Acceleration in water using a water jet

[Aeronautician]

Hi, everyone. I'm working on a personal project and I need some insight from the intelligent minds here. I'm trying to calculate the thrust that a jet motor on a marine craft needs to exert in order to accelerate the craft in a certain direction. What are the necessary factors to determine the force or thrust that the motor needs to accelerate, let's say, 1 kg in the water? My dilemma comes from the nature of the source of acceleration, the motor, utilizing water jet propulsion. The motor has to suck in water and expel it at a high rate which causes acceleration according to Newton's laws. Is the rate of expulsion of water the value that determines how much thrust is attained? Now, this rate of water output, can it be related to the wattage or horsepower of the motor? All in all, I believe my question is this, how is the power of the motor related to the rate of water which it expels? I tried to find solution inspiration from an aircraft jet engine but it eluded me unfortunately. Can you guys guys point me in the right direction? Thanks for any help.

 

[berkeman]

Hi, everyone. I'm working on a personal project and I need some insight from the intelligent minds here. I'm trying to calculate the thrust that a jet motor on a marine craft needs to exert in order to accelerate the craft in a certain direction. What are the necessary factors to determine the force or thrust that the motor needs to accelerate, let's say, 1 kg in the water? My dilemma comes from the nature of the source of acceleration, the motor, utilizing water jet propulsion. The motor has to suck in water and expel it at a high rate which causes acceleration according to Newton's laws. Is the rate of expulsion of water the value that determines how much thrust is attained? Now, this rate of water output, can it be related to the wattage or horsepower of the motor? All in all, I believe my question is this, how is the power of the motor related to the rate of water which it expels? I tried to find solution inspiration from an aircraft jet engine but it eluded me unfortunately. Can you guys guys point me in the right direction? Thanks for any help.

Welcome to the PF.

Does this introductory article help?

http://www.explainthatstuff.com/jetskiseadoo.html

 

[A.T.]

Is the rate of expulsion of water the value that determines how much thrust is attained? Now, this rate of water output, can it be related to the wattage or horsepower of the motor?

The thrust is equal to the momentum change of the water per time. The required shaft power is related to the kinetic energy change of the water per time and propeller efficiency.