5 ms·

I remember reading about this 40 years ago, and have occasionally wondered why it hasn't been implemented. Then I'm reminded of the history of the "Bulbous bow

I remember reading about this 40 years ago, and have occasionally wondered why it hasn't been implemented. Then I'm reminded of the history of the "Bulbous bow"[0] on ships, and how long that took to be adopted. I've submitted the Wikipedia link[1] in case anyone wants to read about it. [0] https://en.wikipedia.org/wiki/Bulbous_bow https://en.wikipedia.org/wiki/Bulbous_bow [1] https://news.ycombinator.com/item?id=25091997 https://news.ycombinator.com/item?id=25091997

worldsayshi 6y ago
Bulbous bows sounds hard or impossible to retrofit on an existing ship but this does sound fairly easy to add.
- hansvm 6y ago
  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.
  - worldsayshi 6y ago
    Are you referring to bows or bubbles?
    - hansvm 6y ago
      bows
- Already__Taken 6y ago
  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.
  - worldsayshi 6y ago
    Are you referring to bows or bubbles?
    - Already__Taken 6y ago
      The bulbous bow.
jcims 6y ago
I always wondered what that was for, cool!
- Balgair 6y ago
  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.
app4soft 6y ago
> 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 https://www.iboats.com/propellers/what-prop-cavitation [1] https://www.thoughtco.com/cavitation-causes-and-remedies-2293276 https://www.thoughtco.com/cavitation-causes-and-remedies-229... [2] https://www.southampton.ac.uk/engineering/research/projects/cavitation_erosion_corrosion_of_ship_propeller_materials.page https://www.southampton.ac.uk/engineering/research/projects/...
- bernulli 6y ago
  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]
  - app4soft 6y ago
    > 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 https://pubs.acs.org/doi/10.1021/es0109242
    - loriverkutya 6y ago
      Let’s forget about the thick layer of paint between the steel and the water...
      - app4soft 6y ago
        > 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.
verroq 6y ago
Related: Propellor Boss Cap Fins https://m.youtube.com/watch?v=a8PjWSeLUzY https://m.youtube.com/watch?v=a8PjWSeLUzY
PicassoCTs 6y ago
Ships are already risky & expensive projects, and to modify them experimentally can have large follow up costs. https://en.wikipedia.org/wiki/Galvanic_anode https://en.wikipedia.org/wiki/Galvanic_anode
Groxx 6y ago
>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.

worldsayshi 6y ago

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

hansvm 6y ago
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.
- worldsayshi 6y ago
  Are you referring to bows or bubbles?
  - hansvm 6y ago
    bows
Already__Taken 6y ago
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.
- worldsayshi 6y ago
  Are you referring to bows or bubbles?
  - Already__Taken 6y ago
    The bulbous bow.

jcims 6y ago

I always wondered what that was for, cool!

Balgair 6y ago
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.

app4soft 6y ago

> 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 https://www.iboats.com/propellers/what-prop-cavitation [1] https://www.thoughtco.com/cavitation-causes-and-remedies-2293276 https://www.thoughtco.com/cavitation-causes-and-remedies-229... [2] https://www.southampton.ac.uk/engineering/research/projects/cavitation_erosion_corrosion_of_ship_propeller_materials.page https://www.southampton.ac.uk/engineering/research/projects/...

bernulli 6y ago
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]
- app4soft 6y ago
  > 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 https://pubs.acs.org/doi/10.1021/es0109242
  - loriverkutya 6y ago
    Let’s forget about the thick layer of paint between the steel and the water...
    - app4soft 6y ago
      > 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.

verroq 6y ago

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

PicassoCTs 6y ago

Ships are already risky & expensive projects, and to modify them experimentally can have large follow up costs. https://en.wikipedia.org/wiki/Galvanic_anode https://en.wikipedia.org/wiki/Galvanic_anode

Groxx 6y ago

>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.