"First, the matter of the vessel's mass. A wooden vessel is not very strong as its size increases, so the builder must use timbers and planking that generally increase in cross-section as at least the square of the vessel's length. Most woods are rather dense and float pretty deeply, so an ark would have little of its unladen mass above the waterline. The ark as described was in the shape of a rectangular prism, so it had a lot of unnecessary material in order to make those square corners, as well as the bracing necessary to reinforce those fragile corners. It would therefore have a mass somewhat greater than the unladen mass of a modern vessel of roughly similar dimensions. The longest well-documented wooden ship ever built, the Wyoming, in 1909, had an unladen mass of 4000 tons: see
http://en.wikipedia.org/wiki/Wyoming_(ship). Her hull was only about 2/3 as long as the ark and only about half as wide. So, multiplying the Wyoming's mass by 1.5 squared (2.25) for the thicker timbers and planks, and by 3 for the difference in size, the ark should mass nearly 7 times Wyoming's (she had 90 diagonal iron braces on each side, yet she "worked" so much she foundered). Allowing for additional wood to replace the much stronger and more rigid iron we can presume that the ark would have an unladen mass somewhere near 30,000 tons, equivalent to 937,500 cubic feet of seawater, about 3/5 of the total volume of 1,518,750 cubic feet (per Oelrich) submerged, leaving a maximum capacity of 581,250 cubic feet (at best, the equivalent of two 33,750 square-foot decks of the ark) for all purposes. I served in an aircraft carrier for some years: she had about 1.7 million square feet of deck space (about 50 times the deck space of the ark) yet could barely accommodate 6,000 men, and that only because we had replenishments of food about every two weeks and made our own water.
You can make a very sturdy small rowboat out of a couple sheets of plywood and a few 1X1s, but you cannot readily scale it up because the larger vessel requires many pieces that cannot span the lengths involved. So, you must use thousands of pieces that will "work" against one another, engendering leaks. Anybody who's worked on wooden boats will tell you that you can't just seal their seams with pitch but must painstakingly caulk (drive pitch-soaked yarn into) every external seam; they'll also tell you that joining the pieces of wood together takes skill and (in the Bronze Age rare and very expensive) metal fasteners, at least for non-trivial vessels. Consider that Wyoming foundered because the crew (larger than Noah's) couldn't keep up with the leaks, despite reportedly having steam-driven pumps. Consider that Wyoming's yellow pine is much stronger than acacia or any other readily-available wood in the Middle East. Even the fabled cedars of Lebanon are structurally poor compared to yellow pine. I discovered today that the NIV says it was cypress but admits that the meaning of the Hebrew word is uncertain. The same problem obtains for cypress. Then multiply Wyoming's 6-inch planking and the underlying structure by a factor to allow for the weakness of local woods, considering that the local woods would have to be doubled and redoubled, making the interior capacity somewhat smaller than the gross, presumably external, measurements of the ark. Consider also that the ark would also have a shape making broaching unavoidable in even moderate seas. Wyoming could carry only 6720 tons of coal, but coal weighs about 88 pounds/cubic foot, about 1.4 times as dense as animals and a whole lot less trouble to carry. That means Wyoming's bunkers held a volume of just over 157,000 cubic feet. Assuming that the ark could carry any load at all, it would need cargo room at many times (see next paragraph) the volume of Wyoming's coal bunkers, not likely considering the inadequate volume before adding timbers required to provide even a modicum of structural stability."
http://www.skepdic.com/comments/noahcom.html
Just a quick search. I can't confirm any numbers, but the general reasoning is there. Just for reference the Wyoming was 450 ft and 2/3 the length of the arc. Making the acctual arc around 675 ft in length.
