This poses a problem for mariners, as trees are not generally available on board boats. Various other methods have been attempted (my own preferred method, for the record, is nibbling a ginger biscuit) - however, nobody has ever doubted the efficacy of simply sitting under a tree.

Let us, therefore, make hats which incorporate small bonsai trees. Sailors everywhere will then be able to remain under a tree while they go about their sailor-y business, thus curing them of sea-sickness. They could also be used as badges of rank - able-seamen would get a small cotoneaster, 2nd Mates get flowering cherries, and Cap'ns get gnarly old oaks.