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Post by the light works on Oct 19, 2013 13:40:21 GMT
let me repeat the weight of the motor: "keep in mind a stock Chevy 350 V-8 weighs around 575 pounds. Read more: citadelofmyths.freeforums.net/thread/775?page=4&scrollTo=27631#ixzz2iARQINNK" so in Australia a pivot defined as a point that moves while the rest of the structure remains in the same alignment around it. in America a pivot is defined as a point that remains stationary while the rest of the structure rotates around it. that must be the source of the misunderstanding. and no, it is not a sled, it is a boat that happens to float on whatever surface it happens to be on whether it is water, dirt, mud, rocks, tree trunks, or asphalt; because it runs over the surface. and yes, it is small, it is only big enough to carry 18 people plus the motor and propeller. The figures you quote for the motor are those you quoted earlier. A pivot point, in the present case. The wheels support the cannon via the axles the limber supports the cannon to the rear at d distance above the plane of the deck. The force of the firing is in a parallel plane to the deck (for maximum transfer of energy) but the gun cannot move backward so all the force is transferred to the limber which will try to rotate about the axis of the axle. yes, they are; since you seem to have gotten confused between the cylinder displacement and the weight; I repeated the post, so you could see that I had said a 350 CID motor weighs in the neighborhood of 600#. why can the gun not move backwards? the recoil will press against the limber, which is secured to the boat, as well as the wheels. my prediction is that while it will try to rock the boat forward, the prow of the boat will prove plenty adequate for the boat to skim forward, instead of rotating; particularly if you install the mounting system in such a way that the weight of the cannon is properly located just aft of the boat's center of balance. |
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Post by privatepaddy on Oct 19, 2013 14:03:02 GMT
The figures you quote for the motor are those you quoted earlier. A pivot point, in the present case. The wheels support the cannon via the axles the limber supports the cannon to the rear at d distance above the plane of the deck. The force of the firing is in a parallel plane to the deck (for maximum transfer of energy) but the gun cannot move backward so all the force is transferred to the limber which will try to rotate about the axis of the axle. yes, they are; since you seem to have gotten confused between the cylinder displacement and the weight; I repeated the post, so you could see that I had said a 350 CID motor weighs in the neighborhood of 600#. why can the gun not move backwards? the recoil will press against the limber, which is secured to the boat, as well as the wheels. my prediction is that while it will try to rock the boat forward, the prow of the boat will prove plenty adequate for the boat to skim forward, instead of rotating; particularly if you install the mounting system in such a way that the weight of the cannon is properly located just aft of the boat's center of balance. Take a toy car hold the wheels of an axle firmly between between two fingers and so that the body of the car is free to rotate push on the top front of the car. |
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Post by the light works on Oct 19, 2013 14:19:37 GMT
yes, they are; since you seem to have gotten confused between the cylinder displacement and the weight; I repeated the post, so you could see that I had said a 350 CID motor weighs in the neighborhood of 600#. why can the gun not move backwards? the recoil will press against the limber, which is secured to the boat, as well as the wheels. my prediction is that while it will try to rock the boat forward, the prow of the boat will prove plenty adequate for the boat to skim forward, instead of rotating; particularly if you install the mounting system in such a way that the weight of the cannon is properly located just aft of the boat's center of balance. Take a toy car hold the wheels of an axle firmly between between two fingers and so that the body of the car is free to rotate push on the top front of the car. okay, yes, if you bury an anchor on each side of the test trench, and use heavy chains to chain the axle to those anchors, then the gun will react as you say. now put the toy car onto a cookie sheet. set the cookie sheet on a table. use tape or something to make sure the toy car does not move around on the cookie sheet. NOW push on the top front of the car. does it still rotate around the axle? are you trying to turn this into another POAT thread? you float a boat on water. you secure a gun to the boat. you fire the gun. does the gun apply torque to the boat or does it apply thrust to the boat? it depends on the design of the boat and the location of the gun. if it is a displacement hull, as a traditional sailing vessel, then it applies torque, because it is pushing against the resistance of the water, and a significantly more massive hull. if it is a full planing hull, then it SHOULD apply thrust to the boat if the boat has enough surface area to allow it to ride on plane instead of plowing through the water; and is light enough that inertia is not a significant factor. I can understand this even if I cannot do the math or apply all the correct names to all the lines in the diagram. this leads me to suspect that you would understand it as well, if you were not so eager for me to be wrong. |
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Post by Cybermortis on Oct 19, 2013 15:33:09 GMT
Airboats are shallow drafted boats that only plane when they get up to speed.
