Major Trends in Boating
In boating, two major trends are converging: electric propulsion, and hydrofoiling. In some ways, this is a coincidence, as battery-electric propulsion is coming now because of the automotive industry, and hydrofoiling has reached new prominence because of the America’s Cup. But these two technologies have the potential to address each other’s limitations.
Electric propulsion brings tremendous advantages to boating – quietness, low maintenance, instant torque, and clean operation – but it also brings a limitation: the low energy density of batteries doesn’t play well with the high drag and weight sensitivity of planing hulls.
Enter hydrofoiling. Since the 2013 America’s Cup, no team has been able to compete without hydrofoils. Not since Enrico Forlanini, Alexander Graham Bell, the Wright Brothers, and others pioneered hydrofoils more than 100 years ago have they reached the level of public consciousness they did after 2013. With its high energy efficiency (up to 80% energy savings), foiling offers the potential to address electric propulsion’s limitations, which has led to a proliferation of electric foiling craft of all kinds – boards, personal watercraft, and even a waterbike.
Foiling Boats, and Limitations
Recently, several foiling electric powerboats have joined the fray. These present a new challenge not faced by the smaller vessels: how do you deal with trailers and boat lifts, when there’s a foil below the hull? The elegant solution for most is a retractable foil – a foil when you want it, and not when you don’t. The issue is that the boat rests on the retraction mechanism. It has to be able to extend and retract, and while extended, carry the entire weight of the boat and its payload. The demands on the mechanism are so great that it becomes expensive and high-maintenance, erasing one of the big benefits of electric propulsion.
These limitations of foiling have existed since well before electric propulsion. Hydrofoils were used on ferries in Russia and elsewhere, and on military Fast Attack Craft in the US in the 1970s and 1980s. But in each of these cases, cost and maintenance were problems, and the programs were terminated. Electric propulsion solves some of hydrofoiling’s problems (like the need for short-term bursts of power to get up onto foils), but not all.
So at Pure Watercraft, we faced a dilemma: how do we realize the benefits of foiling, without consuming in maintenance more than we save? How do we deliver a better boating experience than ever before, at a reasonable cost?
We looked to an innovation from the 1970s: the hydrofoil supported catamaran, pioneered by Dr. Gunter Hoppe of the University of Stellenbosch (South Africa). Instead of a large, retractable foil, a small fixed foil can be placed between the pontoons of a catamaran, lifting much of the boat out of the water, and lowering the energy required at planing speeds.
Here’s the foil-assist on the Pure Pontoon:
When we combine the foil assist with an efficient hull design, we can achieve high performance at a variety of speeds, across the range of sea states that a pontoon boat is likely to encounter.
What we’ve found is that on the Pure Pontoon, at a speed of 23-25 mph, the foil assist enables a 21% reduction in power. Overall, the test hull uses about 1670 Wh/mile at that speed, compared to about 1000 Wh/mile for a full foiling boat of similar size, or 3500-4250 Wh/mile for other electric planing/pontoon boats. In simple terms, a conventional pontoon boat at 23 mph uses about $1.62/mile for gas, while the Pure Pontoon at that speed uses about $0.20/mile for electricity.
But how does it feel? Anecdotally, passengers in our test hull find that it feels like a magic carpet, riding high on the water. When crossing another boat’s wake, they say they feel it, but not like in a conventional boat.
In the end, the Pure Pontoon’s foil assisted hull provides most of the efficiency and ride characteristics of a foiling boat, without the complexity, cost, and maintenance of a full retractable hydrofoil.