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.

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 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.

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.

Calculations

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/P^0.9) 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.

One of the most common questions that comes up when discussing Pure Watercraft is: why did we build so many of our components and capabilities in-house, when there are engineering consulting firms, electric motor manufacturers, and huge battery companies already serving the electric car business?

The short answer is that through the process of testing and iterating, we learned that owning the capabilities ourselves was the only way we could make something truly great – the only thing worth doing.

Product Vision
As we took a closer look, we saw that  people weren’t buying higher-powered electric outboards because they were too heavy, expensive, and unreliable. They cost so much that even when you took the much lower operating costs into account, they’d never come close to paying for themselves. Repair shops said they were even less reliable than gas outboards. Boaters said they were loud; the motor eliminated emissions but noise pollution remained. We needed to achieve simultaneous competing objectives: high performance, low cost, near silence, and rock-solid reliability. Tesla was an inspiration, having broken the previous inverse relationship between cost and performance, so we learned from them and set out to create a better way to experience the water.

Engineering
In the beginning, we partnered with an outside development firm to engineer our first electric runabout.  

It emulated the fast-prototyping method used successfully to launch Internet companies, and gave us speed, which we believed was critical to validating our product idea. In the end, what we got out of it was a pricey prototype. On the positive side, through this partnership we secured a founding engineer with the insight he had gleaned from being embedded with the outside development firm. But we also realized the limitations of working with outside engineering. Much of the learning comes from the details of development and was captured externally. There also was a misalignment of incentives; because we had skin in the game, we were focused on finding paths that would lead to viable products, while engineering firms are in the business of serving the stated needs of the client, regardless of the viability of the product. After the first prototype, we concluded that we needed to build the core capabilities in-house, even if it took more time. The electric vehicle field was so new that available people with outstanding skills and experience were rare. We’d have to start with what we learned from the runabout project, and hire smart people who could learn the field. It was starting to look like a long road, but the only way to develop groundbreaking products.

The Battery Pack
We started with the battery pack because it is 50% of the weight, cost, and complexity of an electric vehicle, and a critical factor in performance.  At first, we reached out to battery companies that manufacture and sell cells, which we would use to build into battery packs – similar to the way Tesla does.

But the big manufacturers didn’t return emails from a marine propulsion start-up. We next looked at companies that built and sold battery packs made using cells from the big manufacturers, but they cost 2-4X as much as the cells themselves as a result of the battery pack IP. If we took their prices as an input cost, then our product was going to cost the customer far more than if we developed the battery pack IP ourselves. We quickly learned that we couldn’t build a competitively priced product if we outsourced the component with the most significant IP.

Besides the economics, we were concerned with performance. The Tesla battery pack was the gold standard, and none of the packs we saw held a candle to theirs in terms of energy density and capacity retention. A boat is more weight-sensitive than a car, so we had to be even more focused than Tesla on getting the most energy per pound.

But how would we build a safe pack, with high energy density, at a cost that was commercially viable, if the cell manufacturers wouldn’t return our emails? How could we build a battery pack when we had never done so? How could it outperform the packs built by big companies? We had to secure access to cells, and learning. Leading-edge battery pack technology wasn’t published. There were tear-downs of electric car battery packs and how-to’s written by hobbyists, but our goals were different than theirs. They were trying to convert an old car into an electric proof-of-concept, and we were building a commercially viable, high density battery pack that would last years.

So we found a partner to co-develop a battery pack with us. We could learn from them, and get a working battery pack quickly. Together, we chose a standard cell type, the 18650 used in power tools and Tesla cars. We thought we could outsource the battery management system (BMS), because every battery pack has similar needs. So we used the same BMS we used in the runabout. However, we later found that the BMS didn’t work on cold days – we had to use a hair dryer to warm it up before we could use it. It weighed too much, it cost too much ($1500, when the chips on it cost < $100) , and we couldn’t improve it because it was someone else’s technology.

We then took a new approach. We tried to use sub-modules from our partner, and take on a bigger share of the development ourselves, but it wasn’t enough. The result was still high cost and heavy. We had to scrap that and start over.

Finally, we got the top battery cell provider to return our emails after 5 years of pursuing them, and they agreed to supply us cells. We would be spending less than half as much on cells, for the best cells available. Our internal engineering build-up was paying off, as we now had the expertise to develop a radical new design. By developing our own BMS, we could use a far smaller set of circuit boards, built to fit our pack, instead of the mess of 97 circuit boards that the off-the-shelf BMS required. This was the fourth battery pack we developed, and finally, we had one that really excelled. It beat our gold standard “the Tesla Model 3 pack“ in energy density. The flywheel of component and team development was finally whirring, after 7 years.

The Outboard
Electric motors have been around for about 150 years: you would think there is a wide variety of motors available at reasonable prices. However most on the market are used in fixed applications, where neither weight nor size is very important, and they can use A/C power from the grid. Most of those used in mobile applications have large diameters and are heavy. Only the motors that have very high volumes of existing products using them are produced at low cost – for example, motors for quadcopter drones. If it’s more powerful than a drone, but less powerful than an electric car, then there are only low-volume, high-cost motors out there.

We looked into building our own motor, as Tesla had done. But where to look? We reached out to one of the gurus of motor design to point us in the right direction. When we explained our objective, he knew what we needed to do, and shockingly, he said he’d do it himself.  We could now build a motor that, compared to those we had found, weighed about half as much, had about 1/3 smaller diameter, and cost 2/3 less per unit. We did it. Our process was unconventional but we created a motor with weight and performance only found in scientific motors, for a fraction of the cost.

In our effort to build the other components, we were often met with similar issues that we faced with the motor. The propeller became a component of surprising importance. Most electric outboards used generic off-the-shelf propellers, but we worked with a skilled propeller designer who ran computer simulations of the performance of design and materials choices. The electric motor’s ability to deliver full torque across a wide range of RPMs enabled a propeller with 30% more efficiency than the off-the-shelf ones.

In the end, our product achieved 3X the propulsion per pound of best electric outboards, and more than 2X the propulsion per dollar.

This could not have been achieved by buying our components off the shelf, as most others did. In designing our own components, we integrated components that we had previously imagined as separate, thus reducing the number we needed. Our relationships with manufacturing partners grew stronger as we sourced more and more components from them.

It would be neat to say that that’s why we built our own components, but we really stumbled into it, through the fog of uncertainty, feeling our way, learning at every stage.