diff --git a/src/virtualship/expedition/ship_config.py b/src/virtualship/expedition/ship_config.py
index 5609c182..8969f1c4 100644
--- a/src/virtualship/expedition/ship_config.py
+++ b/src/virtualship/expedition/ship_config.py
@@ -119,9 +119,9 @@ class XBTConfig(pydantic.BaseModel):
 class ShipConfig(pydantic.BaseModel):
     """Configuration of the virtual ship."""
 
-    ship_speed_meter_per_second: float = pydantic.Field(gt=0.0)
+    ship_speed_knots: float = pydantic.Field(gt=0.0)
     """
-    Velocity of the ship in meters per second.
+    Velocity of the ship in knots.
     """
 
     argo_float_config: ArgoFloatConfig | None = None
diff --git a/src/virtualship/expedition/simulate_schedule.py b/src/virtualship/expedition/simulate_schedule.py
index bec54468..aee01509 100644
--- a/src/virtualship/expedition/simulate_schedule.py
+++ b/src/virtualship/expedition/simulate_schedule.py
@@ -122,11 +122,11 @@ def _progress_time_traveling_towards(self, location: Location) -> None:
             lons2=location.lon,
             lats2=location.lat,
         )
+        ship_speed_meter_per_second = self._ship_config.ship_speed_knots * 3600 / 1852
         azimuth1 = geodinv[0]
         distance_to_next_waypoint = geodinv[2]
         time_to_reach = timedelta(
-            seconds=distance_to_next_waypoint
-            / self._ship_config.ship_speed_meter_per_second
+            seconds=distance_to_next_waypoint / ship_speed_meter_per_second
         )
         end_time = self._time + time_to_reach
 
@@ -137,8 +137,7 @@ def _progress_time_traveling_towards(self, location: Location) -> None:
             while self._next_adcp_time <= end_time:
                 time_to_sail = self._next_adcp_time - time
                 distance_to_move = (
-                    self._ship_config.ship_speed_meter_per_second
-                    * time_to_sail.total_seconds()
+                    ship_speed_meter_per_second * time_to_sail.total_seconds()
                 )
                 geodfwd: tuple[float, float, float] = self._projection.fwd(
                     lons=location.lon,
@@ -164,8 +163,7 @@ def _progress_time_traveling_towards(self, location: Location) -> None:
             while self._next_ship_underwater_st_time <= end_time:
                 time_to_sail = self._next_ship_underwater_st_time - time
                 distance_to_move = (
-                    self._ship_config.ship_speed_meter_per_second
-                    * time_to_sail.total_seconds()
+                    ship_speed_meter_per_second * time_to_sail.total_seconds()
                 )
                 geodfwd: tuple[float, float, float] = self._projection.fwd(
                     lons=location.lon,
@@ -250,7 +248,7 @@ def _make_measurements(self, waypoint: Waypoint) -> timedelta:
                         max_depth=self._ship_config.ctd_config.max_depth_meter,
                     )
                 )
-                time_costs.append(timedelta(minutes=20))
+                time_costs.append(self._ship_config.ctd_config.stationkeeping_time)
             elif instrument is InstrumentType.DRIFTER:
                 self._measurements_to_simulate.drifters.append(
                     Drifter(
diff --git a/src/virtualship/expedition/verify_schedule.py b/src/virtualship/expedition/verify_schedule.py
index fcc77217..d3b01011 100644
--- a/src/virtualship/expedition/verify_schedule.py
+++ b/src/virtualship/expedition/verify_schedule.py
@@ -99,7 +99,7 @@ def verify_schedule(
         distance = geodinv[2]
 
         time_to_reach = timedelta(
-            seconds=distance / ship_config.ship_speed_meter_per_second
+            seconds=distance / ship_config.ship_speed_knots * 3600 / 1852
         )
         arrival_time = time + time_to_reach
 
diff --git a/src/virtualship/instruments/drifter.py b/src/virtualship/instruments/drifter.py
index 378af42f..2fd4180b 100644
--- a/src/virtualship/instruments/drifter.py
+++ b/src/virtualship/instruments/drifter.py
@@ -81,7 +81,9 @@ def simulate_drifters(
     )
 
     # define output file for the simulation
-    out_file = drifter_particleset.ParticleFile(name=out_path, outputdt=outputdt)
+    out_file = drifter_particleset.ParticleFile(
+        name=out_path, outputdt=outputdt, chunks=[len(drifter_particleset), 100]
+    )
 
     # get earliest between fieldset end time and provide end time
     fieldset_endtime = fieldset.time_origin.fulltime(fieldset.U.grid.time_full[-1])
diff --git a/src/virtualship/static/ship_config.yaml b/src/virtualship/static/ship_config.yaml
index 729e4d75..494656c1 100644
--- a/src/virtualship/static/ship_config.yaml
+++ b/src/virtualship/static/ship_config.yaml
@@ -1,4 +1,4 @@
-ship_speed_meter_per_second: 5.14
+ship_speed_knots: 10.0
 adcp_config:
   num_bins: 40
   max_depth_meter: -1000.0
diff --git a/tests/expedition/expedition_dir/ship_config.yaml b/tests/expedition/expedition_dir/ship_config.yaml
index c057d6b5..09f40c0a 100644
--- a/tests/expedition/expedition_dir/ship_config.yaml
+++ b/tests/expedition/expedition_dir/ship_config.yaml
@@ -1,4 +1,4 @@
-ship_speed_meter_per_second: 5.14
+ship_speed_knots: 10.0
 adcp_config:
   num_bins: 40
   max_depth_meter: -1000.0
diff --git a/tests/expedition/test_simulate_schedule.py b/tests/expedition/test_simulate_schedule.py
index ef090b4e..6381b805 100644
--- a/tests/expedition/test_simulate_schedule.py
+++ b/tests/expedition/test_simulate_schedule.py
@@ -17,7 +17,7 @@ def test_simulate_schedule_feasible() -> None:
 
     projection = pyproj.Geod(ellps="WGS84")
     ship_config = ShipConfig.from_yaml("expedition_dir/ship_config.yaml")
-    ship_config.ship_speed_meter_per_second = 5.14
+    ship_config.ship_speed_knots = 10.0
     schedule = Schedule(
         waypoints=[
             Waypoint(location=Location(0, 0), time=base_time),