Ajax 400 error when used inside a plugin

I'm really, really stuck. When I run this code I get a checkbox displayed. When I click the checkbox, the javascript is run. I get test in the console, followed by a 400 POST error. I can get this to work perfectly if I take it out of the plugin (and remove $this from the ajax actions), but I don't want to do that. Please can someone point me in the right direction!

This is the code from my plugin root file

    require_once BUILDNEWBOAT_PATH . 'includes/BuildNewBoatPlugin.php';
    $build_boat_plugin = new BuildNewBoatPlugin();
    $build_boat_plugin-run();

This is inside the BuildNewBoatPlugin class

    public function __construct() {
        add_action( 'wp_enqueue_scripts', array( $this, 'init_plugin' ) );
        add_action( 'wp_ajax_post_new_boat_form', array( $this, 'post_new_boat_form' ));
        add_action( 'wp_ajax_nopriv_post_new_boat_form', array( $this, 'post_new_boat_form' ));
    }

    public function init_plugin() {
        wp_register_script( 'new_boat_form_script', plugin_dir_url( __FILE__ ) . 'js/new_boat_form.js', array() );

        wp_localize_script( 'new_boat_form_script', 'new_boat_form_script_ajax_object',
            array(
                'ajax_url'   = admin_url( 'admin-ajax.php' ),
                //'ajax_nonce' = wp_create_nonce( 'new_boat_form_ajax_nonce' )
            )
        );

        wp_enqueue_script( 'new_boat_form_script');

    }

    public function post_new_boat_form(){

        print_r($_POST);
        ?
        pTesting AJAX/p
        ?php

        die();
    }

    public function run(){
        // displays an html form
    }

And this is my javascript file

    $(#boatFormStep input[type=\radio\]).on(change,function(){

        console.log(test);

        $.ajax({
            url: new_boat_form_script_ajax_object.ajax_url,
            data: {
                action: 'post_new_boat_form'
            },
            method: 'POST',
            success: function (response) {
                console.log(test+response)
                $(#boatFormStep).html(response);
            },
            error: function (error) {
                console.log(error)
            }
        })
    })

});