Hi,
just checked your sitemap but it's correctly generated. Reporting less links that the ones submitted is pretty normal in Google Webmasters, more info at this FAQ:
http://storejextensions.org/faq/why-google-webmasters-tools-reports-less-indexed-links-than-that-contained-in-the-sitemap.html
You can try to submit an alternate link for the sitemap to Google Webmasters like this one to refresh the Google cache:
https://www.navisyachts.com/component/jmap/sitemap/xml/?v=823
No errors at all should be shown, the sitemap is correctly generated in XML not HTML errors or redirects.
John