It is unclear as to exactly how much draft an airboat has at rest, since that would depend on the overall weight of the boat. The figures I've seen appear to be around 2-4 inches. I'm guessing that you'd see around 4-6 inches with a six pounder cannon plus the additional reinforcement needed to protect the hull. (This shouldn't be a problem as it seems that the sides of an airboat are 10 inches high, and we're not talking about trying to take this thing to sea.)
So you will always get inertia and resistance from the water, especially if the thrust is applied all at once as water is not compressible.
Picture a cannon sitting on an airboat and tied in place with thick string.
If you pushed on the cannon you would, eventually, get the boat to move backwards and once it was moving it would be fairly easy to keep it moving. The string would remain intact and the gun is going to stay where it is.
Now imagine the same set up, but instead of pushing on the gun you decide to give it the same amount of energy as needed to push it a certain distance, but by hitting the gun once with a massive hammer. The force would snap the string, the cannon would go flying backwards and the boat is going nowhere, except possibly downwards as the cannon rips the stern of the boat apart.
Because there is not enough room to allow it to do so - note both the distance the gun in the linked footage moved and that its carriage bleeds off the momentum by digging into the ground. On a smooth surface, such as the deck of a boat, such a gun would recoil even further. Far enough that its going to hit the stern with a lot of force.
Besides, if the gun is allowed to move backwards then the thrust from the discharge is going into moving the gun over the deck with little or none of that energy going into moving the boat. Any movement would be due to the weight of the gun shifting not the recoil itself.
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Post by User Unavailable on Oct 19, 2013 17:37:05 GMT
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Post by the light works on Oct 19, 2013 19:36:12 GMT
Airboats are shallow drafted boats that only plane when they get up to speed. It is unclear as to exactly how much draft an airboat has at rest, since that would depend on the overall weight of the boat. The figures I've seen appear to be around 2-4 inches. I'm guessing that you'd see around 4-6 inches with a six pounder cannon plus the additional reinforcement needed to protect the hull. (This shouldn't be a problem as it seems that the sides of an airboat are 10 inches high, and we're not talking about trying to take this thing to sea.) So you will always get inertia and resistance from the water, especially if the thrust is applied all at once as water is not compressible. Picture a cannon sitting on an airboat and tied in place with thick string. If you pushed on the cannon you would, eventually, get the boat to move backwards and once it was moving it would be fairly easy to keep it moving. The string would remain intact and the gun is going to stay where it is. Now imagine the same set up, but instead of pushing on the gun you decide to give it the same amount of energy as needed to push it a certain distance, but by hitting the gun once with a massive hammer. The force would snap the string, the cannon would go flying backwards and the boat is going nowhere, except possibly downwards as the cannon rips the stern of the boat apart. Because there is not enough room to allow it to do so - note both the distance the gun in the linked footage moved and that its carriage bleeds off the momentum by digging into the ground. On a smooth surface, such as the deck of a boat, such a gun would recoil even further. Far enough that its going to hit the stern with a lot of force. Besides, if the gun is allowed to move backwards then the thrust from the discharge is going into moving the gun over the deck with little or none of that energy going into moving the boat. Any movement would be due to the weight of the gun shifting not the recoil itself. so let me get this straight - if the gun installation is properly designed, then when you fire the gun, it will remain still and the boat will shoot out from under it, dropping it into the water. let me be absolutely clear: I am talking about the gun doing this except with a boat bolted to the bottom of it. to make it absolutely clear what I am talking about I am also putting in this clip that at the end of the sequence shows the gun being prevented from moving backward. |
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Post by Cybermortis on Oct 19, 2013 20:39:17 GMT
No...that isn't even remotely what I was saying.
