The Biblical word for Ark is "tebah." It is used 28 times in the OT and is only used of Noah's Ark and for the container in which Moses was hidden among the bulrushes. The Egyptian word meant "box." More likely it was shaped like a rectangular barge which floated rather low in the water.

The Ark had three stories with only one door (I have never seen a 3-story coffin, but....I have seen multilevel graves). The phrase in Gen. 6:16, "Make a roof for it and finish the Ark to within 18 inches of the top," is problematic in that the words used are obscure. Most commentators believe it means an 18 inch space at the top that is open all around the vessel. This then would be for ventilation, and when water entered it would drain out somewhere below. The Ark was to be coated inside and out with pitch.

The phrase in the NIV (6:14) "make rooms" is also problematic in that the word is obscure. The Hebrew is "qnm." Since Hebrew did not have any vowels when it was written, scholars speculate that the word could be either "qinnim" or "qanim." The former would mean either "rooms" or "nest", and the later, "reeds." Most english translations translate as in the former. However, some recent commentaries, believe it should be translated "reeds" since the context is building materials. If in reality it is "reeds", then somehow reeds were part of the construction material. Large boats are still made from reeds and are very seaworthy. The Egyptians still use reeds for caulking their wooden ships. Note: Moses' basket in Ex 2:3, 5.

The size is given in cubits as being 300 cubits long by 50 cubits wide and 30 cubits high. A cubit in the OT was generally app. 17.5 inches. However, an Egyptian royal cubit measured about 20.5 inches. Since, Moses was educated in Egypt the Ark could have measured from 437 feet to 512 feet in length.

The Ark had a ratio (L x W x H) of 30 x 5 x 3. According to ship-builders, this ratio represents an advanced knowledge of ship-building since it is the optimum design for stability in rough seas. The Ark, as designed by God, was virtually impossible to capsize.

With the shorter cubit the Ark would have an internal volume of 1,518,750 cubic feet, or the equivalent of 569 standard railroad boxcars. If the average sized animal was the size of a sheep it means the Ark could hold over 125,000 sheep (over 100,000 sq. ft of floor space).

various sources....