Sailing Diagrams Teaching How To Find The Bhp Of A Ship's Engine ?

How to find the bhp of a ship's engine ? - sailing diagrams teaching

Engine load is changing the charge grasped at sea: the weather, strong currents, water depth, the boiling of the liquid propellers, shafts, etc.
Of course, you can find the IP diagram the force indicated.
How do I find the braking force on the navigation axis P..