Ship stresses

this gives you a proper understanding of stresses acting on a shipping vessel and how to resist their actions

1. SHIP STRESSES Team Irian: Raktim Maitra Piyush Pratik Sahoo Md. Faraz Ansary Md. Shajeed Khan

2. The ship at sea or lying in still water is constantly being subjected to a wide variety of stresses and strains . These forces may initially be classified into: STATIC FORCES DYNAMIC FORCES

3. STATIC FORCES These are the forces due to difference in weight and buoyancy which occur at various points along the length of the ship

4. Vessel at rest Static force

5. Dynamic Forces • A ship is free to move about six degrees of fre e dom. Three linear and three rotational. • • Various forces acting on ship are constantly varying in degree and frequency. • This movement of the ship introduces dynamic forces which result in stresses on the ship’s structure.

6. Forces produce stresses in the ship’s structure which may be divided into two categories: Global stress – affects the whole ship Local stress- affects a particular part of a ship

7. HOGGING If the buoyancy in midship is greater the ship will hog.

8. SAGGING • If the buoyancy in the mid-ship region is lesser than weight the ship will sag

9. RACKING When a ship is rolling, the accelerations on the ship’s structure are liable to cause distortion in the transverse section. Greatest effect is under light ship condition.

10. STRESSES DUE TO WATER PRESSURE Water pressure acts perpendicular to the surface and increases with depth

11. STRESSES DUE TO DRY-DOCKING Tends to set the keel upwards. Due to the up-thrust of the keel blocks. Tendency for the ship’s sides to bulge outwards. Bilges tend to sag.

12. SLAMMING OR POUNDING While heaving or pitching, the forward end leaves and re-enters the water with a slamming effect. the slamming down of the forward region on to the water is known a pounding. Flat areas of plating are brought into violent contact with water at a very acute angle. There is a loud bang and the ship shudders. Momentum of the ship receives a check and energy is imparted to the ship girder to make it vibrate. This is also known as pounding and is a result of Dynamic forces.

13. PANTING This is a stress, which occurs at the ends of a vessel due to variations in water pressure on the shell plating as the vessel pitches in a seaway. The effect is accentuated at the bow when making headway D M S - D O

14. Arrangements to resist Panting In the forepeak side stringers are fited. The side singers meet at the fore end. beams are fited at alternate frames

15. Stresses caused by localized loading Localized heavy loads may give rise to localized distortion of the transverse section. Such local loads may be the machinery (Main engine) in the engine room or the loading of concentrated ore in the holds.

16. Deck opening creates areas of high local stress due to lack of continuity of Structure

17. Thank you and have a great day everyone! 