It’s Exhausting

Marine exhaust systems are actually fairly complex systems: much more complex than a layman would think. They are simply the “tailpipe” of the boat, right?

This misconception is often a problem. One critical part of the vessel exhaust system is the exhaust risers, and these can often fail. The function of the riser is two fold:

  1. They keep water from backing up into the engine.
  2. They channel cooling water to the engine.

The design of the exhaust riser is critical, and is a situation where it often is beneficial for the engine manufacturer and the shipyard or naval architect to work closely together. If the angle of the riser is incorrect, or it is modified, water can accumulate, leading to bad corrosion issues. Poor design, especially with aftermarket additions or modifications, can also create serious back pressure problems on the engine, greatly impacting engine performance.

Water and metal do not mix well. This is why the gaskets and the risers should be frequently inspected and replaced if necessary. Even in cases with no leakage, the risers should be removed and periodically cleared of any rust or scale that may have formed.

Some engine manufacturers provide risers with the engines, and other do not (they are optional with Marinediesel). In some cases, they must be custom designed in order to fit into an engine compartment. In any event, there is a golden rule with exhaust risers: NEVER use aluminium risers. Yes, they are cheap, and risers can be one of the more expensive components to buy, but they are short on life span and can cause serious problems over the life of the engine.

Maintenance Tip of the Week: Zincs 10/26/2015

Maintenance Tip of the Week – Zincs 10/26/2015

The pencil zincs your engine came with are absolutely critical to preventing galvanic corrosion, which can ruin your engine very quickly. Always change your zinc anodes after 100 hours of operation, more frequently if the vessel is in water with high salinity or if the vessel is inoperative in the water for an extended period of time. Zincs are cheap protection.

Maintenance Tip of the Week – Exhaust Risers 10/12/2015

Maintenance Tip of the Week – Exhaust Risers 10/12/2015

Always inspect your exhaust risers and gaskets for corrosion as stated in your manual’s maintenance schedule. Exhaust riser failure is a leading indicator of critical, and very expensive, engine damage.

Maintenance Tip of the Week – Zincs 03/30/2015


Maintenance Tip of the Week – Zincs

Zinc anodes are one of the most important maintenance items for your boat. Always make certain that zincs are replaced when necessary, even if they are not yet scheduled in the manual. Differences in seawater salinity and temperature can greatly increase the amount of zincs required, as can the installation of new equipment on the vessel.


Maintenance Tip of the Week – Grease 03/23/2015


Maintenance Tip of the Week – Grease

Avoid using graphite grease, which can increase the rate of corrosion. Instead, use lithium grease which can limit galvanic corrosion.


Sacrificial Anodes: Cheap protection for your engines


Galvanic corrosion is often a problem in the marine industry. This is basic chemistry, but the results can become extremely expensive if ignored. When dissimilar metals are placed together in an electrolyte (like seawater), there is an electric current produced. Effectively, this process is the same way that a battery works. Your engine and propulsion system become batteries, and are subject to corrosion. The term “noble” metals is used to define a specific resistance to corrosion. Therefore, a hierarchy, like the chart pictured above, can be made. When two metals are placed in an electrolyte, the less noble metal “sacrifices” itself to protect the more noble metal. An example would be a bronze propeller connected to a stainless steel shaft. The propeller, made of bronze, will corrode faster than the shaft.

The solution to this corrosion is the use of sacrificial anodes made of less noble metals that will corrode faster than the expensive vessel components. Anodes can be made of many metals and alloys, but the most common in the marine industry is zinc, followed by aluminium and magnesium.

Since engines are connected to components that are in contact with seawater, they, too, must be protected. Zinc “pencil” anodes are typically part of our recommended spare parts list. They are cheap, and easy to replace (as in, no excuses).

How many anodes will a vessel require? Though the answer may sound flippant, it is, “It depends”.

Seawater conditions. More salinity generally requires greater quantities of anodes.

Water temperature. Warmer water typically requires greater quantities of anodes.

Hull material. An aluminium hull will require greater quantities of anodes than a GRP hull.

Amount of exposure. Corrosion impacts the entire system, but stern drives and surface drives will usually require more anodes.

Freshwater use requires different anode alloys than salt water. However, pollution will also impact the anode choice.

Sacrificial anodes are cheap. However, care must be taken to ensure that the anodes are really made of the proper material. Ultra cheap anodes are often made of substandard materials, and their use can get very expensive in the long term.

The downside to anodes? They are heavy. There is a balance between protecting a vessel and over protecting a vessel. Over protection can lead to hull damage or paint / coating damage, in addition to the extra weight involved.

Another solution is the use of electronic cathodic protection systems. These systems create an opposite charge from the charge produced by the vessel. These systems, though often expensive, are useful on vessels that are in varying environments, and can instantly be changed before corrosion occurs.





Maintenance Tip of the Week – Heat Exchanger 03/16/2015


Maintenance Tip of the Week – Heat Exchangers

Periodically inspect and clean your heat exchangers as detailed in your MarineDiesel manual. Corrosion and scaling can build up over time, and the heat exchanger is a vital part of your engine’s cooling system.



Maintenance Tip of the Week – Batteries 02/23/2015


Maintenance Tip of the Week – Batteries

Always check your battery connections and cables for corrosion. Corrosion can start and progress quickly and weak cables lead to electrical system problems.





Corrosion can be a big headache in terms of vessel maintenance. Galvanic corrosion occurs when two dissimilar metals are connected in seawater. The electrons from the base metal attach themselves to the more noble metal. The result is that the base metal eventually corrodes away. In order to prevent this corrosion, sacrificial anodes must be attached to vessel components made of base metals in order to prevent this corrosion from occurring.

The chart above lists the various metals commonly used in marine manufacturing. Note that Zinc is at the bottom of the list. The nearer to the top of the list, the more “noble” a metal is. Therefore, anodes are usually manufactured from materials near the bottom. Hence, the common use of zinc in anodes. It is base, and usually cheap.

An alternative solution is electro-cathodic protection of the entire vessel. These systems measure the current level of the seawater, and produce an opposing current, thus preventing corrosion by keeping the elements from moving. These systems are often quite good at preventing corrosion, though they can often become expensive. It is also important to note that salinity, water temperature, and other factors impact the current level in the water, and such systems nearly always require monitoring.



Maintenance Tip of the Week – Batteries 09/22/2014



Maintenance Tip of the Week:

Generally, there is no harm in using larger batteries if you have the space in your engine compartment and the voltage / amperage is correct. Keep in mind that your vessel was designed with the battery bank it currently uses, based on the power requirements of the vessel. Before upgrading, however, we recommend that you check to see why the voltage is low, and if there are any drains on the electrical system. Corrosion on the terminals or bad glands can greatly reduce battery life, as could faulty or worn cables.