Man Day Control in Warship Construction

36 yea sold navy technical commander's Ryouji Nishijima took charge of construction of Yamato.
He is the person in charge of hull construction. In the Kure navy arsenal, construction of a battleship was since of Nagato.
There was no construction of a battleship for 20 years in the Kure navy arsenal for the disarmament treaty.

Yamato is a huge battleship which the navy has not experienced until now, and furthermore structure of Yamato is complicated.

For this reason, he needs to estimate the budget and the total man day which construction takes.
His duty is to advance smootgly a construction and to complete a battleship by the date of a schedule.
Then, he calculated the weight of Yamato from the drawing. As a result, the weight of Yamato was twice Nagato.

Nagato was started of the construction in August 1917, Man days was 1,960,000. (First ship)
The start of the construction of Mutsu in1918, Man days was 1,740,000. (Second ship)
From this record, he presumed that about 4 million man day was required for the total man day of construction of Yamato.
(The man day which hull construction takes estimated as 1,600,000 man days).

Generally, construction of a warship decides on a date for every main processes of construction.

For example:
Commencement of construction work,
Loading of Boiler,
Loading of the main machine,
Launching,
The main gun loading,
Rehearsal trial.
Official trial.
Completion.

If it judges that construction is behind, a person in charge increases a workman and will order all-night construction,and a completion date is held.
That is, a naval system gives top priority to a date. Unlike a private factory, the navy considers neither the efficiency of work,nor an economical thing.

In case of the construction of Yamato of the total man day 4 million(estimated) will be completed in four years, a man day becomes an average of 83,333 persons everymonth.
And a daily man day is 2,688 persons. But as for the peak period of construction, about 4,000 per day woekers are expected.

However, this is the number of only a shipbuilding part.
Furthermore, the worker of other sections joins.
(For example, a gun manufacturedepartment steel-manufacture part etc...)

If it does so, the construction persons concerned will become the number of many workers.
By the case, there is a possibility that it may become impossible to take supervisor control of construction.

All workers of a shipbuilding part of those days are 6,000 persons.
(In the whole Kure arsenal in wartime, they were 100,000 employees.)
But all of 6000 workers of a shipbuilding part cannot be engaged in construction of Yamato.

They must be engaged also in construction of other warships.
Therefore, shortage of a worker will become certain if construction of Yamato begins.

Then, Nishijima plans introduction of man day control.
The aim of man day control is to finish construction at a low cost moreover, for a short period of time.
(Man day control is called a 'efficiency curve' or 'Nishijima Curve'.)

This curve devised in Showa12(1937)
And, it is the prototype of the man day control in the shipbuilding community in present Japan.

Showa 40(1965) in postwar period,
The IHI Kure shipyard(the former navy arsenal shipbuilding part)planned introduction of PC system, in order to plan efficiency of management. And PC-ization of the Nishijima curve was tried.
The person in charge of a program was surprised, that, the Nishijima curve devised before as long as 40 years was smoothly inputted to PC without making fundamental correction.

Hull construction takes a pattern of steel materials by loft, and according to this pattern, steel materials cuts. .
And a hull is assembled one by one..

Nishijima planned taking record of the weight of these steel, and simultaneously, also records a man day.
This record carried out for each work section, for each work kind, and it graph-izes of this data.

The weight of steel material fill out in the horizontal axis of graph.
(that is, the weight of steel materials expresses a work load).
And the man day which hull construction totaled fill out in the vertical axis of graph..

And plots on graoh the man day and weight of steer for every seven days oreveryten days.
If does so, the graph of transition of a work load and a man day will be obtained. (this is 'Nishijima curve')
Recording of each work section and work kind is important for statistics of this graph.

In the navy, the sum of a man day was always recorded from the former.
However, this is the total of the last date. Nishijima judged, that such a total was valueless.
This Nishijima's thinking is epoch-making as an opinion of those days.

The idea of Nishijima, the estimated total man day of construction fill out in the vertical axis of graph.(In the case of Yamato, it is the man day of 4 million)
Next, the gross weight of steel materials fill out in the horizontal axis of graph..
And, connects from the zero point of graph in a straight line to the last process.
(the last process is intersection of the total man day and steel-materials gross weight)
This straight line graph makes for each work section, work kind.

This curve shows a straight line upward slanting to the right. Namely, the graph of this straight line expresses the process of ideal efficiency construction..

