First you must understand what a sealer does. Tung oil, or Linseed Oil, saturates the cellular structure of the wood filling each cell. A second and third coat brings the finish closer to the surface and will give you a fine furniture finish if you desire.
The water, or salt water, is not going to be absorbed into the cellular structure of the wood, thus the reason they call it a "sealer". Without it, your on your own, good luck.
Incidentally, the "marine grade product" is the "same" tung oil sold to "boaters" that are willing to pay a little more for a "marine grade Product".