ros2 navigation planner with boats

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First off, I'm still learning nav2, and I've never used it for a boat before. But..

I don't know which local planner you're using, But if you happen to be using DWB, you should be able to tune the PathAlign.scale and PathDist.scale parameters to allow it to turn into the path more. At least as far as I understand it.

To stop it from re-planning a global path, you can make a new behavior tree that would look something like

<root main_tree_to_execute="MainTree">
  <BehaviorTree ID="MainTree">
  <PipelineSequence name="NavigateWithReplanning">
    <RateController hz="0.00000001">
      <ComputePathToPose goal="{goal}" path="{path}" planner_id="GridBased"/>
    </RateController>
    <FollowPath path="{path}"  controller_id="FollowPath"/>
  </PipelineSequence>
</BehaviorTree>

</root>

The hack is here is to change the Rate controller to something real small, such that this would only replan once every 3.17 years. If you wanted to be more elegant with it, you could make a new "Decorator" plugin to replace the RateController with something to only run it once. (The SingleTrigger decorator may do this already... but I've never used it.) To use it, either change the bt_navigator default_nav_to_pose_bt_xml param to point to your new behavior tree, or set this path in your navigate to pose action goal request.