I would expect fuel efficiency to be related to the size and complexity of the engine. Producing some amount of force is going to require the same amount of fuel assuming energy loss due to resistance/friction is the same, and the engine is the same.
If true, we could e.g. have absurdly large trains on lots of rails? I would expect energy loss due to rubbing on rails and changing elevation to be similar to energy loss due to rubbing on water.
Is the quadrupling of drag and octupling of rolling resistance related to the assumption that drag is proportional to the surface area of the side on which the drag is produced, and that rolling resistance is proportional to weight? Either way, cost would still decrease due to larger and more complex engines, as rolling resistance per kg would not change.
Of course, railway sizes are fixed, so there is little to be done. I was just speculating where the relative efficiency of cargo ships comes from. I made an edit at the end of the post which contains a very rough approximation of how large savings on wages are in the case of cargo container ships.
Is the quadrupling of drag and octupling of rolling resistance related to the assumption that drag is proportional to the surface area of the side on which the drag is produced, and that rolling resistance is proportional to weight?
Yes. It’s a little more complex than this since rolling resistance is irrespective of speed, whereas drag increases with speed. But if you’re aiming for efficiency you’ll go at low speeds, so we can hold speed fixed and see what happens as we scale.
Either way, cost would still decrease due to larger and more complex engines, as rolling resistance per kg would not change.
Even if the engine is 100% efficient, you still lose energy to drag and rolling resistance, so sooner or later increased engine efficiency doesn’t buy you very much.
I was just speculating where the relative efficiency of cargo ships comes from.
I think it’s the fact they’re so much larger, and so drag/capacity is very low.
I would expect fuel efficiency to be related to the size and complexity of the engine. Producing some amount of force is going to require the same amount of fuel assuming energy loss due to resistance/friction is the same, and the engine is the same.
If true, we could e.g. have absurdly large trains on lots of rails? I would expect energy loss due to rubbing on rails and changing elevation to be similar to energy loss due to rubbing on water.
As you double each dimension, capacity octuples, drag quadruples, but rolling resistance octuples.
Ships only have drag from the water, but trains also have rolling resistance from the tracks.
This means trains don’t get significantly more efficient as they grow larger, but ships do.
Interesting, thank you.
Is the quadrupling of drag and octupling of rolling resistance related to the assumption that drag is proportional to the surface area of the side on which the drag is produced, and that rolling resistance is proportional to weight? Either way, cost would still decrease due to larger and more complex engines, as rolling resistance per kg would not change.
Of course, railway sizes are fixed, so there is little to be done. I was just speculating where the relative efficiency of cargo ships comes from. I made an edit at the end of the post which contains a very rough approximation of how large savings on wages are in the case of cargo container ships.
Yes. It’s a little more complex than this since rolling resistance is irrespective of speed, whereas drag increases with speed. But if you’re aiming for efficiency you’ll go at low speeds, so we can hold speed fixed and see what happens as we scale.
Even if the engine is 100% efficient, you still lose energy to drag and rolling resistance, so sooner or later increased engine efficiency doesn’t buy you very much.
I think it’s the fact they’re so much larger, and so drag/capacity is very low.