Hacker News Reader

Comment by moocow01 | Hacker News Reader

Without knowing much about ship dynamics it sounds suspicious that you could make an unsinkable ship based upon this concept. Isn't the above water mass of the ship held up by the (large) amount of air in the hull? If you punctured the hull (releasing the air) then wouldn't this material have to support the entirety of the ship with the minuscule layer of air bubbles across the surface of the hull? I notice the person's hand pushing the disc down with relative ease so I'd assume its buoyant but not super-buoyant

View on HN

It’s not the air holding a ship up, it’s the displaced water. Once the weight of displaced water is equivalent to the ship’s weight, it floats.

Another way to think about it is specific weight. Ships have fewer kilograms per cubic meter than water does so they float. When pierced they start filling up with water which makes their specific weight go up and eventually become more kilo per cubic meter than water. At that point the ship sinks.

I think the concept also works with displaced water, those hydrophobic surfaces create air containers that make the whole thing lighter.

But why so complicated? A 10cm metal hull seems much safer than a 5mm opening with hydrophobic coating.

Also with a chamber system ship's can be made pretty robust and almost unsinkable.

Yes, it’s displaced water... So I’m guessing the trapped air bubbles here increase the displacement of the water while only adding the weight of the air? It seems like such a small amount of displacement you’d get from these tiny air bubbles. Then again, those discs look super thin too.

You'd only need as much air volume as you have volume of things heavier than water. A boat sinks because air is displaced by water, increasing the density of the boat. If you make sure the displaceable air runs out before the density of the boat is higher than water it'll never sink.

In practice this is something that's actually done quite a bit. Fill a lot of air spaces in a boat with foam and you get to the point where if your boat fills with water you can simply pull the plug in de bottom of the boat and it will un-sink itself most of the way. You see this for example on small sailboats, the only caveat being you can't be on the boat as it's un-sinking since you'd weigh it down.

That said, seems to me that foam is a lot cheaper and easier than micro-engineering every surface on the boat.

Reply on news.ycombinator.com