Air travel has significantly reduced the demand for commercial transportation by passenger ships. Today, passenger ships are primarily used for tourism and recreational purposes, according to Marine Insight.
Hull Design Characteristics
There are some critically specific denominators when it comes to all passenger cruise vessels:
Hull Form
The fine hull form is the foremost characteristic of all cruise vessels, irrespective of operations and size. This is owing to the speed considerations of cruisers that need to cater to a stringent timetable not only expected by the passengers but also to the liner itself.
Bluffer hull forms, as in almost all tankers or bulkers, cater for more space in the hull ahead of midships, and these incur more significant profit margins in terms of higher freight volume carried in one charter voyage from point A to B. However, they come at a cost of speed and, thus, consequently, more voyage times.
Advantages of Large Superstructures
The volume space reduction in the main hull of finer-form vessels like passenger ships or cruise ships is compensated by the fact that most of the amenities, facilities, provisions, and even accommodation spaces in the majority are in the superstructure.
Stability and Seakeeping
Understanding The Location of the Vertical Centre of Gravity
The most crucial aspect in terms of a cruise vessel from a basic design point of view is understanding the location of the transverse vertical center of gravity or the VCG.
From the first principle, the greater the vertical extent of a body, the higher the tendency for the vertical center of gravity or VCG to be at an elevated height above the baseline.
Consider a block of 10 meters and another block of 5 meters in height (assuming the same width and length). Who has a higher G? Of course, the first one being taller, has a higher position of G as compared to the latter. Now, consider another case. Consider two blocks of both 10 meters but of dissimilar widths.
VCG In Cruise Ships
A modern cruise vessel design has a problem in terms of VCG from both angles. First, owing to larger and taller superstructures, and second, the finer hull form, as discussed above.
The subsistence of both these factors tends to elevate the VCG location of cruisers at dangerously high levels from a geometric point of view, increasing the chances of the intact transverse stability of the vessel being compromised.
External Loading
Due to the form of the vessel, the effects of hydrostatic and hydrodynamic loading are more pronounced. Moreover, owing to the large superstructure of the vessel, and greater freeboard (as compared to bluffer vessels like tankers or bulker), cruise vessels also essentially have a greater windage area.
What is the windage area? Windage area is the sum of all surface areas of a vessel that are exposed to the weather, that is the part of the vessel above the waterline when viewed from a particular direction. Thus, the action of wind forces on a passenger cruiser, with greater superstructures and increased freeboard, is far more than a tanker or a bulker.
Damage Stability
Damage stability is the other pillar of stability that deals with the integrity of the vessel after structural damage. Without delving into the intricacies of the damage stability, in a nutshell, it is sufficient to say that a higher degree of subdivision is desired in cruise ships, as in the event of damage and accidental flooding, the vessel does not lose its buoyancy much.
Remember Titanic? The century-old tragedy is still considered more to be an aftermath of the design rather than what caused it. Experts all over the years have postulated that if the subdivision of the vessel had been better, the iceberg impact would still not have been catastrophic as the flooding of the compartments could have been contained within proper limits of the force-buoyancy static equilibrium.
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Source: Marine Insight
