How to find Delivered Power

So, I have calculated PC and then Pd, but I was directed to use below which is I guess why I am struggling.

 

Directed by whom?

 

Guy running the course, I am happy to use the right method. I have done both and they provide almost the same answer. I just made an assumption for Nr. I would use this to find PC

 

So... how do you go from:

To using these:

You can't... there is insufficient data provided in the question.

You can only answer the question using the data provided in the question and using that data from known formula to assist you.

But using those that you have been directed to... where do you get the Kt, where do you get the diameter etc etc... none of this is possible from the question provided.

Do you understand this?

 

I had these values in the post when you asked for all the details, with the exception of the diameter (sorry):

P/D = 1
Kt = 0.194
Eff = 0.728
Jadvance = 0.670
Kq = 0.033
D = 1.7m

I used this data to find Np and then used the above formula for power delivered.

 

So the above values are values provided in the original question, despite being asked what was the original question and data provided, yet none of the above noted was with the question??

Your role as an engineer./naval architect is to be clear concise without ambiguity.

Your replies thus far have been anything but!!

 

Mitch, was the spreadsheet included with the assignment, or was it something you found on your own?

Let's go back to basics. For the vessel to go 14 knots the propeller has to be able to deliver enough thrust. So in addition to selecting the engine you need to ensure the selected/assumed propeller is sufficient. Note that Power = Thrust x Speed and Thrust = Power / Speed with the appropriate units used.

 

Sorry I missed the diameter in my first post on the question, I know this is key. I really do appreciate your help.

 

The spreadsheet was included and the data provided was from the optimum efficiency for that particular prop, the only assumptions I have made are for the thrust deduction factor and wake factor. I then used the effective power and speed provided along with the assumed thrust deduction factor to find the thrust. The effective power provided is 600kW so I have halved this to be distributed to each shaft.

My original issue I think was understanding what delivered power means. I think it is probably better referred to as propeller power. This is followed by having no experience in this area at all meaning I can't compare any of my results to anything I have done previously.

My calcs resulted in 488kW per propeller using the original formula I provided which seems appropriate as I have used the method suggested by Ad Hoc and it resulted in 515 kW per propeller. From here it is just mechanical losses in the transmission equipment.

Thank you for the help provided. I do really enjoy this forum and hope to provide advice back in the future.

 

Several possibilities.

1) There is a mistake in your calculations. The most common source of mistakes is probably using the wrong units / unit conversions, or using a dimensional quantity where a non-dimensional version is needed.

2) The propeller needs to operate at other than optimum efficiency for the vessel to go 14 knots. Start with the speed and effective power at 14 knots and work out the propeller operating conditions.

 

In the hope of not facing the firing squad.... there may have been a coefficient error in the macro.... I should have checked this first before disputing the maths... thanks again for your time