I am afraid the developers do not want to change the layout, I have made a similiar suggestion already.
The Mac OS X operating system has a gadget in the window title bar to switch off and on a toolbar, so the chart screen is larger. But there is still no stable Mac OS X version of OpenCPN, it's a beta right now. Best to have a menu choice also when the toolbar is switched off.
The toolbar will probably change in the future release to be dockable so you'll be able to float it or dock it wherever you want. It'll probably be split in multiple parts (main, plugins, etc...) That's suggested a few months ago but it requires big code changes no one did yet.