diff -Nur -Xfreecivdiff.ignore freeciv-cvs/ai/aiunit.c freeciv-patched/ai/aiunit.c
--- freeciv-cvs/ai/aiunit.c	2003-07-21 13:58:22.000000000 +0100
+++ freeciv-patched/ai/aiunit.c	2003-07-24 17:03:26.000000000 +0100
@@ -370,18 +370,29 @@
 Is there a chance that a trireme would be lost, given information that 
 the player actually has.
 ***************************************************************/
-static bool is_likely_trireme_loss(struct player *pplayer, int x, int y) 
+static bool is_likely_ship_loss(struct unit *punit, int x, int y) 
 {
+  struct player *pplayer = unit_owner(punit);
+
   /*
    * If we are in a city or next to land, we have no chance of losing
    * the ship.  To make this really useful for ai planning purposes, we'd
    * need to confirm that we can exist/move at the x,y location we are given.
    */
-  if ((likely_ocean(x, y, pplayer) < 50) || 
-      is_likely_coastline(x, y, pplayer) ||
-      (player_owns_active_wonder(pplayer, B_LIGHTHOUSE))) {
+  if (!unit_flag(punit, F_TRIREME) || likely_ocean(x, y, pplayer) < 50
+      || is_likely_coastline(x, y, pplayer)) {
     return FALSE;
   } else {
+    struct eff_iter iter;
+    struct map_position mp;
+    mp.x = x;
+    mp.y = y;
+    eff_iterator_unit_init(&iter, punit->type, unit_owner(punit), &mp);
+    while (eff_iterator_next(&iter)) {
+      if (iter.imeff->type == EFT_NO_SINK_DEEP) {
+        return FALSE;
+      }
+    }
     return TRUE;
   }
 }
@@ -424,8 +435,7 @@
    * is a city on the tile, or if the tile is not accessible, or if the 
    * tile is on a different continent, or if we're a barbarian and
    * the tile has a hut, don't go there. */
-  if ((unit_flag(punit, F_TRIREME) && 
-       is_likely_trireme_loss(pplayer, x, y))
+  if (is_likely_ship_loss(punit, x, y)
       || map_get_city(x, y)
       || map_get_continent(x, y) != continent
       || (is_barbarian(pplayer) && map_has_special(x, y, S_HUT))) {
diff -Nur -Xfreecivdiff.ignore freeciv-cvs/common/aicore/pf_tools.c freeciv-patched/common/aicore/pf_tools.c
--- freeciv-cvs/common/aicore/pf_tools.c	2003-07-22 16:29:32.000000000 +0100
+++ freeciv-patched/common/aicore/pf_tools.c	2003-07-24 17:03:26.000000000 +0100
@@ -322,8 +322,7 @@
     parameter->get_zoc = NULL;
   }
 
-  if (unit_flag(punit, F_TRIREME)
-      && base_trireme_loss_pct(unit_owner(punit)) > 0) {
+  if (base_ship_loss_pct(punit, NULL) > 0) {
     parameter->turn_mode = TM_WORST_TIME;
     parameter->is_pos_dangerous = trireme_is_pos_dangerous;
   } else {
@@ -363,8 +362,7 @@
 
   parameter->get_zoc = NULL;
 
-  if (unit_flag(punit, F_TRIREME)
-      && base_trireme_loss_pct(unit_owner(punit)) > 0) {
+  if (base_ship_loss_pct(punit, NULL) > 0) {
     parameter->is_pos_dangerous = trireme_is_pos_dangerous;
   } else {
     parameter->is_pos_dangerous = NULL;
diff -Nur -Xfreecivdiff.ignore freeciv-cvs/common/unit.c freeciv-patched/common/unit.c
--- freeciv-cvs/common/unit.c	2003-07-24 17:02:27.000000000 +0100
+++ freeciv-patched/common/unit.c	2003-07-24 17:03:26.000000000 +0100
@@ -1343,9 +1343,9 @@
 }
 
 /**************************************************************************
-  Like base_trireme_loss_pct but take the position into account.
+  Like base_ship_loss_pct but take the position into account.
 **************************************************************************/
-int trireme_loss_pct(struct player *pplayer, int x, int y)
+int ship_loss_pct(struct unit *punit, int x, int y)
 {
   /*
    * If we are in a city or next to land, we have no chance of losing
@@ -1353,28 +1353,46 @@
    * we'd need to confirm that we can exist/move at the (x, y)
    * location we are given.
    */
-  if (map_get_terrain(x, y) != T_OCEAN || is_coastline(x, y)) {
+  if (!unit_flag(punit, F_TRIREME) || map_get_terrain(x, y) != T_OCEAN
+      || is_coastline(x, y)) {
     return 0;
   } else {
-    return base_trireme_loss_pct(pplayer);
+    struct map_position mp;
+    mp.x = x;
+    mp.y = y;
+    return base_ship_loss_pct(punit, &mp);
   }
 }
 
