steamer said:
full astern
2 linked up ahead
full ahead
That's my guess....you generally never have a need to link up in astern....
Ray was a very practical man.
Dave
In Marine engines, using Stephensons link, the links are arranged so that when going astern the linking up mechanism is vertical to the link shaft so no adjustment is possible and the engine is operating line in line.
OK so what does that mean. ???
Linking in - This is is when the cut off of steam to the cylinder is made earlier and the steam expands for a greater portion of the stroke. More economy, less power
Line in Line. The point where the eccentric rod is directly in line with the valve rod. i.e. the design position of the mechanism. Where top and bottom lap and lead equal the design parameters between the valve and the cylinder steam ports.
Linking out - This is when the cut off of steam to the cylinder is made later and the steam expands for a smaller portion of the stroke. More power, less economy.
The general idea is to get each cylinder to do an equal amount of work on each stroke. e.g. in a 3 cyl triple expansion engine of 900 HP each cylinder should indicate 300 HP, (150 up and 150 down). Running ahead.
Finally, as you don't normally bop around flat out, these settings are usually refined for economical cruising speed. Say 90-100 out of a possible 140 rpm. This is for a typical merchant / passenger ship. All this changes with a warship where shaft speeds are generally higher and economy is intrinsically lower. Still it was fun playing around if ever they stayed at one speed for long enough.
Hope this helps
Best Regards
Bob
Hope this helps