13-year-old wins science fair for attempting to demonstrate Archimedes' fabled "Death Ray"

[zohaibahd]

What just happened? We all learned about Archimedes, the brilliant ancient Greek mathematician and inventor, in school. He introduced us to fascinating concepts like levers, pulleys, and even determined density while taking a bath. However, one of Archimedes' most intriguing creations has remained in the realm of legend for centuries – the death ray. A young enthusiast set out to prove how it might have worked and has now earned a couple of medals for his contraption.

In the 200s BC, historical accounts suggest that Archimedes used an array of mirrors to focus sunlight and set enemy ships ablaze during the Siege of Syracuse. Fast forward to today, Brenden Sener has earned two medals for his miniaturized version of the solar death machine. This project was part of the 2023 Matthews Hall Annual Science Fair.

Sener hypothesized that, as the mirrors focused light energy onto cardboard, the target's temperature would increase with each added mirror. He conducted three trials using different light bulb wattages – 50 and 100 watts. These bulbs were rigged with small concave mirrors to concentrate light beams onto a marked target.

As he added more mirrors, angling them to converge on the same spot, the temperature at the focal point kept climbing. With just the lamp alone, the target maintained a mild 81°F. However, after positioning the fourth mirror, the heat concentrated to over 128°F. Sener described the results as "remarkable," illustrating how curved mirrors intensified the sun's rays into a single searing point.

While the experiment didn't set the paper on fire (it wasn't meant to), Sener demonstrated how his setup reflected and concentrated light to increase the temperature at a focal point. He noted in his science paper that to set a wooden ship ablaze, the setup would require a very powerful light source like the sun and several large mirrors.

A scientist at Sandia National Labs commended the project, noting that while it didn't revolutionize physics, the findings nicely confirmed the first law of thermodynamics regarding energy transfer.

So, was Archimedes' original death ray a real invention or an exaggerated legend that has grown taller over millennia?

While we may never know for certain, Sener's pint-sized experiment suggests that the core idea could have worked. Archimedes was a certified genius ahead of his time. Concentrating solar heat with mirrors to defeat enemies doesn't seem far-fetched coming from the mind that gave us concepts like levers, pulleys, and displacement.

However, the 'death ray' remains a hotly debated topic due to the lack of archaeological evidence for its existence. Setting moving ships on fire, even with supersized mirrors, seems far-fetched, as demonstrated by the magnifying glass experiment – it takes several seconds to ignite a piece of paper. Even if Archimedes could weaponize mirrors this way, scientists argue that the ships would need to be anchored for it to be effective.

At the very least, Sener demonstrated that the physics behind Archimedes' suspected death ray were legitimate. Not bad for a middle schooler's science fair project.

Found is a TechSpot feature where we share clever, funny or otherwise interesting stuff from around the web.

Image credit: Melanie Sener, CNN

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https://www.techspot.com/news/102206-13-year-old-wins-science-fair-attempting-demonstrate.html

 

[wiyosaya]

This is awesome.

Congrats and kudos to Brenden Sener.

A similar concept is used in today's weaponized laser systems which use a process called phase conjugation to combine the output of several different fiber lasers in a way where their output is phase aligned and thus, makes the power of their output effectively combine.

There's no phase conjugation in Sener's experiment, but it seems that is not needed. What must be happening is that the mirrors are simply focusing more of the light from the bulbs on the target - thus raising its temperature.

We don't know how many mirrors Archimedes had, however, if the ships were moving, it would seem that there were enough mirrors that were also large enough to concentrate enough of the Sun's light on the ships to set them afire. We know from the weaponized lasers that they must track their target in order to destroy the target. In Archimedes day and age, tracking the target seems like it would not have been an easy task. Thus more mirrors that were large enough, meaning that enough power was concentrated on the target, may have been a way to overcome the lack of ability to track the target.

 

[Dr Roboto]

Give the kid kudos for a job well done and making it on the news and even techspot.

