PFN305 - Lashing Forces 1 [PDF]

Zitiervorschau

LASHING FORCES - EASEACON LASHING MODULE

Faculty of Maritime Studies - SPLIT Prepared by : Capt.Goran Belamaric, Mag. Eng. Master Mariner

Split, listopad.2011.

SUMMARY > 1. Theoritic Approach of ship‟s motion and lashing forces. > a. Review of the basic parameter & forces based on BV rules > b. Deck securing

> c. Cargo Holds Stowage

> 2. Lashing module on Easecon > a. Presentation of calculation display > b. Example of optimisation of bay plan

.

Capt.Goran Belamaric, Mag. Eng

Container loss at sea THE BASIC CAUSE of many collapsed container stows and the loss of containers overboard can be attributed to inadequate or incorrect securing, resulting from either lack and/or misunderstanding of instructions/information on-board concerning applicable stowage and securing arrangements

.

Capt.Goran Belamaric, Mag. Eng

EASEACON LASHING MODULE

Common reason why stows collapse (source “West of England P&I”)

> > > > > > > > > >

Container stacks being too heavy and too high overall, exposing the lower containers to excessive transverse racking and compressive forces due to the tipping effect. Containers at the top of the stack being significantly heavier than those below. The wind force acting on the outboard stacks not being taken into account. Loose lashings allowing the stacks to tilt and arrest sharply as the slack is taken up. Two 20 foot containers placed in a 40 foot slot, leaving insufficient space for lashing rods to be fitted to the inward facing ends. Out of gauge containers, such high cube boxes, mixed randomly with standard units High cube boxes stowed cumulatively Securing equipment not applied correctly Portable and/or fixed securing equipment in damaged or worn condition The movement of inadequately secured heavy cargo within a container resulting in damage to the container walls

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Ship motion Ship at sea may move in six different direction simultaneously. Rolling, pitching and heaving generate the highest forces

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Pounding

Heavy pounding at bow and stern increases considerably vessel motion and lashing forces EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Ship movement and forces on containers and lashing > Rolling > affects container corner posts, twistlocks, hatch covers and the deck by inducing compression and tension forces. > The motion also creates transverse racking forces which, if excessive, may distort the walls and ends of container frames > Deck cargo racking forces are resisted primarily by lashing rods and turnbuckles

> Pitching > Forces are similar to forces created by rolling, but acts longitudinally

> Heaving > Increases tension and compression forces on twistlocks and container posts

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Acceleration forces > When considering the shipboard stowage location of cargo items, acceleration forces should be borne in mind: > Lower accelerations forces occur in the mid-ship sections, lowest cell position under deck and as close to the centerline as possible > Higher accelerations forces occur at ship's extremities, high on deck and in the outrigger slots by the ship's side. > The higher is GM the greater is righting moment when ship is rolling, consequently transverse acceleration forces intensify with increase of GM Acceleration correction for ship length and speed

v = speed (knots) L = Length between perpendiculars (m)

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Forces effecting container stack

Standard ISO Racking force door end Racking force doorless end Racking force side walls -Corner post compression *closed box containers

20’ 150 kN 150 kN 75 (150*) kN 864 kN

EASEACON LASHING MODULE

40 ’ 150 kN 150 kN 75 (150*) kN 864 kN

.

Capt.Goran Belamaric, Mag. Eng

CLASS REQUIREMENTS The following forces are to be considered: > static (gravity) forces, (20’ – 24 T, 40 ‘ – 30, 48 T) > inertial forces due to ship motions (roll and heave, pitch and heave, GM=0.07B)

> wave impact forces (forward of 0.25L, lashing strength increased for 20%)

> wind forces, (20’ – 10kN, 40’ – 20kN) > forces imposed by the securing arrangements.

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Lashing bridges Advantages: > shorter lashing bars > easier and safer lashing > Possibility to secure fourth tier > Heavier containers may be loaded on higher tiers > Lashing system is simple > Easy access to reefer containers on 2nd tier Disadvantage: > Lashing bridge is fixed structure while containers are moving with hatch covers, resulting effect is that lashing become slack or takes excessive load > Difficult maintenance of lashing bridge - painting > Additional weight on deck, reduces stability > 45‟ container can not be loaded on 1st and 2nd tier

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Lashing in holds is done with cell guides

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Lashing system Container vessel should be equipped with approved lashing system.

