work boats
How does torque work with boats/ships?
I understand how low end torque works for cars. What would be the point of having it on a tugboat or ship? You wouldn’t need any turning power because the prop is always going to be working against the same forces of water, no matter what is tied to the craft or how much weight is on board…..am I crazy?
Torque and power are always restricted by the engine input and then divided by the gearing in the output. In a boat there is a gear reduction just like in a car, and the final reduction is found in the pitch of the propeller, much like how in a car it is found in the drive tire size. There is some “slip” due to the hydraulic contact of the propeller and the water, but this can be considered a loss due to a power transition inefficiency. This being said, the only difference seems to be that there are more power losses in a boat than in a car, but this is not true because most boats do not offer variable speed drive. Therefore, engine speed is almost directly proportional to watercraft speed with any deviation due to the power or traction losses at different propeller speeds. This means that a good marine powertrain needs good low end torque to overcome the fact that there are no low gears to use to achieve it.
I reread your question and realized I did not answer a main point of yours about the force of the water… Just as a boat only has to power against the water it is pushing against, so must a car only power against the pavement it is pushing against. My point is that if you draw an adequate free body diagram you will see that the boat (and the car) have to push harder on the concrete or water to accelerate themselves if they weigh more. F=ma, if the car weighs more it will take more force to accelerate at the same rate, the same is true for boats. You will see this if you realize that the boat is not accelerating the same if it is 1 ton as it would if it were 10 tons.
tugs and work boats
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