The true myth of the death ray was never the science, but is instead if it could actually be used as a "portable/directional" weapon in combat. It was more than likely just militarily propaganda and not an actual functional weapon. There is even Myth Busters episode about this at full scale with the help from MIT.
https://web.mit.edu/2.009_gallery/www/2005_other/archimedes/10_Mythbusters.html

Not to mention that solar power towers have been around for a long time (1978) and work on the same principle.

Solar power tower - Wikipedia

en.wikipedia.org

Once again, I do like the fun tech article, but some real research and journalism behind it would be nice. Why did the author not include some of the obvious info on Archimedes, that we already understand the physics not the weapon, and the recent things like Myth Busters. Sigh.

 

[ScottSoapbox]

This kid is winning by watching Myth Busters. Gold star!

 

[FrodBonzi]

Ships back in the 200s BCE wouldn't have been moving very quickly - and in order to unload troops, would have had to be stationary... Also, shipping lanes were pretty much set - it would have been fairly simple for Archimedes (or anyone else) to calculate exactly where a ship would have to be in order to attack a city.

So perhaps Archimedes could have devised a way for this to work without needing any advanced tracking methods.

Also, considering the tech of every other civilization in the area, imagine being on one of those ships and watch flames just start to appear seemingly out of nowhere - I suspect that they would be quick to attribute this to a godly death ray or other such thing.

 

[v1l3ba5tard]

Congratulations and stay green you can ask your old Man to explain that to ya

 

[p51d007]

He's a "Young Sheldon". Good for him!

 

[kinetix]

"The hyperboloid of the engineer Garin".. I mean.. Sener

 

[ferrellsl]

I'm sorry, but no 7th grade middle schooler put that presentation together. He had adult help. In fact, I'd wager his helicopter mom and dad put together the entire project.

 

[Bluescreendeath]

Ships back in the 200s BCE wouldn't have been moving very quickly - and in order to unload troops, would have had to be stationary... Also, shipping lanes were pretty much set - it would have been fairly simple for Archimedes (or anyone else) to calculate exactly where a ship would have to be in order to attack a city.

So perhaps Archimedes could have devised a way for this to work without needing any advanced tracking methods.

Also, considering the tech of every other civilization in the area, imagine being on one of those ships and watch flames just start to appear seemingly out of nowhere - I suspect that they would be quick to attribute this to a godly death ray or other such thing.

The mythbusters did an episode on this and revealed that you need perfect conditions - a lot of mirrors that gets the angle just right, warm and sunny sky with no clouds, no wind, no waves, a perfectly still boat, and everything up close (it doesnt work at a distance) in order to remotely set cloth or wood on fire. Even the slightest cloud, wind, or waves bopping the target up and down throws off the target from a consistent focal point of mirror's ray. Mirrors back then were all expensive objects.

Basically, this was a myth because it is completely impractical and need absolutely perfect conditions with expensive equipment. You're far better off just throwing flamming pots or shooting flamming arrows at a ship which is cheaper, dont need perfect conditions, and will light a ship on fire much faster.

Not to mention the entire story was anachronistic and didnt appear in later writings until many centuries after the original siege happened.

 

[gamerk2]

Ships back in the 200s BCE wouldn't have been moving very quickly...

Depends on sail alignment and wind direction. If we assume a simplified straight sail alignment, 10 Knots wouldn't be an unreasonable maximum speed. Hardly "fast", but "fast enough" to make such a system unreasonable.

 

[Endymio]

A similar concept is used in today's weaponized laser systems which use a process called phase conjugation to combine the output of several different fiber lasers...There's no phase conjugation in Sener's experiment, but it seems that is not needed. What must be happening is that the mirrors are simply focusing more of the light from the bulbs on the target - thus raising the temperature involved.

