Tim Morris, Torquay, Devon GBR asks:
Hi Scott, your riveting read continues. Please let me have your
'for and against' regarding dry stack exhaust. Thank you
Scott Flanders from Egret responds:
Tim, good question. We are hugely pro keel cooling/dry stack. A very
recent example was mentioned in a VofE just a while ago. Egret went aground
in a soft mud during the night on the falling tide. The wind picked up
straightning the anchor chain and swinging us onto a mud bank. We started
the engine (bottom in the mud), used the windless to pull ourselves forward
a bit then motored to a deeper spot to re-anchor. A raw water cooled engine
(sea water) would have to rely on her house batteries to pull herself
forward with the windless in this case. As you know windlasses draw a lot
of amps at 12 volts quickly lowering the battery voltage without alternator
input. (This causes its own problems...voltage drop = increased heat in the
wiring/windlass motor = less efficiency for the moment and potentially less
life long term.) If a raw water cooled engine were started in the mud it
would cause a number of issues, impeller damage for sure but the biggest
concern is filling the engine's cooling system with mud. The time to
properly flush the cooling system of mud is considerable. To flush the
system properly the pump should be run at higher rpm, not something you want
to do out of gear, so to be diligent you should get underway for a while.
Not something you want to do here in the Chilean archipelago at night. This
is one small example and of course there are many more pros such as zero
corrosion from sea water inside the engine and exhaust manifold. The only
liquid that sees the inside of Egret's engine cooling system is antifreeze
and distilled water mixed 50/50.
The downside of a keel cooler/dry stack is cost and sooting in certain conditions. Sooting comes from condensation forming little soot balls dispersing on a cold startup. On anchor sooting isn't an issue because the boat faces the wind, stack facing aft. On the dock the exhaust stack may or not face away from or into the wind/rain. These are the only times Egret has sooted, and then only on few occasions. To prevent this while on a dock we have taken a small boat fender and cut the fender cap off near one end. We tied loops on the long piece and by using a boat hook we slide it over the stack and place the cap over the throttle/shift lever as a reminder not to start the engine without removing the fender.
Cost is relevant. Most well built commercial workboats are dry stacked and keel cooled. If this increased cost didn't pay dividends few or no commercial vessels would spend the money. The initial cost comes back many times over in reliability. Downtime in a commercial venture just means lost revenue but for we wayward cruisers far from shore at times the additional cost is immaterial. Safety is everything, taking a chance isn't prudent.
To prove the point, during Egret's 5704 keel cooled/dry stacked Lugger engine hours we have changed the serpentine coolant/alternator belt once and flushed the cooling system twice by dropping the keel cooler during a haulout. Total cooling system maintenance: ZERO repairs, zero problems in 6 years and accumulated miles. Ciao.