10. STEELWORK PRODUCTIVITY 10.1 Background

The University of Southampton School of Engineering Sciences

10. STEELWORK PRODUCTIVITY

10.1 Background

In general terms, productivity is a measurement to indicate how well an operation

has been run by a unit or a system. It can be defined as the relationship between the

volume of goods and services (output) and the quantity of goods and services

required to produce that output.

Productivity =Output

Input

where: output could be the number of units produced, weight of units, length of

joint, area of manufactured units, etc. and

input represents all the effort both by the use of labour and the use of

equipment which is required to produce the output. Manhours, equipment,

design, facilities, etc. are all inputs to the system. These input are affected

by some influences over which no immediate control could be made. Work

rules, environmental conditions, economic conditions and government

regulations illustrate a few of these factors.

Productivity is then the output related to one or more of the inputs. The following

diagram shows this relationship.

Man hours Equipment Design Facilities Supervision

Work rules

The number of input

measurement.

(i) Total Productivity = La

Professor R A Shenoi

TOTAL
Economic conditions Statutes/regulations INPUT
variables used in the ratio provides two cla

Output

bour + Equipment + Facilities + . . .

Part II - S10-1

OUTPUT

sses of productivity

hip Production Technology


Such an index on the one hand evaluates the appropriate results obtained for the

whole firm but, on the other hand, it often omits the exact value of individual

activities.

(ii) Partial Productivity = Output

One Factor of Input

Labour and machine productivities are the more commonly used partial

measurements. In this sense, labour productivity is the amount produced divided

by the time worked and it expressed as output per manhours or vice-versa. This is

the meaning of productivity used in measuring shipyard efficiency.

Labour productivity can be further subdivided to cover major cost centres:

- Steelwork

- Outfitting

- Engineering

Steelwork productivity can be measured in terms of:

- Weight

- Wield length

- Measured day work.

Outfitting and engineering can be measured in terms of:

- Total manhours/contract/trade

- Total manhours/activity/trade

- Measured day work.

The rest of this chapter is devoted to an examination of steelwork productivity

indices.

Professor R A Shenoi Part II - Ship Production Technology 10-2


10.2 Weight Based Criteria

(A) Manhours/Gross Tonne

Many shipbuilders throughout the world use their own system of productivity index

in terms of manhours required to fabricate one tonne of steel. This requirement can

relate to performance of workers in different shops – eg. preparation, assembly or

fabrication. The indices for the different shops can and do vary. Some aspects of

labour are excluded. These include steelwork manhours spent after launch, all

steelwork servicing to sub-contractors, percentage claims on fabricated units, etc.

In terms of steel weight, no correction is applied for higher tensile steels and

aluminium.

(B) BSRA Manhours/Gross Tonne

In an attempt to provide a basis for inter-firm comparison and also to show the

general trend of industry, British Ship Research Association (BSRA – the force

runner of BMT – defined manhours and steel weight content to be used in the

performance calculation as follows:

Manhours - to include all shipyard boilermakers, platers, drillers, shipwrights,

loftsmen, welders, chargehands, apprentices, to exclude foremen,

supervisors, storemen. (Everything excluded here is transferred in

the fitting out on overhead returns).

Steel - to include invoiced steel (plates and sections) and all steelwork

items made in the yard such as lawsepipes, deck and machinery

seats, sternframes, etc.

to exclude bought-in items such as rudder castings, propellers, etc.

When high tensile steel and/or aluminium are used, the following

equivalents are recommended:

1 tonne of Aluminium = 2½ tonnes of mild steel.

1 tonne of HTS = 1⅛ tonnes of mild steel.



(C) BSRA Manhours/Equivalent Gross Tonne

Up to now no difference in complexity of different ship types has not been allowed

for. For example, it is obviously easier to construct a box shaped tanker than a fine

shaped refrigerated ship. To allow for this, BSRA suggested the concept of using

the bulk carrier and cargo ship as the basis ship and applying corrections to the

gross tonnes for:

(i) Block coefficient – increase tonnes by 1% - for every 0.0% decrease in Cb

from 0.70 and vice versa if above 0.70.

(ii) Ships of complex specification (such as reefer ships) – add 5% to the

equivalent tonnes. For cargo ships, the correction is not to exceed this value.

(iii) Corrections for steel – as mentioned in the previous section above.

Example of application: consider a refrigerated ship of 10,000 tonnes deadweight

with a Cb of 0.60.

