of the lowest bearing. This diameter may then be tapered to the diameter required in way of the tiller. The length of the taper is to be at least three times the reduction in diameter. Particular care is to be taken to avoid the formation of a notch at the upper end of the taper.

2.1.3 Sudden changes of section or sharp corners in way of the rudder coupling, jumping collars and shoulders for rudder carriers, are to be avoided.

2.2.1 Definitions and symbols for use throughout this Section are indicated in the appropriate tables.

2.3.1 Where the rudder is of a novel design, high aspect ratio or the speed of the craft exceeds 45 knots the scantlings of the rudder and rudder stock are to be determined by direct calculation methods incorporating model test results and structural analysis, where considered necessary by LR.

2.4.1 Alternative methods of determining the loads will be specially considered, provided that they are based on model tests, full scale measurements or generally accepted theories. In such cases, full details of the methods used are to be provided when plans are submitted for approval.

2.5.1 Rudders considered are the types shown in Figure 3.2.1 Rudder types, of double plate or single plate construction, constructed from steel, stainless steel or aluminium alloy. Other rudder types and materials will be subject to special consideration.

Figure 3.2.1 Rudder types

2.6.1 The rudder profile coefficient f _R for use in Table 3.2.6 Rudder stock diameter is to be as indicated in Table 3.2.1 Rudder profile coefficient f _R .

2.7.1 The rudder position coefficient, f _p, for use in Table 3.2.6 Rudder stock diameter is to be as indicated in Table 3.2.2 Rudder position coefficient f _p .

2.8.1 The rudder speed coefficient, f _v, for use in Table 3.2.6 Rudder stock diameter is to be as indicated in Table 3.2.3 Rudder speed coefficient f _v .

Figure 3.2.2 Rudder profiles

Table 3.2.3 Rudder speed coefficient f _v

Design criteria	f V
Craft with	1,00
Craft with	1,12 - 0,005V
Symbols
L WL = as defined in Pt 3, Ch 1, 6.2 Principal particulars 6.2.5 V = as defined in Table 3.2.6 Rudder stock diameter f v = rudder speed coefficient for use in Table 3.2.6 Rudder stock diameter

Table 3.2.4 Pintle arrangement coefficient N

Support arrangement	Value of N
Two or more pintles Upper stock	N=0
One or no pintle
Symbols
N = coefficient for use in Table 3.2.6 Rudder stock diameter A 1,A 2 = part rudder areas, in m2, see Figure 3.2.1 Rudder types y 1 y 2 y 3 = vertical dimensions, in metres, see Figure 3.2.1 Rudder types
Any values of y and A not indicated in Figure 3.2.1 Rudder types are to be taken as zero.
NOTE
If, in semi-spade (Mariner) type rudders, the pintle is housed above the rudder horn gudgeon and not shown in Figure 3.2.1 Rudder types, y 2 and y 3 are to be measured to the top of the gudgeon.

2.9.1 The pintle arrangement coefficient, N, for use in Table 3.2.6 Rudder stock diameter is to be as indicated in Table 3.2.4 Pintle arrangement coefficient N .

Table 3.2.5 Position of centre of pressure

Design criteria	Value of x PF and x PA to be used in Table 3.2.6 Rudder stock diameter
Rectangular rudders;
(a) Ahead condition	x PF	=	(0,33ex B-x L), but not less than 0,12x B
(b) Astern condition	x PA	=	(x A- 0,25x B), but not less than 0,12x B
Non-rectangular rudders;
(a) Ahead condition	x PF	=	as calculated from geometric form (see Note) but not less than:
(b) Astern condition	x PA	=	as calculated from geometric form (see Note) but not less than:
Symbols
x PF = horizontal distance from the centreline of the rudder pintles, or axle, to the centre of pressure in the ahead condition, in metres
x PA = horizontal distance from the centreline of the rudder pintles, or axle, to the centre of pressure in the astern condition, in metres
x B = breadth of rudder, in metres
y R = depth of rudder at centreline of stock, in metres
A R = rudder area, in m2
x L and x A = horizontal distances from leading and after edges, respectively, of the rudder to the centreline of the rudder pintles, or axle, in metres
x S = horizontal length of any rectangular strip of rudder geometric form, in metres
e = hull form factor at ahead condition
for L < 65 m , e = 1,0
for L ≥ 65 m, e= or
e=
whichever is the lesser, but not less than 1,0 and need not be taken greater than 1,5
L R, B and C b are as defined Pt 3, Ch 1, 6.2 Principal particulars is as defined in Table 3.2.6 Rudder stock diameter
NOTE
For rectangular strips the centre of pressure is to be assumed to be located as follows:
(a) 0,33ex S abaft leading edge of strip for ahead condition.
(b) 0,25x S from aft edge of strip for astern condition.