To address the physics here, no amount of mirrors or bulbs, or arrangement thereof will generate a focus hotter than the surface of one bulb itself -- the "perfect" case we call diffraction limited. If the mirrors are focusing sunlight, then the limiting factor is the temperature of the sun's surface itself. There are plenty of videos of people using low-quality mirrors (far from diffraction limited) just a few feet in diameter to set wood on fire and even cut steel and aluminum with focused sunlight.

As for phase conjugation in military laser systems, that allows us to perform phase conjugate amplification, which allows us to exceed diffraction-limited performance.

 

[Endymio]

Depends on sail alignment and wind direction. If we assume a simplified straight sail alignment, 10 Knots wouldn't be an unreasonable maximum speed. Hardly "fast", but "fast enough" to make such a system unreasonable.

Except for the fact that such ships, to attack an enemy port, must by definition sail towards it. Therefore the velocity component of the ship relative to the mirror installation would be very near zero.

Mirrors back then were all expensive objects.

Except you don't need mirrors. What we call a "mirror" today is a thin foil of metal (silver, aluminum, or tin usually) with glass on the front. In ancient times, the glass would have been the expensive part -- but the mirror actually works better without the glass. We call such objects "first surface" mirrors, and they're used extensively in optics.

 

[Bluescreendeath]

Except you don't need mirrors. What we call a "mirror" today is a thin foil of metal (silver, aluminum, or tin usually) with glass on the front. In ancient times, the glass would have been the expensive part -- but the mirror actually works better without the glass. We call such objects "first surface" mirrors, and they're used extensively in optics.

What you've described is still called a mirror. And they were still expensive objects even without glass. Highly polished and smooth metal plates (eg. Discs) without any glass were used as mirrors and they were expensive to produce. The pure metal mirrors found in the ruins of the ancient Romans, Egyptians, Chinese, etc were usually found in tombs or areas of people with wealth or status. And they were also fairly small in size too as they were handheld mirrors.
To create an entire line of highly polished larger metal reflectors of good purity would be very expensive not to mention completely impractical/ineffective.

This is just one nail in the coffin of this myth in addition to a dozen other nails.

 

[gamerk2]

Except for the fact that such ships, to attack an enemy port, must by definition sail towards it. Therefore the velocity component of the ship relative to the mirror installation would be very near zero.

Not if they attacked with the wind at their backs.

 

[Gigabob]

Great inspiration and execution. Most forget how much of a genius Archimedes really was. in addition to the physical accomplishments that survived - it now seems apparent that he was the first to discover the derivative in calculus - which he used to measure volumes with.

Archimedes made several engines for Syracuse Defense Industry, so called SDI. In addition to the large claw used to lift ships out of the water, catapults and bellows to shoot Greek Fire on Roman ships and then focus large mirrors to concentrate Mediterranean Sun which may have accelerated burning sails, rope and pitch used on nearly stationary ships during the long siege.

 

[Endymio]

Not if they attacked with the wind at their backs.

Um, what? The wind velocity and direction is irrelevant here. If you're moving directly *towards* a point, then your velocity component normal to that vector is zero.

What you've described is still called a mirror. And they were still expensive objects even without glass. Highly polished and smooth metal plates (eg. Discs) without any glass were used as mirrors and they were expensive to produce.

The point you're missing is that you don't need a highly pure or highly polished disc of metal. We're not working with the diffraction-limited case here, so *any* reflective object works. Archimedes unquestionably understood conic sections such as parabolas. Create a large enough parabolic form made of wood and coat it with nothing but plain white beach sand, and you can focus enough sunlight to start fires and even cut metal.

 

[Endymio]

Great inspiration and execution. Most forget how much of a genius Archimedes really was. in addition to the physical accomplishments that survived - it now seems apparent that he was the first to discover the derivative in calculus - which he used to measure volumes with.

This is a stretch entirely too far. Archimedes methods were entirely mechanical, case-by-case calculations of progressing sums. While they resemble the methods used in differential (and integral) calculus, all the basic mathematical foundations of calculus are missing. Newton and Leibniz deserve the credit, and properly so.

