Determining prop thrust

[YuriB]

Hi everyone.
Who knows how to find out what thrust bearing size i should install on my boat? The boat was former navy and was towing an array, so that existing thrust bearings were too big and were dismantled because of wear. Is there any formula to calculate the thust?

[FAST FRED]

A rough rule of thumb is each HP the engine can deliver will give MAX 25 lbs of thrust.

Very few are better than 20 lbs per hp in real life.

FF

[YuriB]

Thank you Fast Fred

[DMacPherson]

Just a follow up. The figure of 25 lbs/hp is a fairly traditional value that is still a reasonable estimate for free-running vessels. However, for vessels with propulsion systems designed for towing (i.e., bollard pull) it is not uncommon to see values approach 30 lbs/hp or even higher. For example, we evaluated a bollard test for one of the newer ducted systems (with a contemporary propeller design and high-efficiency nozzle) which reached 32 lb/hp.

Regards,

Don MacPherson
HydroComp, Inc.