>Large ships with bulbous bows generally have twelve to fifteen percent better fuel efficiency than similar vessels without them.

Wow, that's a much larger effect than I expected.

Related: Propellor Boss Cap Fins https://m.youtube.com/watch?v=a8PjWSeLUzY

> have occasionally wondered why it hasn't been implemented.

Because underwater hull part may be caused via cavitation erosion.[0,1,2]

[0] https://www.iboats.com/propellers/what-prop-cavitation

[1] https://www.thoughtco.com/cavitation-causes-and-remedies-229...

[2] https://www.southampton.ac.uk/engineering/research/projects/...

Those are two very different things. The OP article talks about introducing air bubbles into the stream along the hull, the articles you linked talk about cavitation bubbles, i.e. water that vaporizes when the pressure locally drops. The latter collapse spectacularly and do indeed damage to surfaces. The former don't.

[edit: clarified which articles I mean]

> introducing air bubbles into the stream along the hull

Placing air bubbles into the stream along the iron/steel hull in seawater... This is the worst idea as it would drastically increase oxidation.[0]

[0] https://pubs.acs.org/doi/10.1021/es0109242

Let’s forget about the thick layer of paint between the steel and the water...

> Let’s forget about the thick layer of paint between the steel and the water...

If seawater oxidation around the boat would be increased then thick layer of paint should be thinned to prevent steel corrosion, which also means increasing cost of the boat.

Most boats/ships already get wet with (sea)water, alternating with air at the water level. Hardly a new problem.

There is research into solving this with sacrificial material? Last i remember, there was the idea to have a coat of carbon fibre enhanced ice to ablate and soak up the damage, while regenerating from below?

> Last i remember, there was the idea to have a coat of carbon fibre enhanced ice

It may be used (probably with low profit) for small vehicles/boats, but not for big ships.

Ships are already risky & expensive projects, and to modify them experimentally can have large follow up costs.

https://en.wikipedia.org/wiki/Galvanic_anode

I always wondered what that was for, cool!

For anyone that didn't read the article: Without the bulb, the prow slices through the water and causes the water to ride up the sides of the ship.

The bulb on the bow is under the waterline. This forces water up in front of the ship before the prow. The bulb is designed so that the bulb-rise of water cancels the prow-rise of water in destructive interference.

The bulb design only works at certain speeds, water conditions, etc.

Bulbous bows sounds hard or impossible to retrofit on an existing ship but this does sound fairly easy to add.

It isn't, but it also is not a fix-all. They work for a very specific, narrow range of speeds and wave conditions. If that's not in your shipping route it's not helpful.

Are you referring to bows or bubbles?

The bulbous bow.

It might be harder for larger ships but for anything under a couple hundred tons those are straightforward to retrofit in anything that doesn't have an exotic hull construction.

Are you referring to bows or bubbles?

bows