turny transome , beach cat

Your question, what makes a boat fast and safe. Taking the last one first; No boat is entirely safe. Recall the Titanic.

What makes a boat fast is a question that has way too many answers. Are you talking about power boats, sailboats, or human powered boats? Each type has a set of design characteristics that tend toward speed or lack of it. If you are serious about learning, then I recommend this book: Hydrodynamics of High Speed Marine Vehicles by Odd M. Faltinsen, ISBN-0-521-84568-8 This a graduate level book that contains a gold mine of information that is backed by elaborate research, and sound mathematical science. A less strenuous but very informative book is; Sailing Theory and Practice by C.A. Marchaj. The Marchaj book may succeed in showing you that sailboats are steered by more elements than the rudder. Aside from the book or books, other sailors will show you that they can and often do steer the boat with no rudder input whatsoever. Rudders are for tacking and jybing. Trimming and balance are for steering if you want to maximize speed.

 

I agree and disagree,
as hull physics and hydro physics fundamentals change with varying speeds .

certain speeds I'm quite sure? the sail positions steer the boat to a greater percentage than the rudder
but I kinda think that once a certain speed is obtained
the the dagger boards ( keel ) yield most control back to the rudder.

thank you for your book suggestions much appreciated.