What I was saying was that to PREVENT the gun from flying backwards, and to ensure that as much of the recoil force as possible is passed onto the boat, the gun has to be securely attached to the boat with as little movement as possible.
Boats that have mounted guns on them have always either used very small guns that had little recoil, or have used gun carriage designs that absorb much of the recoil energy - usually both. This is because even a 28 foot long ships boat that was quite capable of sailing several thousand miles over open ocean would be seriously damaged if not sunk if it tried to fire a four or six pound cannon it was carrying, no matter how well it was secured.
Here we don't want the recoil to be absorbed by anything other than the boat, so however the gun is secured it has to be as immobile as possible. The catch is that doing this places huge stresses on the connection between boat and gun, and on the structure of the boat overall - its not a question of the total energy being placed into the system. Rather it is the fact that all that energy is arriving in the same instant, and that spike in energy is what will overload and damage the various structural elements.
That spike also causes problems to the idea of the boat gliding over or through the water, since water is incompressible it will provide far more resistance that you'd think. (If this was not the case then any warship that fired a broadside would have moved sideways).
The only type of vehicle that would have almost zero resistance would be a hovercraft...which does raise the interesting possibility of them building a fairly basic hovercraft and seeing how far gunfire could move it. Just for fun of course...you've got to wonder what would happen if you fired a punt gun on a hovercraft....
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Post by the light works on Oct 20, 2013 1:17:56 GMT
No...that isn't even remotely what I was saying. What I was saying was that to PREVENT the gun from flying backwards, and to ensure that as much of the recoil force as possible is passed onto the boat, the gun has to be securely attached to the boat with as little movement as possible. Boats that have mounted guns on them have always either used very small guns that had little recoil, or have used gun carriage designs that absorb much of the recoil energy - usually both. This is because even a 28 foot long ships boat that was quite capable of sailing several thousand miles over open ocean would be seriously damaged if not sunk if it tried to fire a four or six pound cannon it was carrying, no matter how well it was secured. Here we don't want the recoil to be absorbed by anything other than the boat, so however the gun is secured it has to be as immobile as possible. The catch is that doing this places huge stresses on the connection between boat and gun, and on the structure of the boat overall - its not a question of the total energy being placed into the system. Rather it is the fact that all that energy is arriving in the same instant, and that spike in energy is what will overload and damage the various structural elements. That spike also causes problems to the idea of the boat gliding over or through the water, since water is incompressible it will provide far more resistance that you'd think. (If this was not the case then any warship that fired a broadside would have moved sideways). The only type of vehicle that would have almost zero resistance would be a hovercraft...which does raise the interesting possibility of them building a fairly basic hovercraft and seeing how far gunfire could move it. Just for fun of course...you've got to wonder what would happen if you fired a punt gun on a hovercraft.... funny you should mention that. the interwebz says the muzzle velocity you can expect from a six pounder is between 1000 and 2000 FPS, (depending on model) and the light ones as having a curb weight of around 1700 pounds. given an additional 300 pounds for the boat hull, to make for easy math, that would mean in a frictionless environment, throwing a 6 pound ball forward at 1000-2000 FPS should throw the cannon and boat back at 3-6FPS. (assuming my math is correct) which is in the neighborhood of 2-4 MPH. (in the neighborhood meaning I used the most simple math and rounded to the nearest MPH) so theoretically, the effect of firing the gun with the carriage rigidly anchored to the boat would apply the same shock loading as running the boat into an unyielding object at 2-4 MPH. or running head on into another boat at (if I remember the head on vs wall episode correctly) 2-4 MPH EACH. |
