I'm 3.2 million gold in debt, and sabres are a distant memory. Attacking towns from the sea is too hard and takes an age. I could get out of debt if only I could attack towns by land. Problem is, without sabres, sometimes you're only given the option of attacking by sea, sometimes you attack with too few men despite having 10 battleships with 2,000 crew, and sometimes you attack with lotsa guys, and it works.

I was wondering if there was some way of knowing in advance which of these things will happen.

To be honest, I would start over and play a bit smarter.

If you have already captured a great amount of ships, sell off everything you do not need.
**First, set up a battle fleet then sell off every thing else!

If you can carry 2000 troops, you must have at least 10 Ships of the Line.

A good tactic to taking a town is to move half your men around to the second gate, even get them to attack it, whether or not they have swords or guns, then use your other men to attack the other gate.

Most of the troops guarding the gates will rush to the other gate that is attacked first and it takes very little time for 1000 men to kick down the other unguarded gate before the defending troops return.

I hope this helps and I must add that I play my game my way.

The advice I give here is from my own experience and not to taken as an experts opinion.