1. General - Stiffener/web connection
Size of welding gun compared to typical stiffener height
Continuous welding difficult
Start and stop defects
50mm
Approval Centre Sydney

2. General - Stiffener/web connection
Bracket or flat bar added
Not too difficult to weld
Difficult to weld
Small shear capacity

3. General - Stiffener/web connection
Cover plate will improve shear capacity and improve force distribution
If possible avoid scallops, snipe corner of collar plate to allow space for longitudinal weld and then weld continuously around collar plate
Approval Centre Sydney

4. Edge Stiffening Requirements
General - Brackets
Edge Stiffening Requirements

5. General - Tipping Brackets
Approval Centre Sydney

6. General - Termination of Sniped Stiffeners
D<25mm
30 degrees
Sniping allowed when:
buckling stiffeners
dynamic loads/vibrations of minor importance

7. General - Pillar Connections to Deck
Should not be applied if tension through pillar may occur
Approval Centre Sydney

8. General - Pillar Connections/Cross Ties connection
Applicable to pillars/cross ties that may be under compression and tension

9. General - Alignment in Way of Section Joints
Bulkhead or Deck
Section Joint
Easier to get acceptable alignment when a continuous member is penetrating the bulkhead or deck structure

10. General - Longitudinals through Web Frames
Approval Centre Sydney

11. Longitudinals at Watertight Bulkhead
Longitudinal continuous through bulkhead
Longitudinal terminated at bulkhead with soft-nose brackets
Approval Centre Sydney

12. Edge Support of Cut-Outs
Edge support when length of free edge exceed 50t or D50t
Cut-outs to be kept well clear of end of brackets and locations where shear stresses are high

13. Hard Chine / Knuckle
Problem: Cracking due to unfavourable detail design.
Possible Cause: The knuckle represents an elastic element in the plate, the effective flange will be reduced and the stresses will increase locally in way of the web / bulkhead, in addition large dynamic pressures act on the planing strip / spray rail.
Integral spray rail
Cracks
External spray rail
Cracks in web
and shell plating

14. Hard Chine / Knuckle
Solution:
KNUCKLE SUPPORT
CHINE SUPPORT

15. Pillar Connections/Cross Ties connection
Problem: Cracking and buckling of frame webs and ties.
Possible Cause: Unfavourable detail design.
Buckling and tripping of frame
Cracks
Position

16. Pillar Connections/Cross Ties connection
Add tripping brackets
Soft toe brackets
Solution:
Additional tripping brackets should be fitted to support cross tie or pillar.
Soft toe brackets to be fitted

17. Transverse Frames - Buckling
Problem : Buckling and tripping of frame in way of sharp radius.
Buckled web and tripped flange
Position

18. Transverse Frames Buckling
Solution: as illustrated below, or various combinations to increase buckling capability
Tripping brackets
Additional
buckling stiffener
Additional bracket
Tripping brackets

19. SKEGS FOR DIRECTIONAL STABILITY
Problem:
Cracks in various locations starting from weld to bottom plating, edges and slot welds
Possible Cause:
Unfavourable detail design.
Insufficient stiffening
Unfavourable weld method
Cracks
Bottom Pl.

20. SKEGS FOR DIRECTIONAL STABILITY
Solution:
Introduce additional stiffening.
Improve weld connections by using double sided fillet welds or full penetration with backing bar where access is difficult.
Avoid scallop welds, replace with continuous welds against permanent backing
Additional Stiffening /
Continuous Welding

21. SCALLOPS AND CHAIN WELDS
Problem:
Cracks originating from end of chain weld propagating into stiffener. Cracks originating from scallops propagating into web or shell plating, along HAZ of weld
Possible Cause:
Vibrations from machinery or high dynamic sealoads. Unfavourable detail design for area. Unfavourable weld execution at starts and stops of chain welds and at ends/terminations of scallops
Cracks in web along HAZ of weld,
crack in bottom plating
Crack

22. SCALLOPS AND CHAIN WELDS
Solution:
Longitudinal stiffeners in area should be welded with double continuous welds. Scallops should be avoided, necessary drain holes may be cut in web above weld to bottom plating
Scallops avoided, necessary
drain holes cut above weld.
Re-weld with continuous
welding

23. Thrust Bearing, Shaft Bearing and Engine Foundations
Problem:
Cracks in various parts of foundations originating from weld toes at ends of brackets, stiffeners and scallops, ends of sniped flanges, or at ends of buttwelds in flanges in way of thickness transitions.
Possible Cause:
Unfavourable detail design, weld execution at ends, in way of scallops and at buttwelds of thickness transitions. Insufficient thickness of critical parts.
a : a
Cracks in bracket supports starting
from bracket ends and scallops
Cracks in foundation flanges in way
of thickness transitions a

24. Thrust Bearing, Shaft Bearing and Engine Foundations
Reposition weld in relation to
supports and increase taper
a : a
New thicker transverse webs cut from
one piece welded without scallops and
with weld toes ground. Reposition girder
webs inside line of gear bed bolting. a
Solution:
Improve detail design, by avoiding brackets and stiffening with unfavourable details as indicated previously.
Increase thickness in certain locations. Improve position and profile of transitions between thick and thinner parts.
Improve structural continuity by adding brackets or new flange pieces replacing sniped flanges.
Careful grinding of critical welds and rounding of edges of foundations, flanges and transitions will improve fatigue life.