2.10.1 The position of centre of pressure for use in Table 3.2.6 Rudder stock diameter is to be as indicated in Table 3.2.5 Position of centre of pressure.

2.11.1 Tubular rudder stock scantlings are to be not less than that necessary to provide the equivalent strength of a solid stock as required by Table 3.2.6 Rudder stock diameter, and can be calculated from the following formula:

Table 3.2.6 Rudder stock diameter

Requirement

1. Basic stock diameter, d s, at and below lowest bearing:

2. Diameter in way of tiller, d SU: d SU = d s calculated from (1) with N=0

3. Lateral force on rudder acting at centre of pressure of blade, P L:

Symbols

f c = 79 for craft of Rule length, L R, 50 m and below varying up to 83,3 at a Rule length, L R, of 70 m. Intermediate values to be obtained by interpolation = 83,3 for craft of Rule length, L R, 70 m and above

f p = rudder position coefficient, see Table 3.2.2 Rudder position coefficient f p

f v = rudder speed coefficient, see Table 3.2.3 Rudder speed coefficient f v

f R = rudder profile coefficient, see Table 3.2.1 Rudder profile coefficient f R

m = 0,75 for σ0 > 235 = 1,0 for σ0 ≤ 235

σ0 = minimum yield stress, in N/mm2, of material used, and is not to be taken greater than 0,7 σT

σT = ultimate tensile strength of the material used, in N/mm2

V = the maximum speed for the astern and ahead condition, in knots. In no case to be less than 5 knots

A R = rudder area, in m2

x P = x Pa or x Pf, for the astern and ahead condition respectively, see Table 3.2.5 Position of centre of pressure

N = coefficient dependent on rudder support arrangement, see Table 3.2.4 Pintle arrangement coefficient N

Note Where higher tensile steel is used for the rudder stock, σ0 is not to be taken as greater than 450 N/mm2.

2.12.1 The scantlings of a single plate rudder are to be not less than required by Table 3.2.7 Single plate rudder construction, see also Pt 3, Ch 3, 2.5 Rudder arrangements 2.5.1.

2.12.2 Rudder arms are to be efficiently attached to the mainpiece.

2.13.1 The scantlings of a double plated rudder are to be not less than required by Table 3.2.8 Double plated rudder construction.

2.13.2 In way of rudder couplings and heel pintles the plating thickness is to be suitably increased.

2.13.3 On semi-spade (Mariner) type rudders a notch effect in the corners in the bottom pintle region is to be avoided (see AA, Figure 3.2.3 Semi-spade (mariner) type rudder). An insert plate, 1,6 times the Rule thickness of the side plating, is to be fitted at this position, extending aft of the main vertical web and having well rounded corners. The main vertical web is to be continuous over the full depth of the rudder and have a thickness not less than three times the thickness required by Table 3.2.8 Double plated rudder construction, Item (4). Where an additional continuous main vertical web is arranged to form an efficient box structure, the webs are to have a thickness not less than required by Table 3.2.8 Double plated rudder construction, Item (4).

2.13.4 Adequate hand or access holes are to be arranged in the rudder plating in way of pintles as required, and the rudder plating is to be reinforced locally in way of these openings. Continuity of the modulus of the rudder mainpiece is to be maintained in way of the openings.

Table 3.2.8 Double plated rudder construction

Item		Requirement
(1) Side plating
(2) Webs - vertical and horizontal
(3) Top and bottom plates and nose plates		As (1) above
(4) Mainpiece
		Stress due to bending ≤ 78,0 N/mm2
Symbols
β = A a (1-0,25A a) A a = panel aspect ratio, but is not to be taken as greater than 2,0 F a = 1,0 for mild steel, 0,95 for aluminium alloy and 0,9 for stainless steel. Other materials will be specially considered. y w = vertical spacing, in mm, of the horizontal webs or arms, but is not to exceed 900 mm d s = basic stock diameter, given by Table 3.2.6 Rudder stock diameter, in mm t N = thickness, in mm, of top and bottom plates and nose plate tS = thickness, in mm, of side plating tW = thickness, in mm, of webs

Figure 3.2.3 Semi-spade (mariner) type rudder

2.13.5 Connection of rudder side plating to vertical and horizontal webs, where internal access for welding is not practicable, is to be by means of slot welds onto flat bars on the webs. The slots are to have a minimum length of 75 mm and in general, a minimum width of twice the side plating thickness. The ends of the slots are to be rounded. The space between the slots is not to exceed 150 mm and welding is to be based on a weld factor of 0,44.

