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Port TTETTE-6755 Planning and Design Lecture #17 Moorings and Fenders Luis Prieto-Portar 2009 Introduction. When the earliest seafarers set sail in search of new lands, food or trade they secured their vessels either by beaching them or tethering those craft to shore with a mooring line. As craft become bigger and larger and regular patterns of trading were established, ports were built allowing vessels to berth to a wharf. A mooring is defined as a compliant (usually a tensile structure) that restrains a vessel against the forces of the sea and the movements generated by by wind, wave, and currents acting upon the vessel. For thousands of years, the traditional practice of mooring with ropes has remained unchanged. Even today, the traditional mooring is essentially as it was at the beginning of last millennium. Mooring Points. A mooring is a structure that restrains a vessel against forces generated by wind, waves, and current forces. The purpose of moorings are, 1) Loading/unloading stores, cargo, fuel, personnel, ammunition, etc; 2) Ship storage to reduces fuel consumption and personnel costs; 3) Maintenance and repairs are easier to perform; 4) Mission support such as surveillance, tracking, training, etc; 5) Reduce the ships motions and the dynamic loads that are produced by waves. For harbors, marine terminals, floating terminals and offshore structures, optimizing the mooring system is important for improving safety and minimizing downtime. Moored objects are subject to external forces in the form of wind, waves, current and interaction effects from passing ships. These forces may have various impacts, including: 1- Hampering the cargo handling operations due to large motions (downtime); 2- Damaging the moorings due to large loads; 3- Endangering ship' crew and terminal personnel; s 4- Causing discomfort for passengers of cruise-vessels and pleasure craft. Mooring Systems. A) Fixed mooring systems, consists of a structural element permanently fixed in position to which a vessel is moored. These structural elements include: (i) Platforms, (ii) Cells, (iii) Dolphins, (iv) Spuds, and (v) Bollards. B) B) Fleet mooring systems are structural elements that are not permanently fixed in position, such as buoys, ships anchor systems, lines, anchors, etc. C) A pile system. D) The mooring line system: (i) Natural fiber rope, (ii) Synthetic-fiber rope, (iii) Wire rope, and (iv) Mooring chains. The (i) mooring platforms consist of isolated concrete, steel, or timber decks supported on concrete, steel or timber piling. A platform may be used as a mooring structure (a mooring platform) or a breasting structure (a breasting platform). Mooring platforms are not designed to withstand the impact of berthing vessels (only a breasting platform can do that). Breasting platforms have an arresting system to absorb the impact of berthing vessels, such as battered piles which are loaded in compression (bearing) and flexure, while others in the group are loaded in tension (uplift). The (ii) mooring cells are usually round, isolated sheet-pile cofferdams or concrete caissons. Cells can be used as mooring or breasting structures. However, cells are most often used as breasting structures because they can withstand very large berthing loads. Breasting cells are rigid structures, which usually require a substantial fendering system to absorb large berthing energy exchanges. Mooring and breasting cells are commonly used in water depths less than 40 feet. Mooring Lines. There are four types of mooring lines used to secure a vessel to a fixed mooring: natural-fiber lines, synthetic-fiber lines, wire rope lines and mooring chains. Natural-fiber, synthetic-fiber, and wire rope are most often used at fixed moorings, which service active vessels. Mooring chain may be used to moor inactive vessels. The most important characteristics of a mooring line are its strength, elasticity, and construction: 1- Strength. For a given rope diameter, wire rope is the strongest, followed by synthetic-fiber rope and then natural-fiber rope; 2- Elasticity. Most synthetic mooring lines are polyester, polypropylene, or nylon, or a combination of these materials. Kelvar rope is also available, but due to its relative inelasticity, it may not be desirable for mooring installations. Synthetic lines are easier to handle than wire lines, because