Design Challenges of Electric Boats

Designing motorboats is all about compromise. Anyone working in this industry knows this well. But when electric boats and electric propulsion enter the picture, that compromise takes on an entirely new dimension. For several years I have been designing electric motorboat hulls in the 5.5 to 10-metre range, and I’d like to share what I face on a daily basis as a designer.

Electric Boats — A Technology Problem or an Engineering Problem?

I often hear the question: why are electric boats still a niche? Is electric propulsion technology for boats not ready yet? The answer is simpler and at the same time more complex than it might seem. The technology exists and is becoming increasingly advanced. The problem lies elsewhere — in how to reconcile the physical, financial, and operational constraints that act simultaneously and, most often, against one another.

Batteries for electric boats are either too heavy or too expensive. The hull of an electric boat must be appropriately designed for a specific speed range. High-power electric motors for boats require higher voltage, which not every customer wants on their vessel. The customer wants comfort, but comfort means weight, and weight limits range. And so on — each of these constraints pulls along the next.

Space and Batteries in Electric Boats — The First Design Dilemma

On a small electric boat, space is simply limited. To achieve a reasonable cruising range, you need a large battery capacity, and large capacity means large mass and large volume. On a vessel just 5.5 metres long, there is not much room to negotiate — space is simply scarce.

On larger electric motorboats, up to 10 metres, the situation is no simpler — because customer expectations grow along with the size of the boat. The customer wants comfort, living space, an extra cabin, storage. And here the classic design dilemma in electric boat design emerges: another cabin or space for batteries? Storage or greater range?

Lightweight and compact batteries for electric boats are expensive. The cheaper ones are too heavy to use without significantly affecting the vessel’s buoyancy. The result is that prices for small electric boats are considerably higher than their combustion-engine equivalents — and this is one of the real market challenges for electric boats. With fewer batteries you get less range, and with more expensive batteries you have less budget for quantity. The direct consequence of this compromise is range — the range the customer expects, which at the current state of battery technology in electric motorboats up to 10 metres is simply difficult to achieve.

Electric Motor Power vs. Boat Weight

Electric boat motors at low supply voltage offer relatively modest power output. High-power electric motors exist, but they require significantly higher voltage — and not every customer wants a high-voltage system on their electric boat. At the same time, there are many fans of fast boating on electric vessels, for which high power is needed. This is a genuine engineering challenge in electric motorboat design that technology is still grappling with.

For a low-power electric drivetrain to make any sense at all, the boat must be as light as possible. That’s easy to say, harder to achieve. The structure of an electric vessel together with its equipment and drivetrain already results in a given base weight that is difficult to reduce — particularly on early electric boat prototypes. The heavier the electric boat, the lower the speed and the greater the power and battery consumption, which directly affects range and performance. The result is that an electric version of a boat delivers noticeably lower performance than its combustion counterpart — and automatically narrows the pool of potential buyers. This is not only an engineering problem but a market one as well.

Hydrodynamics and Electric Boats — The Most Important Design Challenge

And here we get to the heart of the matter. For an electric motorboat to operate efficiently, the hull must be designed with a specific speed range in mind. The physics here are simple and unforgiving: a displacement hull and a planing hull are two entirely different worlds. You cannot design a single electric boat hull that performs equally well in both cases.

Yet more and more electric boat manufacturers want to offer the same hull with a high-power combustion engine and an electric motor as a drop-in alternative. And most available and affordable electric boat motors offer low power output — and this is precisely where the design problem begins.

A boat hull designed for planing performance behaves on electric propulsion in a completely different way than the customer would expect, and the energy efficiency of the electric boat is far from optimal — much like a combustion drivetrain on planing hulls at low speeds. A planing boat at low speed moves through the water, but inefficiently. Conversely, a displacement boat with electric propulsion will never cruise efficiently at high speeds — or may not reach them at all. And this is precisely the point at which the design compromise in electric boat design becomes most visible.

Electric Boats — Design — A System of Communicating Vessels

Each of these design challenges in building electric boats would be manageable on its own. The problem is that they all act at once and influence one another: the weight of the electric boat limits range, range requires batteries, batteries take up space and drive up the price of the electric boat, price and comfort determine who buys it and whether anyone buys it at all — and on top of that, there is no universal electric boat hull shape that can satisfy all of these requirements simultaneously.

The electric motorboat industry already has considerable experience behind it and we know more and more. But much lies ahead — and understanding these challenges on the part of designers, manufacturers, and engineers is the key to offering the market electric motorboats that genuinely meet user expectations.

Why Is It Still Worth Designing Electric Boats?

Because of the silence. Boating on an electric vessel in nature is a completely different experience from what combustion-powered craft have accustomed us to. No engine noise, no exhaust fumes — you hear the water, the wind, your surroundings. That is something that cannot be overstated. And that is precisely why it is worth designing electric motorboats as well as we possibly can.

Our Electric Boats

If the topic of electric motorboats is close to your heart and you are looking for an experienced designer — I invite you to browse our portfolio of electric motorboat design projects. We design both monohull and catamaran electric boats in the 5.5 to 10-metre range. If you have questions or would like to discuss your project — I’d be happy to talk.

BEST REGARDS!

Marta Anna Zawadzka

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Photos: CANNA One — designed by Intuition Yachts | Built by CANNA Boats

Photos by: ALAN DĄBRAOWSKI

Learn more about our design philosophy and projects: Intuition Yachts Find out more about CANNA Boats: cannaboats.com