A Thousand Cars Off the Road

A Thousand Cars Off the Road

What attracts most people to Pure Watercraft is the promise of a thrilling yet quiet ride in a high-performance electric boat. They want to catch more fish, have more peaceful conversations, and hear the sounds of nature. They want to tinker with boats less, and enjoy experiences more.

The environmental impact matters, too. It matters to our employees, who dedicate their professional lives to making boating more enjoyable, accessible, and environmentally friendly than ever before. And it matters to our customers, who care about taking good care of the water and the outdoors they enjoy so much.

MRA Boathouse (building and photo credit: Winder Gibson Architects)

One of those customers is Marin Rowing Association (MRA) in California. In 2014, they installed solar panels to make their boathouse carbon-neutral. They even sized their solar array to account for charging the outboard motors on their coaching launches, even though at the time, there were no electric motors capable of powering them. Enter Pure Watercraft.

MRA installing solar panels (photo credit: MRA)

MRA is purchasing 8 Pure Outboards to replace their 25 HP gas outboards, which average about 4 years old. (Normally, they’re replaced every 5 years, as they reach the end of their useful life.) Marin’s coaches understand that precise communication is key to success.  For the first time, they will be able to help the rowers improve without yelling over engine noise, and listen to rowers speaking at a normal volume. They’ll also benefit from more accurate speed control, reduced maintenance, and lower cost of ownership. (The Pure Outboards pay for themselves in 2 years, and over their lifetime, they cost less than half as much as gas outboards.)

As part of their process, Marin is applying for grants (such as the Carl Moyer Program), and quantifying the environmental impact of their conversion. The bottom line is that their 8 coaching launches, with small gas-powered outboard motors, create about the same non-CO2 pollution as 1,000 passenger cars. Think about that – each of these coaching launches that use just 2 gallons of gas per day pollutes as much as 125 cars. Imagine the more mainstream boats, like bass boats, that can use 20-30 gallons of gas in a day, polluting 10-15X as much.

MRA 50th Anniversary, with launches in background (photo credit: MRA)

Switching to the Pure Outboard, the direct pollution is eliminated. Of course, there is some pollution driven by generating the electricity to charge the batteries; however, the Pure Outboard is so efficient that on an MRA launch, it uses about 2/3 the energy per day that an electric car uses. Therefore, for MRA, switching a single gas outboard to the Pure Outboard eliminates 125X as much cancer-causing pollution as switching from a typical gas powered car to an electric car.

The beautiful thing is that the boater gets a vastly superior experience, at a lower cost, with a positive impact on the environment (including noise reduction far in excess of that required by state law) as a bonus.


The first step was to analyze the pollution from modern, four-stroke outboard motors of the type that MRA uses. 

Carbon dioxide has garnered most of the recent attention, because of global warming, but more immediate harm is caused by other pollutants: carbon monoxide (CO), oxides of nitrogen (NOx), hydrocarbons (HC), and particulates (P10 and P2.5). Catalytic converters are very good at reducing CO, NOx, and HC, but no outboard motor has a catalytic converter because they were tried (once) and failed. Therefore, non-CO2 pollution is their Achilles’ heel.

To calculate the emissions from outboards, we looked at the EPA pollution limits (which began in California with the CARB 3-Star level regulation), because the manufacturers design to just meet these limits. There was a push to eliminate two-stroke engines from outboards, but instead, CARB implemented emission standards that would apply to all engine types, and some manufacturers, like Evinrude, improved their two-stroke outboards just enough to meet the new limits. (Note: they’re much worse on particulate emissions – 30X as bad.)

Federal regulations on emissions from outboard motors depend on the power level. A 25 HP (18.64 kW) gas outboard must not emit more than 2.1 + 0.09 * (151 + 557/P0.9) g/kWh of HC + NOx, and no more than 500 – 5.0 * P g/kWh of CO, where P is the power level (in kW) of the outboard. That results in a limit of 19.29 g/kWh of HC + NOx, and 406.8 g/kWh of CO. Because there are 34 kWh of energy per gallon of gasoline, this equates to 13.831 kg/gallon of CO and 655 g/gallon of HC + NOx.

To compare outboard motors to cars, we use fuel consumption as the common metric. 

The EPA limits the emissions of cars and places each one in a “bin”, the highest level (most polluting) of which is Bin 160. Under this least-stringent set of standards, a car can emit 4.2 g/mile of CO, and 160 mg/mile of NOx + NMOG (approximately the same as “HC” as referenced in the marine emissions standards). To convert miles to gallons, we use the new vehicle average miles-per-gallon in the US of 24.9. Therefore, a new car can emit 104.6 g/gallon of CO, and 3.98 g/gallon of NOx + NMOG.