Invoiced steel: Mild Steel 4000

H.T Steel 200

Aluminium 50

The equivalent gross tonnes (EGT’s) are as follows:

Mild Steel = 4000 x 1 + = 4000

H.T Steel = 200 x 1⅛ = 225

Aluminium = 50 x 2½ = 125

4350 tonnes

BSRA factor at given deadweight 1.173

Correction for Cb (0.70 – 0.60) = 0.01 1.010

Correction for specification @ 5% 1.050

Total complexity factor = 1.173 x 1.010 x 1.050 = 1.244

Equivalent gross tonnes = 1.244 x 4350 = 5411 tonnes



A further refinement in the use of indices can be made by allocating proportions of

the total EGTs to the various steelwork departments such as:

Preparation 10%

Fabrication 40%

Erect, fair and weld 30%

Jobbing, service, etc 20%

By applying BSRA manhours as defined in (B) for each department, the

manhours/equivalent gross tonne target figures can be deduced.

10.3 Weld/Joint Length Based Criteria

This method, though not extensively used in UK yards, is adopted in some Japanese

shipyards; it measures performance in terms of cumulative manhours against

welded length. The control centres usually cover sub-assembly, fabrication and

berth with a further subdivision in terms of the weld position. The results can be

plotted in the form shown below.

Cumulative Manhours

For quality control purpose

the target line, will initiate

Refinements in the approac

Professor R A Shenoi

Cumulative Weld Length

s any negative deviance, say, greater than 15-20% from

an investigation to determine and rectify the fault.

h include:

Part II - Ship Production Technology 10-5


(a) thickness correction which takes into account the fact that thicker plates

may require more time to align and would need more weld passes – see

Figure 10.1.

(b) weld position correction which accounts for the fact that downhand

(manual) welding is easier and quicker than vertical or overhead work.

(c) unit complexity which allows for differences between various stages of

work (eg. preparation, fabrication, erection) and for relative structural

complexities of different units – see Table 10.1.

As an example, consider a double-bottom unit at the fabrication stage. Assume that

all welds are performed in the downhand position.

From the material list, it was noticed that the average plate thickness of the unit was

11mm. From the drawings, the joint length was found to be 5200 mm. (An

alternative approach is for a shipyard to record hull steel weight versus weld length

data as shown in Figure 10.2. Such data can be recorded as pertaining to assembly,

sub-assembly or erection stages). From job cards, the labour content was found to

be 3061 manhours.

Thickness factor = 1.22 (From figure 10.1)

Weld position factor = 1.00 (Down hand)

Unit complexity = 1.51 (From Table 10.1)

Performance Index = 5200

30611 22 1 00 151 313 m / manhour× × × =. . . .



Figure 10.1: Thickness Correction Factor

Table 10.1: Unit Complexity Factors



Figure 10.2: Hull steel weight versus welded length

Figure 10.3: Basic structure of work study



10.4 Work Study Approach

One definition, attributed to the International Labour Organisation, states that

“work study is a term used to embrace the techniques of method study and work

measurement which are employed to ensure the best possible use of human and

material resources in carrying out a specified activity.

Figure 10.3 illustrates the general structure of work stud techniques. It will be

noticed that method study is concerned with establishing optimum work methods

and work measurement deals with establishing time standards for these methods.

Method study is normally conducted before work measurement.

Figures 10.4 and 10.5 illustrate the manner in which the data is recorded. The

problem concerns specifying a time rate for fairing and tacking flat bars and angles

up to 6”. Figure 10.4 shows the problem and summarises the results. Figure 10.5

lists the method, ie. the steps required to do the job. The times would have been

recorded through the use of work measurement techniques.

The end result from work measurement is the allocation of a standard time for a

job. This can be in standard minutes or, in shipbuilding, standard hours. These

standard time values can be established from one of several methods which are

outlined in standard text books on this topic.

Standard times correspond to “the average rate at which qualified workers will

naturally work at a job, provided. They know and adhere to the specified method,

and provided they are motivated to apply themselves to their work” (quoted from

BS3138). A comparison of the actual rate of working against the standard work

rate is achieved through a performance rating index.



Figure 10.4: Example of application – work study



Figure 10.5: Example of method specification – work study



Various methods of rating have been evolved and the four most popular scales are

shown in Figure 10.6. The standard performance using a British standard 100 is

considered to be equivalent to a walking speed of 4 miles/hour, are to dealing a

pack of cards into 4 hands in 22½ seconds; but unfortunately neither of these jobs

occurs frequently in industry! Hence a company needs to train the time study

analyst to recognise what the company (poor industry in general) regards as

“standard performance”.

