diff --git a/s57_layer/src/s57_layer.cpp b/s57_layer/src/s57_layer.cpp
index 5a51f89..fe08693 100644
--- a/s57_layer/src/s57_layer.cpp
+++ b/s57_layer/src/s57_layer.cpp
@@ -139,11 +139,14 @@ void S57Layer::updateBounds(double, double, double, double* min_x, double* min_y
       {
         tide_offset_ = new_offset;
         RCLCPP_INFO_STREAM(logger_, "Tide offset updated: " << tide_offset_ << " m (water above chart datum)");
+        // Mark tiles for regeneration but keep the cached costmap as a
+        // fallback so the controller has a usable costmap during regen.
+        // generateTile rebuilds the costmap from grids when chart_count=0,
+        // and the empty-charts early-return clears the pointer for safety.
         for(auto& t: tiles_)
         {
           t.second.complete = false;
           t.second.chart_count = 0;
-          t.second.costmap = nullptr;
           t.second.needs_update = true;
         }
         current_ = false;
@@ -303,9 +306,10 @@ void S57Layer::generateTile(TileID id)
   if(current_charts_.empty())
   {
     tiles_[id].complete = true;
-    // No tile costmap is created. In updateCosts, a nullptr tile
-    // with complete=true is recognized as uncharted territory and
-    // handled according to allow_uncharted_.
+    // Clear any stale costmap from a prior era when this tile had
+    // chart coverage. updateCosts treats nullptr+complete as uncharted
+    // and handles it according to allow_uncharted_.
+    tiles_[id].costmap = nullptr;
     return;
   }
 
@@ -336,6 +340,19 @@ void S57Layer::generateTile(TileID id)
       else
         all_charts_available = false;
   }
+
+  // No chart from current_charts_ overlaps this tile. Treat as uncharted —
+  // same handling as the empty-current_charts_ early return — and clear
+  // any costmap left over from a prior era when this tile had coverage.
+  if(grids.empty() && all_charts_available)
+  {
+    tiles_[id].complete = true;
+    tiles_[id].costmap = nullptr;
+    tiles_[id].chart_count = 0;
+    tiles_[id].needs_update = true;
+    return;
+  }
+
   tiles_[id].complete = all_charts_available;
   if(grids.size() > tiles_[id].chart_count)
   {
@@ -523,6 +540,17 @@ void S57Layer::getDatasetsCallback(GetDatasetsClient::SharedFuture future)
     RCLCPP_DEBUG_STREAM(logger_, "Received " << result->datasets.size() << " datasets from service");
   }
 
+  // Compare new dataset labels against current_charts_ before overwriting.
+  // bounds_need_update fires every ~5% of window movement, so this callback
+  // runs frequently while the boat moves; in steady-state survey areas the
+  // label set rarely changes. If unchanged, skip the per-tile invalidation
+  // at the end of this function so the cache survives.
+  std::unordered_set<std::string> new_labels;
+  for(const auto& d: result->datasets) new_labels.insert(d.label);
+  std::unordered_set<std::string> old_labels;
+  for(const auto& c: current_charts_) old_labels.insert(c.label);
+  bool chart_list_unchanged = (new_labels == old_labels);
+
   current_charts_ = result->datasets;
   chart_bounds_.clear();
 
@@ -593,9 +621,22 @@ void S57Layer::getDatasetsCallback(GetDatasetsClient::SharedFuture future)
     grids_.erase(grid);
   }
 
-  // mark all tiles as needing regeneration
-  for(auto& t: tiles_)
-    t.second.complete = false;
+  // Mark tiles as needing regeneration only when the chart set actually
+  // changed — unchanged callbacks are common while the boat moves and
+  // would otherwise force a full re-evaluation of every cached tile.
+  // Also reset chart_count so the rebuild branch in generateTile fires
+  // unconditionally; otherwise a same-count chart swap (one chart removed,
+  // one added) would leave stale tile costmaps because grids.size() would
+  // equal the previous chart_count.
+  if(!chart_list_unchanged)
+  {
+    for(auto& t: tiles_)
+    {
+      t.second.complete = false;
+      t.second.chart_count = 0;
+      t.second.needs_update = true;
+    }
+  }
 
 }