I have a Bertram 21 with a 2001 Mercruiser 4.3L. I was getting ready
to put the boat into the water when I found a blue plug under the
motor.

Looking for the place where it should be, I found four similar drain
plugs:
o One on starboard motorblock
o One on a tube on starboard side
o one on a tube on port side
o one on the front of the motor on a tube.

Despite a desperate effort I could not find the place for the loose
plug. I am a bit nervous this plug is essential.

Does anyone has any idea where that plug belongs?

Best Regards
Fredrik