What's with the underwater noses?

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[Badwebdiver]

Why do big ships have underwater "noses" on their front?  Is that a sonar dome, or something to do with the thrusters, or what? 

[Mr Robville]

Those are called bulbous bows. They develop a pressure zone generating a wake that runs completely contra to the bow wake itself, neutralizing the wake height therefore reducing the ship's drag.

Here is an image of Titanic (no bulbous bow) compared to MS Oceana that does have one:




And here's a closeup of Oceana's bulbous bow during optimization stages. The pressure zones are colored as Blue with an underpressure and Red as an overpressure.


The size of the bulbous bow depends on what the optimal speed of the ship is.
On Oceana, for example, the bulbous bow works best at a speed of 30 knots. If Oceana sails slower or faster, the wake it creates becomes either longer or shorter therefore resulting that the wakes not matching properly anymore.


http://en.wikipedia.org/wiki/Bulbous_bow

[Badwebdiver]

Thank you for the quick reply.    That had me curious.

[Mr Robville]

No problemo  
I wondered the same thing a few years back. I initially always assumed that it was only meant for extra displacement for the overhanging bow above.

[Traddles]

It used to be assumed that a sharp bow would make a vessel travel faster for a given amount of power, and then some very bright person realised that fishes swam very fast with round noses!!!!  Look at a trout for a perfect example. It took a long, long time for the penny to drop.

[Mr Robville]

Hehe, I imagine the guy coming up with the plan being turned down by all of his colleagues and being laughed at. And as soon as they saw the effect it had their jaws dropped to the floor and they obeyed him like a god for bending the rules of physics.  

"What kind of sorcery is this?!"