This is an area I have some peripheral involvement with. For retrofitted sails on bulkers, the figure of 10% saving in fuel is the usual one mentioned rather than 20%. However given the long life of ships, there is much more interest in retrofit than in new build.

You mention container ships. I haven't seen anything explicit on these, and I think the reason is probably that they cruise much faster than bulkers and tankers, which means the potential savings from sail is smaller. I would have thought 20% optimistic even for a new-build.

Retro fit is clearly a preferred path for a new approach given ship life spans and size of existing global transport fleet.

My gut objection to the container approach taken above in the first link was existing container locking mechanisms for ships can struggle in severe weather to keep the boxes on the boat .. additional forces from a sail (in good weather) might well mimic the forces that break stacks in bad weather.

Your point is well taken, I might suggest that container ships could be segregated into fast and slow cargo and that might help somewhat with total fleet fuel consumption. (pure spitball notion).

I'm sure there's plenty of businesses out there who'd love to advertise near zero or zero emissions transport for their goods, with the caveat that they have to plan a few more months ahead.

"suggested masts are better as integral parts of ships rather than bolt on after thoughts."

It seems quite mad that we even need to debate this. Wind is free power and we have at least 2000 years of engineering to draw on how to use it.

Any propulsion unit needs to be effectively attached to a ship. Screws are attached longitudinally, low down and push. Sails are a bit more tricksy. A triangular sail mounted along the long axis will generally work best because it can handle more wind angles but a square sail mounted across the long axis will provide more power on a "reach" to a "run" (the wind is mostly from behind, so pushing).

The cutting edge of sailing ships that carried stuff are the tea clippers. Think "Cutty Sark" which is now a visitor attraction in London, Greenwich. Note the stay sails - the triangular sails at the front. Then note the three masts. Each mast has several main sails that are huge rectangles for "reaches" and additional extensions. There are even more triangular infill sails above the main sails.

It's quite hard to explain how wind and sails work but you need to understand that a sailing ship can sail "into the wind". Those triangles are better at it than those rectangles but those rectangles can get more power by being bigger. Even better, you can use the front triangular sails (stay sails) to moderate the wind to feed the other sails with less turbulent wind.

Wind is free power and it is so well understood. How on earth is this news?

I thought (and think) that the teaclipper‘s square sail rigs wouldn’t be considered state of the art for any course the ship might sail.

This is all interesting, but is there a reason trianglular and rectangular sails can't be bolt on after thoughts?

For the sails to be an effective means of propulsion they need to transfer a lot of force through the mast and stays to the hull. This require the attachment points to be very solid. Not something you can easily do as a retrofit. You'd need to reinforc the hull aroud the mast and stay attachments.

They likely can but with reduced changes for being optimal. Sails, keel and rudder should be balanced so that adjusted sails cause minimal pivoting force to mitigate with the rudder. Also the supports below the mast and plates for the stays likely need planning to allow sufficient structure without limiting the working angles of boom too much.

Wasn't the main issue with this that fuel is paid for by cargo ship customers (the container owners), not the shipping company? So the shipping company doesn't want to spend a ton of capital to get a 10% discount to all their customers, and there was no way for thousands of random customers to exert pressure on the shipping company to do so. Basically the economics didn't make sense.

The economies of this make sense if there's more than one shipping company (they'll be cheaper and get more business) or if they just change how they charge, neither seems that hard.

> EDIT: Wingsails to reduce cargo ship fuel consumption (April 2023) > https://news.ycombinator.com/item?id=35426482

> I’m Joseph, and along with Arpan and Bailey we are the founders of OutSail Shipping. We’re building a sail the size of a 747 that rolls up into a shipping container.