Did some searching and came across this appropo discussion
Gentlemen, we have been having an active discussion on another BB about the adaptation of a jet drive to a submarine.
http://groups.yahoo.com/group/vulcania_submarine/
Quick background; Pat Regan who has a functional Disney Nautilus submarine wants to adapt a jet ski pump to the sub. He has the belief that similar to a Jet Ski the pump develops its greatest thrust at the surface. I, however, don’t think it would lose any /much thrust placed 16 inches below the surface.
The logic he presents seems sound, that the whole jet column is related to maximum thrust and that in air the thrust is greater than underwater because it encounters less friction leaving the Nozzle than under water.
Another view is that once the water leaves the jet nozzle, thrust has already been developed and it is immaterial what happens to the water after since the kinetic energy for thrust has already been imparted to the water and any remaining energy dissipates whether in a jet column or up against a wall. Realizing of course that the Nautilus will never plane like a Jet Ski or jet boat is there any advantage to having the jet located on the surface or will there be a loss of thrust if located 16 inches below the surface. The pump will never load at Jet Ski speeds.
To summarize, does a jet pump lose thrust submerged 16 inches below the surface as opposed to “at” the surface.
Can you shed any light on this?
Tom, otherwise tewrecks on Pat’s BB thanks
I have a jet model sub
http://www.rcgroups.com/forums/member.php?u=40728