2.13.6 For testing of rudders, see Table 1.7.1 Testing requirements in Chapter 1.

2.13.7 Where the fabricated mainpiece of a spade rudder is connected to the horizontal coupling flange by welding, a full penetration weld is required.

2.14.1 The requirements in this section are based on spade rudder constructions of composite material with an aspect ratio not less than 3,0. Requirements for rudders with a lesser aspect ratio will be specially considered. Requirements for rudders made from a metal stock and composite blade will be specially considered. Requirements for rudder arrangements with pintles will be specially considered.

2.14.2  The requirements in this section are based on construction using carbon/epoxy composite but can be used for alternative constructions using other reinforcement and matrix materials with due consideration for the properties of these materials.

2.14.3 The requirements in this section are based on a structural arrangement with a single stock of generally rectangular or trapezoid shape, extending from the upper bearing through the lower bearing, down to not less than 0,75 times the height of the rudder blade from the upper edge of the rudder blade. In this arrangement, the blade is moulded around a core made of structural foam bonded to the fore and aft side of the stock. The foam transfers the shear load to the stock. The bending in the horizontal plane is taken by the skin of the blade.

2.14.4 The requirements are based on the stock being built from interleaved layers of unidirectional fibres providing bending strength and biaxial fibres to provide torsion and shear strength, wrapped around a foam core.

2.14.5 The limiting stress fraction, f_σ, to be used in the design is 0,25.

V, f_p, f_R see Table 3.2.5 Position of centre of pressure

2.14.8 At and above the lower bearing, at any section along the length of the stock the amount of biaxial material is to be sufficient to withstand the combined action of shear load and torsion without exceeding the limiting stress fraction. The position of the tiller is to be considered.

The torsion load can be taken as the torsion load in way of the lower bearing.

2.14.10 The laminate in way of the mounting position of the tiller is to be suitably protected and reinforced where necessary to take the loads from the tiller.

2.14.12 The laminate of the skin of the blade is determined by the envelope of the following criteria:

• tensile stress due to load carried to stock
• compressive stress due to load carried from blade to stock
• wrinkling under this compressive stress
• minimal weight of reinforcement criterion as for shell laminate.
• below the lower end of the stock, strength required to support the part of the blade below.

2.14.13 The lower end of the blade, extending below the stock, can be executed as a sacrificial piece to save the stock in case of grounding.

2.15.1 Where rudders are cast, the mechanical and chemical properties of the metal are to be submitted for approval. If the rudder stock is cast integral with the rudder blade, abrupt changes of section and sharp corners are to be avoided.

2.16.1 The design of the lowest bearing is to comply with the requirements of Table 3.2.9 Lowest main bearing requirements.

2.17.1 Bearings are to be of approved materials and effectively secured to prevent rotational and axial movement.

2.17.2 Where it is proposed to use stainless steel for liners or bearings for rudder stocks and/or pintles, the chemical composition is to be submitted for approval. Where the two surfaces are stainless steel materials, they should have suitable resistance to galling. When stainless steel material is used, arrangements to ensure an adequate supply of seawater to the bearing are to be provided to protect against stagnant sea-water initiated corrosion.

2.17.3 Synthetic rudder bearing materials are to be of a type approved by LR.

2.17.4 When roller bearings are used on the rudder stock, the bearing must be of a size, material and type suitable to sustain the loads from the rudder. Arrangement must be made in the design to make them watertight.

2.18.1 Where liners are fitted to rudder stocks or pintles, they are to be shrunk on or otherwise efficiently secured.

2.18.2 Where it is proposed to use stainless steel liners, the requirements in Pt 3, Ch 3, 2.17 Bearings 2.17.2 are to be complied with.

2.18.3 When stainless steel liners are used, arrangements to ensure an adequate supply of sea-water to the liner are to be provided.

