Trawler, tugs, small coastal merchants and Elco's are all fine cannon fodder for my flack guns in the stock stand version of the game
, I belive it's a differnet story for Grey Wolves or NYGM verisons.
The 20mm does the job, the twin 20mm is better, 37mm auto loader better still (the semi-auto 37mm is slower than a week of Mondays) the twin 37mm is best
Make sure the 37mm is using the AP ammo or you won't get the results you wish for. Ammo used depends on the size of the ship (trawler will take less than a coastal), what size and type of weapon used (A twin 37mm beats a single 20mm anyday), any damage done to the vessal beforehand and wherever you shoot stragit enough to hit it!
The smaller the ship, the quicker they sink!
They can be used to finnish off larger ships if the deck gun has runn out of ammo, take out deck cargo, lifeboats, funnels, vetlation ducts and masts, then start working over the hull around the waterline, near the engine room, fuel tanks and the like.
Good Hunting!