Soot Case

Maintenance Q & A — September 2001
Maintenance Q & A — September 2001
By Capt. Ken Kreisler

Soot Case
How to reduce diesel exhaust residue, the difference between electrolysis and galvanic corrosion, and more.

 More of this Feature

• Part 1: Q & A
• Part 2: Q & A continued

 Related Resources
• Maintenance Q & A Index

What can I do to reduce the soot buildup on my transom from my diesel's exhaust? J.H., via e-mail
Soot is unburned fuel. In this form it is an insoluble carbon particle that can plug oil filters and usually indicates a dirty air cleaner, excessive fuel delivery, or poor fuel quality.

First make sure you are keeping a regular preventive-maintenance regimen when it comes to both fuel and oil filters as well as your air filter. If you have twin engines, do all oil and filter changes at the same time.

You may want to consider installing a Walker Fuelsep for your fuel system. According to Walker, the system can improve fuel economy and engine performance while reducing soot.

As shown in the accompanying diagram, the Fuelsep is installed between your boat's existing fuel-water separator and your engine. Acting like a minirefinery, the unit purifies the fuel one last time before it enters your engine.

Without getting into too much of the chemistry of fuel, diesel fuel is made up of chains of hydrocarbons--a compound containing hydrogen and carbon--that can best be described as being short, medium, and long lengths. As medium chains produce the most efficient burn, the Fuelsep process shortens the longer chains to a medium length and combines the leftover sections so that they, too, are of a medium length. The result is more medium chains and a better grade of fuel.

The unit requires no maintenance, will not clog, and is rated for a 5,000-hour life. For more information contact Walker Phone: (818) 252-7788 or at

Is there a difference between electrolysis and galvanic corrosion? S.D., via e-mail
Yes. Most technical journals and organizations, such as The American Boat & Yacht Council (ABYC), discourage usage of the term electrolysis when referring to the wastage of metal parts in water.

Technically, electrolysis involves only one metal and a major change occurring in an electrolyte, a liquid with chemical properties that make it capable of conducting an electrical current. An example would be when a lead-acid battery discharges and produces a major change in the concentration of the electrolyte, in this case the battery acid.

Galvanic corrosion involves dissimilar metals where the major change occurs in the metals, not the electrolyte, which in this case is the water surrounding the boat. Consider what happens to your bronze props and stainless steel shaft when immersed in sea water, an excellent electrolyte. Mechanically connected, they create what is essentially a battery in which current flows from the bronze (possessing a high electrical potential) to the stainless steel (possessing a relatively low electrical potential). The bronze becomes the anode and the shaft the cathode, resulting in a deterioration of the bronze with the electrolyte remaining unchanged. Hence, no electrolysis.

Sacrificial zincs that are galvanically active and designed to corrode more easily do, of course, protect your running gear against galvanic corrosion. They should be checked periodically for deterioration and replaced if necessary.

What does it indicate when bottom paint flakes or peels? W.R., via e-mail
Flaking or peeling usually indicates that the most recent topcoat is incompatible with the previous coat of paint. There may also be an excessive film buildup or severe contamination between the existing coat and topcoat.

There's no cure for this but to completely strip the entire antifouling application. Once the paint is removed, a light sanding is necessary, followed by a thorough cleaning with a solvent recommended by the manufacturer of the new paint you will be using. The bottom should now be ready for reapplication.

Next page > Q & A continued > Page 1, 2

This article originally appeared in the June 2003 issue of Power & Motoryacht magazine.

Vetus Maxwell Tip of the Week

Hot Today

Featured Brands

Costa Palmos logo MCY logo
HMY Yacht Sales logo Volvo Penta logo
Absolute logo Sunseeker

Boat-Name Generator

cube puzzel Thinking of a unique name for your new boat can be tough, that's why we created a Boat Name Generator.
Try it here. ▶

Select Brokerage