25. Thrust Bearing, Shaft Bearing and Engine Foundations
Foundations supporting oscillatory equipment will be exposed to varying degrees of vibrations at high frequency.
Fatigue failure must therefore be taken into consideration.
Typical details that may give rise to high stress concentrations and for which it is difficult to obtain a good surface finish are scallops, cutouts, sniped flanges etc.
It is therefore very important to maintain structural continuity, avoid scallops and sniped flanges whenever possible and improve details by grinding smooth surfaces at critical locations.

26. FOIL AND APPENDAGE FOUNDATION
Problem:
Cracks in various parts of foundations originating from weld toes at ends of brackets, stiffeners and scallops, or at ends of buttwelds in flanges in way of thickness transitions.
Possible Causes:
Unfavourable detail design. Poor execution of welds. Insufficient dimensions of critical parts. Lack of structural continuity
Foil internal
supporting
structure
Cracks in various of the flange
junctions and bracket end connections

27. FOIL AND APPENDAGE FOUNDATION
Solution
Improving detail design by ensuring soft transitions at cruciform joints, positioning of buttwelds outside areas of stress concentrations, avoiding scallops or ensuring proper weld finishing at the scallop toes, fitting of soft toe brackets at ends of girders.
Use proper soft transitions
between girder flanges
and soft toe brackets at
girder ends
Approval Centre Sydney

28. BULKHEAD STIFFENING ARRANGEMENT
Problem: Cracks in brackets or stiffener at ends or cracks in bulkhead plating in way of unsupported stiffener ends
Possible Cause: Unfavourable detail design. Fatigue cracking from sloshing of liquid in tanks or varying sea pressure
Typical cracks at unsupported
ends of vertical stiffeners
Cracks
Cracks

29. BULKHEAD STIFFENING ARRANGEMENT
Solution
Soft toe brackets
Provide full shear connection of webs
Provide end support to unsupported stiffeners.
End connection of bulkhead stiffeners
Soft toe brackets, stiffener
webs welded continuously to bulkhead.

30. Approval Centre Sydney
BRACKET CONNECTIONS
Problem
Cracks in brackets and longitudinal stiffener, cracks originating from weld toes in various locations propagating into plating or along HAZ of weld.
Possible Causes
Vibrations from machinery or high dynamic sealoads. Unfavourable detail design for the area. Unfavourable workmanship. Insufficient scantlings.
Cracks
Intermittent welding
Approval Centre Sydney

31. BRACKET CONNECTIONS(cont)
Solution
Connect webs of longitudinals to bulkheads or frames with continuous welds, avoid scallops and weld start / stops in critical positions. Fit soft toe brackets. Toe height should be limited - refer soft toe bracket detail
Soft bracket possibly of
increased size.
Webs welded continuously.

32. TRANSVERSE FRAMES Problem
Cracking in plate buttweld in knuckle. Cracking in webs and bulkheads in way of knuckle.
Possible Causes
Unfavourable detail design. The knuckle represents an elastic element in the plate, the effective flange will be reduced and the stresses will increase locally in way of the web / bulkhead.
Cracks in webs from scallop
Crack in longitudinal
butt weld in shell
Cracks in webs and along
shell plating butt weld

33. TRANSVERSE FRAMES Solution
Knuckles should be supported with brackets which are properly connected to stiffeners on bulkheads or flanges of web frames.
For knuckles with small change of direction, a plate insert made from a bent plate may be introduced to move butt weld out of the knuckle area.
Alt. 2, on one
side of frame
Alt. 1, on both
sides of frame
Add brackets to support knuckle
Insert bent plate

34. STRUCTURAL DESIGN - POINTS TO REMEMBER
1. Bottom slamming will be dimensioning to all structures in this area. Shear area requirement to longitudinal stiffener may be severe.
2. Chines and knuckles have to be supported
3. Side plating (L>50m) may need increased thickness for shear buckling.
4. Vertical pillars to be positioned correctly first time.
5. Transverse deck girders will often have long spans which need appropriate section properties.
6. Deck plates of catamarans need to be checked for buckling due to transverse bending moment. 5 3 4 6 2 1