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Comment by wood_spirit | Hacker News Reader

It’s obscure but there was such a contraption trialled by the seals and cia in the 1950s http://www.hisutton.com/CIA_Water-Air_1958.html

Here’s a pedal powered smuggling submarine from the 1940s http://www.hisutton.com/Swiss-Pedal-Powered-Smuggling-Submar...

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Interesting that the CIA conclusion for a device very similar to the article is "Not recommended for operational use due to its discomfort and very slight gain in speed over that of a swimmer equipped with fins."

Yeah I think for most uses I would still prefer fins for their agility. Cool idea though, and we probably haven't seen peak efficiency here.

Peak efficiency probably looks like this:

https://newatlas.com/marine/jetcycle-hydrofoil-pedal-bike/

Nice - yeah that looks more optimal to me.

30x the cost though...

That looks absolutely amazing. Super cool that you can maintain elevation at less than 6 MPH — I was expecting it to be closer to 10 or 15 MPH.

6mph is nothing to sneeze at on the water, in terms of the power it takes to sustain that kind of speed.

A person paddling can't sustain 6mph for very long, if they get there at all.

World record for a human powered hydrofoil is 21.3 mph. https://en.wikipedia.org/wiki/Decavitator 6mph looks a lot more reasonable in that context.

Sure, but a person paddling isn't hydrofoiling, right? They're using their arms instead of legs and contending with tons of additional friction/drag. I see this as being akin to bicycling, since it uses the same muscles.

Here's what I am getting at...

https://youtu.be/SDX3Hz2gsas

A guy on one of these doing the minimum speed. He doesn't look like he's casually pedaling, no?

It's probably harder to maintain 6mph than you might think.

Eh, it's hard to tell power output from pedaling cadence unless it's a fixed gear ratio. Most people pedal between 70-100 rpm regardless of the watts they're producing.

There are some clues in their body language. they appear to be straining. And the pedal movement looks a little jerky, as if the load is changing dynamically in relation to the effective flywheel/inertia of the system. Spinning a higher speeds with less torque is supposedly less tiring. So they might want to gear this down a bit and include a larger flywheel/inertia. Very impressive device tho. Maybe a hybrid approach with a solar panel for charging on the beach...

To me it doesn't look like it they were struggling with the physical exertion, but it does seem like they are struggling to properly hold on to the boat. It looks like the boat suffers from poor ergonomics, and needs some proper handles for holding on and steering.

  >A guy on one of these doing the minimum speed.

Counterintuitively, that probably makes it harder.

With any wing, the faster you go in level flight the less drag is caused by lift. This strange fact is because moving a large amount of fluid slowly is more efficient than moving a small amount of fluid fast, and a faster wing can interact with more fluid mass per second ("m dot").

https://en.wikipedia.org/wiki/Lift-induced_drag#Calculation_...

Since skin drag increases with speed, adding these two drag curves together forms a 'valley' in the overall speed-vs-drag curve. Going slower or faster than this ideal speed will result in increased energy per mile.

The math is better explained in David MacKay's brilliant ebook, 'Sustainable Energy Without the Hot Air.'

https://www.withouthotair.com/cC/page_269.shtml

They seem to be struggling a bit and the there's no wind or waves. Maybe coupled with a battery like an ebike it might be sustainable for longer than a few minutes.

6 mph is a gentle paddle in a rowing shell, albeit using an additional set of muscles.

It depends what they're paddling in. Long, slim racing kayak - easy. Short whitewater kayak - impossible.

Looks like pretty hard work compared to land bikes. You never get to coast downhill. I wonder if you can get it to surf on waves.

With bicycle love the idea that you still can feel yourself as a fish

Especially in the water I neither want the burden of being attached to something nor the burden of retrieving it.

probably should read "trained swimmer with fins"

It can take some time to get used to fins and the motions needed. Many more people have ridden a bike

Training isnt a problem for government run operations which is their context

Yes, but it's not my context.

Context of the reply thread…

... which was itself in the context of a device for civilians. To avoid litigating the primacy of nested contexts in a casual conversation, maybe let's agree to not be so picky about which caveats are on topic?

A reply is always in the context of the thing that is being replied on. It’s how replies work…

If there is an article about berries and you say you love blueberries and I reply saying “I hate them”, it in the context of blueberries. It doesn’t mean I hate all berries. And I shouldn’t have to clarify that, since I’m replying to a comment about blueberries.

How else could this work?

And everything is always in exactly one easily defined context, right? So for a comment reply we already know the full context just by looking at its immediate parent. That's how nested replies work, right?

Yes..?

Really? Go into the next HN thread and see how many deeply nested comments you can make sense of by looking only at their parent.

You are not doing HN right if you are only reading the parent

Yeah, you both seem to agree. The larger context matters.

Me:

> And everything is always in exactly one easily defined context, right? So for a comment reply we already know the full context just by looking at its immediate parent. That's how nested replies work, right?

noncoml:

> Yes..?

But somehow, also noncoml:

> You are not doing HN right if you are only reading the parent

I give up.

Correct. Why is that? Apply this logic to the current comment chain, starting from OP.

Using fins is extremely intuitive for anyone who has swum before.

Toss a battery on it though and what does it look like then? Perhaps you're able to augment a human's ability to traverse longer distances more quickly. That's tech that didn't really exist back then!

They already have those, seabobs

And it would probably do a decent job of cutting you or your friends up when human and the propellor come into contact...

The article says they move slow enough to not be dangerous. That could be true even battery powered.

Sea scooters already exist. They pull not push from what I see. Basically they’re EDFs with a place to hold on.

There's tens of different companies that make these from about $300

https://scootermotion.com/shop/seascooters/

"Wartime paddleboards" is not a phrase I ever expected to read.

Brings a new meaning to "Charlie don't surf". At this point though, you have to pretty much imagine that the military has researched any and every mode/method/means of achieving the goals of a mission. I'm sure roller blades and skateboards have been considered at some point as well.

Not sure about the military, but French police has been using rollerblades to patrol the streets of Paris.

Taliban rollerbladers:

https://nypost.com/2023/11/15/news/taliban-seen-patrolling-k...

My memory is fuzzy but I think the Australian SAS or SBS made raids on the Japanese using paddle boards in the Second World War.

It’s described in the H I Sutton book, from the website above, but I think it’s out of print now

H. L. Hunley (submarine)

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

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