The Union sufficient advantages. And you've found the right one of them. The Union advantage cruisers. Therefore, it may try to destroy the trade of the South.
In addition, the US has more ships and more money. And as you know for war only need three things. Money, money and money! When intercepting merchantman (blockade runner) you will receive a cash prize.
The game has 48 turns (months). Two-towered US 1300t monitor built 16 months. Ironclads are actively used in the second half of the game.
P.S. Rock Paper Shotgun about Totem Team:
http://www.rockpapershotgun.com/2015...head-reflects/