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Comment by ri0t | Hacker News Reader

I'd wager to say that on most civilian vessels, the engine noise is far louder than what the prop could generate. I'm happily using a 600W outboard electrical - while it would be different than with a combustion engine, i don't think it can get much quieter even with better prop-design. It's a blessing! Almost like sailing the boat, i.e. not much louder than a gust of wind.

Energy efficience on the other hand.. It is driven by a fairly average car battery, so every little Watt saved helps keep the drinks cooled.

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600W? Is that a typo? That’s less than 1HP.

I don't know anything about boats, but some boats can be rowed by a single person, which I guess would typically be much less than 600w. It fits with the car battery part too.

Most people are capable to do about 500-800W for long time (30 minutes or more), and up to few kilowatts for short time, 1-3 minutes.

Source? In cycling those numbers are elite level if not beyond. Numbers for rowing are hard to come by but lower[1], probably drag lowering efficiency (bicycle drivetrains are 90+% efficient).

To put it into perspective, 250Wh translates to 800~900 calories burned in a half hour[2]. That's not something most people around me can do.

[1] https://rowinglevel.com/rowing-times/10000m-times

250Wh = 900kJ = 215 kcal at 100% efficiency; humans are ~25% efficient at turning food into mechanical work so ~860 with error bars

Yeah, they are wrong.

  During a bicycle race, an elite cyclist can produce close to 400 watts of mechanical power over an hour and in short bursts over double that—1000 to 1100 watts; modern racing bicycles have greater than 95% mechanical efficiency. An adult of good fitness is more likely to average between 50 and 150 watts for an hour of vigorous exercise.[clarification needed] Over an 8-hour work shift, an average, healthy, well-fed and motivated manual laborer may sustain an output of around 75 watts of power.

- https://en.m.wikipedia.org/wiki/Human_power

Also see “How Much Electricity Can a Human Generate?” https://www.pedalpc.com/blog/how-much-electricity-can-human-....

I guesstimate my 100k cycle place to be about 80w so that tracks. At the end I'm about ready to devour anything and everything that's put in front of me.

"The Gossamer Albatross is a human-powered aircraft built by American aeronautical engineer Dr Paul B MacCready's company AeroVironment. On June 12, 1979, it completed a successful crossing of the English Channel to win the second Kremer prize worth £100,000 (equivalent to £538,000 in 2021)" ... "In still air, the required power was on the order of 300 W (0.40 hp), though even mild turbulence made this figure rise rapidly"

https://en.wikipedia.org/wiki/MacCready_Gossamer_Albatross

Probably not. Even large, 40'+ boats designed to operate primarily by sail can get by with 10-20HP. Motorsailers -- racing sailboats designed to go faster by leveraging both the wind and a motor -- typically aren't much more than 40HP.

What's interesting about this prop (to me, anyway) is that most of the sea-faring boats that need it the most will likely not use it because it doesn't feather or fold-away when not in use. For ocean-faring sailboats, that's critical, as the drag of trad props will cap their speeds by half a knot or so, which (over the span of a multi-week journey) might add meaningful amounts of time to a trip that you're just hoping to finish with.

Kilowatt is ~ 1.3 hp, so 600W = 0.8HP.

But, here important, that electric engines have much better torque on low rpm, even exist electric engines which give high torque just from zero. Also it is typical, to overdrive electric engines for short time.

And other important thing, aging - electric engines could nearly not have aging at all, but gas engines have significant drop of power/torque at hundreds of hours of work, even if properly serviced.

Overall, You will really not see gas engine claimed power, but something much less, ~ 70-90% in good cases. But in case of electric engine, it will not only give claimed power, but could make up to 100% boost for limited time.

I don't know much about marine motors but, unlike for ground vehicles, I don't think that having a ton of starting torque helps in a marine environment. The torque required probably increases as the propeller speed increases which matches traditional ICE engines much better than DC motors.

UNLIKE for ground vehicles, marine and air.

- From tutorial for auto engineers: "more than 90% of time, auto engine working at fast switching conditions, and extremely low load, near zero", vs marine (and air), where prop does near linear load-rpm function at working diapason.

BTW, because autos special requirements, there widely used turbo-compressors, but they are rarely used in marine motors and not too distributed in air.

This is because, turbine only eat power and does not give anything at low rpms, only effective on medium-high diapason.

For planes, turbine only gives an increase at significantly high altitudes, so, for example, typical light plane does not got improvement if flight on typical 1000-2000m, but got if go much higher, 5000m and more.

What is "diapason"? I looked it up and the closest definition was "a burst of sound", the rest pertained to pipe organs.

Band, range.

I'd only seen the word used for musical instruments, where it refers to the scale length and/or the tonal range. Seems like here the same general idea when applied to an engine refers to its operational RPM (frequency) range.

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