THE SECOND VERSION
Whereas in the first version the height of the water, which is the key element of the story, was linked with the number 40, the second version had reasons for linking the height of the water with the number 150. Hence, it introduced a new concept that was not in the original versions: a period of rising water and a period of ebbing water. This was done in order to lengthen the entire period of the events to a full year: Noah came out of the Ark at the moment in which the new year begins (8:13a). There was left the original period of 47 days, which was followed by a period of flooding of 150 + 150 days. As I have explained, this period of 150 + 150 days was introduced by adding section B to the narrative. After that the narrative continued with the original section C which dealt with the staying in the Ark for 7 days after the end of the flooding. Hence the total length of the staying in the Ark was 150 + 150 + 7 days, but since the flooding began on the 18th day of month II after Noah had entered the Ark on the 17th day, the total period involved in the calculation is a lunar year of 354 days.
In order to understand why in the account of Genesis there was inserted a version according to which the flood lasted 300 days, divided into 150 days of rising water and 150 days of ebbing water, it must be kept in mind that the story of the Deluge was based on practical formulas employed by navigators and land transporters.
I have explained that according to the original version of the story of the Deluge, the height of the water was calculated as 40 x 40 x 14 cubits, whereas the radius of the earth was calculated as 40 x 40 x 30 x 300 cubits or as 40 x 600 x 600 cubits. The circumference can only have been calculated as 3,000 x 30,000 or 300 x 300 x 1000 cubits. Hence, it was natural that somebody should have thought of formulating the mathematics of the Deluge in terms of the factor 300.
Most commentators do not try to explain why a formulation based on the number 300 was chosen. An exception is represented by the commentary of Umberto Cassuto who, as a Jewish fundamentalist, cannot assume that the writers of the Old Testament wrote down figures at random. He states that 300 is "one of the round figures in the sexagesimal system, being half 600, which is 10 x 60," that 50 is "half one hundred, one of the basic numbers of the decimal system," and that 30 is "half of 60, the fundamental number of the sexagesimal system." This may have the appearance of an explanation, but in truth it does not say anything more than that the writers of the Old Testament chose round figures.
A formulation based on the number of 300 was chosen because it was found that the height of the water could be expressed as 150 x 150 cubits = 22,500 cubits. This formula is neater than that of 40 x 40 x 14 cubits = 22,400 cubits followed in the original version; further, it is closer to the correct figure of 22,464 cubits.
Because of the necessity of dividing the factor 300 into 150 + 150, there was introduced the concept of a period of rising water and a period of ebbing water, a concept that does not appear in the Mesopotamian versions and in the original biblical version. The new version is mathematically more definite in that it implies that the water rose and fell 150 cubits a day. The new account is more realistic and more rationalistic, but it is cosmologically less pregnant in meaning. The original biblical account, like the Mesopotamian account, implies a new creation of the cosmos, in which the water rose and remained higher with a new landscape emerging from the new level of the waters.
The new account aimed at being more systematic. If one counted that the water began to rise when 47 days of the year had elapsed and the water was over the earth for 300 days, there were left 7 days more to the end of a lunar year of 354 days, which were assigned to the episode of the sending of the dove. And in fact verse 8:13 reflects a version according to which Noah left the Ark on the first day of the second year. The first day of a new year was a most proper time to start a new cosmic age, the post-diluvial world.