The S.S. Cybertruck may not be shipshape quite yet, but the electric pickup's alter ego as a boat is coming together.

Elon Musk's recent assertion that the Cybertruck "will be waterproof enough to serve briefly as a boat, so it can cross rivers, lakes & even seas that aren’t too choppy," has been met with its fair share of criticism.

Many have pointed out that numerous vehicles can float briefly, and the Washington State Department of Natural Resources warned its followers on Twitter that "Our derelict vessel crews are begging you to understand that anything that ‘serves briefly as a boat’ should not be used as a boat."

Another issue that has been raised is that, even if the Cybertruck can float, it's not clear how it would move under its own power.

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Tesla Cybertruck with new wiper

Elon Musk claims that the Tesla Cybertruck is watertight enough to allow it to float briefly.  (Nic Coury/Bloomberg via Getty Images)

"One thing that is still uncertain is the speed the Cybertruck will be able to travel on water so the calculations might be off due to that, but I suspect it might be anywhere between 3-10 knots. @elonmusk any insight on this?" RGV Aerial Photograph tweeted with an image of the channel separating the SpaceX Starbase in Texas from South Padre Island, which Musk used as an example of a body of water the Cybertruck could be used to cross to save the time it normally takes driving around it.

"You’d need an electric propeller mounted on the tow hitch to go faster than a few knots. There might a creative wheel hub design that can generate meaningful thrust," Musk responded.

Elon Musk

Elon Musk has now suggested that a propeller could be attached to the Cybertruck to drive it through water. (Frederic J. Brown/AFP)

Musk has made similar claims about the Tesla Model S.

"We *def* don't recommended this, but Model S floats well enough to turn it into a boat for short periods of time. Thrust via wheel rotation," he tweeted in 2016.

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As for the propeller, while Musk said Tesla is working on a rocket pack for the upcoming Roadster sports car, no alternative propulsion system is known to be in development for the Cybertruck.

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However, propellors are available for pickup trucks, they just don't work in the water.

pickup propeller

Truck accessories company Bully makes a novelty propellor that fits in a pickup's tow hitch receiver, but isn't powered. (Bully)

A number of companies, including Bully, make novelty covers for hitch receivers that look like propellors and spin, but only as the air passes through them.

Of course, Musk does have some experience with amphibious vehicles. In 2013, he bought a Lotus Esprit-based submarine known as "Wet Nellie" that was used during the making of the James Bond film "The Spy Who Loved Me" for nearly $1 million.

wet nellie

"Wet Nellie" was featured in "The Spy Who Loved Me." (RM Auctions)

At the time, he said he was disappointed to learn that it was fixed in its submarine configuration and couldn't actually transform into a car, but that he would redesign it to be able to do that.

A decade later, a functional updated vehicle has yet to surface, but the Lotus does have another connection to the Cybertruck.

Musk has said the pickup's flat, sloping windshield and hood were inspired in part by the similarly shaped Esprit.