4 Hopper Knuckle Connection

4.1 Design standard C to H

4.1.1

The welded knuckle between hopper plating and inner bottom plating for double-hull oil tankers is to be designed according to the design standard C in Table 3. The design standard D in Table 4 may be used as an alternative to increase fatigue strength at the hopper connection.

4.1.2

The welded knuckle between hopper plating and inner bottom plating for bulk carriers is to be designed according to the design standard E in Table 5.

4.1.3

The radiused knuckle between hopper plating and inner bottom plating is to be designed according to the design standard F in Table 6 for double hull oil tankers.

Alternative structural arrangements may be accepted based on verification in accordance with Ch 9, Sec 5, [3.3].

4.1.4

The radiused knuckle between hopper plating and inner bottom plating for bulk carriers is to be designed according to the design standard G in Table 7.

4.1.5

The radiused knuckle between hopper plating and inner side plating for oil tankers and double side bulk carriers is to be designed according to the design standard H in Table 8.

4.1.6

In general, the prescribed minimum requirements for welding, weld dressing and building tolerances as given in Table 3 to Table 8 are to be followed. Alternative positioning and/or dispensation of some support structure, such as transverse and longitudinal brackets may be accepted subject to demonstration of acceptable fatigue lives. Inserts and/or weld dressing additional to those prescribed may be required as a consequence of hot spot fatigue analysis.

Table 2 : Design standard B – scallops in way of block joints

Welding of deck stiffeners in way of block joints
Critical areas	Design standard B


Critical locations
	Note 1: Alternative scallop geometry to that shown in option II may be accepted subject to demonstration of satisfactory fatigue life based on hull girder loads taking into account additional stress concentration factor in way of weld
Critical location	Welding of deck stiffeners in way of block joints in cargo tank region, the strength deck and side above 0.9 D from the baseline.
Detail design standard	All scallops are to be fitted according to detail design standard B.
Building tolerances	Ensure alignment of all structural members according to IACS Recommendation No. 47.
Welding requirements	Full penetration butt weld, free of undercut or notches, around the web and flange of the longitudinal stiffener at block joints, particularly in way of the weld termination at the scallop for option II.

Table 3 : Design standard C – hopper knuckle connection detail, welded, without bracket, double hull oil tanker

Connections of floors in double bottom tanks to hopper tanks Hopper corner connections employing welded inner bottom and hopper sloping plating
Critical areas	Design standard C

Critical locations

Minimum requirement	As a minimum, detail design standard C or D is to be fitted. The ground surface is to be protected by a stripe coat of suitable paint composition, where the lower hopper knuckle region of cargo tanks is not coated.
Critical location	Hopper sloping plating connections to inner bottom plating in way of floors. Floor connections to inner bottom plating and side girder in way of hopper corners.
Detail design standard	Elimination of scallops in way of hopper corners, extension of inner bottom plating to reduce level of resultant stresses arising from cyclic external hydrodynamic pressure, cargo inertia pressure and hull girder loads. Scarfing bracket thickness is to be close to that of the inner bottom in way of the knuckle.
Building tolerances	Median line of hopper sloping plate is to be in line with the median line of the girder with an allowable tolerance of t_as-built/3 or 5 mm, whichever is less, where t_as-built is the as-built side girder thickness. The allowable tolerance is to be measured parallel to the inner bottom.
Welding requirements	Full or partial penetration welding is to be applied to hopper sloping plating and inner bottom plating connection. Partial penetration welding is to be applied to connections of side girder to inner bottom plating, to connections of floors to inner bottom plating and to side girder, to connections of hopper transverse webs to sloping plating, to inner bottom and to side girder in way of the hopper knuckle. Definition of full and partial penetration welding and their required extent are given in Ch 12, Sec 3 Weld between hopper plating and inner bottom plating to be enlarged and ground smooth. Visible undercuts are to be removed, see Ch 9, Sec 3, [6]. Weld enlargement and grinding are applicable to minimum 200 mm on each side of the floor.

Table 4 : Design standard D – hopper knuckle connection detail, welded, with bracket, double hull oil tanker

Connections of floors in double bottom tanks to hopper tanks Hopper corner connections employing welded inner bottom and hopper sloping plating
Critical areas	Design standard D
	Note 1: Bracket to be fitted inside cargo tank. Note 2: Bracket to extend approximately to the first longitudinal. Note 3: The bracket toes are to have a soft nose design. Note 4: Bracket material to be same as that of inner bottom. Note 5: Slenderness of bracket to be in accordance with Ch 8, Sec 2, [5.2].
Critical locations

