Restrict search results to post_type only while on post_type archive

When a user visits an archive.php with post_type ‘boats’ AND they use the search function, I’d like to restrict the search results to display only results of ‘boats’. Make Sense?

I can display my post_type properly. I can even set the filter….

add_filter('pre_get_posts','SearchFilter');

function SearchFilter($query) {
  if ($query->is_search) {
    // Insert the specific post types you want to search
    $query->set('post_type', array('boats'));
  }
  return $query;
}

I am trying the following code…..

if( get_post_type() == 'boats') {
    add_filter('pre_get_posts','SearchFilter');
   }

I think that “pre_get_posts” is run before “get_post_type” so this will always fail. How can I restrict search results only while searching from said post_type?