of elasticity. These are the typical fixed mooring lines for a large tanker or cargo vessel. The nuclear attack submarine USS Newport SSN75 moored at Port Everglades. This photo was taken while aboard the USS Cole destroyer, April 2000 Moorings for a Ro-Ro and a container vessel at Port Everglades. A cell type mooring system is a fixed mooring which consist of round, isolated sheet-pile cofferdams or concrete caissons. The breasted cells are often used because they withstand large berthing loads. Mooring and breasting cells are commonly used in water depths less than 40 feet. The (iii) dolphin systems are generally flexible structures constructed of either timber piles or steel-pipe piles. Dolphins can also be used as mooring or breasting structures. Timber-pile dolphins typically consist of timber piles driven in clusters of three to nineteen or more, wrapped at their tops with galvanized wire rope and connected with bolts and chocks of wood. Steel pipe-pile dolphins may consist of either one or a group of steel-pipe piles. Steel pipe-pile dolphins are particularly well suited as breasting structures due to their flexibility. flexibility. Dolphins are flexible structures constructed of timber piles or steel-pipe piles. They are also used as mooring or breasted structures. Timber-pile dolphins consist of timber piles driven in number from three to nineteen. The steel-pipe piles are mainly used for breasted dolphins. Mooring dolphins at the Port of Miami. Cellular moorings. Design a steel sheet-pile cellular dolphin for a mooring bollard that will be subjected to an equivalent horizontal load of 60 kips. The live load upon the dolphin will be 250 psf, and assume that there are negligible wave forces because it is located in a shielded area. Mooring geometry limits the diameter of the dolphin to 20 feet or less. Choose a FS = 2.5. Solution: Step 1: Determine the Required Depth of Embedment D of the steel sheet-pile cell. For = 30 , Ka = 0.33 and Kp = 3.0 and Kp Ka = 2.67. ( ) Apply the factor of safety to the K p K a factor, (K p Ka ) (K = p Ka ) actual ( 3.0 0.33) = ( 2.67 ) = 1.07 = FS 2 .5 2 .5 Using Tschebotarioff's analysis, the forces E1 and E 2 are, reduced E1 = area ( abc ) 2d E 2 = area ( cfg ) 2d where d is the cell diameter 20 = feet In granualar soils, the maximum pressure pmax is ( ) pmax = K p K a D = (1.07 ) D The embedment depth D is usually estimated through trial and error. The depth (ac) is estimated by having the force E1 be a bit larger than the mooring force P. Now locate the point (f) so that the force E2 will satisfy equilibrium, or FH = 0 P + E2 = E1 Taking moments about the center of the circular base yields, P h = ( E1 + E2 )( 0.318 ) d tan ( ) + E2 e2 E1e1 Ma = 0 and with = 20 , P h=E 2 ( 0.12d + e2 ) E1 ( e1 0.12d ) First try D = 20 feet. This yields ac = 16 feet and cf = 4 feet Therefore, 1 (16' )(16' )( 0.065 kcf )( 40' ) = 333 kips 2 1 E2 = ( 4' )( 2.67' )( 0.065 kcf )( 20 )( 40' ) = 278 kips 2 Check equilibrium, FH = 0 P + E 2 = E1 60 kips + 278 kips 333 kips GOOD E1 = M a = 0 P h=E 2 ( 0.12d + e2 ) E1 ( e1 0.12d ) (16' ) = 10.7 feet and e2 = 16' + 2 ( 4' ) = 18.7 feet 3 ( 60 kips )( 42 ft ) = ( 278 kips ) ( 0.12 )( 20' ) + 18.7' ( 333 kips ) 2 , 520 kips ft < ( 5 , 866 2 , 764 ) kips ft = 3,102 kips ft where e1 = 2 3 10.7' ( 0.12 ) ( 20' ) the D = 20-foot embedment is conservative (could be reduced). Step 2: Check the cells Stability against the Over-turning Moment. The forces F1 and F2 are, F1 = E1 tan = E1 tan ( 2 ) = ( 333kips)( 0.36) = 121kips 3 F2 = E2 tan = E2 tan( 2 ) = ( 278 kips )( 0.36) = 101kips 3 and the distance f = ( 0.318) d = ( 0.318)( 20' ) = 6.36 feet Find the total weight of the cell above a plane throuogh point A above, W= D 2 h= ( 20' ) 2 ( 2' ) ( 0.150 kcf ) + ( 4' ) ( 0.106 kcf ) + ( 55' ) ( 0.065kcf ) 4 4 Note that W R in the figure. = 1,350 kips The total moment about point A is, M A = ( 62' )( 60 k ) ( 9.3' )( 333 k ) ( 6.36' )(121 k ) ( 6.36' )(101 k ) + (1.33' )( 278 k ) M A = 400 kip ft Therefore, the reactive force R has an eccentricity e of, M A 400 kip ft = = 0.25 ft R 1, 350 kip This eccentricity is negligible, and clearly the resultant falls in the middle third. M A = Re e = The cell is stable with respect to the over-turning moment. Step 3: Check the cells Stability against Horizontal Sliding. It is clear from the figure that the cell will tilt before it will