Bjorn:
    For a cat take any unpaid bill laying on your desk in an unopened envelope ;-).    Draw a diagonal line from corner to corner.    Stand it upright on the short side of the envelope, with the long side pointing up.   The long side is the mast.  The diagonal line is an imaginary shroud leading all the way from the mast head to the pivot axis.  Now pivot the envelope about that corner, and note that the masthead continues to rise relative to the surface of the desk (ocean), until the shroud (diagonal line) is vertical.   Now flip the envelope over so the diagonal line cannot be seen for the HP.   Now the envelope is stood up again, and the one corner is the pivot axis of the hull with the mast, and the long side above that is the mast.  Pivot on the corner again, and you will see that the mast head will immediately begin moving downward slightly as soon as you begin to pivot. 

    This of course ONLY works with unopened unpaid bills, past due notices, collection agency letters, or court summonses  ;-)    

                                                                                                                        H.W.

Rick, you wrote (in another thread):

" An interesting feature of the harryproa configuration with regard to heeling is that the heeling moment reduces as the boat heels.  A cat with the mast in the middle or on both hulls has initial increase in heeling moment when one of the hull lifts.  "

Why does the heeling moment reduce on the harryproa, but increase on the cat?