The standard time foran element or a job is calculate as follows:

Standard time Observed timeRating

100 percent total allowance= × ×

In a shipbuilding context, the interest is centered around what information can be

obtained from the system and the corrective action that can be initiated. In terms of

management, reporting, industrial engineers can provide the following:

(A) Breakdown of hours

This comprises:

- Total attendance hours

- Total standard hours

- Unmeasured hours (eg. for marshalling of material)

- Rectification hours

- Waiting time

- Productive time (= Total attendance time – waiting time)

(B) Performance Indices:

These can be subdivided into two major groups as shown in Figure 10.7.

Based on the information recorded, the indices can be calculated and

performance criteria for both labour and machines known. The management

reports, say, produced on a weekly basis will then provide departmental

managers with sufficient information on performance and the degree to which

it is influenced by waiting time, rectification and machine utilisation, thus

prompting remedial action – see Table 10.2.



100 Standard Performance

80 100 133

60

75

100

B.S SCALE 60/80 75/100 100/133 Scale Scale Scale

Figure 10.6: Work study rating scales

Performance Indices

Labour Machines Effective Operator Effective Operator Machine Performance Performance Performance Performance Utilisation

Effective Performance =

Unmeasured Attendance Hours at the

Standard Hours + Previous Weeks Effective Performance

Total Attendance Hours× 100

Operator PerformanceStandard Hours

Productive Hours= × 100

Machine Utilisation =

Unmeasured Attendance Hours

Standard Hours + at Previous Weeks Eff. Perf.

Manning Machine Available hours

×× 100

Figure 10.7: Performance Indices



10.5 The Learning Curve Concept

The concept of the learning curve is that a worker learns as he works; the more

often he repeats an operation, the more efficient he becomes with the result that

direct labour per unit output declines with a corresponding increase in productivity.

Moreover, and importantly, the rate of movement is regular enough to be predicted.

Research in a number of industries has shown that there is a regular pattern of

improvement and that this is likely to be a constant percentage when cumulative

production doubles. On a double logarithmic scale the experience curve is

represented as a straight line. Figure 10.8 and 10.9 show decreases both in terms of

manhours/tonne and of weld length/manhours for bulk carriers at different

production stages and for varying modules/units respectively. The reduction in

labour time per unit can be considered as raising productivity.

In a steelwork particularly, a large percentage of work is represented by direct

labour. The learning curve could be used for four purposes.

(a) It could be used to measure the “learning productivity performance” of each

work station. After the learning curves are drawn, the learning productivity

performance will be given by their slope.

(b) It could be used to predict the manhours per tonne (Figure 10.8) or the

manhours per joint length (figure 10.9) for each of a series of ships. Having

established such graphs for the first two or three repeat ships, the prediction

of manhours per tonne required for each production stage and the total

manhours content can easily be predicted by projecting the curve.

(c) It is useful in predicting the manhours per unit length of joint for specific

units/modules for each ship, such as a stern unit, bow unit, double-bottom

unit, a deck unit, etc. (See Figure 10.9). Knowing the length of joint of each

unit and having recorded the manhours required to construct such units for

the first two or three repeat ships, the slope of the curve can be established.

It is then a simple matter to extrapolate the curve to cover requirements for

the next ships in the same series.



Figure 10.9: Learning curve – production units Figure 10.8: Learning curve – production areas



(d) It is necessary for purposes of comparing the learning productivity

performances of different shipyards.

The learning curve concept offers four-fold benefits.

(1) It offers a practical solution for fairly accurate forecasts of direct labour

and productivity. It’s most obvious use is forecasting output.

(2) When the rate of learning falls below the standard productivity

improvement, management and supervision would be alerted to look

for the correct causes.

(3) Realistic production goals can be set (with the learning curve effect in

mind). This would enable management to compare actual performance

with goals.

(4) If a new innovation in the production process is introduced, it will

change the slope of the learning curve. This will indicate whether the

innovation is productive or not.

Today, if a shipyard wishes to complete successfully in an increasingly

complex technological and market-orientated environment, it needs to use

every available production/productivity control tool. Productivity indices and

the learning curve concept are two simple but powerful such aids.


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10. STEELWORK PRODUCTIVITY 10.1 Background