Feature: [NewGRF] Allow higher max speeds for ships

src/saveload/afterload.cpp

@@ -3273,6 +3273,13 @@ bool AfterLoadGame()
 		}
 	}
 
+	if (IsSavegameVersionBefore(SLV_SHIP_ACCELERATION)) {
+		/* NewGRF acceleration information was added to ships. */
+		for (Ship *s : Ship::Iterate()) {
+			if (s->acceleration == 0) s->acceleration = ShipVehInfo(s->engine_type)->acceleration;
+		}
+	}
+
 	for (Company *c : Company::Iterate()) {
 		UpdateCompanyLiveries(c);
 	}

src/saveload/saveload.h

@@ -371,6 +371,7 @@ enum SaveLoadVersion : uint16_t {
 	SLV_ECONOMY_DATE,                       ///< 326  PR#10700 Split calendar and economy timers and dates.
 	SLV_ECONOMY_MODE_TIMEKEEPING_UNITS,     ///< 327  PR#11341 Mode to display economy measurements in wallclock units.
 	SLV_CALENDAR_SUB_DATE_FRACT,            ///< 328  PR#11428 Add sub_date_fract to measure calendar days.
+	SLV_SHIP_ACCELERATION,                  ///< 329  PR#10734 Start using Vehicle's acceleration field for ships too.
 
 	SL_MAX_VERSION,                         ///< Highest possible saveload version
 };