Thinking of a heavy patrol/brownwater/siege and assault ship pressed into navy service. Part turtle ship, historical to Korea. 

Kind of heavier guns, lower draft, part turtle ship, but slower, and harder to get moving, armoured partly mounting longer barreled cannon, magazine fed crossbows. (weaker than guns, faster rate of fire). Also maybe ability to fire rockets or some other kind of historical weapons system like mortars. 

(all historical to eastern states of the period or before, including influences from China etc. )

It can be out positioned by faster more agile ships, and has sails yes, but also oars and ability to function on man power alone. 

Not as effective in open sea as a river/costal vessel it has a lower draft rendering it less stable in waves, storms and such.