2.19.1 Rudder pintles and their bearings are to comply with the requirements of Table 3.2.10 Pintle requirements.

2.19.2 Where the lower pintle is housed above the rudder gudgeon see Figure 3.2.5 Lower pintle housed above rudder gudgeon, and not below as shown in Figure 3.2.6 Lower pintle housed below rudder gudgeon, C _PL is to be measured to the top of the gudgeon.

Figure 3.2.5 Lower pintle housed above rudder gudgeon

Table 3.2.10 Pintle requirements

Item	Requirement
(1) Pintle diameter, see Note 2
	For single pintle rudders and lower pintle of semi-spade rudders:
	but for semi spade rudders need not be taken greater than A R
	Upper pintle on semi-spade rudders:
	or 0,35A R m2, whichever is the greater
	For rudders with two or more pintles (except semi-spade rudders):
(2) Maximum pintle taper	Method of assembly	Taper (on diameter)
	Manual assembly, key fitted	1 in 6
	(pintle ≤ 200mm diameter)
	Manual assembly, key fitted	1 in 9
	(pintle ≤ 400mm diameter)
	For keyed and other manually assembled pintles with diameters between 200mm and 400mm, the taper is to be obtained by interpolation.
	Hydraulic assembly, dry fit	1 in 12
	Hydraulic assembly, oil injection	1 in 15
(3) Bearing length	Z PB ≥ 1,2δPL mm
	May be less for very large pintles if bearing pressure is not greater than that given in (4), but Z PB must not be less than 1,0δPL mm
(4) Bearing pressure (on projected area)	Bearing material	Pressure
	Metal	7,0 N/mm2
	Synthetic	5,5 N/mm2
	Using force acting on bearing:
	A PL as for item (1)
(5) Gudgeon thickness in way of pintle (measured outside bush if fitted)	but need not normally exceed 125mm
(6) Pintle clearance (note should be taken of the manufacturer's recommended clearances particulary where bush material requires pre-soaking). Value of proposed minimum clearance is to be indicated on plans submitted for approval.	Bearing material	Minimum clearance, mm
	Metal	0,001δPL + 1,0
	Synthetic	0,002δPL + 1,0 but not less than 1,5
Symbols
δPL = pintle diameter, in mm V = as defined in Table 3.2.6 Rudder stock diameter but not less than 10 knots A PL = rudder area supported by the pintle, in m2 C CP, C PL = dimensions in metres, as indicated in Figure 3.2.5 Lower pintle housed above rudder gudgeon and Figure 3.2.6 Lower pintle housed below rudder gudgeon A R = rudder area, in m2 σo = as defined in Table 3.2.6 Rudder stock diameter N PL = number of pintles on the rudder Z PB = pintle bearing length, in mm P PL = force acting on bearing, in kN b G = thickness of gudgeon material in way of pintle, in mm f R = rudder profile coefficient, see Table 3.2.1 Rudder profile coefficient f R m = as defined in Table 3.2.6 Rudder stock diameter
Note 1. Proposals for higher pressures or other materials will be specially considered on the basis of satisfactory test results. Note 2. The length of the pintle housing in the gudgeon is not to be less than the maximum pintle diameter.

Figure 3.2.6 Lower pintle housed below rudder gudgeon

2.19.3 Special attention is to be paid to the fit of the pintle taper into its socket. To facilitate removal of the pintles, it is recommended that the taper is to be not less than half the maximum value given in Table 3.2.10 Pintle requirements.

2.19.4 The distance between the lowest rudder stock bearing and the upper pintle is to be as short as possible.

2.19.5 Where liners are fitted to pintles, they are to be shrunk on or otherwise efficiently secured. If liners are to be shrunk on, the shrinkage allowance is to be indicated on the plans. Where liners are formed by stainless steel weld deposit, the pintles are to be of weldable quality steel and details of the procedure are to be submitted.

2.19.6 The bottom pintle on semi-spade (Mariner) type rudders are:

1. If inserted into their sockets from below, to be keyed to the rudder or sternframe as appropriate or to be hydraulically assembled, with the nut adequately locked, or

2. If inserted into their sockets from above, to be provided with an appropriate locking device, the nut being adequately secured.

2.19.7 Where an *IWS (In-water Survey) notation is to be assigned, see Pt 3, Ch 3, 2.37 In-water Survey requirements.

2.19.8 Where it is proposed to use stainless steel liners, the requirements in Pt 3, Ch 3, 2.17 Bearings 2.17.2 are to be complied with.