Now let’s compare these numbers. Per gallon of gasoline consumed, a car can emit 104.6 grams of CO, and an outboard motor can emit 13.831 kg (132 times as much). Again, per gallon of gasoline, a car can emit 3.98 grams of NOx + NMOG and an outboard motor can emit 655 grams of HC + NOx (165 times as much)

For MRA, that means that its weekly fuel usage of 70 gallons of gasoline drives the same amount of (CO + HC + NOx) pollution as 9240 gallons burned in cars, which is about 1000X the weekly fuel usage of a typical car. Therefore, their impact will be to reduce (CO + HC + NOx) pollution by about as much as you would if you replaced 1,000 cars with electric cars (which would cost the federal government up to $7.5 million in subsidies).

With this big an impact for one rowing club, what about the bigger picture? There are about 1,000 rowing clubs in the US, with a total of about 4,000 launches. If the average launch is used about the same amount as MRA’s, then replacing their gas outboards with the Pure Outboard would have the same impact as getting 500,000 cars switched to electric (requiring subsidies of up to $3.75 billion).

How can the impact be this significant? There are two major reasons:

  1. Gas powered cars are about 16-25% efficient, while gas outboards are only about 8%. There is much more room for improvement.
  2. Not requiring catalytic converters on outboards leaves us at the pollution mitigation stage where cars were in 1975.

We still need to take into account the compensating pollution driven by the power plant generating the electricity to charge the batteries. To do this accurately across the board would require an impractical level of complexity, involving time-of-day (to know how much power is baseline and how much is peak), the specific power plants involved, the grid efficiency, and the round-trip charge efficiency of the battery pack. The answer would vary in some cases by orders of magnitude. But we can simplify this problem by comparing to electric cars, which have the same conditions to deal with. 

By experience, we’ve found that a coaching launch with the Pure Outboard uses approximately 4.8 kWh for a hard rowing practice that would normally require a gallon of gasoline in a gas outboard. Therefore, we can translate the MRA gasoline usage in gallons by 4.8 kWh/gallon to get the electricity usage. Electric cars use between 248 and 455 Wh/mile, and the average car drives 11,500 miles/year, so an electric car uses between 2,852 and 5,233 kWh/year, with the average (weighted by sales volume) about 290 Wh/mile, or  3,335 kWh/year.

MRA uses 70 gallons of gas per week, with 8 launches, so the average launch uses 455 gallons/year of fuel. The replacement Pure Outboard will use 2,155 kWh/year, which is about 2/3 of the power used by a typical electric car. The club as a whole will use 17,472 kWh/year, equivalent to just over 5 electric cars.

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5 thoughts on “A Thousand Cars Off the Road”

  1. Thanks for this detailed information. I did not know that catalytic converters did prevent pollution this way, and that fossil outboards were so far off the chart.
    Regarding the environmental footprint of the power supply, why not get your customers to switch to a CCA supplier (or peninsulacleanenergy.com) which can ensure a high renewable content of the energy that is bought (under various schemes) ?
    Thanks for the inspiration, and keep on trucking (from France) !

  2. I like your emissions comparison to cars for using something most people can easily relate too. Part of that comparison is valid in that most gas or diesel powered outboards use automotive technology in their design and construction, even if in most cases they are not directly interchangeable without significant modifications. And as you indicated, it has been difficult to get marine outboard motors to meet land based motor vehicle emissions compliance requirements due to packaging and incompatibilities of making catalytic converters work in water, let alone salt water. But that is not where your comparison fails to float the boat. Cars operate on land, boats operate on and in the water. So the power loads very massively. Pushing a 2000 pound boat through the water is not the same as pushing a 4000 pound car down the road. Pushing a boat through or across the top of the water takes a large continuous rated power load to maintain the speed it has reached due to water resistance and friction. A car utilizing rubber tires reduces that resistance and friction to a very minor power requirement in comparison. If you were to place an equivalent load on the car that matches what the boat is encountering, it’s continuous power and fuel requirements would increase to those match the boat and its emissions would rise accordingly. So the car equivalent emissions drops to only a few cars.

    Make it an apples to apples comparison. Not lobsters to watermelons.

    Oh by the way, a E-Tec G2 Evinrude was the one of the most if not the most emission and fuel efficient outboards out there on the market. It used a very precise crankcase oil injection and lubrication system along with its direct cylinder fuel (gas) injection system.

    I am interested in your outboards. I am looking for a 30 to 50 hp electric outboard package to be used on a flat bottom plywood launch weighing about 600 to 750 pounds without engine or fuel. My planned speed operating range is 15 to 28 mph. Top speed about 32.

    • The main point of your post is that a boat requires more continuous power than a car. That’s right. For that reason, we do not focus on the highest-power boats, because the continuous power of a wake boat could be 10X as high as that of a car. But we produce a 25 kW continuos power outboard motor, which is about the same continuous power of a Tesla Model S at 65 mph.

      But that misses the point of my post, which was that the pollution reduction is much greater for a boat switching to our outboard than for a car switching to an electric car. That holds true, even though cars are very different than boats, because the reduction in emissions in each case is apples-to-apples. The comparison between those two is only between emissions reduction figures, so the very different operating characteristics of the two don’t matter.

      The bottom line is that you reduce toxic pollution by far more, for much lower cost, by switching your outboard to ours, than by switching your car to an electric car (if you actually use your boat much).


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