Honestly, I've held back responding to this thread because I'm trying to avoid arguments. But I can't not answer your question either. In the simplest terms, all of the force that makes your boat move happens inside the pump. The reason it turns when you change the angle of the nozzles is due to something called "thrust vectoring" which simply means that when you change the angle of the center of the low pressure area (the water escaping the high pressure of the pump), the center of the high pressure area (inside the pump opposite the nozzle) changes as well. And for the record, boat propellers, airplane propellers, helicopter rotors, aircraft wings and our jet pumps, all work on the same physics principles and to a certain extent, yes, it actually is rocket science. It really works off of two simple principles. 1: Any gas or liquid will flow from a high pressure area to a low pressure area. 2: All actions have an equal and opposite reaction. As an answer to your last question, yes the pumps are pushing the boat, just the jet of water is not pushing the boat directly. You could put your boat 20 feet in the air, and if you feed your jets water, the boat will move forward, turn, etc. Hell, you could put the boat in a vacuum and it would still work if you fed the jets water.
Sort of......a pump without a nozzle is just a water mover. The nozzle or "jet" in this case is what causes the boats movement. The pump itself creates a pressure differential that moves a high volume of water. Accelerating that volume of water through the jet nozzle is what creates the thrust. The water is accelerated rapidly through the nozzle due to the decrease in volume (actually integrated area) from the inlet to the outlet. Mass balance must be maintained, so in order for a high volume(mass) of water to traverse from a large opening to a small opening, it must accelerate. That ratio (in the AR190 case 155mm inlet and 85mm outlet or ~3.3:1 ratio) is what dictates the magnitude of the acceleration in the water.
Due to the equal and opposite reaction principle, we get a net result of a force on the hull, moving us forward. This is why things like the L13 cone work........This only works at high pump flows, otherwise the net force from the water acceleration is LESS than the net force from simply running a mass of water into another.....which....is why at low speeds this dynamic changes, and that is exactly what happens.
Flow rate, and given time interval greatly affect how these two principles play into one another. Slow speed is literally a "push on the nearest water" scenario, and use the pump flow to propel/move the boat around. Like what happens with a garden hose in a pool (except that wild movement has more to do with the significant lack of rigidity in the hose itself and it's inability to maintain a column shape under a light load).
A pump without a nozzle does nothing but move a bunch of water. A nozzle without a pump is just a parachute with a hole in it. The combination of the two in close proximity can create significant forward thrust.
Interestingly enough in a jet engine, because gasses are compressible, and there is combustion happening, the pumping action is actually a minor player. The expanding gasses from the combustion exit the nozzle fast enough to create thrust. Same concept as our water pump/nozzle interaction, but with an added element.
Yes and this is why things like the flyboard actually work. Notice none of the water from the jet is shooting into the water but rather the forces from the jet are pushing the rider/board.
This same concept is a great example of how the pressure differential in the pump moves the water, and the nozzle creates the thrust. The surrounding water is just acting as a big reservoir for the pump. Check out the relative sizes of the hose vs the nozzle outlets. Keep in mind every inch in diameter is worth ~3in of area (and subsequent volume per unit time)!!!
......This has been bugging me for a day now, but I think I figured out how the nozzles turn my boat even though they are out of the water. It must be the impact of the jet water stream hitting the side of the deflected nozzles like undisturbed air hitting the deflected rudder on the tail of an airplane, basically pushing it to the right or left (or not). I don't have an articulated keel with a rudder to enhance turning or fixed fins sticking down in the water. I showed Will's video to some of my staff today and they were also blown away.
You're close........Think of the nozzle as creating a "line of action" that has a force associated with it. You can use your finger and a small box on the table as an example. Push on the box (your finger is the jet nozzle and thrust) such that your finger lines up with the center of the box in all dimensions, and is perpendicular to the side you're touching. The box moves forward and in a straight line. NOW, don't move where you touched the box, but change the angle of your finger, the box will start to spin because you have now moved the line of action to direction that is no longer in line with the center of mass of the box. This induces a force moment around the center of the box, and it spins.
In rocket science there is a center of pressure and a center of thrust. So long as the center of thrust is kept behind of the center of pressure the rocket goes straight. There is a REALLY REALLY good explanation of this concept in the move "The Worlds Fastest Indian" where the main character sticks a toothpick through a cigar and blows air across it. This same concept applies to our boats, but in a smaller magnitude.
ALSO.....I found my books, but haven't dug through them yet to get you guys the cool formula's to play with
