Index: src/ship_cmd.cpp
===================================================================
--- src/ship_cmd.cpp	(revision 16021)
+++ src/ship_cmd.cpp	(working copy)
@@ -558,6 +558,26 @@
 	}
 };
 
+/** Find ship in front and keep distance of 2 tiles between ships */
+static Vehicle *PutSpaceBetweenShipsEnum(Vehicle *v, void *data)
+{
+	const Vehicle *u = (Vehicle*)data;
+	if (v->type != VEH_SHIP ||	v->vehstatus & VS_STOPPED ) return NULL;
+	if (v->direction == ReverseDir(u->direction)) PlayShipSound(v); // imminent frontal collision
+	if (v->cur_speed <= u->cur_speed) v->cur_speed >>= 1; // go half speed to let other ship pass
+
+	return v;
+}
+
+static const DiagDirection _next_tile_direction[6][4] = {
+	{ DIAGDIR_NE, DIAGDIR_SE, DIAGDIR_SW, DIAGDIR_NW },
+	{ DIAGDIR_NE, DIAGDIR_SE, DIAGDIR_SW, DIAGDIR_NW },
+	{ DIAGDIR_SE, DIAGDIR_NE, DIAGDIR_NW, DIAGDIR_SW },
+	{ DIAGDIR_SE, DIAGDIR_NW, DIAGDIR_NE, DIAGDIR_SW },
+	{ DIAGDIR_NW, DIAGDIR_SW, DIAGDIR_SE, DIAGDIR_NE },
+	{ DIAGDIR_SW, DIAGDIR_NW, DIAGDIR_SE, DIAGDIR_NE }
+};
+
 static void ShipController(Vehicle *v)
 {
 	uint32 r;
@@ -660,6 +680,51 @@
 			track = ChooseShipTrack(v, gp.new_tile, diagdir, tracks);
 			if (track == INVALID_TRACK) goto reverse_direction;
 
+			assert(track != TRACK_END);
+			/*try to avoid collision and keep distance between each other*/
+			TileIndex next_tile = TileAddByDiagDir(gp.new_tile, _next_tile_direction[track][diagdir]);
+
+			if (HasVehicleOnPos(gp.new_tile, v, &PutSpaceBetweenShipsEnum) || HasVehicleOnPos(next_tile, v, &PutSpaceBetweenShipsEnum)) {
+
+				switch (tracks) {
+
+					case TRACK_BIT_NONE: break;
+
+					case TRACK_BIT_3WAY_NE:
+						if (track != TRACK_X) {
+							track = TRACK_X;
+						} else {
+							track = TRACK_RIGHT;
+						}					
+						break;
+
+					case TRACK_BIT_3WAY_SE:
+						if (track != TRACK_Y) {
+							track = TRACK_Y;
+						} else {
+							track = TRACK_LOWER;
+						}					
+						break;
+
+					case TRACK_BIT_3WAY_SW:
+						if (track != TRACK_X) {
+							track = TRACK_X;
+						} else {
+							track = TRACK_LEFT;
+						}					
+						break;
+
+					case TRACK_BIT_3WAY_NW:
+						if (track != TRACK_Y) {
+							track = TRACK_Y;
+						} else {
+							track = TRACK_UPPER;
+						}					
+
+					default: break;
+				}
+			}
+
 			b = _ship_subcoord[diagdir][track];
 
 			gp.x = (gp.x & ~0xF) | b[0];