The variance from the established practice tells us one thing and hints at another. What it tells us is that Nephi knew the difference. This may mean that he had some passing familiarity with ships, or simply that the Lord let him know that there was a difference. As there was little reason for the Lord to so indicate, it is more likely that Nephi was grossly familiar with the more common practice.
The second item is that there must have been some reason why the common methods were insufficient. The Lord tends to be conservative with his children (Nephi built a ship with sails, not a steam engine). The instruction from the Lord likely had to do with increasing the sea-worthiness of the ship for the oceanic voyage, and distance not part of the design of the more common ships of the era.