The MARY A WHALEN is a rare surviving example of a bell boat. 

On a bell boat, the person steering (the captain or the mate) has no direct control over the speed of the engine, nor whether the ship goes forward or in reverse. The engineer, as the name suggests, controls the engine.  On the MARY, as was typical on other bell boats, the engineer's station is two levels down from the pilot house, in a space with no view to the outside.  

How did the engineer know what speed and direction the captain wanted? Bells and jingles.  On both sides of the pilot house, both inside and out, are two sets of pulls.  The large handled one rings a gong-shaped bell near the engineer; likewise a smaller handled one jingles a littler bell.  An established code of bells and jingles told the engineer what to do.  As a safeguard the captain and engineer could yell to each other through a speaking tube.

Note found posted in the MARY WHALEN: 

Remember:
Bells are Direction                       
Jingles are Speed

 From Stop

1 bell = ½ Ahead  (200 rpm)

1 bell + 1 jingle = Full Ahead (300 rpm)

1 bell + 2 jingles = Slow Ahead (140 rpm)

2 bells = ½ Astern (200 rpm)

2 bells + 1 jingle = Full Astern (300 rpm)

2 bells + 2 jingles = Slow Astern (120-140 rpm)

 

1 bell from any position Astern = STOP

 

From Full Ahead

1 bell = ½ Ahead

2 jingle = Slow Ahead

 

From Slow Ahead

1 bell + 1 jingle = ½ Ahead

1 jingle = Full Ahead.