Also, as an aside: you measure volumes with integral methods, not derivatives. Archimedes used a derivative-like method to calculate tangents, and an integral-like method to calculate areas of conic sections and volumes of conic solids.

 

[Bluescreendeath]

The point you're missing is that you don't need a highly pure or highly polished disc of metal. We're not working with the diffraction-limited case here, so *any* reflective object works. Archimedes unquestionably understood conic sections such as parabolas. Create a large enough parabolic form made of wood and coat it with nothing but plain white beach sand, and you can focus enough sunlight to start fires and even cut metal.

The point you're missing is the difference between recreating something in a perfect laboratory condition (eg. something being theoretical possible if all the stars align) VS something actually making enough sense to use and working in reality.

The Mythbusters used a lot of highly reflective mirrors to try to set a ship on fire and found out you need a sunny day, clear & cloudless sky, no rain, no wind, no movement of the object (eg. no waves moving the ship up and down), the object has to be upclose, etc. Only then can you set something on fire after focusing all of those mirrors on the perfectly still wood for several minutes in absolutely perfect weather and wave conditions.

The less reflective item you use (eg. white sand vs an actual mirror), the much greater size and quantity of those reflect items will be needed to generate enough energy to set something on fire...and the bigger something is needed, it becomes exponentially more and more impractical.

So sure, you can hypothetically get enough shiny enough objects to reflect enough light to set things on fire if everything is under perfect laboratory conditions where the wood is up-close to you, perfectly stationary with zero movement, the sky is sunny and cloudless, no wind or rain, the ship doesn't contain anybody on it trying to shoot back at you or trying to put out the fire, etc etc etc.

That's why it's a myth. It's completely impractical even if someone decided to waste their money, manpower, and resources to create such objects and get people to man it. Throwing a pot full of flammable materials onto a ship from some type of catapult or by even by hand (from a wall) or shooting flaming arrows at a ship is significantly easier, cheaper, and more effective.

As for what Archimedes understood, sure he probably understood how things like it worked. That's likely why he didn't bother trying to actually create one due to how impractical it is since there are no contemporary historical sources claiming he ever tried to make a death ray. All of those death ray legends comes many centuries after he had long died.

 

[Endymio]

The Mythbusters used a lot of highly reflective mirrors to try to set a ship on fire and found out you need a sunny day, clear & cloudless sky, no rain, no wind, no movement of the object (eg. no waves moving the ship up and down), the object has to be upclose, etc. Only then can you set something on fire after focusing all of those mirrors on the perfectly still wood for several minutes in absolutely perfect weather and wave conditions.

You realize Mythbusters is an entertainment show, right? Some of their segments are accurate, others -- including this one -- are based on a number of false premises. One is that Bushroe used a single dish, whereas a number of smaller, widely spaced dishes would have a far larger effective aperture (similar to the principle by which radio telescope arrays work). Another is the assumption that, to be effective, you must set a thick piece of lumber instantly on fire -- when ships of the period were waterproofed with highly-flammable tar, and contained large quantities of hemp rope and canvas sails.

Does this mean Archimedes' death ray actually existed? No -- the story is likely apocryphal -- but not because "Mythbusters says so".

 

[Bluescreendeath]

You realize Mythbusters is an entertainment show, right? Some of their segments are accurate, others -- including this one -- are based on a number of false premises. One is that Bushroe used a single dish, whereas a number of smaller, widely spaced dishes would have a far larger effective aperture (similar to the principle by which radio telescope arrays work). Another is the assumption that, to be effective, you must set a thick piece of lumber instantly on fire -- when ships of the period were waterproofed with highly-flammable tar, and contained large quantities of hemp rope and canvas sails.

Does this mean Archimedes' death ray actually existed? No -- the story is likely apocryphal -- but not because "Mythbusters says so".

