There is a fairly lengthy discussion of draft issues here: Mast height/Draft - What limitations will I have?
But you don't say what length boat you're looking for. 4 foot draft on a 20 footer could be considered "deep draft", on a 50 footer it would be considered extremely shoal draft. We would need more parameters to help you on this. But, off hand, I am curious where you plan to go that you feel you'll be constrained by more then 4' draft ? Are you heading to the headwaters of the Nile?