For advanced offshore operations, position-keeping becomes more and more important. 

For example, placing  a large wind turbine on a water depth of up to 30 metres puts heavy requirements on the hardware (rudders,  propellers and thruster units) and Dynamic Positioning software onboard the vessel.  

Similarly, Dynamic Positioning (DP) Drilling platforms  are today used in harsher environments  than previously, thereby putting heavier requirements  on the DP capability of the platforms.  Since the early 1980’s, FORCE Technology has  performed R&D within DP. Our experience is  rooted in DP of drilling platforms and other  offshore structures and vessels. 

When the offshore  wind turbine areas have been expanding, our knowhow has been used in a large number  of projects with wind turbine installation vessels  and service vessels.  Through our knowledge and experience, FORCE  Technology has developed three different services  within DP. These three services offer different  knowledge of the operational constraints  and can be used both individually and in connection with each other.  

DPLab – Static Holding Capability

Embarking on a new project with a dynamically  positioned ship or platform immediately poses the following three questions once the  site has been: 
  1. Is station-keeping possible under the  anticipated conditions?  
  2. What sizes of thrusters are required, and  where do we install them to maximize our  station-keeping capability?  
  3. How are the thrusters best utilised? 
These three problems do not, of course, have  independent solutions, instead a common solution  solving all three must be found. FORCE  Technology has developed the Holding Capability  Module for the DPLab software for inhouse  use or as software sold in a package with  wind & current predictions or wind tunnel model  tests. The program follows the recommendations  of IMCA M 140. 

The tool performs static calculations, balancing  the available thrust and the environmental forces.  The holding capability is defined as the  limiting environmental (arising from wind, current  and waves) forces that can be balanced by  the vessel using its propulsive systems in an  optimal way. DPLab has been sold to leading Asian shipyards and a number of consultants world-wide.

Time Domain Simulations

While DPLab provides only a static picture,  FORCE Technology also offers dynamic possibilities  in our simulators where it is possible to  perform DP simulations with varying degrees  of current, wind and waves. The core of the  simulations is the in-house developed DENMark1  model which is acknowledged to be the  most accurate mathematical model with regard  to maritime simulation.  With the time domain simulations you find out  how precisely it is possible to keep the needed  position under the influence of wind, current  and waves. Furthermore, the time domain  simulations in six degrees of freedom provide  a strong indication of the motions of the ship  during operation.  

DP Model Tests  

The final service FORCE Technology offers within  DP is scaled model testing. During these tests,  thrusters, propellers and rudder are tested together  with the DP system. These tests give a very realistic representation of the precision you  could expect during your actual DP operation.  

Besides this important knowledge, the tests also  include effects such as green water, slamming  and advanced wave systems which are hard to  copy in numerical simulations. The DP tests can  be performed with our in-house DP system or  with a vendor-provided DP system.  Through a model test you also get all the dynamic  and non-linear effects. Thereby, model  tests offer a more precise representation of the  ship’s ability to hold the position during operation.  

Model tests are usually preferred when  the design is locked, and the DP capacity is to  be documented.  To be able to perform DP model tests, FORCE  Technology has prepared a series of advanced  model thruster units. The units are controlled  via advanced EPOS controls and are able to  measure heading, RPM and the delivered thrust  from each thruster unit. The development has  taken place over the last 20 years, and our model  thruster units are now in their 3rd generation  and available for both integration into semisubmersible hulls and deck mounting on monohull vessels such as drilling vessels.