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Post by privatepaddy on Oct 20, 2013 3:09:19 GMT
I imagined a set up similar to the last link you provided re the sled. IIRC there is something called ground effect in aerodynamics, it acts as a multiplier in lift. If I am correct the lower the cannon is to the waterline the more effective it should be. Interesting links by the way. |
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Post by privatepaddy on Oct 20, 2013 3:39:07 GMT
Take a toy car hold the wheels of an axle firmly between between two fingers and so that the body of the car is free to rotate push on the top front of the car. okay, yes, if you bury an anchor on each side of the test trench, and use heavy chains to chain the axle to those anchors, then the gun will react as you say. now put the toy car onto a cookie sheet. set the cookie sheet on a table. use tape or something to make sure the toy car does not move around on the cookie sheet. NOW push on the top front of the car. does it still rotate around the axle? Are you under the misapprehension that you cannot have static torque? Why would you say that? surely you don't want to bring that here. Or is your intent to sling shi........... stuff again normally yes although is it possible to float it on liquid nitrogen? Nope you clearly do not understand the concept of static torque I am trying to explain to you how your idea of a gun carriage including the force multiplying limber is going to effect the outcome. Also there is absolutely no reason you "cannot do the math or apply all the correct names to all the lines in the diagram" The WWW has it all. |
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Post by silverdragon on Oct 20, 2013 8:58:00 GMT
Fail.
Sorry, I just cant do that....
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Post by silverdragon on Oct 20, 2013 9:22:17 GMT
Some serious thinking through here.
First, what about recoil.
Recoil we need to "Harvest" as the propulsion for this craft, so we cant dampen it, but we CAN use a shock-absorber, such a s forklifting BIG spring.
As mentioned before, I am just chucking in ideas here....
But wasnt this the original idea that bought us recoilless weaponry?...
To divert the recoil into a slower more gentle push that a rigging hard SHOVE.
If we had a BIG spring, bungee or whatever type here, with multiple anchor points to the transom, would that not give the right thrust in the right direction on the right part of the boat designed to harvest thrust?...
I am thinking BIG long deep U-Bar affixed to top of transom, end to end, with chains attached that would spread thrust all the way along the transom....
Onward, someone mentioned gun "Sledge"....
Ok, so, Rocket sledge anyone?...
Can the go to that rocket sledge test track and replace the rockets with some big-donky-cousin-barrel gun and let 'em rip, see how far the equal and opposite reaction chucks a sledge down the track?....
Less chance of it sinking at this point.
I dont think any gun owner is going to mind having their precious gun solidly strapped down (Road transport wise) to a big sledge for test firing purposes, are they?....
Moving on, can I say rowlocks to you all.
(I think I just did?.. hows THAT for cross thread pollution, and free speech....)
Rowlocks on any rowed craft are designed to take a heck of a lot of thrust, I have done some digging, and found that the mounting point for a punt gun is no more or less than a fettled rowlock ... it took some of the recoil, the rest going through the person firing the gun in prone position to his feet and specially placed boards into the frame of the craft...
The floor of a punt is heavily redesigned when adding a Punt Gun, to accommodate seating whilst paddling and comfortable position lying down with legs and feet under the rear decking.
Extra strengthening needs adding for that.
My digging by the way is visiting someone I know who owns a chandlers shop (Marine supply) and asking him... he has some deep knowledge of the unexpected when it comes to all craft used on inland waterways, and he is one of the only persons I know who can strip down and rebuild a single cylinder "Bollinder" diesel engine without the need for manuals.
As always, any excuse to talk to him is a good one....
He knew someone who knew someone who had a Punt Gun.....
He is trying to contact them?
