Tug Bullard Pull Calculations

Hello all

Can you help me to calculate the required engine power for tug boat with 40 tons Bullard pull?
the type of propeller will be ASD

is there are any good reference I can use for such calculations ?

Thanks in advance

 

The big item is going to be propeller diameter. Rule of thumb is 35 lbs of bollard thrust per shp in at the prop if the prop is properly sized. This means swinging a big prop for 40 tons. Once you have the prop diameter, and estimated shp, you need to pick a prop shape and P/D ratio to start the design spiral for all the other requirements; space, weight, engine HP, gearing, max speed, etc.

 

Thanks for your help

is there any kind of books or papers I can use as reference for these kind of calculations ?

 

PNA has a good write up on how to do this. Do you have a prop shape/nozzle selected? From there it is fairly straightforward for prop selection.

 

I think the propeller is with nozzle but I didn't choose the propeller size yet .... I'm asking to know where to start

about propeller sizing ... also go for PNA ?

 

Yes. start with a P/D of ~1 and then work out the diameter needed by momentum theory to get the 40 tons. You will see that as diameter increases, velocity through the disk (i.e. n*P) decreases. Then check for cavitation at the tip, his is basically what a Bp-delta chart does for maximum efficiency but bollard efficiency =0. Or using a Kq vs J prop chart you could plot Kq vs D for J= 0 until you match the chart for your given P/D.

 

ok i will check PNA, but is there are like direct instruction on how to do it, may be a flow chart or something like that ?