In each section and each work kind, N-curve records every moment.
And puts this N-curve on straight line graph..
If the line overlaps with two graph , work will advance ideally with the fixed base .
But, the inclination of graph is unstable, or when separated, a certain problem will have occurred on the spot. That is, it means that the efficiency of work is falling.

In this case, the measure of solution can be taken, and the cause of an efficiency fall can be solved immediately.
As a result, the influence to the following process can be controled to the minimum.

The method of the navy before construction of Yamato,
Balancing finally was important for the budge,. that is, the last result was important.
But, in this case, efficiency was bad in which work kind ? or, was inefficient in which section of woek ?
Moreover, did which section have good efficiency ?
It cannot grasp exactly a cause..

Under construction, it always records the efficiency curve. And this data accumulates for every construction of each ship.
If it does so, it will become the useful reference data when constructing a ship newly.
Furthermore, it can use also for the exact estimate of proper distribution of a worker and a budget.

In this time, the shipyard in the world is inexperienced in block construction ,
But Nisijima determines this block construction and adoption of a precedence fitting construction in order to promote the efficiency of construction of Yamato..

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*Originally the word of 'block construction' was Japanese.　It is the same as that of English of a 'typhoon'.

Generally, a warship builds the same type ship(2 to 4 ships)by the necessity on tactics.
The first ship of a warship was custom build.in the Kure arsenal.
Construction ofthe first ship various problems occur.So that, construction is delayed by failure or redo of construction, etc.
For this reason, a man day and construction cost will increase.
But, about the second ship, third ship, has full knowledge of a procedure, so, failure is not repeated like the first ship.
hence, a man day decreases as a result. This is an obvious fact.
However, the construction which showed the reverse result existed in the past.
The battle cruisers Nachi and Atago of the first ship, they were built in the Kurenavy arsenal.
And Myoko and Takao of the second ship were built in the Yokosuka navy arsenal.
These costs of construction were reverse. Namely, the second ship had more man days than the first ship.
Then, The battle cruiser Mogami was built succeedingly in the Kure arsenal.
It is a Mogami type first ship, and Suzuya of the second ship was builtin the Yokosuka arsenal.
However, as for the result, the second ship had many man days thanthe first ship.

Nishijima investigated about this strange phenomenon these past data,
and he obtained the following results of an investigation.
That, in Yokosuka which takes charge of the second ship, the construction man day until launching has very few with these ships. However, the fitting construction after launching had increased extremely.
Then, Nishijima obtained the following conclusion from this result.
That is, the hull construction before launching is comparatively efficient. therefore, a man day is also efficient.
However, since fitting construction is complicated and various, a man day increases. Efficiency of man day is bad

Therefore, Carries out fitting construction as much as ppossible in the period to launching.
Namely, he decided to use the following method abundantly for construction of Yamato.

1:Block construction, precedence fitting,

1932(Syowa,7),

The Submarine mother ship Taigei is a warship of block construction. However, various problems occurred.
For this reason, block construction is not carried out until construction of Yamato.

2:Adoption of a mock-up,

In really,
Construction of Yamato made the model of the actual size of a bridge and the armoured vital part in the arsenal, and researche of various kinds was made. Usual, it is thought the increase in a man day to make a mock-up.
However, in the warship of complicated structure, It is very effective to confirm structure in advance by a mock-up.
Especially, efficiency promotes the hull of rivet structure. The armor of the steel of the hull of Yamato has the thickness of 410mm.
Furthermore, armor takes charge of a part of hull intensity.For this reason, the mock-up needed to determine the position correctly of the rivet hole of the jointing portion of armor.

(The armor of a foreign warship is the structure where it does not take charge of hull intensity)

3:Electric welding,

To a man day reduction sake,
The component which is not related to the intensity of a hull uses welding.

The estimates of the man day of the beginning of hull construction were1,600,000.(All man days are 4 million).
However, a man day is falling gradually as construction progresses.

And finally the man day of hull construction showed 990,000.After all,
Construction of Yamato was less than the all total man day 2 million for adoption of the man days control, and the improvement of the construction method.
It was the brilliant result.

As for Musashi of the second ship, The man day is the almost double man day of Yamato by the difference of the construction method.

In addition,
National power of Japan of those days, GNP is 1/13 of the U.S. and the quantity of production of steel was 1/18 of the U.S.