slide. Therefore, this analysis is unnecessary. Step 4: Check the Bearing Capacity of the soil beneath the cell. The ultimate bearing capacity of a soil under a cellular dolphin is given by the formula shown below. The bearing capacity factors are functions of the angle of internal friction = 30, Nq = 22.5 and N = 20. The ultimate bearing capacity of the soil beneath the cell is, 1 1 qultimate = qN q + ( 0.6 ) dN = D f N q + ( 0.6 ) dN 2 2 1 qultimate = ( 0.065 )( 20' )( 22.5 ) + ( 0.6 )( 0.065 )( 20' )( 20 ) = 37 ksf 2 The total load pressure ptotal from the cell is, ptotal = ( 2' )( 0.150 pcf ) + ( 4' )( 0.106 pcf ) + ( 55' )( 0.065 pcf ) + ( 0.250 psf ) = 4.6 ksf The Factor of Safety is FS BearingCapacity = qultimate 37 ksf = = 8 GOOD ptotal 4.6 ksf Step 5: Check the steel Sheet-piling inter-lock Tension. The maximum internal pressure at ground level is, Use an "at-rest" lateral pressure rather than an "active" pressure, Ko = 1 tan = 1 tan( 30) = 0.50 Therefore, the pressure pa is given by, pa = Ko ( z) = ( 0.50) ( 2' )(150 pcf ) + ( 4' )( 0.106 pcf ) + ( 35' )( 65 pcf ) + 250 The tension is, 1 1 T = pa D = (1,625 psf ) ( 20' ) = 16, 250 lb / feet = 1,350 lb / inch 2 2 Use a PSA-23 steel sheet-pile. The wall requires 46 pieces. The actual diameter is 19 feet 6.25 inches. = 1,625 psf Pile Systems. Pile systems consist of both battered and vertical steel pipe piles. In general, pile systems are recommended for shallow waters and where deployment of anchors by vessels is difficult or impossible. The use of plumb piles may result in unacceptable horizontal displacements of the structure. Other drawbacks to pile systems include the difficulty in removing piles for their possible replacement due to damage, and corrosion. Dolphins. Dolphins and a flexible breasting platform. A flexible breasting platform. Steel pipe breasting dolphin. The (iv) spud system consist of a steel member, usually a round pipe, an H-pile or a built-up section. Spud moorings are designed to resist transverse loads (shear) or longitudinal loads (tension). The end spuds are designed for tension and the intermediate spuds for shear. Tension spuds are connected vertically to the pier or quay wall with a steel shoe. Shear spuds are connected with a spud guide. Finally, (v) bollards are short single-column cast steel fittings that extends up from a base plate that is secured to a strong point of a shore structure or berthing facility. Bollards are used in snubbing or checking the motion of a ship being moored, by tightening and loosening mooring lines that are fastened to them. Bollards are also used for securing a ship that has been placed in its final moored position. Bollards without ears should not be used in facilities where a high vertical angle of the mooting line is anticipated, to prevent lines from slipping off the bollard. Double inclined bollards. Mooring lines Mooring lines An aircraft carrier moored at Port Everglades using natural-fiber rope. Note the highly compressed fender about twenty meters from the bollards. Note the concrete apron around the cast steel double bitt bollards, which outlines the pile cap beneath the deck. A shop drawing showing a J.C. MacElroy Co. cast steel double bitt bollard. A shop drawing showing a J.C. MacElroy Co. cast steel single bitt bollard. Fender Systems. Definition: A device or framing system placed against the edge of a dock, to take the impact from berthing or berthed vessel. In essence, a system designed to prevent vessels and/or the dock from being damaged during mooring. Common Types of Fenders: - Seibu V and H types; - Cylindrical floating rubber fenders; - Rubber tires; - Combination of wood timbers or piles and rubber tires. A Seibu fender. Floating rubber fenders. A timber-rubber tire fender. Cast steel double bitt bollards and fender systems at the south quay of the Port of Miami (FIU field trip). Rubber tires used as fenders. Temporary fender for a construction site. References. - Quinn, Alonzo, Design and Construction of Ports and Marine Structures, McGraw-Hill Book Company Inc., 1961; -Tsinker, Gregory P, Floating Ports Design and Construction Practices, Gulf Publishing Company, 1986; - Alkyon, Hydraulic Consultancy and Research; - - - Tait, S.M., Offshore Mooring System Approval for Insurance Purposes, Thomas Telford Ltd., London, 1982; ... View Full Document

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