Rev 3.1
5 | P a g e
2
Operating Parameters
2.1
General
The FROG-XT range has been designed to ensure passenger safety in the most demanding
conditions.
There are a large number of factors that affect the safe conduct of marine personnel
transfers. These include crew skill and experience, met-ocean conditions, landing areas,
vessel station keeping capability and response to sea conditions, visibility and line of sight. A
combination of many factors will determine the risk involved and careful planning is a
prerequisite for safe operations (see Introduction)
2.1.1
Sea State
The FROG-XT4 has a suspension and damping system which prevents passengers from
experiencing shock loads up to relative landing of 4.5 m/s. The maximum recommended
significant wave height is based on the maximum relative velocity between the load (or
hook) and the deck.
The calculated operational sea states detailed below are based on vertical impact speeds
and bio-mechanical considerations. They reflect the ability to withstand such impacts with
minimal risk of injury to the human body. However, there are many additional factors that
may affect the safety of crane transfer operations. These include vessel station-keeping,
crew competence, wind and visibility. The operator should always refer to general guidelines
on crane transfers operations to assess overall risks.
Technical note:
The calculation for relative velocity used here is based on the European offshore crane standard,
BS EN 13852-1:2013. Whereby the maximum anticipated relative velocity between a load and a
vessel deck, is given by the following;
Relative velocity = (0.5*Hook velocity)
1
+ √ (Vessel deck velocity
2
+ Boom tip velocity
2
)
1
Equal to 1.67 m/s (100 m/min) for lifts below 5 tonnes. Higher crane hook speeds may be available, and it
follows that the higher the available crane speed the higher the possibility of a heavy landing or take off.
However, with a qualified Crane Operator, it is considered unlikely that the FROG-XT will be landed at full
hook speed on a deck rising at full speed.
If there are concerns about heavy landings, operators may wish to consider the following methods to reduce
risks; dry runs without passengers, landing in centre of deck where there is less vessel movement,
transferring fewer passengers to increase damping, using a hook speed indicator.
