According to Dr. Sami Hanna, an expert in Semitic languages, in Ether 2:17 we learn that the Jaredites built their barges under the direction of the Lord, and that "the length thereof was the length of a tree." In the Semitic culture, common objects are used to relate distances, etc. Therefore, this phrase is completely within Semitic context. [Brenton G. Yorgason, Little Known Evidences of the Book of Mormon, p. 38]
“The Length Thereof Was the Length of a Tree”
The Jaredite barges were built to "the length of a tree" (Ether 2:17). According to Paul Hedengren this might have been to avoid having joints at the ends of planks. The movement of a vessel through waves produces longitudinal flexing that would tend to separate joints at the ends of planks. Thus the Jaredite ships were not longer than the length of the available trees. [Paul Hedengren, The Land of Lehi: Further Evidence for the Book of Mormon, p. 79]
“The Length Thereof Was the Length of a Tree”
According to Randall Spackman, Worcester has written that "most of the timber" used in East Asia for boatbuilding was pine. This "light, soft and tough" wood was obtained from trees that were cut for sale when they were "over 20 years old and about 50 feet high." If the same sort of materials were used by the Jaredites, then the phrase "the length of a tree" (Ether 2:17) might simply mean that the barges were about 50 feet long or less.
On the other hand, the phrase "the length of a tree" could also be interpreted as a reference to the Jaredites' use of a particular method for constructing their barges. Unlike modern boatbuilding techniques, which involve the creation of a keel and frame before the planking is applied, Mesopotamian boatbuilders first created a box-like hull of edge-joined planks into which they inserted frames, a central shelf or spine, and deckbeams. For the greatest rigidity and strength, a single beam made from one large tree was required for the central shelf of the vessel. . . . Thus it would seem logical to assume that "the length of a tree" had some direct connection with the extreme tightness of the Jaredite hulls. [Randall P. Spackman, The Jaredite Journey to America, pp. 76-77, unpublished]
Ether 2:17 The length thereof was the length of a tree ([Illustration]): Figure 11, Mesopotamian And Egyptian Boatbuilding System, The Jaredite Journey to America, p. 78, unpublished]