Fish Facts

FISH FACTS: Outboard issues

The plume of emissions from this old two stroke should really be a thing of the past – every one of them removed from the water makes room for up to 50 newer outboards.

FOR those readers who have had the pleasure of owning and/or fishing in an outboard-powered boat less than 20 years old, its easy to forget how bad the “good old days” of boating were.

Since 2008 I have been lucky enough to fall into this category after selling my venerable early 90’s 4 m Stessl Edgetracker to move firstly into a 4.35 m Bluefin Wildcat, then most recently into a CrossXCountry/Enlightened Boating 4.8 m rig.  Both the latter have had the latest in marine electronics as well as modern fuel injected outboards in the 50-60 hp bracket. Not coincidentally, the motors on both my most recent rigs have been completely trouble free, quiet, low maintenance and use less fuel than guzzled by the old loop charged carburettored 25 hp Mariner that was on the Stessl.  

The latter point is significant, not only environmentally, but also from a running costs perspective. These two modern outboards have more than double the horsepower but use less fuel than the older 25 hp. A reasonable question to ask, then, is how did that old loop-charged carburettored outboard use so much fuel and produce so little horsepower?  The answer is those old motors literally pour excess unburnt fuel and oil into the water – simply because the carburettor allows fuel to pass into the engine and out the exhaust port during the port overlap stage of the engine cycle. In contrast, modern 2-stroke outboards use direct fuel injection to only inject fuel on the compression stroke after the exhaust port is closed, maximising energy extracted from every drop of fuel, while fuel injected 4-stroke engines are equally efficient and their excellent combustion control can mean they are even more miserly on fuel than the direct injected 2-strokes under certain conditions. 

All this is important, because compared to other modes of transport, boats are really heavy on fuel. For example, emissions testing done by the US Environmental Protection Agency (US EPA) found that one hour of operation of a boat (with a relatively clean engine that met the 2006 EPA regulations) produced the same pollution as about 50 cars operated at a similar ground speed. However, they also found that older style outboard engines that did not comply with US EPA 2006 limits were likely to emit around 10 times the amount of pollution compared to conforming outboard engines – that’s the equivalent of 500 cars! The older style engines thus represent a significant water pollution threat as all but a very few of the smallest outboard engines discharge most of their exhaust (including all that unburnt fuel and oil) under water. Yuk.

To help boat owners choose cleaner outboard engines, Outboard Engine Distributors Australia (OEDA) implemented an emissions ratings system for new outboard engines, similar to energy and water efficiency ratings schemes for household appliances. The labelling specs are shown in Table 1 and are based on Hydrocarbon (HC) and Oxides of Nitrogen (NOx) emissions. The ratings confirm that modern outboards that meet OEDA 3 star ratings produce less than 1/10 to 1/50 the emissions of the old noxious 2-strokes of years gone by (which get a “zero star” rating). 

Another thing to keep in mind is that there is a direct relationship between CO2 production and fuel use, so by using less than half of the fuel and oil of the old motors, the modern outboards greatly reduce your greenhouse gas footprint as well – worth bearing in mind as CO2 emitted in an outboard exhaust will quickly acidify any water that it contacts. 

Table 1.  Outboard Engine Distributors Australia (OEDA) emissions ratings system for new outboard engines.  The dirty old “zero star” 2-strokes should be avoided like the plague, as the emissions from a single old outboard is equivalent to between 10 and 50 new outboards of equivalent horsepower!

OEDA Australia Star Rating

Star Rating Description

OEDA Emissions Limit*

Zero Star

High emission: Will be a handful of older design two-stroke engines

> 250

One Star

Low emission: Most traditional two-stroke engines

68.4 – 250

Two Stars

Very low emission: Some two-stroke direct injection and four-stroke engines

30 – 64.8

Three Stars

Ultra low emission: Most two-stroke direct injection and four-stroke engines

5 – 30

Four Stars

Super ultra low emission: For future technologies

< 5

* The OEDA Emissions Limits rate engines based on Hydrocarbon (HC) and Oxides of Nitrogen (NOx) emissions, measured in grams per kilowatt per hour.

So, the science is in and these modern outboards really are that much better – pouring unburnt fuel and noxious fumes into the water has never been good for the environment (or the wallet), and those volatile organic compounds (VOCs) contained in those old 2-stroke fumes are well known to be toxic to aquatic organisms and humans alike. In contrast, the clean EFI technology has now been proven for at least 20 years – so its time to throw that old stuff away – there are really no excuses today for putting up with that old 2-stroke technology, especially given its nasty environmental and human health impacts.

This point was bought home to me recently when I had the “pleasure” of going out on a colleague’s boat to do some shellfish reef monitoring using an underwater drone. The contrast between the cutting edge state-of-the-art underwater drone and the boat that was used to transport us and the drone to the research reefs we were monitoring couldn’t have been more stark.  The rig was a late 1970’s 4 m Quintrex hull set up with a steering wheel arrangement linked to an old 2-stroke outboard of similar vintage. The rig was well set up as a functional fishing platform by its previous owner, and no doubt was cutting edge for back in the day, but from the moment that motor started, I realised how far we’ve come. To its credit the outboard started on the third hit of the starter (it was a cold morning in SE Queensland) and idled relatively smoothly. But what was unmistakable was the cloud of blue smoke billowing out from the telltale and from the bubbles from the prop, and that distinctive 2-stroke smell I remember from fishing in the 1970s with my grandfather. The problem was, the smell didn’t go away as the motor warmed up, and the next 6 hours on the water were decidedly unpleasant. The noxious fumes remained detectable even when we were fully underway at 40 km/h, and were particularly bad whenever the motor was idling and the wind was from astern. If you looked closely you could even see smoke rising from the surface of the water, and the oily film left behind us was also obvious. When we hit the dock after being trapped working in that old tinny for 6 hours, I couldn’t get away fast enough (after a chat about how best to update the tinny of course). 

So if you love fishing and your health – get rid of that old outboard for good. As an investment in the environment and your health, you can bet your next day out on the water will be far more enjoyable. An example of a responsible approach to outboard engines can be found HERE


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