2.20.1 Rudder coupling design is to be in accordance with Table 3.2.11 Rudder couplings to stock.

Table 3.2.11 Rudder couplings to stock

Arrangement	Parameter	Requirement
		Horizontal coupling	Vertical coupling
(1) Bolted couplings (see Notes)	n	≥ 6		≥ 8
	δb
	m	0,00071nd Sδb 2		0,00043d s 3
	t f	δb see Note 1		δb
	αmax see Note 2			-
	αas built see Note 2	≤ αmax		-
	w f	0,67δb		0,67δb
(2) Conical couplings	θt
	l t	≥1,5d s
	w
	P u	Approximately equal to
	P o	Approximately equal to
	σ o
Symbols
n = number of bolts in coupling
δb = diameter of coupling bolts, in mm
d s, d su = rudder stock diameters as defined in Table 3.2.6 Rudder stock diameter
m = first moment of area of bolts about centre of coupling, in cm3
k 1 = the greater of k s and k f
k s = where σo is the specified minimum yield stress at the rudder stock and m is as defined in Table 3.2.6 Rudder stock diameter
k f = where σo is the specified minimum yield stress at the upper coupling flange and m is as defined in Table 3.2.6 Rudder stock diameter
h = vertical distance between the centre of pressure and the centre point of the palm radius, R, in metres, see Figure 3.2.7 Rudder stock connection
R = palm radius between rudder stock and connected flange, not smaller than , in mm
t f = minimum thickness of coupling flange, in mm
t fa = as built flange thickness, in mm
αmax = maximum allowable stress concentration factor
αas built = stress concentration factor for as built scantlings =
w f = width of flange material outside the bolt holes, in mm
θ t = taper of conical coupling, on the diameter, e.g.: =
t = length of taper, in mm
= required mean grip stress, in N/mm2
w = corresponding push-up of rudder stock, in mm
P u, P o = corresponding push-up, pull-off loads respectively, in N
σo = minimum yield stress of stock and gudgeon material, in N/mm2. σo is not to be taken greater than 70 per cent of the ultimate tensile strength
R = effective weight of rudder, in N
= mean diameter of coupling taper, in mm
= diameter of coupling taper at any position, in mm
= mean external diameter of gudgeon housing, in mm
= external diameter of gudgeon housing at any position, in mm
=
f =
M T = maximum torque applied to stock, and is to be taken as the greater of M F, M A or M W.
M F = P L X PF x 106 Nmm in the ahead condition
M A = P L X PA x 106 Nmm in the astern condition
M W = the torque generated by the steering gear at the maximum working pressure supplied by the manufacturer, in Nmm. M W is not to exceed the greater of 3,0M F or 3,0M A
P L = lateral force on rudder acting at centre of pressure in ahead and astern conditions, as defined in Table 3.2.6 Rudder stock diameter, in kN
X PF, X PA = the horizontal distances, in metres, see Table 3.2.5 Position of centre of pressure
K 1, K 2, K 3 = constants depending on the type of assembly adopted as follows:
			K 1	K 2	K 3
	Oil injection method	with key	15	0,0064	0,025
	Oil injection method	without key	15	0,0036	0,025
	Dry fit method	with key	12	0,0128	0,170
	Dry fit method	without key	12	0,0072	0,170
Note 1. For spade rudders with horizontal coupling, t f is not to be less than 0,25d s. Note 2. This requirement is applicable only for spade rudders with horizontal couplings, see Figure 3.2.7 Rudder stock connection. Note 3. Where materials vary for individual components, scantling calculations for such components are to be based on d s for the relevant material.

2.20.2 Where coupling bolts are required they are to be fitted bolts. Suitable arrangements are to be made to lock the nuts.

2.20.3 For rudders with horizontal coupling arrangements, where the upper flange is welded to the rudder stock, a full penetration weld is required and its integrity is to be confirmed by non-destructive examination. Such rudder stocks are to be subjected to a furnace post-weld heat treatment (PWHT) after completion of all welding operations. For carbon or carbon manganese steels, the PWHT temperature is not to be less than 600^oC.

2.20.4 The connecting bolts for coupling the rudder to the rudder stock are to be positioned with sufficient clearance to allow the fitting and removal of the bolts and nuts without contacting the palm radius, R, see Figure 3.2.7 Rudder stock connection. The surface forming the palm radius is to be free of hard and sharp corners and is to be machined smooth to the Surveyor's satisfaction. The surface in way of bolts and nuts is to be machined smooth to the Surveyor's satisfaction.

