Reducing the fuel consumption of ships

Do you have any evidence that this idea works ? - to demonstrate a scale model would be very interesting.

Mike.

Georgeb: 
 

We could greatly reduce the fuel consumption and emissions of ships if we used the energy of waves…... 

There is no change to the laminar flow of water below sea level.

This is contradictory. If the pipe is able to take in water at the bow, it must be below the level of the water, and therefore affecting the flow of water round the hull. The amount of energy available from this would be minimal, bearing in mind the engine power required to propel the ship (for a large ship we are talking of tens of MW) and the drag would cause more losses than would be gained.

For a small ship, the bow would pitch up with the waves and the system might not take on any water anyway.

I think if you want to reduce fuel consumption on ships it can be done by utilising wind power. There is, after all, a correlation between the height of the waves and the power of the wind. If we were to fit tall masts on the ships with horizontal bars and hang large squares of canvas to be driven by the wind, this might work……. 

now you mention it something like that has been done. But squares are not always the best shape unless you want to run from the wind.

Ah yes, that's probably what you are thinking of.

Nuclear ships is the obvious answer.

The last time I looked the bow of a ship was above sea level. Due to the motion of the ship,  waves will strike the ship at the pointed front end rather than the sides. Wave energy is more concentrated and available for more of the time than wind energy. The plumbing necessary to capture wave energy would be a lot cheaper than using masts and sails and would be much  easier to operate.

Wave energy is equal parts potential energy and kinetic energy. When a wave strikes a wall such as the side of a ship the kinetic energy is transformed into pressure energy and more potential energy plus friction losses. This pressure and potential energy can be piped to the rear of the ship to be reconverted to jets of kinetic energy to push the ship forward.

Waves have potential energy so all the pipework to capture it is above sea level. There is no impediment to flows below sea level to increase drag.

There will be less energy lost by the ship forming bow waves.

I'm not a naval architect, but…

When the waves hit the bow of the ship, they are forced into constricted openings. This increases the pressure of the water (compared to a sharp bow cutting through the wave), pushing back on the ship.

Interesting idea, but I suspect that it would create more drag than the propulsive force that it generates.

An interesting concept.

Would the addition of a pipe to the ship not ruin it's streamlined design and introduce more drag and increase the power requirement to move through the water? I'm thinking that the bow is rather smooth and sharp to cut through the water more easily.

I also think that a ‘passive pipe’ wouldn't be very useful for propulsion. I use the phrase ‘passive pipe’ as opposed to that of say a jetski where water is forced through. What about adding a dynamo into the pipe to generate power from the water rushing through it (assuming that water does enter the pipe)?

Could we perhaps tow a series of turbines behind the ship which generate electricity? (Again adding drag, of course)

I'm no expert (not even an amateur really), just my stream of thought…

The waves are not ‘hitting the ship’ since they are transverse waves - the water itself merely moves up and down. What is actually happening is the ship is hitting the waves - I am of course referring to the behaviour of waves in deep sea rather than in shallow water close to shore where the action of the water does change.

In hitting the waves the ship is losing energy and adding pipes would result in more energy being lost due to the reduction in streamlining. We are battling with the second law of thermodynamics here and I can't see a way that we can get more energy than is being lost. However if anyone wants to do a study with a model and a tank I would be interested in seeing the results - just don't ask me to contribute to the cost.