Minimum requirement	As a minimum, detail design standard C or D is to be applied.
Critical location	Hopper sloping plating connections to inner bottom plating in way of floors. Floor connections to inner bottom plating and side girder in way of hopper corners. The bracket connection to inner bottom and hopper sloping plate.
Detail design standard	Elimination of scallops in way of hopper corners, extension of inner bottom plating to reduce level of resultant stresses arising from cyclic external hydrodynamic pressure, cargo inertia pressure and hull girder loads. Scarfing bracket thickness similar to that of the inner bottom in way of the knuckle.
Building tolerances	Median line of hopper sloping plate is to be in line with the median line of girder with an allowable tolerance of t_as-built /3 or 5 mm, whichever is less, where t_as-built is the as-built side girder thickness.
Welding requirements	Partial penetration welding is to be applied to hopper sloping plating and inner bottom plating connection, to connections of side girder to inner bottom plating, to connections of floors to inner bottom plating and to side girder, to connections of hopper transverse webs to sloping plating, to inner bottom and to side girder in way of the hopper knuckle. Partial penetration welding is to be applied to the bracket connections to inner bottom and hopper sloping plate, full penetration welding is to be applied at bracket toes. Definition of full and partial penetration welding and their required extent are given in Ch 12, Sec 3.

Table 5 : Design standard E – hopper knuckle connection detail, welded, bulk carrier

Connections of floors in double bottom tanks to hopper tanks Welded knuckle connection of hopper tank sloping plating to inner bottom plating
Critical areas	Design standard E

Critical locations

Minimum requirement	As a minimum, detail design standard E is to be fitted. Ballast holds: No scallops or close scallops with collars; scarfing bracket; intermediate bracket if floor spacing greater than 2.5 m. Dry holds: No scallop or close scallops with collars and scarfing bracket.
Critical location	Hopper sloping plating connections to inner bottom plating in way of the floors. Floor connections to inner bottom plating and side girder in way of the hopper knuckle.
Detail design standard	Elimination of scallops in way of hopper knuckle, extension of inner bottom plating to reduce level of resultant stresses arising from cyclic external hydrodynamic pressure, cargo inertia pressure and hull girder loads. Scarfing bracket net thickness is to be minimum 80% of that of the inner bottom in way of knuckle and steel material to be of the same yield strength.
Building tolerances	Median line of hopper sloping plate is to be in line with the median line of girder with an allowable tolerance of t_as-built/3 or 5 mm, whichever is less, where t_as-built is the as-built side girder thickness.
Welding requirements	Full or partial penetration welding is to be applied to hopper sloping plating and inner bottom plating connection for the length of the cargo hold. Partial penetration welding is to be applied to connections of side girder to inner bottom plating, to connections of floors to inner bottom plating and to side girder, to connections of hopper transverse webs to sloping plating, to inner bottom and to side girder in way of the hopper knuckle. Weld between hopper plating and inner bottom plating is to be enlarged and ground smooth. Visible undercuts are to be removed. Weld enlargement and grinding are applicable to minimum 200 mm on each side of the floor. Definition of full and partial penetration welding and their required extent are given in Ch 12, Sec 3.

Table 6 : Design standard F – hopper knuckle connection detail, radiused type, for double hull oil tanker

Connections of floors in double bottom tanks to hopper tanks Hopper corner connections employing radiused knuckle between inner bottom and hopper sloping plating
Critical areas	Design standard F

Critical locations
	Note 1: Distance from side girder to centre of knuckle is to be as small as practicable, but is not to exceed 50 mm. Note 2: The knuckle radius is not to be less than 4.5 t_as-built or 100 mm, whichever is the greater, where t_as-built is the as-built thickness of the knuckle part. Note 3: Additional transverse brackets offset at a suitable distance on either side of transverse floor/hopper connection. Note 4: Additional longitudinal bracket on the side of sloping plate. Note 5: Longitudinal and/or transverse brackets may be omitted if it can be demonstrated that the girder provides sufficient support at the knuckle line, i.e. that fatigue requirements according to Ch 9, Sec 5 and local strength analysis requirements according to Ch 7, Sec 3 are fulfilled.
Critical location	Floor and hopper transverse web connections to inner bottom plating and hopper sloping plate, respectively and to side girder in way of hopper knuckle. Side girder connections to inner bottom plating in way of floors.
Detail design standard	Elimination of scallops in way of hopper/girder connection and additional transverse and longitudinal brackets to reduce peak and range of resultant stresses arising from cyclic external hydrodynamic pressure, cargo inertia pressure, and hull girder global loading, and provide additional support to sloping plate.
Building tolerances	The nominal distance between the centres of thickness of the two abutting members (e.g. floor and hopper web plate) is not to exceed 1/3 of the as-built thickness of the side girder.
Welding requirements	Full penetration welding is to be applied to connections of floors to hopper/inner bottom plating in way of radiused hopper knuckle. Partial penetration welding is to be applied to connections of floors/hopper transverse webs to the side girder in way of hopper corner, and to connections of side girder to hopper/inner bottom plating. Definition of full and partial penetration welding and their required extent are given in Ch 12, Sec 3. In order to improve the fatigue strength, weld enlargement and grinding are applicable to full and partial penetration welds with a minimum distance of 300 mm from the intersection point between the radiused knuckle, the floor and the side girder.