You do realize that while they are an entertainment show, their staff has background experience in engineering, animatronics, pyrotechnics, etc and they use engineering and experimentation? Them being an entertainment show does not invalidate their actual experimentation showing how impractical the idea is.

The mythbusters tested both a single reflector and multiple reflectors because they actually tested the myth twice.

A single dish has to be huge and is expensive but worked better in the test under perfect weather and wave conditions. Multiple dishes require difficult coordination from a lot of people manning the devices and failed to do much in the older test.
While the single dish was able to set some small parts of the ship on fire over time under perfect weather/wave conditions, they found throwing flaming objects at the ship was far more effective at setting it on fire.

While ships do contain flammable materials lile tar, the wood and other materials would also have a high mositure content due to constantly being in the water (near and below the waterline) and around evaporating & splashing water (above the waterline). So the wood on a ship that has been in the water would be significantly harder to ignite than a plank you buy at a hardware store that has been dried.

Furthermore, if the wood doesnt ignite instantly (like in the tests even when they were using dry wood in a newly built ship) and only create small fires slowly over time, then soldiers and sailors can easily put out the fire.

And as I mentioned above, there are zero contemporary or 1st hand sources mentioning the death ray and all mentions to it comes centuries after the death of Archimedes

Mythbusters tried to recreate it and even in the best case situation, the entire thing is impractical. So it is implausible due to experimentation showing how impractical it is, not because they "said so."

You spend tens of thousands of dollars building that thing and even under perfect weather and wave conditions (where the slight imperfection in conditions will make it nearly useless), it was less effective at setting the ship on fire than throwing a few bottles of flaming moltov cocktails that cost $10 or less a piece.

IIRC, I read the entire story could have been misinterpreted where the mirrors were actually used to just used to distract/disorient enemy sailors on the ships while defenders used more practical weapons like flaming pots to set fire to the ships...and later this story was mixed up and confused into mirrors setting fire to the ships.

 

[Endymio]

Them being an entertainment show does not invalidate their actual experimentation

Correct. It's the mistakes in this particular experiment that do that.

Multiple dishes require difficult coordination

Err, no they don't. How hard is it to point a dish at a ship? Furthermore (and this is the mistake Mythbusters made) if you have a large number of reflectors, they can be flat, rather than parabolic dishes. The parabola is contained within the arrangement of objects itself. In fact, if you *don't* do it in this manner, then there's no advantage to multiple dishes over a single, large one, as the effective aperture is no greater than that of any single dish.

While ships do contain flammable materials lile tar, the wood and other materials would also have a high mositure content due to constantly being in the water

The entire history of naval warfare proves you wrong. The portions above water burn like tinder, and, while the submerged sections are a different story, naval records include countless incidents of ships "burning to the waterline."

In counterpoint to Mythbusters, I give you this:

"... in 1973 [a] Greek engineer undertook his own experiment to get to the bottom of Archimedes' death ray. He assembled 70 soldiers, each holding a 5-feet by 3-feet (1.5-m by 0.9-m) mirror. The concentrated beam reflected by the mirrors set a row boat 160 feet (49 m) offshore aflame. It is possible, then, that Archimedes' death ray could have worked...."

I've looked for details on this particular event without success, but it seems unlikely this engineer arranged his soldiers in a parabolic line, which would have dramatically increased the overall effectiveness.

 

[Bluescreendeath]

Err, no they don't. How hard is it to point a dish at a ship? Furthermore (and this is the mistake Mythbusters made) if you have a large number of reflectors, they can be flat, rather than parabolic dishes. The parabola is contained within the arrangement of objects itself. In fact, if you *don't* do it in this manner, then there's no advantage to multiple dishes over a single, large one, as the effective aperture is no greater than that of any single dish.

