Hide your navbar untill you need it. When scrolling down, navbar disappears. When scrolling up a little bit, navbar appears again like an "overlay"
Live example (original): http://wicky.nillia.ms/headroom.js/
With bootstrap theme: http://webprofis.nl
NOTE: this plugin is made for tpl based themes
1. enable the plugin
2. open your default.master.tpl in themes/your theme/views and catch your desired area by putting between header tags like below;
<header id="header" class="header"> // your navbar goes here </header>