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

On deck lashing

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Capt.Goran Belamaric, Ma EASEACON LASHING MODULE

15

TURNBUCKLE DUAL FUNCTION TWISTLOCK

LASHING BAR

ISO LASHING GAP

BASE TWISTLOCK

LOCKABLE STACKING CONE EASEACON LASHING MODULE

16

.

Capt.Goran Belamaric, Mag. Eng

Cargo securing manual > The International Convention for the Safety of Life at Sea (SOLAS), 1974, Chapter 6 (Carriage of Cargoes), Regulation 5 and Chapter 7, Regulation 5 (Carriage of Dangerous Goods), requires that cargo units, including containers, shall be loaded, stowed and secured throughout the voyage in accordance with a Cargo Securing Manual approved by the Administration.

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

CSM permitted vertical container weight distribution

EASEACON LASHING MODULE

Vertical distribution in CSM GM < 1 m

GM < 2.5 m

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Mixed stowage vertical weight distribution 20 FEET -> 2 tiers

20 FEET -> 3 tiers

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

CSM - loading in holds

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Mixed stowage stack calculation 16 22 AFT

18

14

24

26

FWD

19.5

MAX STACK LOAD 40’

120 MT

MAX POINT LOAD 40’

30 MT (max stack load / 4)

CURRENT POINT LOAD 40’ AFT

(16+22+18+24) / 4 = 20 MT

CURRENT POINT LOAD 40’ FWD

(16+22+14+26) / 4 = 19.5 MT

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Effect to on stack due to shifting of mass, wind force, missing lashing

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Easeacon – „Bay planner‟ operates in two modes: (Ctrl+L switches Lash mode while focus is on Bay Planner window) STACK MODE

LASH MODE

When Easeacon is in STACK MODE, stack alarm (red color) appears if stack weight is exceeded. In LASH MODE red color means that at least one lashing force is excessive. EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Bay 11, lashing / no lashing NO LASHING

WITH LASHING

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Bay 11, Red flag on GAP end LASHED SIDE

GAP END

When 20’ containers are loaded with ISO gap then lashing is from one side of container only. Unlashed side shows increased racking force. If container is lashed from both sides then Easeacon warning for GAP forces may be ignored. EASEACON LASHING MODULE

Bay 11, Wind or no wind WIND

NO WIND

Identical stack when loaded in inner slot will have smaller lashing forces then stack loaded at a ship side due to wind effect. FORCE BY WIND = 1kN/m2

EASEACON LASHING MODULE

27

EASEACON and max stack Easeacon often shows some forces to be 100 to 105% although stack is loaded as per cargo securing manual. Small differences are acceptable due to different hydrostatic data used in calculation. Even Easeacon lashing test condition exceed lashing forces in some parameters. CSM VALUES

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Change of GM and lashing forces With change of GM acceleration forces changes, consequently all lashing forces will change accordingly

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Change of container COG COG at 45%

COG at 60%

Easeacon default container vertical center of gravity is at 45% of container height. Value might be changed to 50 or 60% for safer more pessimistic GM calculation. Change of VCG reduces calculated GM consequently lashing forces are lower. EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng

Warnings >

>

> >

>

>

Exceeding the permissible stack mass may result in: > overstressing hatch top construction, > overstressing stowage and securing devices, > damaging containers, > loss of containers overboard. Neglecting permissible sequences of masses in stacks may result in: > overstressing stowage and securing devices, > damaging containers, > loss of containers overboard. Failing to properly lock Twistlocks may result in: > loss of containers overboard. Failing to apply lashings as lined out in the relevant bay plans may result in: > overstressing Twistlocks, > damaging containers (racking), > loss of containers overboard. Exceeding the recommended pretension of 5 kN in lashings may result in: > overstressing these lashings, > damaging containers, > loss of containers overboard. Exceeding of the max. GM-value in the stowage plan result in: > higher transversal acceleration, > overstressing stowage and securing devices, > damaging containers.

EASEACON LASHING MODULE

.

Capt.Goran Belamaric, Mag. Eng