Maybe fixed updating boat list on FX thread.

racevisionGame/src/main/java/visualiser/model/VisualiserRaceState.java

@@ -1,6 +1,7 @@
 package visualiser.model;
 
 
+import javafx.application.Platform;
 import javafx.collections.FXCollections;
 import javafx.collections.ObservableList;
 import javafx.scene.paint.Color;
@@ -182,7 +183,7 @@ public class VisualiserRaceState extends RaceState {
 
                 boat.setCurrentLeg(getLegs().get(0));
 
-                existingBoats.add(boat);
+                Platform.runLater(() -> existingBoats.add(boat));
 
             }