Pile-guided Floater

Technological Challenges


Two solutions have been employed for large installations offshore: the GBS (gravity-based structure) type and the floating platform type. Since the GBS type stands on the seabed, it can be applicable only to shallow to medium depth waters. 

 

The floating type usually looks like a ship or a rectangular platform. It is normally kept in place by a series of mooring lines. It has almost no limitation regarding the water depth. The floater motion, however, is the critical weakness of this type. The dynamic motion due to waves may cause large fluid motion within storage tanks (sloshing) which lead to severe fluid impact (slamming) against the tank walls creating damage. This is particularly a problem for LNG tanks of the membrane type. These problems may prevent this type of tanks from being used out at sea with partial filling; which typically prevent such tanks from being used in connection with FPSOs and floating LNG terminals (FLNG). Yet another floating platform type should also be mentioned, the tension leg platform (TLP), which makes use of pre-tensioned, straight anchoring cables (tethers). These platforms can typically be used for water depth ranges of 300 to 1000m; unfortunately they are not suited for carrying large storage tanks.

Solution by Lattice Technology

 The concept of the Pile-guided Floater is illustrated in below. The piles are fixed to a seabed holding frame, and the floater moves up and down along the piles in accordance with tides and ocean swells. Since the horizontal movement of the floater is restricted by the pile system, only the slow vertical movement will take place. In consequence, the sloshing load in the cargo tanks will be negligible for this type of floater.


Concept of Pile-guided Floater: Principle

 A major advantage of the Pile-guided Floater is that it provides satisfactory conditions for ship-to-ship cargo transfer even in rather rough sea conditions. A shuttle tanker is moored to the guiding piles or the floater itself. The relative motion between the shuttle tanker and the floater becomes negligible in horizontal direction and small in vertical direction. If necessary, the seabed frame can be strengthened by an additional structure to withstand all the horizontal loads from the floater and the shuttle tanker.


Pile-guided Floater: 60m depth

 The Pile-guided Floater will be best suited for shallow water and near coastal applications, such as for various types of fluid storage and fluid transfer terminals. Not shown in the figures is a capability of extending the height of the pile fixing bottom frame into a subsea frame support system with considerable height. In such case this type of platform may also be used in deep waters (often defined as more than 60 m) up to more than 100 m.

Bunkering terminal as a Pile-guided Floater mooring an LNG carrier and two bunkering shuttles