Table 7 : Design standard G – hopper knuckle connection detail, radiused type, bulk carrier

Connections of floors in double bottom tanks to hopper tanks Hopper corner connections employing radiused knuckle between inner bottom and hopper sloping plating
Critical areas	Design standard G

Critical locations
	Intermediate bracket arrangement (Section B-B). Two intermediate brackets at both sides of floor/transverse web.
	Note 1: Distance from side girder to centre of knuckle is to be as small as practicable, but is not to exceed 50 mm. Note 2: The knuckle radius is not to be less than 4.5 t_as-built or 100 mm, whichever is the greater, in cases where t_as-built is the as-built thickness of the knuckle part. Note 3: Additional transverse brackets on both side of transverse floor/hopper connection. Note 4: Transverse brackets may be omitted if it can be demonstrated that the girder provides sufficient support at the knuckle line, i.e. that fatigue requirements according to Ch 9, Sec 5 and local strength analysis requirements according to Ch 7, Sec 3 are fulfilled.
Critical location	Side girder connections to inner bottom plating in way of floors. Floor and hopper transverse web connections to inner bottom plating and hopper sloping plate, respectively, and to side girder in way of hopper corners.
Detail design standard	Elimination of scallops in way of hopper/girder connection. Ballast holds: Intermediate brackets fitted at approximately 0.5 floor space from floor/hopper web. Dry holds: Intermediate brackets fitted at 0.5 floor space from floor/hopper web if floor spacing is equal to or greater than 2.5 m.
Building tolerances	The nominal distance between the centres of thickness of the two abutting members (e.g. floor and hopper web plate and additional supporting brackets) should not exceed 1/3 of the as-built thickness of the side girder.
Welding requirements	Full penetration welding is to be applied to connections of floors to hopper /inner bottom plating in way of radiused hopper knuckle. Partial penetration welding is to be applied to connections of floors/hopper transverse webs to side girder in way of hopper corners, to connections of side girder to hopper /inner bottom plating. Definition of full and partial penetration welding and their required extent are given in Ch 12, Sec 3.

Table 8 : Design standard H – upper hopper knuckle connection detail, radiused type, oil tankers and double side bulk carrier

Connections of transverse webs in double side tanks to hopper tanks Hopper corner connections employing radiused knuckle between side longitudinal bulkhead and hopper sloping plating
Critical areas	Design standard H

Critical locations

	Note 1: Distance from side stringer to centre of knuckle is to be as small as practicable, but is not to exceed 50 mm. Note 2: The knuckle radius is not to be less than 4.5 t_as-built or 100 mm, whichever is the greater, where t_as-built is the as-built thickness of the knuckle part , according to Ch 12 Sec 1 [3] & [4] Note 3: Additional transverse brackets offset at a suitable distance on either side of transverse floor/hopper connection. Note 4: Additional longitudinal bracket on the side of sloping plate. Note 5: Longitudinal and/or transverse brackets may be omitted if it can be demonstrated that the girder provides sufficient support at the knuckle line, i.e. that fatigue requirements according to Ch 9, Sec 5 and local strength analysis requirements according to Ch 7, Sec 3 are fulfilled.
Critical location	Side stringer connections to side longitudinal bulkhead in way of transverse webs. Double side tank transverse web and hopper transverse web connections to side longitudinal bulkhead and to side stringers in way of hopper corners.
Detail design standard	Elimination of scallops in way of hopper corners, closer knuckle distance from side stringers. Additional longitudinal/transverse brackets to reduce peak and range of resultant stresses arising from cyclic external hydrodynamic pressure and cargo inertia pressure.
Building tolerances	The nominal distance between the centres of thickness of the two abutting members should not exceed 1/3 of the as-built thickness of the side stringer.
Welding requirements	Partial penetration welding is applied to connection of side stringers to side longitudinal bulkhead, connection of double side tank transverse webs to side longitudinal bulkhead and to side stringers, connection of hopper transverse webs to sloped side longitudinal bulkhead and to side stringers in way of hopper corners. Small scallops of suitable shape, which are to be closed by welding after completion of the continuous welding of side stringers to longitudinal bulkhead, are to be provided where scallops are eliminated. Definition of full and partial penetration welding and their required extent are given in Ch 12, Sec 3.