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Post by silverdragon on Oct 20, 2013 9:31:58 GMT
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Post by privatepaddy on Oct 20, 2013 9:52:12 GMT
Some serious thinking through here. First, what about recoil. Recoil we need to "Harvest" as the propulsion for this craft, so we cant dampen it, but we CAN use a shock-absorber, such a s forklifting BIG spring. As mentioned before, I am just chucking in ideas here.... But wasnt this the original idea that bought us recoilless weaponry?... To divert the recoil into a slower more gentle push that a rigging hard SHOVE. If we had a BIG spring, bungee or whatever type here, with multiple anchor points to the transom, would that not give the right thrust in the right direction on the right part of the boat designed to harvest thrust?... I am thinking BIG long deep U-Bar affixed to top of transom, end to end, with chains attached that would spread thrust all the way along the transom.... All guns recoil (barrels) that I know of except for 105 mm recoilless rifle, legend had it when I was a cadet (aus army) they mounted it on a land rover fired it what fell off stayed off. It was advised you did not stand behind it when it was fired as some of the gasses vented out of the breach to make it "recoil less". By using a spring/recoil mech you are in effect storing energy to return the gun to its firing position without affecting its firing orientation or reducing the affect. In the present scenario this energy is lost to propulsion. But depending on the shear forces on the mounting some form of damping may be required. As a side myth or test concept a sledge mounted on a rail track is not a bad idea, it may even have similar characteristics to its water based equivalent. (trying not to sound to much like Cyber) I believe testicles* is a word that causes concern,,,,, and hey it has one cylinder what could possibly go wrong  {*Mod note; Yes the word you originally posted would cause concern as it is a profanity in British-English. That word has been added to the censored word list - although I suspect that neither SilverDragon or myself, who are both British, would take offence - which is why your post ended up getting auto-modded. It was just one of those words I neglected to add to the list for some reason. Probably because it isn't used in American-English - CM} |
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Post by silverdragon on Oct 20, 2013 10:41:10 GMT
Yes, and I am using that technology in my suggestions... The 7.62 SLR I am well trained in using (Which gives some indication to my age at the start of training...) used the recoil to re-load the weapon. I suggest "Up-Scaling" the technology of recoilless weaponry, or reduced recoil weaponry, to harvest the recoil and deliver it in a slower less destructive force for propulsion?.... We dont want the barrel to return to its previous position, more rather we want the vehicle it is attached to to catch up with it?.... Does that answer the suggestion in a sensible way?... This may require testing to work out what strength of "Spring" is required to provide vehicle motion before thrust is lost due to barrel returning..... As in, the ideal would be that the barrel shoots back, and stays stationary whilst vehicle accelerates to a catch-up position.... Is that making sense?... That is easy to replicate, take a force gauge to "The" boat and tow it forward. Replicate that force via some form of braking as necessary to the sledge to give an equal force to pull the sledge... I am believing at this stage that that would be almost identical results?.... plus or minus a little room for error..... As it only had one cylinder, and a two stroke diesel at that, the accepted and practised method of obtaining reverse was to slow the engine and "Kick", literally, the flywheel, in the opposite direction, to completely reverse the whole engine. Go wrong as in take your bloomin foot off.... But this was in the days before elf-and-safe-tea, so nay mither eh?... (You have to sign a disclaimer to operate these antique engines these days?... take your bit of paper and use it as a fire-lighter...) Starting the thing was an art. No warmer plugs, no pressure gauges, no technology, you warmed the cylinder head with a blow-torch to the right kind of glow, pumped the fuel by hand a few times, then kick the flywheel and hope it starts?.... without, obviously, having it explode..... But the sound of a slow "Bomp bomp bomp bomp bomp" was a reassuring low tech high mileage reliable low running cost engine that would outlast much modern crud if kept in good condition. (I think 600 rpm was overly fast...) And you get plenty of free hot water from it as well..... Edit, and possible side myth for discussion... I am led to believe it would run on "Anything" as well.... Diesel, Kerosene, light oil, petrol...... citadelofmyths.freeforums.net/thread/796/diesel-engine-multi-fuelAny further discussion in that thread to prevent thread pollution here. |
