The future of maritime propulsion

[farmerben]

There is a lot of interest in making maritime propulsion green.  I've been looking at sailboats.  Most yachts have a sail area to displacement ratio of 10-20m2 per ton.  If you scale that up, it doesn't work for anything like a modern cargo ship.  There are some videos out there about Magnus effect sails and inflatable sails.  Nobody really breaks down the performance of these devices.  I suspect they motor sail all the time and get maybe an extra 1/2 a knot of speed boost under ideal conditions. The Magnus device is powered so it's really a question of air propellers vs underwater propellers.   I love sailboats, but they are mostly just expensive toys.  Back in ye old days sailing cargo ships were all we had, but they were terribly slow by modern standards.

The idea that you could use solar alone, also doesn't really scale.  I suspect methane and hydrogen to become prominent as maritime fuels before they make it into other transportation sectors.

[darthgently]

3 hours ago, farmerben said:

There is a lot of interest in making maritime propulsion green.  I've been looking at sailboats.  Most yachts have a sail area to displacement ratio of 10-20m2 per ton.  If you scale that up, it doesn't work for anything like a modern cargo ship.  There are some videos out there about Magnus effect sails and inflatable sails.  Nobody really breaks down the performance of these devices.  I suspect they motor sail all the time and get maybe an extra 1/2 a knot of speed boost under ideal conditions. The Magnus device is powered so it's really a question of air propellers vs underwater propellers.   I love sailboats, but they are mostly just expensive toys.  Back in ye old days sailing cargo ships were all we had, but they were terribly slow by modern standards.

The idea that you could use solar alone, also doesn't really scale.  I suspect methane and hydrogen to become prominent as maritime fuels before they make it into other transportation sectors.

Very slow cargo craft that could take advantage of wind, currents, and tides is worth exploring for loads that are consistent but not in a hurry but they would almost have to be mostly uncrewed and automated as labor costs are big deal the slower you go

[Hannu2]

Ammonia is seriosuly investigated as ship fuel.  It  can  be made from air and water with renewable energy and it does not produce any carbon dioxide because NH3 does not contain carbon. Ship Diesel engines can use ammonia with relatively minor modifications.

Negative things which need more development are toxicity, lower energy density than methane or diesel fuel and tendency to produce nitrogen oxides.

https://spectrum.ieee.org/why-the-shipping-industry-is-betting-big-on-ammonia

Edited 2 hours ago by Hannu2
Typo error correction

[magnemoe]

Square cube law is sails enemy. Above 10.000 ton displacement it become very hard to use sail power only as the sail area become inpractical. 
Yes you have larger sailing ship but they tend to be Great Eastern or smaller modern cruise ships who often don't have to go far island hopping. And they are sail assisted, granted an cruise ship island hopping don't need much speed and they have an huge crew  
Going up to 50.000 ton and above and sails don't add much while crew count and fuel cost / ton carried goes down. 
This goes both ways, you can cross the pacific in an pretty small sailboat but an motor boat has to be more of an ship to do this.