 /**************************************************************************
  Triremes have a varying loss percentage. based on tech. Seafaring
- reduces this to 25%, Navigation to 12.5%. The Lighthouse wonder
- reduces this to 0.
+ reduces this to 25%, Navigation to 12.5%. The No_Sink_Deep improvement
+ effect (e.g. Lighthouse wonder) reduces this to 0. (Units that are not
+ Triremes always have a loss percentage of 0.)
+ mp should point to a map position, or be NULL if this is indeterminate.
 **************************************************************************/
-int base_trireme_loss_pct(struct player *pplayer)
+int base_ship_loss_pct(struct unit *punit, struct map_position *mp)
 {
-  if (player_owns_active_wonder(pplayer, B_LIGHTHOUSE)) {
+  struct player *pplayer = unit_owner(punit);
+
+  if (!unit_flag(punit, F_TRIREME)) {
     return 0;
-  } else if (player_knows_techs_with_flag(pplayer, TF_REDUCE_TRIREME_LOSS2)) {
-    return 12;
-  } else if (player_knows_techs_with_flag(pplayer, TF_REDUCE_TRIREME_LOSS1)) {
-    return 25;
   } else {
-    return 50;
+    struct eff_iter iter;
+    int losspct = 50;
+    if (player_knows_techs_with_flag(pplayer, TF_REDUCE_TRIREME_LOSS1)) {
+      losspct = 25;
+    }
+    if (player_knows_techs_with_flag(pplayer, TF_REDUCE_TRIREME_LOSS2)) {
+      losspct = 12;
+    }
+    eff_iterator_unit_init(&iter, punit->type, pplayer, mp);
+    while (eff_iterator_next(&iter)) {
+      if (iter.imeff->type == EFT_NO_SINK_DEEP) {
+        return 0;
+      }
+    }
+    return losspct;
   }
 }
 
diff -Nur -Xfreecivdiff.ignore freeciv-cvs/common/unit.h freeciv-patched/common/unit.h
--- freeciv-cvs/common/unit.h	2003-07-24 17:00:39.000000000 +0100
+++ freeciv-patched/common/unit.h	2003-07-24 17:03:26.000000000 +0100
@@ -262,8 +262,8 @@
 struct unit *is_non_attack_unit_tile(struct tile *ptile,
 				     struct player *pplayer);
 
-int trireme_loss_pct(struct player *pplayer, int x, int y);
-int base_trireme_loss_pct(struct player *pplayer);
+int ship_loss_pct(struct unit *punit, int x, int y);
+int base_ship_loss_pct(struct unit *punit, struct map_position *mp);
 
 bool is_my_zoc(struct player *unit_owner, int x0, int y0);
 bool unit_being_aggressive(struct unit *punit);
diff -Nur -Xfreecivdiff.ignore freeciv-cvs/server/gotohand.c freeciv-patched/server/gotohand.c
--- freeciv-cvs/server/gotohand.c	2003-07-22 16:29:32.000000000 +0100
+++ freeciv-patched/server/gotohand.c	2003-07-24 17:03:26.000000000 +0100
@@ -709,8 +709,7 @@
 	    && !same_pos(x1, y1, dest_x, dest_y)) {
 	  continue;
 	}
-	else if (unit_flag(punit, F_TRIREME)
-		 && trireme_loss_pct(unit_owner(punit), x1, y1) > 0) {
+	else if (ship_loss_pct(punit, x1, y1) > 0) {
 	  move_cost = 2*SINGLE_MOVE+1;
 	} else {
 	  move_cost = SINGLE_MOVE;
diff -Nur -Xfreecivdiff.ignore freeciv-cvs/server/unittools.c freeciv-patched/server/unittools.c
--- freeciv-cvs/server/unittools.c	2003-07-24 17:01:33.000000000 +0100
+++ freeciv-patched/server/unittools.c	2003-07-24 17:03:26.000000000 +0100
@@ -530,8 +530,7 @@
     }
 
     /* 4) Check that triremes are near coastline, otherwise... */
-    if (unit_flag(punit, F_TRIREME)
-	&& myrand(100) < trireme_loss_pct(pplayer, punit->x, punit->y)) {
+    if (myrand(100) < ship_loss_pct(punit, punit->x, punit->y)) {
       notify_player_ex(pplayer, punit->x, punit->y, E_UNIT_LOST, 
 		       _("Game: Your %s has been lost on the high seas."),
 		       unit_name(punit->type));