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Post by privatepaddy on Oct 20, 2013 11:07:18 GMT
Yes, and I am using that technology in my suggestions... The 7.62 SLR I am well trained in using (Which gives some indication to my age at the start of training...) used the recoil to re-load the weapon. I suggest "Up-Scaling" the technology of recoilless weaponry, or reduced recoil weaponry, to harvest the recoil and deliver it in a slower less destructive force for propulsion?.... We dont want the barrel to return to its previous position, more rather we want the vehicle it is attached to to catch up with it?.... Does that answer the suggestion in a sensible way?... This may require testing to work out what strength of "Spring" is required to provide vehicle motion before thrust is lost due to barrel returning..... As in, the ideal would be that the barrel shoots back, and stays stationary whilst vehicle accelerates to a catch-up position.... Is that making sense?... That is easy to replicate, take a force gauge to "The" boat and tow it forward. Replicate that force via some form of braking as necessary to the sledge to give an equal force to pull the sledge... I am believing at this stage that that would be almost identical results?.... plus or minus a little room for error..... As it only had one cylinder, and a two stroke diesel at that, the accepted and practised method of obtaining reverse was to slow the engine and "Kick", literally, the flywheel, in the opposite direction, to completely reverse the whole engine. Go wrong as in take your bloomin foot off.... But this was in the days before elf-and-safe-tea, so nay mither eh?... (You have to sign a disclaimer to operate these antique engines these days?... take your bit of paper and use it as a fire-lighter...) Starting the thing was an art. No warmer plugs, no pressure gauges, no technology, you warmed the cylinder head with a blow-torch to the right kind of glow, pumped the fuel by hand a few times, then kick the flywheel and hope it starts?.... without, obviously, having it explode..... But the sound of a slow "Bomp bomp bomp bomp bomp" was a reassuring low tech high mileage reliable low running cost engine that would outlast much modern crud if kept in good condition. (I think 600 rpm was overly fast...) And you get plenty of free hot water from it as well..... Edit, and possible side myth for discussion... I am led to believe it would run on "Anything" as well.... Diesel, Kerosene, light oil, petrol...... citadelofmyths.freeforums.net/thread/796/diesel-engine-multi-fuelAny further discussion in that thread to prevent thread pollution here. Had a chance to think about the spring, it needs a force to oppose the recoil otherwise the spring won't compress. |
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Post by silverdragon on Oct 20, 2013 11:18:46 GMT
I was thinking the other way, the gun fires and moves forward, stretching a spring(s) attached to the transom.....
Or Bungee cord, or something else, literally pulling the craft forward ....
The recoil is the whole part of the force we are trying to trap in the first place is it not?....
Trap as in harvest, use, transfer to forward motion as propulsion.....
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Post by privatepaddy on Oct 20, 2013 11:26:43 GMT
I was thinking the other way, the gun fires and moves forward, stretching a spring(s) attached to the transom..... will it? what's the opposing force? that allows the energy to be stored? |
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Post by silverdragon on Oct 20, 2013 11:34:29 GMT
Gun pointing backwards over the transom to fire to the rear of the boat.
I know Punt guns face forwards, but it seems generally accepted on this thread that the larger gun or cannon should face backwards and make use of the transom as an anchor point, as the transom is generally used as the anchor point for may engines, and therefore accepted as the strongest part of the boat?.......
So in mind the gun facing backwards will go forwards, if a bungee cord is attached to the gun and the transom, the recoil will "Pull" the boat forwards...?.. yes?...
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Post by privatepaddy on Oct 20, 2013 11:42:55 GMT
Gun pointing backwards over the transom to fire to the rear of the boat. I know Punt guns face forwards, but it seems generally accepted on this thread that the larger gun or cannon should face backwards and make use of the transom as an anchor point, as the transom is generally used as the anchor point for may engines, and therefore accepted as the strongest part of the boat?....... So in mind the gun facing backwards will go forwards, if a bungee cord is attached to the gun and the transom, the recoil will "Pull" the boat forwards...?.. yes?... Firing over the stern I concur, the way I would do it less drag going forwards than backwards. But the only reason to use a force modifier/damper would be to reduce the shear force on the cannon mounting structure. |
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