2.20.5 For spade rudders fitted with a fabricated rectangular mainpiece, the mainpiece is to be designed with its forward and aft transverse sections at equal distances forward and aft of the rudder stock transverse axis, see Figure 3.2.7 Rudder stock connection.

2.21.1 Where a rudder stock is connected to a rudder by a keyless fitting, the rudder is to be a good fit on the rudder stock cone. During the fit-up, and before the push-up load is applied, an area of contact of at least 80 per cent of the theoretical area of contact is to be achieved, and this is to be evenly distributed. The relationship of the rudder to stock at which this occurs is to be marked, and the push-up then measured from that point. The upper edge of the upper mainpiece bore is to have a slight radius. After final fitting of the stock to the rudder, positive means are to be used for locking the securing nut to the stock.

2.21.2 Where a keyed tapered fitting of a rudder stock to a rudder is proposed, a securing nut of adequate proportions is to be provided. After the final fitting of the stock to the rudder, positive means are to be used for locking this nut.

2.22.1 The weight of the rudder is to be supported at the heel pintle or by a carrier attached to the rudder head. The hull structure supporting the carrier bearing is to be adequately strengthened. The plating under all rudder-head bearings or rudder carriers is to be increased in thickness.

2.23.1 Suitable arrangements are to be provided to prevent the rudder from lifting.

2.23.2 Jumping collars are not to be welded to the rudder stock.

2.24.1 Where rudders are of plated construction, drain plugs are to be provided to ensure that all compartments can be adequately drained. These plugs are to be locked and details of their scantlings, arrangements and position clearly indicated on the rudder plan.

2.25.1 All metalwork is to be suitably protected against corrosion. This may be by coating or, where applicable, by a system of cathodic protection, see Ch 15 Corrosion Prevention of the Rules for Materials.

2.25.2 Metalwork is to be suitably cleaned before the application of any coating. Where appropriate, blast cleaning or other equally effective means are to be employed for this purpose.

2.26.1 Where materials vary for individual components, they are to be compatible to avoid galvanic corrosion. Scantling calculations for the components are to be based on d _s for the relevant material, see Table 3.2.6 Rudder stock diameter.

2.27.1 Internal surfaces of the rudder are to be efficiently coated or the rudder is to be filled with foam plastics. Where it is intended to fill the rudder with plastic foam, details of the foam are to be submitted.

2.28.1 For testing of rudders, see Table 1.7.1 Testing requirements in Chapter 1.

2.29.1 Tillers and quadrants are to comply with the requirements of Table 1.4.1 Connection of tiller to stock in Pt 14, Ch 1.

2.29.2 The steering gear is to be mounted on a seat and adequately secured.

2.30.1 Connecting bars are to comply with the requirements of Pt 14, Ch 1, 4.3 Rudder systems 4.3.3.

Figure 3.2.7 Rudder stock connection

2.31.1 Where the tiller or quadrant is bolted, a key having an effective cross-sectional area in shear of not less than 0,25d _SU ² mm² is to be fitted. The thickness of the key is to be not less than d _SU/6 mm. Alternatively, the rudder stock may be machined to a square section in lieu of fitting a key. d _SU is as defined in Table 3.2.6 Rudder stock diameter.

2.31.2 Keyways are to extend over the full depth of the tiller boss.

2.31.3 Keyways in the rudder stock are to have rounded ends and the corners at the base of the keyway are to be radiused.

2.32.1 Suitable rudder stops are to be provided to limit the rudder angle to the desired level port and starboard. These stops are to be of substantial construction and efficiently connected to the supporting structure.

2.33.1 Where rudders are of a novel design they may be specially considered on the basis of the Rules. Alternatively the Builder's/designer's calculations are to be submitted for consideration.

2.34.1 FRP double plated rudders are to have an internal structure of suitable strength and material. Details of the rudder are to be submitted to LR for approval.

2.34.2 Where rudder blades are moulded in halves they are to be effectively joined together by means of external overbonding of the joint or suitable mechanical fastening or equivalent.

2.34.3  The internal structure of FRP double plated rudders may be a metallic framework. It is to be made up of a mainpiece fitted with arms, within the blade, or an equivalent arrangement. Both halves of the rudder blade moulding are to be effectively connected to the metallic framework and mainpiece by either mechanical means or suitable bonded connection.

