Date: Thu Oct 4, 2001 3:04 am
My boat has sooty stern syndrome. This happened during the course of extensive motor sailing when we delivered her from Corpus Christi to the Galveston-Clear Lake area where we live together. A boating friend said that it's because I use Chevron DELO 400 oil. Could it be old fuel causing it? My engine runs fine. Someone suggested that I put a short pipe extension on my exhaust thru hull. What is the best cleaner for this?
Date: Thu Oct 4, 2001 8:13 am
Ah, the dreaded badge of departing diesel dishonor.
The good news is there is likely nothing wrong with the engine, the fuel or the crankcase oil.
All internal combustion engines leave behind some percentage of hydrocarbons in the form of gases and oily vapor. Just about all older diesels without the new electronic fuel injectors do it quite well in fact.
As all good sailors generally never motor when the wind is a-beam the low pressure area at the transom created by the (collective) apparent wind slipping around the transom when the engine is running is the biggest culprit. It sort of sucks the mix upward and outward to finally be swept off into the great beyond. The oily part of the unburned fuel creates a slick that captures the sooty gas after a few miles you are starting a collection. The inevitability of this is somewhat exacerbated by the placement of the exhaust discharge location.
On my boat as with most I presume the exhaust exits quite low on the transom and near the centerline. This gives the slick quite a large low pressure area to distribute the soot. Added to the problem is the fact that once the hull is pushed forward and she squats down in the water the exhaust discharge was below the water further diffusing the now burbling mix.
I have raised the through-hull 3 inches and found some relief. I did experiment with curved PVC tube mounted to a PVC pipe flange and directed the mix outboard (but not upward) and closer to the slipstream of apparent air. It did work for a while but the glue I used to attach the "ugly stinger" soon succumbed to heat and disappeared. Proving only that the next time I am move to distaste of the job of mopping the transom from the cockpit with soapy Joy and seawater I may just built a shiny stainless steel unit and install it over the discharge flange. But it would certainly be an ugly addition to a very pretty boat.