View Single Post
Old 12-26-2012, 10:33 AM   #94 (permalink)
ryannoe
Not Ordinary Engineering
 
Join Date: May 2011
Location: Alabama
Posts: 57
Thanks: 9
Thanked 27 Times in 14 Posts
Quote:
Originally Posted by donee View Post
Hi Virg,

I am no expert, but the bow bulb on a ship has to do with the interface between water and air. The bulb lifts the water ahead of the ship, which then falls away from the above water bow. Apparently its takes less work to lift the water than to push it aside (air is more compressible than water, and one is pushing against air when lifting the bow water).

On a car, or submarine, or airplane there is no such interface involved, and hence no bulbs.
When a boat pushes through the water, it creates a bow wave (high pressure area in the front, just like cars). This bow wave lifts the front of the vessel and raises the angle of attack of the boat. Instead of the boat sitting flat in the water, it is now climbing a constant hill... the faster it tries to go, the steeper the hill (because the wave builds bigger). To try and reduce this constant hill, the bulb was introduced to build a wave in front of the boat hull. Every wave consists of two parts, a crest and a trough. The crest is above the average waterline and the trough is below the average waterline. So if you can build a crest in front of the hull and position the trough where the hull wave builds... the bulb trough (positioned at the hull) and the hull crest should cancel themselves. Cancelling the bow wave allows the boat to sit level in the water as it powers through it.

Yes, you have to pay for the bulb wave's energy, but less energy is required to build the bulb wave than to power the entire boat up a hill.

I hope this helps!

Ryan
  Reply With Quote
The Following 2 Users Say Thank You to ryannoe For This Useful Post:
aerohead (07-31-2020), MetroMPG (12-26-2012)