Excalibur is now in the Chesapeake after a winter in the
Caribbean and the Bahamas. Summer destination is New England.
After 20 years of Amel ownership (Maramu & Super Maramu), I can
offer the following insights into the soot problem:
Causes: On the Super Maramu, the problem is usually caused by
running a turbo-charged diesel engine at too low RPMs. Why Amels
have turbochargers is a good question, but a turbo-charged diesel
needs to run at high RPMs to burn the fuel efficiently. On Maramus,
running at low speed causes the same problem. Soot is caused by
incompletely burned diesel, not lubrication oil. Unless the engine
is run at 2400 RPM and above (for the Volvo, probably similar for the
Yanmar), soot will form in the exhaust system, and deposit on the
outside of the hull. However, most of us don't like the noise and
fuel consumption associated with high RPMs, so we run at closer to
2000 RPM. At lower RPMs, the turbo doesn't provide enough air to the
engine, and the result is incomplete combustion.
Solutions: Run the engine hard, at least once in a while.
Otherwise, clean the hull often. I recently came across a good
product for removing soot: ROLL-OFF, sold by Boater's World (but not
West or Boat US), if applied as directed, and soon after the soot
forms, will remove it easily. Use it every day you motor more than a
couple of hours, and you won't have any soot. To get rid of old soot
the first time, follow Joel's recommendations, posted here a few
Good sailing! Roy