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# Ship Saw

A variation and competitor to the skipping disk catapult
 (+1, -2) [vote for, against]

This would be a stone disk launched in a vertical orientation at an oncoming trireme or other ancient invading ship. Rather than skipping across the water, it would roll towards the target being kept afloat by logs attached around the perimeter. Picture a paddle wheel from an old river boat made of a stone disk with only the outside being the floaty part.

I'd like to enter this design as a competitor to the skipping catapult if there's ever such a competition. I would propose that my variation would be more accurate due to the elimination of the bouncing and would cut the ships in half when they hit.

 — doctorremulac3, Sep 25 2011

Inspired by this Skipping_20sidearm_20catapult
When I grow up, I'd like to build both, test them against each other and make a documentary of the whole thing [doctorremulac3, Sep 25 2011]

Um. I could be wrong but I think you need more surface area in order to skip or roll on top of the water. This will sink and slow down very quickly.
 — 2 fries shy of a happy meal, Sep 25 2011

We suspect that the spinning disk is actually held clear of the water; in not, you are correct, drag will quickly stop it unless there is a substantial external power input.
 — 8th of 7, Sep 25 2011

 Well, the logs would be just long enough to supply the necessary surface area to keep the thing afloat and vertical. Remember, it's spinning very fast, and unlike the Wallace bomb, it's spinning in the direction of travel so the spin you impart to it would help it "roll" to some extent. The downward movment of the logs on the leading edge would act to lift the unit above the water as it rolled as well. I'd think a foot wide, six foot tall stone disk might have 3 foot long logs placed every couple of feet around the perimeter.

 As for a 3 ton stone disk traveling at 60 miles an hour bouncing off the side of a ship because of it's got logs acting as bumpers, I don't see that happening.

But it's this controversy that would make for a great reality show. The thing burning down, falling over and sinking into the swamp would be just as entertaining as it cutting a 3/4 scale ancient Roman warship in half.
 — doctorremulac3, Sep 25 2011

 A trireme, when ramming without intent to board, doesn't aim for the hull, but rather to shear along one side, shattering oars and maiming the oarsmen*. The same principle would apply here. Against ancient oared warships the rolling disk needn't cut anything, nor strike the hull.

*Not sure where I read this. Probably something by Gene Wolfe.
 — mouseposture, Sep 25 2011

I saw three ships...
 — MaxwellBuchanan, Sep 25 2011

 The rolling/floating business probably won't work. You'd be giving up all of the skipping across water advantages for a whole lot of floats, most of which aren't in use at any time. They would act as bumpers, probably, and might make the whole wheel just roll up and over the ship.

I'd make a stone disk, put some interesting lifting shapes around the rim, and spin it backward when I fired it out. That way you'd get the skipping business working twice as fast, and when it hit a ship, it would dig in and go downward, making some under the waterline damage.
 — baconbrain, Sep 25 2011

 I don't think several tons of stone hitting the ship hard enough to get airborn is going to leave that ship in floating condition. But if it's a clean cut you want, you could move the float logs a couple of feet in from the edge of the stone towards the center. Then they'd act like more of a floating axle.Then by the time the float logs hit the hull, the stone has already penetrated a couple of feet in.

 Like the backspin idea to make it go down though. I picture that actually lifting the ship up and cutting through the keel rendering 2 half ships out of 1 with a single shot.

 Don't know if it would work or not, but no other ancient weapon could split a ship in two like that. I'm thinking a fortress lined with these would probably be left alone.

Oh yea, and I'd soak them with Greek fire juice and light 'em before launch just for effect.
 — doctorremulac3, Sep 25 2011

 I don't think you could get the stone disc moving fast enough using ancient technology. Now days we could simply use a motor to impart this speed but there are few triremes to destroy it.

 Also, as noted earlier, there is a limit to the buoyancy you can achieve without a formal hull to displace sufficient water. Each log out of the water become an extra weight that has to compensated for so lengthening the log's won't work - it is the ratio of buoyant logs to burden logs that counts, even ignoring the weight of the stone.

However it is an interesting idea and I would love to have seen such devices used in the Ancient World.
 — Aristotle, Sep 26 2011

 Well, there's one thing about this idea that's intriguing. I think it would scale pretty accurately, that is, you could make a small model that would behave enough like a scaled up version to test the concept.

As for getting the speed up, if twisted ropes and such aren't enough, I was thinking of rolling these down a ramp or even the side of a cliff. Perhaps you could have 6 or 7 ramps going down the side of a cliff aimed in different directions. If the cliff were high enough, you might be able to get these things going 100 miles per hour or so.
 — doctorremulac3, Sep 26 2011

 I envision this as a floating wheel that rolls along the water. The only parallel I can envision are attempts, during float trips, to roll an unoccupied inner tube across an expanse of river such that it rolls onto an occupied tube. It is hard to roll an inner tube any distance across the water, and inner tubes are largely above the surface. Maybe they are not going fast enough / not firm enough.

However if you watch something rolling through water, or ride a bike at speed thru a puddle, you will be impressed by how much water moves as well - water that is drawn up by the passage of the wheel (low pressure next to moving surface?) and flung off circumferentially, but especially onto your back if you are riding the bike. Moving that water drinks kinetic energy.
 — bungston, Sep 26 2011

 Yea, thought of that too. This thing would throw up a pretty huge "rooster tail" as they call it in speed boating.

 That would sap lots of energy but it would certainly add to the show. Especially if the thing was on fire as well.

It's down to an issue of range. How far can you roll a 6 ton stone wheel on the water using logs placed around the perimeter or center? You'd probably be pretty safe saying "Not very" but you never know until you try.
 — doctorremulac3, Sep 26 2011

Maybe one could mount sails on either side of the axle and sail the rolling wheel around. You could roll it thru one trireme after another, then take it up along the beach to roll thru the ones that thought they would be safe if they pulled up out of the water. Sort of a bronze age amphibious assault vehicle.
 — bungston, Sep 26 2011

 Sounds like it would be picturesque at least.

 I feel like there's a definate calling for a show called "Modern DaVincis" where people come up with stuff DaVinci might have invented using the materials and technology of the day.

Hmm.
 — doctorremulac3, Sep 26 2011

A waterborn version of their Buzzsaw from Emperor Battle for Dune. The Harkonnen like.
 — RayfordSteele, Sep 26 2011

I'm thinking that even if some of these things didn't work in real life they'd make for great movie props.
 — doctorremulac3, Sep 26 2011

The Wild Wild West meets Pirates of the Caribbean perhaps.
 — RayfordSteele, Sep 26 2011

The words 'great pandjandrum' spring to mind...
 — Alterother, Sep 27 2011

A certain kind of mind, yes.
 — mouseposture, Sep 28 2011

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