You're not simply pointing a mirror at a motionless ship. When dealing with multiple mirrors, you're pointing at a tiny spot on the ship and everyone else has to point at the exact same spot. Everyone also has to coordinate their movements carefully for any slight movement

The Mythbusters tired both one large single reflector and multiple smaller ones. Yes, the larger single reflector is better as you remove the issue with having to coordinate multiple people at once. Though the large one requires a much more expensive and more complicated setup.

The entire history of naval warfare proves you wrong. The portions above water burn like tinder, and, while the submerged sections are a different story, naval records include countless incidents of ships "burning to the waterline."

The entire history of naval warfare proves you wrong by never recording anybody using mirrors to light other ships on fire in any first hand accounts or primary source historical records.

Yes, ships can burn above the waterline...and those portions of the water that burn are burnt with practical weapons like pots filled flammable materials, flamethrowers, and gunpowder weapons.

However, a mirror setup that already has a hard time slowly burning perfectly dry wood of a freshly built ship under the absolute perfect weather and wave conditison will have an even harder time burning wood exposed to moisture like those on a ship.

In counterpoint to Mythbusters, I give you this:

"... in 1973 [a] Greek engineer undertook his own experiment to get to the bottom of Archimedes' death ray. He assembled 70 soldiers, each holding a 5-feet by 3-feet (1.5-m by 0.9-m) mirror. The concentrated beam reflected by the mirrors set a row boat 160 feet (49 m) offshore aflame. It is possible, then, that Archimedes' death ray could have worked...."

I've looked for details on this particular event without success, but it seems unlikely this engineer arranged his soldiers in a parabolic line, which would have dramatically increased the overall effectiveness.

Yes, I've seen that account. No mention of how long it took them to burn the motionless ship, how big was the fire, ship construction/what part was set on fire, weather & wave conditions, how many tries it took (the Mythbusters tried many times in their first attempt to even get proper coordination between the multiple mirrors before they moved to a single giant mirror in their second attempt), etc.

So no way to gauge how practical it was (eg. they could've tried every day for a week and finally after a hundred attempts they got a part of the perfectly motionless ship to burn after concentrating the mirrors on one spot on a hot & sunny & cloudless & windless & waveless day).

 

[Endymio]

When dealing with multiple mirrors, you're pointing at a tiny spot on the ship and everyone else has to point at the exact same spot.

But not a random spot. It's not difficult to tell people to aim at the mainsail clew or the tarring of the foremast.

...a mirror setup already has a hard time slowly burning perfectly dry wood of a freshly built ship under the absolute perfect weather and wave conditions...

I'm not sure why you keep harping on this "weather and wave" conditions nonsense. You realize that a full-scale warship loaded with hundreds of men isn't going to bob about on the waves like the toy boat Mythbusters used, right? And no sane military commander orders his ships to land on even a friendly coast during foggy or bad weather conditions, much less an enemy one.

Mythbusters didn't even use a parabolic dish for their reflector (the tensioning system Bushroe employed results in a less efficient catenary curve), much less align their multiple reflectors on a parabolic curve.

You can go online now and find videos of people using small (1.5meter) dishes to set solid wood on fire in under one second's time. And in the case of a warship, you don't even need to target solid lumber -- sails, hemp rope, and pitch tarring burn far easier.

Yes, ships can burn above the waterline...and those portions of the water that burn are burnt with practical weapons like pots filled flammable materials

So you admit the "ships are too waterlogged to burn" bit was incorrect?

 

[Bluescreendeath]

But not a random spot. It's not difficult to tell people to aim at the mainsail clew or the tarring of the foremast.

It doesn't have to be a random spot for coordination of multiple mirrors to be difficult.
Did you watch the Mythbusters first test of trying to coordinate multiple people to aim at the same spot? It was very hard, and even small variations where someone's aim was off by a few centimers or inches caused the rays to not line up and vary greatly when it reached the target.

