There is no real way to model naval transport in ETW, I generally sent a full fleet just as not to lose the army. In actual practice you had dedicated transport ships which might carry 50-200 people over any meaningful distance; a good point of reference would be Dutch actions against England during the "revolution" prior to William of Orange and Mary QOS deposing James-whatever in 1688, in which an army around 15000 strong was moved that short sea voyage by around 180 ships of note and probably a good number more of smaller ones.