# Power prediction based on Bollard pull

Discussion in 'Diesel Engines' started by deier, Apr 2, 2020.

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### deierJunior Member

Hello guys,i think this is the right place to post my question,how can i predict my engine power,based on the bollard pull?My tractor tug needs to develop 50 TBP and i have 2 azimuth propellers with D=2.1m,n=273 rot/m,T=263 KN.

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### TANSLSenior Member

Perhaps this can help you, considering that it is only a rough calculation.

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• ###### Propeller Thrust.docx
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### deierJunior Member

it’s not that helpful for my problem in particular but thanks for your response.

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### TANSLSenior Member

Maybe I am very wrong and I misinterpret your problem. You know the thrust provided by the propeller and you need to know the power of the motor. Is that so?

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### deierJunior Member

Exactly.The trust provided by the propeller is 263kn and the bollard pull is 50 tbp.I want to know the power of the motors.There are 2 propellers FPP.

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### jehardimanSenior Member

TANSL's calculation is very close to the old empirical rule of thumb of 32-35 lbs (142-155 N) of thrust at bollard condition for every shp in for a properly designed propeller. I know this works for props 1m-10m, tunneled or not, as long as you don't cavitate them too much. FWIW 263kN is 26.8 tonnes. So first estimate for shp would be 263/.142 = 1852 shp delivered to each prop. But you need to make sure that the props don't starve or cavitate.

Edit to add at bollard condition.
Edit II: also see this thread bollard pull/ propulsion and torque in a tug/towboat

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### deierJunior Member

Thank you for your response. So that means I need an engine with at least 1909 hp, it’s enough to ensure a 25 tbp per propeller?

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### jehardimanSenior Member

That is not the end answer. That is where I would START the design.

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### deierJunior Member

Ok, so starting from the beginning, I have a tractor tug to design. I searched for a azimuth drive dwg that I can fit on my tug, and the diameter of the propulsor is 2.1 and has the 263 kn thrust. I don’t have an Ae/A0 or a p/D . With the selected propellers I want to select an engine that can develop 50 tbp from both propellers. I just want to know what is the required power onboard to develop that. And in addition at the speed of 15 nd, what thrust does it develop and what power does it require a propeller in my case?

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### gonzoSenior Member

It would also make sense to decide which requirement is a constraint. For example, if the Bollard pull is your constraint as a minimum, the design can't deviate from it. However, the minimum speed may be acceptable at 13 knots. Also, be aware of other constraints. For example, maximum length, minimum turning radius, maximum draft, etc.

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