The clew and tarring of the foremast isn't a tiny spot. You're talking about something that can be several square feet in area. The beam of light from those mirrors however will have a small focal point of several inches across. By saying something like focus on the mainsail cleft, you're already dispersing those beams across several feet of area when they should be focusing on a tiny spot few inches across. And even if you gave very specific instructions, a person moving a mirror even a few centimeters in either direction could greatly throw off the location of the beam by several feet when it hits the target if the target is 100+ foot away.

I'm not sure why you keep harping on this "weather and wave" conditions nonsense. You realize that a full-scale warship loaded with hundreds of men isn't going to bob about on the waves like the toy boat Mythbusters used, right? And no sane military commander orders his ships to land on even a friendly coast during foggy or bad weather conditions, much less an enemy one.

Why do you hold onto the ideal conditions nonsense that a ship in the water is going to be perfectly still during a perfectly clear & sunny day while the crew waits around for you to slowly burn their ship?

If the ship's sail is up for you to burn, then even the slightest breeze will cause the ship to be moving. Hence, whether there is wind is important. If the ship is going towards a harbor to land, the ship will obviously be moving via its sails or rows. And you do realize a warship loaded with men is going to be MOVING and putting out small fires? They are not going to be waiting perfectly still and doing nothing for the enemy to set them on fire. And while a large warship won't be bobbing up as much as a small ship, it will still move bob around a few inches at a time due to waves - which is enough to throw off the narrow focal point of the beam that is a few inches in circumference to prevent it from precisely being locked onto one spot.

And it's almost as if you didn't even watch the Mythbusters episodes. You don't need "bad weather" or foggy conditions to invalidate the beam. Even a good weather day with some clouds that cover up the sun will make the beam useless. This was seen in the Mythbuster experiment. A clear day with some light rain will also make the beam useless. A clear day with no fog but gray skys will neuter the beam. And anything at dawn or dusk when there is significantly less sunlight, then the beam is also neutered.

You think a military commander is afraid of landing a ship during a clear day if there are some clouds in the sky, if the sky is grey, if there is some wind, etc?

You need a perfect day of sunny & clear skies, no clouds, no wind, no grey skies, and no rain for this thing to work. And that also includes the crew of the ship waiting around like *****s and not moving the ship at all and not bothering to put out any fires while they are being attacked by this mirror beam.

Mythbusters didn't even use a parabolic dish for their reflector (the tensioning system Bushroe employed results in a less efficient catenary curve), much less align their multiple reflectors on a parabolic curve.

You can go online now and find videos of people using small (1.5meter) dishes to set solid wood on fire in under one second's time. And in the case of a warship, you don't even need to target solid lumber -- sails, hemp rope, and pitch tarring burn far easier.

You mean those videos where they have to put targets a few inches away from the parabolic mirror?

The thing about concentrating more light in a parabolic dish and in other types of curves with steeper angles is that they focus the light at a closer and closer point, which means their range gets shorter and shorter. Greenpowerscience has a video with a ~4 foot wide parabolic mirror and the creator has to hold an object right up close to the mirror (like a foot away) for it to start cooking/burning.

So sure, that will work if you put the parabolic mirror right up close to the ship. If you scale up a parabolic mirror, you're still dealing with very close distances. At that very close distance, someone can just chuck a spear at you or throw a rock at you (let alone use their own bows or ship artillery).

So you admit the "ships are too waterlogged to burn" bit was incorrect?

Except I never said waterlogged wood and/or wet wood is impossible to burn. I said it was harder to burn.

This is what I actually wrote above (which you left out in your quote):

"While ships do contain flammable materials lile tar, the wood and other materials would also have a high mositure content due to constantly being in the water (near and below the waterline) and around evaporating & splashing water (above the waterline). So the wood on a ship that has been in the water would be significantly harder to ignite than a plank you buy at a hardware store that has been dried."

Do you see the words "significantly harder" in that sentence when I said wet wood is significantly harder to burn?

The words "significantly harder" does not mean "impossible."

Do you admit that wood with a higher mositure content is significantly harder to burn than dry wood?