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

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

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

Edge Stiffening Requirements General - Brackets Edge Stiffening Requirements

General - Tipping Brackets Approval Centre Sydney

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

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

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

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

General - Longitudinals through Web Frames Approval Centre Sydney

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

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

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

Hard Chine / Knuckle Solution: KNUCKLE SUPPORT CHINE SUPPORT

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

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

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

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

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.

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

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

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

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

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.

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.

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

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

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

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.

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

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.

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

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

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