Bosch Rexroth Marex SB Manual page 30

Conditions when reversing from ahead to astern:
When reversing from ahead to astern, the gearing is at first shifted to neutral, the shaft is disengaged
from the engine (1). As the ship continues to move ahead, the propeller is driven like a windmill by the
water streaming against it so that the shaft continues to turn. When the gears are then shifted to
astern, the engine must work against the shaft which is still turning. In an unfavourable case, the
engine might stall.
1 gears neutral
ship -
velocity
2 gears astern
ship -
veloccity
To avoid stalling the engine, the control can wait an adjustable time (reversing delay time) before
reversing. The delay time depends on the given lever position of the control head.
The reversing delay time must be determined experimentally during a sea trial. For this, the ship must
st
accelerate from 1 detent ahead to full ahead. The time, the ship needs to reach 2/3 of its maximum
speed, has to be preset as reversing delay time. Afterwards, reversing maneuvers need to be carried
out covering the full speed range.
During the reversing maneuvers, start with a slow speed first and increase gently.
If necessary, the reversing delay time must be adjusted (lengthened, if the engine
!
revolutions drop too heavily or shortened if no deceleration of the engine speed is
recognisable.
If the reversing delay time is too short, clutch, gearing and engine may be
damaged, if it is too long, the manoeuvrability may be restricted.
nominal speed
power boost
idle speed
nominal position gears
ahead
astern
TIME reversing delay time
0 s 1 s 2 s 3 s
5
1
2
3
4
5
6
7
8
For applications with 2 control units, only the portside system must be adjusted.
27
neutral
shaft speed depends
on ship velocity
astern
shaft speed works
against engine speed
reversing delay time
time
time
4 s 5 s 6 s 7 s 8 s
engine speed
1
delay time before clutch
2
3
delay time after clutch
4
5
6
reversing delay time
7
8
TIME
9 s 10 s 11 s 12 s 13 s
engine
engine
14 s 15 s