Use of Bp~Delta diagram for prop selection

I am learning to use the Bp~Delta diagram for propeller selection.
The process i go through is:
at first i assume a suitable and reasonable value of rpm and shaft power.
then according to calculated Bp ; using the optimum efficiency line i find the value of delta and p/d and from the value of delta i can find the diameter.

But if the found open water efficiency doesnot give my required effective power then i run along the fixed delta curve(with delta value previously found) changing the rpm (power is constant) and i find new values of diameters.
then i plot a Diameter vs Effective power curve and select the diameter gives my desired effective power.

I dont have good books on propeller selection. So want to know how much right my process is and what additional things should i do to select the propeller.

thanks in advance

 

After finding the diameter, if the open water efficiency does not give the reqd effective power, then its better to change the delta value rather than move away from the optimum efficiency line. You can have a changed rpm and shaft power to modify your assumed engine parameters.

However, I feel that its better to start with an initial prop dia from the minimum clearances required, and then fix the engine rpm and MCR to provide the effective power. Then work back with the engine parameters selected and arrive at a suitable prop dia, pitch and expanded area ratio.

Basic Ship Propulsion by Ghose and Gokarn is a good reference..

 

Usually you get the best efficiency with the largest diameter possible. If you need to compromise, more blade will help reduce blade pressure to prevent cavitation. Have you read the "Propeller Handbook" by Gerr? It is really easy to use and covers all the basics.