xifis on "Responsive Boat Child Theme"

How do you make a responsiveboat child theme? I'm getting the following error:

The "responsiveboat" theme is not a valid parent theme.

I'm not a stranger in making child themes. Then again, I may be doing something simple and stupid. This responsiveboat child theme has me stumped. I believe it is because responsiveboat is not a traditional WP theme -- responsiveboat is already a child theme of zerif-lite.

Here are the style.css headers for my child style.css and responsiveboat's style.css (respectively):

=== My Child style.css ===

/* Theme Name: ResponsiveBoat Child Theme URI: http://wordpress.org/themes/responsiveboat/ Description: ResponsiveBoat Child Theme; Zerif Lite Child Theme Author: CWM Webmaster Author URI: http://wordpress.org/themes/responsiveboat/ Template: responsiveboat Version: 1.0.0
*/
/* =Imports styles from the parent theme
-------------------------------------------------------------- */
@import url('/wp-content/themes/responsiveboat/style.css');

=== responsiveboat style.css ===

/*
Theme Name: ResponsiveBoat
Description: ResponsiveBoat is a free responsive WordPress theme, with a friendly and colorful design. It comes with a full-screen layout, a full-width homepage header, elegant parallax effect, and nice animations. It can be used web agencies, digital studios, corporate, product showcase, personal and business portfolio. Overall, ResponsiveBoat looks very mode and interactive.
Author: Themeisle
Author URI: https://themeisle.com
Template: zerif-lite
Version: 1.0.8
License: GNU General Public License version 2
License URI: license.txt
Text Domain: responsiveboat
Tags: black, gray, red, white, one-column, two-columns, right-sidebar, responsive-layout, custom-background, custom-menu, editor-style, featured-images, threaded-Idea, translation-ready
*/
[standard CSS code follows; no css import of zerif-lite]