Thank you for taking the time to type this and post it Kevin. Much obliged!
I'd like to add there are several variations of water-jets, including mixed-flow and axial-flow pumps. There are also several different jet-pump manufacturers, in which some are not as efficient as others (not naming brands).
This was good side-by-side comparison, however... it can be misleading to the reader who doesn't understand the difference in pump technologies and brands. Although the powerplants and hulls were identical in this test, you would likely find that if another pump was utilized, the results may have been different (good or bad).
Although I haven't had the opportunity to test the current crop of jet-pumps on the same platform, I've studied the different designs and formed my own conclusions, based on my experience with them.
You might have heard the name "Lipps" in the yachting world recently, or in reading the equipment list of some of the new "jet-yachts" recently launched (such as the M-140). There's a reason why an unheard of manufacturer has made quick in-roads into the industry, against long term established names.
I didn't want to make one of our latest new members (Capt. J) uncomfortable by challenging his post. I'm sure he was just relaying information he gathered elsewhere. However, nothing could be further from the truth. Properly designed jet-pumps are absolute models of concentrated thrust. Quite simply, a ducted prop is more efficient than a non-ducted (or shrouded) prop, unless ofcouse... the drag created by the shroud outweighs the benefits of encapsulation. This isn't the case with a jet-pump on boats.
This being said... I have to clarify one thing. Application is critical!!! There are applications better for pumps and application better for props. In depends entirely on the operating parameters of the craft. An offshore race boat would be the wrong application for a pump, just like a Bravo drive would be the wrong application for yacht.
