Fanny Price's father

I have read several Hornblower books recently. In Lieutenant Hornblower, C.S. Forester writes that a lieutenant earned about £100 a year, which is still more than most people, but pretty poor by gentry standards. Fanny Price's father is a lieutenant in the Royal Marines, so presumably that is £100 a year to feed all his children. John Sutherland in one of his puzzles of Victorian literature books points out that, given the number of children he has, he cannot have been away to sea very often. That is rather odd, considering the Napoleonic Wars were raging. Sailors, officers anyway, could only get rich if they captured enemy ships as prizes. The Crown would buy the ship and the money would be divided among the crews that took part. If Lieutenant Price is hardly ever at sea, he would not get any prize money. Another problem with being an officer of the marines is that career progression must have been quite limited. Your superior officer would be the ship's captain. As a lieutenant of the marines you could not become a ship's captain, because you would not have the skills. What did Lieutenant Price do if he does not go to sea? Was he some sort of administrator? I wonder if he leads press gangs.