Joe,
[snip]  the fact that you're 
  considering an ambient sub doesn't really help your displacement, right?  
  The construction is easier in that you don't need a 1 inch thick pressure hull 
  but unfortunately the boat needs to weigh just as much as if you 
  did.
   
  Paul
   
  Hi, Joe, Paul - if the interior volume of the 
  cockpit is kept to a minimum (Joe's aesthetics come into play here), then 
  less keel ballast is required.  I'll be keeping air pockets to a minimum 
  in Magical Child.
   
  Rick
  Vancouver