Would a small arsenal ship be useful to support offshore patrol vessels?
Short answerNo: if an OPV needs that level of fire support, it is in the wrong environment; the funding would usually buy more useful frigates.
NotesOffshore patrol vessels are presence and maritime-security ships intended for patrol, counter-terrorism, coast-guard encounters, and wayward fishing vessels. They are not designed to fight hostile surface combatants. If an OPV needs a dedicated arsenal ship to survive its assigned waters, the force has already put it in the wrong threat environment. Applying the same money to additional frigates would produce a more coherent and independently useful war-fighting force.