Ship Construction: Design Notches and Minimization Methods

Gross Tonnage is a function of the moulded volume of specific enclosed spaces on a vessel.

Net Tonnage is a function of the moulded volume of all cargo spaces (or those available to passengers).

Lightweight refers to the mass of the ship's hull and machinery, including some minimal working fluids.

Deadweight is the difference between the vessel's Lightweight and its Displacement.

Displacement is the total weight of the vessel, including its Lightweight and Deadweight, when it is fully loaded and immersed in water.

Depth = Freeboard + Draft, where Freeboard is the vertical distance between the waterline and the top watertight deck, and Draft is the vertical distance between the waterline and the bottom of the hull.

Amidships refers to the middle portion of the ship, while Bow and Stern refer to the forward and aft ends, respectively. These terms are used to specify the dimensions and characteristics of different sections of the vessel.

Pounding refers to the 'slamming' of the vessel's forefoot as it drops back into the sea. It is caused by the cyclic pushing in and out of water around the waterline in the bows as the ship moves through head seas.

Panting stringers and panting beams are the key structural components designed to provide support against the effects of panting.

Camber refers to the transverse curvature of the deck, where it rises from the shipside to the centerline. Its purpose is to assist drainage from the deck.

Length between perpendiculars is the distance between the forward and aft perpendiculars, while length overall is the length measured between vertical lines at the extreme contours of the vessel, perpendicular to the designed waterline or keel.

Sheer refers to the longitudinal curvature of the deck, which is an important design feature that contributes to the overall strength and seaworthiness of the vessel.

Draft marks are markings on the hull that indicate the depth of the vessel's draft, which is the vertical distance between the waterline and the bottom of the hull. They are typically located on the stem and stern of the ship.

Draft refers to the vertical distance between the waterline and the bottom of the hull, while depth is the vertical distance between the bottom of the hull and the highest point of the deck.

To minimize stress concentrations and prevent crack propagation that can lead to material/structural failure.

Pounding refers to the violent slamming of the yacht's bow into the water as it rises and falls in heavy seas, causing high impact loads on the hull.

Panting refers to the cyclic flexing and deformation of the hull plating and structure due to the dynamic wave loads and motions of the ship.

Hulls are strengthened with additional framing, stiffeners, and reinforcements to increase their rigidity and ability to withstand the cyclic loads and impacts of panting and pounding.

A design notch is a discontinuity or sharp corner in the structural design that can act as a stress concentration point, potentially leading to crack initiation and propagation, ultimately resulting in structural failure.

Designers aim to eliminate sharp edges and corners by rounding them, placing welds away from high-stress areas, and incorporating cut-outs or brackets to redistribute loads and reduce stress concentrations.

Panting refers to the cyclic flexing and deformation of the hull plating and structure due to dynamic wave loads, which can lead to fatigue cracking and eventual structural failure if not properly addressed.

Lightweight + Deadweight = Displacement. The lightweight represents the weight of the ship's structure and equipment, while the deadweight is the weight of the cargo, fuel, water, and other variable loads. The sum of these two weights equals the total displacement of the vessel.

The moulded depth is the vertical distance from the moulded baseline to the level coincident with the inside of the upper deck plate at the side. It is usually measured at amidships.

The moulded draft is the vertical distance from the moulded baseline to the level coincident with the waterline, while the moulded depth is the vertical distance from the moulded baseline to the inside of the upper deck plate at the side. The moulded draft may be quoted for any point along the length of the vessel, while the moulded depth is usually measured at amidships.

Flare refers to the outward curvature of the bow plating upwards from the waterline. It increases the upper deck breadth and buoyancy, and reduces deck wetness in heavy seas, thereby improving the vessel's seaworthiness and performance.

Given: Lightweight = 5,000 tons, Deadweight = 10,000 tons, Displacement = 15,000 tons. Since Displacement = Lightweight + Deadweight, the moulded draft would be the same along the entire length of the vessel, and it would be equal to the draft corresponding to a displacement of 15,000 tons.

Sheer refers to the upward curvature of the deck from the midship section towards the bow and stern, while freeboard is the vertical distance between the waterline and the upper deck. Both sheer and freeboard contribute to the vessel's stability and seaworthiness by increasing the reserve buoyancy and reducing the risk of shipping water on deck.

Given: Lightweight = 8,000 tons, Displacement = 20,000 tons. Since Displacement = Lightweight + Deadweight, Deadweight = Displacement - Lightweight = 20,000 tons - 8,000 tons = 12,000 tons.

The moulded depth of a vessel is influenced by factors such as the vessel's intended cargo capacity, stability requirements, deck strength, and operational conditions. A greater moulded depth generally provides more internal volume for cargo and improves stability, but it also increases the vessel's weight and construction costs.

Increased flare at the bow improves the vessel's ability to shed water and reduces the amount of deck wetness in heavy seas, thereby enhancing seaworthiness and crew safety. However, excessive flare can also increase the vessel's resistance and reduce its speed and fuel efficiency. Naval architects must strike a balance between the desired seakeeping qualities and the vessel's hydrodynamic performance.