How Quiet Electric Boats Protect Marine Life
When you switch off a petrol engine and drift in silence, you notice something remarkable: the water comes alive. Fish break the surface. Birds call from the shore. The gentle slap of wavelets against the hull becomes the only soundtrack. Now imagine that silence being your default, not a moment between engine starts, but the permanent state of your vessel. That is what electric boating offers. And for marine life, it matters more than most people realise.
The Science of Underwater Noise
A landmark study conducted by University College London and RAD Propulsion, published in the Journal of the Acoustical Society of America, found that electric propulsion reduced underwater noise by up to 43 decibels at 4 knots compared to conventional engines. To put that in perspective, every 10 dB reduction represents a halving of perceived loudness. A 43 dB reduction means the electric vessel is roughly 20 times quieter underwater than its combustion equivalent.
A separate study found that electric vessels were 8 dB quieter than conventional boats during transit and 17 dB quieter while loitering. The loitering difference is particularly significant because anchored or slow-moving recreational boats spend the majority of their time in this mode: fishing, swimming, lunching, watching wildlife. For marine life in the vicinity, the noise profile of a loitering vessel is what they are most consistently exposed to.
Impact on Whales and Dolphins
Marine mammals are particularly sensitive to underwater noise because sound is their primary sense. They use it to communicate, navigate, find food, and care for their young. Research comparing whale behaviour near petrol engines (measured at 151 to 139 dB) versus electric motors (136 to 140 dB) found dramatic behavioural changes. During exposure to petrol engine noise, mother whales showed a 29 percent reduction in resting behaviour, and calf nursing dropped by 81 percent.
An 81 percent reduction in nursing is not a minor disruption. For whale calves that depend entirely on their mother’s milk during the first months of life, sustained noise interference can affect growth, survival, and ultimately population recovery. The implications are especially serious for species like the Southern Right Whale and Humpback Whale, both of which calve in Australian waters.
A natural experiment in the Bay of Fundy provided further evidence. After the September 11, 2001 attacks in the United States, shipping traffic in the Bay dropped significantly. Researchers measured a 6 dB reduction in underwater ambient noise during this period and found correspondingly lower stress hormone levels in North Atlantic right whales, one of the world’s most endangered whale species.
Beyond Mammals: Invertebrates and Fish
The damage from underwater noise is not limited to charismatic megafauna. Research on sea hares found that exposure to boat noise caused a 21 percent reduction in embryo development and 22 percent higher death rates. These are invertebrates, organisms at the base of the marine food web. When noise disrupts their reproduction, the effects ripple up through entire ecosystems.
Fish are also affected. Many species use sound for spawning communication, predator detection, and territory defence. Chronic noise exposure has been linked to elevated stress hormones, reduced feeding, and displacement from preferred habitats. In areas with heavy recreational boat traffic, the cumulative acoustic impact on fish populations is a growing concern for marine biologists.
Australian Regulations and Approach Distances
Australian regulations reflect the sensitivity of marine mammals to vessel disturbance. The national approach distance is 100 metres for whales and 50 metres for dolphins. Caution zones extend to 300 metres for whales and 150 metres for dolphins, within which vessel speed must be reduced and course changes avoided.
On the Great Barrier Reef, stricter rules apply: vessels must stay 300 metres from whale calves and 150 metres from dolphin calves. In Victoria and South Australia, jet skis must maintain a 300-metre distance from both whales and dolphins. These regulations exist because the science is clear: vessel noise and proximity cause measurable harm to marine mammals.
A Nuance Worth Noting
Electric boats are not perfectly silent underwater. Research has noted that electric propulsion systems can produce noise at higher frequencies than combustion engines. These higher-frequency sounds are within the hearing range of some species, particularly porpoises. However, the overall noise energy output is dramatically lower, and the elimination of low-frequency engine rumble, which propagates furthest underwater, represents a substantial net benefit for the vast majority of marine species.
A Quieter Way to Share the Water
Every time you take a boat onto the water, you are entering someone else’s home. The choice of propulsion you make determines how much you disrupt the residents. Electric boating is not just quieter for you. It is quieter for every living thing beneath your hull.
Cat Cruisers’ electric E-Class propulsion systems deliver the silence that lets you truly experience the water, and lets the water’s inhabitants experience their world undisturbed. To hear the difference for yourself, visit catcruisers.com.au or reach out at catcruisers.com.au/contact.