2.34.4  When the internal structure of the FRP double plated rudder is metallic or of a material that may detach from the blades at the point where the structure extends outside the rudder blade, a suitable seal is to be provided to avoid ingress of water.

2.34.5 Rudders are to be filled with a suitable material upon completion of the join up, details of the filler material are to be submitted.

2.34.6 The diameter of the top of the rudder mainpiece must not be less than that of the rudder stock. For spade rudders this diameter may be gradually reduced for the lower third to not less than 75 per cent of the rudder stock diameter.

2.34.7 The rudder arms are to be efficiently attached to the mainpiece.

2.34.8 The laminate weight of moulded fibre reinforced plastics double plate rudders is to be determined by direct calculation, subject to a minimum laminate thickness of 5 mm.

2.35.1 The rudder tube construction may be of aluminium alloy, steel, bronze or fibre reinforced plastic.

2.35.2 The scantlings of rudder tubes will be individually considered.

2.35.3 For steel and aluminium hulls, the bottom shell in way of the rudder tubes is to be additionally reinforced by means of an insert plate to increase the bottom shell thickness by 50 per cent.

2.35.4 For F.R.P hulls, the bottom shell laminate in way of the rudder tubes is to be locally increased by 50 per cent. The increased thickness in way of the rudder tube need not exceed the rule keel thickness requirement.

2.35.5 For F.R.P sandwich hulls the shell in way of the rudder tube connection is to be either:

1. Reduced from the sandwich hull construction to single skin laminate for a distance of a least three times the rudder tube diameter about the rudder stock axis. The single skin region is to be additionally reinforced by a minimum of 50 per cent of the sum of the inner and outer sandwich laminate subject to this being at least equivalent to a 50 per cent increase in thickness of the Rule minimum bottom shell laminate for a single skin F.R.P. craft of the equivalent Rule length L _R. The reinforced laminate need not be greater than the Rule keel laminate thickness.

2. Reduced from the sandwich hull construction to a single skin laminate for a distance of three times the rudder tube diameter about the rudder stock axis. After bonding in the rudder tube to the single skin laminate the foam core and inner skin are then reinstated.

3. Proposals to replace the sandwich core with a core having higher core shear strength and compressive strength than that of the adjacent structure prior to bonding the tube to the inner and outer skins will be the subject of special consideration.

2.35.6 The rudder tube may be connected to the shell by bonding, bolting or welding as applicable depending upon the construction material of the shell.

2.35.7 When bonding in rudder tubes the bonding angle is to be not less than the Rule minimum bottom shell weight. F.R.P. tubes are to be thoroughly abraded and degreased prior to installation and laminating. Bonded in metallic tubes are to be knurled in way of the bonding material and thoroughly degreased prior to installation.

2.35.8 Where rudder tubes are to be retained by bolting they are to be provided with a substantial flange securely attached to the hull structure. Where bolts are used, the nuts are to be suitably locked.

2.35.9 Where rudder tubes are to be welded to hull insert plates full penetration welding is required.

2.35.10 Rudder tubes are to be supported by suitable brackets and deep floors to avoid hard spots on the shell and to ensure continuity of the main hull structure.

2.35.11 Rudder bearings are to be secured against rotation within the rudder tubes by suitable pinch bolting or keys. Details are to be submitted for approval.

2.36.1 In rudder trunks which are open to the sea, a seal is to be fitted above the deepest load waterline, to prevent water from entering the steering gear compartment and the lubricant from being washed away from the rudder carrier. If the top of the rudder trunk is below the deepest waterline two separate seals are to be provided. Rudder trunk boundaries, where exposed to the sea, are to have a corrosion protection coating applied in accordance with the manufacturer's instructions.

2.36.2 Lip seals or 'O' rings may be used either in isolation or in combination with one or other of the seal arrangements.

2.36.3 A watertight gland body may be used. It is then to be formed by the top of the fabricated or cast rudder tube, the gland packing being retained against the top bearing or a check in the wall of the rudder tube and is compressed by a gland packet which may be of the flange type, screwed cap or other suitable arrangement.

2.37.1 Where an *IWS (In-water Survey) notation is to be assigned, see Pt 1, Ch 2, 3.8 Other hull notations, means are to be provided for ascertaining the rudder pintle and bush clearances and for verifying the security of the pintles in their sockets with the craft afloat.