Ulstein X-BOW inverted bow | Hacker News Reader

Ulstein X-BOW inverted bow

ulstein.com

124 pointsjen729w28 comments

It's a sort of tumblehome bow, similar designs were popular in the past. For instance this late 19th century French battleship: https://en.wikipedia.org/wiki/French_battleship_Jaur%C3%A9gu...

No doubt computer simulation / etc have let them optimize this shape more than in the past, but it's not wholly unprecedented.

I hear that drachinifel intro…

Edit: https://youtu.be/fkRJxgYgTVA Great introduction to hull design

Or Viking Long ships.

I'm no hull designer, but I have worked on many ships with X-bow in the past decade and change, and anecdotally will claim that they feel much more comfortable in rough seas - say, North Atlantic, winter conditions - than conventional designs.

They provide for much gentler vessel movements. (Not gentler in the sense that those prone to seasickness will no longer be sick - but you will be able to get useful work done with an X-bow vessel in weather where you would be busy holding on for dear life in a conventional design.

Incidentally, the Ulstein design workshop is located within walking distance of me as I write this.

Seems that the 'generic name' for this concept is "inverted bow":

> In ship design, an inverted bow (occasionally also referred to as reverse bow) is a ship's or large boat's bow whose farthest forward point is not at the top. The result may somewhat resemble a submarine's bow. Inverted bows maximize the length of waterline and hence the hull speed, and have often better hydrodynamic drag than ordinary bows. On the other hand, they have very little reserve buoyancy and tend to dive under waves instead of piercing or going over them.

* https://en.wikipedia.org/wiki/Inverted_bow

In the maritime industry it is referred to as x-bow and widely recognized as such

Overlapping but not identical concepts. I suppose you could say the x bow is a refinement of an inverted wave piercing bow. The thing that's distinct about the x bow is it has reserve buoyancy in both pitch directions, but is fine and wave piercing at the waterline. This gives advantages above an inverted bow in general.

I thought this was an article about archery. Still satisfied though.

I’ve seen some of these bows on seismic survey ships out the window where I live.

I assumed the funky bow shape was due to them being ice breakers/science ships, but looking the ships back up they’re indeed examples of this X-BOW design.

I wonder what the downsides are? The site does the classic thing of listing the advantages but not the opposite.

The vertical component of the force exerted by the sea would be down instead of up. So I guess it's good if pushing the front of the boat down is OK. Sounds like go faster => sink to me, but as they seem to work I guess buoyancy overcomes it.

The bow is only down as it pierces the oncoming wave in extreme seas. The important thing to consider about ship stability is that water on the deck of a ship is immediately inducing free surface effect and modifying the vessel buoyancy. The xbow design sheds the water and prevents free surface effect while reducing the impact of the bow on the wave.

They don't pay me, but I wish they did...

There are few downsides compared to traditional bows. Those that do exist relate to capacity. In large ships, the bow shape is really only providing any kind of input during extremely rough seas. All modern ships will have a bulbous bow beneath the waterline for efficiency in calm waters. The x-bow design adoption is seen, to-date, in vessels that will operate in heavy weather and rough seas. So, we see the xbow in OSV and MODU type vessels particularly in the northern latitudes.

Yeah I wondered about lateral stability.

I do not have a lot of experience of rough seas, but I did the crossing from the Antarctic peninsula to southern Argentina going through the drake passage and holy fuck it was rough, but not just up and down but also huge rolling left and right.

It seems like a traditional bow and hull shape would resist rolling (more buoyancy the further over you go) but this design has less?

AXE bow is competing hard with Ulstein's X-Bow design. There are some interesting journal published papers on both, and IMHO Axe bow seems to perform better in most conditions.

Example CFD analysis of Axe bow trimaran performance: https://ijtech.eng.ui.ac.id/article/view/4659

The main disadvantage of the X-Bow is that ships need to be very high. This kind of bow can plunge very deep so you need protection against it.

Damen's AXE bow can also be used for smaller ships but ships need to be long.

What it doesn't have is a bulbous bow which at a critical cruising speed sets up a counter bow wave to reduce hull drag. So the X-Bow probably isn't efficient for ocean transiting tankers and container ships.

Bulbous bow is important in high cruising speeds speeds Drag ~ flow velocity squared.

The new trend in cargo shipping is energy saving with slower cruising speed. Slightly slower speed and thinner ships don't need bulbous bow.

You're talking about Slow Steaming but these ships still use a bulbous bow. Indeed older ships are actually being taken into dry dock and re-nosed to tune the cruising speed down to a slower more efficient speed.

What happened was that a container ship could cruise across the Pacific at say 28 knots which is fast. But no one was paying for that speed which in fact used more fuel. On the other hand, a slower boat (Slow Steaming) used less fuel. It was more efficient and less polluting.

https://www.marineinsight.com/wp-content/uploads/2013/01/The...

Nose job often means complete removal of the bulbous bow.

At slow speeds the wave resistance is smaller relative to frictional resistance, the bulbous bow increase hull wetted surface area and increases frictional resistance. It's function of to Froude number and block coefficient.

No, they aren't simply removing them. They are replacing them with new ones tuned for a slower more efficient speed.

http://www.oldsaltblog.com/2013/03/container-ship-nose-jobs-...

Even with daily operating costs at ~25k or more?

Reviewing Ulstein’s marketing material got me to naive wondering - what’s the state of generative design in this field? Why not just throw all the parameters of the problem (expected vessel usage, capacity, range, geography etc) into a model and have the system generate the most optimal designs?

In order to do that, the 'test' for each iteration needs to be relatively quick/cheap. To see how good a bow design is you need to do some computationally expensive CFD, making iteration incredibly computationally expensive.

I've read some papers about generative design for wind turbines and antennas and in most cases the special sauce is an approximation of the simulation that can be run more quickly.

video in bad weather https://ulstein.com/innovations/x-bow/comparison-tests

Did anyone else open this article to wonder about how you would do archery with an inverted bow?

Me, but got pleasantly surprised. I don't know much about archery either.

Yep.

For some reason I expected this to be about a new gadget to play string instruments (e.g. cello or violin) with an interesting effect on sound.

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