I always wondered: It is obvious that the "noses" at the lower bow featured on vessels like the Normandie and the Andrea Doria are the product of painstaking studies of hydrodynamics and surely improve on the ship's performance/friction.
Why then does the great SS United States, last and deservedly winner of the Blue Ribband, built 17 years later than the Normandie have no nose-shaped lower bow but rather a plain bow similar to those found on the Cunard Queens?
Does anyone know how this shape of the lower bow came to being and if it really improves the performance?
Hi christian!
I think it has really to do with the ship´s friction. Plain bow shapes are producing bigger bow waves flowing alongside the hull - an energy wasting effect. Think of modern frigates and destroyers having their sonar-dome incoorporated into the bow bulge design. Modern freighters and tankers also have it - but for not wasting energy the bulge has to be completely under water - otherwise you have a braking effect. On many ships the bulbous bow is only visible when you´re looking directly from the front to it - not from the side.
Hope this helps a bit,
Cheers, Olaf.
Christian;
The balbous bow has the effect of making a hole in the water there by allowing the hull to slip through the water with less resistance. The size and shape is determined in part by the size and shape and projected service speed of the hull it's fit on. Modern cruise ships and merchant vessals have very pronounced bulbs at the fore foot of their bows. These ships tend to have a service speed of twenty knots or less. The faster the ship, the smaller the bulb. Of course a tremendous ampunt of tank testing goes into the final determination of bulb size. By the way, the United States did have a bulbous bow. She owed more to Normandie that Gibbs would ever be willing to admit. The two Queens were very old fashioned and actually outdated in hull form even at the time of their comissioning.
Harry
The resistance of a ship is broken into three elements:
1) Frictional resistance (the friction between the water and the hull surface which is proportional to the wetted surface); 2) Wave resistance which is dependent on the hull shape (the energy created by the wave propagation) and 3) Air resistance (the projected fontal area of above-water structure). The bulb reduces the wave resistance by generating an initial wave before the actual bow wave. This initial wave induces an underpressure immediately aft (where the "real" bow starts)of it that reduces the overpressure that occurs when the water hits the "real" bow (cancellation effect).
Bulbs are found in different shapes and sizes depending on the slenderness of the hull, the main dimensions, the hull speed and the hull's loading conditions. A passenger ship has always about the same draught, a tanker can vary with over 20 meters. A bulbous bow need not be totally submerged, it depends on the bulb type. On modern passenger ships the top of the bulb is always above the waterline.
The Normandie's hull was designed by the famed Russian naval architect Yourkevitsj. The bulbous bow was his theory thus subsequently named the "Yourkevitsj Bow". Why contemporary ships did not have this bow even though it was invented? Naval architects are by tradition very conservative. They all have their scepsism to new gadgets - sometimes it was simply considered an un-necessary expence (they do cost money) and may have been so then. Today however, the advantages of the bulb is so well documented you would not go without it. The energy savings may be up to as much as 6-7 %.
The NORMANDIE achieved practically the same speed as the QUEEN MARY on two-thirds of the fuel consumption, due to the highly-efficient bulbous bow. The QUEEN MARY was faster due to having an additional 40,000 shaft-horsepower to overcome the resistance of her traditional clipper-style cutwater. If you look at aerial photo's of both ships at speed, notice all the froth and turbulence surrounding the QUEEN, while the NORMANDIE moves through the water in a "clean" fashion with little or no froth around her graceful hull-no turbulence. The s/s US certainly had a NORMANDIE-style cutwater. This was a closely-guarded secret for many years, which is why the Revell s/s US kit is a waterline model and the Ideal/Glencoe kit has a clipper-bow. Pete
I'm sitting in my hotel room in Pusan, Korea. Room has free computer with internet access. Searched for the message board and clicked on the first result which was a mighty old thread. Thought I would post....didn't see the dates...it's getting late. Now time to check out the re-opened DF! Congrats fellas!!