Punt Gun Possibilities

In both cases you are dealing with a massive amount of thrust being delivered in a fraction of a second, rather than spread over a slightly greater period. This influx of energy has the potential to cause elements of the vessel to fail under the strain, so ways need to be found to reduce the amount of energy being delivered.

This differs from conventional engines, which produce thrust over a much greater length of time which makes it a lot easier for the structure to handle the forces involved. A sailing ship, for example, would never drop all her sails at once even in a fairly light breeze, as the sudden burst of energy would most likely damage the yards, masts and rigging.

For the pulse-propulsion design the weakest part is the squishy human, but controlling the force is 'easier' as the propellant force is being produced by an external explosion. So you can control the amount of energy being delivered by having the explosive detonate further away from the craft.

In our 'gun boat' we don't have to worry about a squishy human, only the frame and structural strength of the boat. Unfortunately this is complicated because the propellant force is being produced by something connected to the boat but not part of it. We not only have more mass to shift, but have to realise that the 'engine' is going to possess greater momentum than the boat. It is this momentum that is the cause for concern as the momentum is going to dump energy through its mounting into the boats frame in an effort to balance the system. So the connection between gun and boat, and the part of the frame, has to be capable of handling a considerable amount of energy or it will fail.

We could include recoil dampening systems in the boat, but such systems are intended to limit the amount of energy passed onto the firing platform. Here we need as much energy as possible to be passed directly onto/into the boat as this is the energy that will be used to move it.

I was taught that energy can be neither created nor destroyed; but only change form; so unless the recoil damping system discharges propellant gases from the back to oppose the recoil, all the damping system does is prolong the thrust, while attenuating the "impact" of the thrust.

well, that answers that question quite thoroughly. I take it you also haven't sailed much.

yep. here should be a fair to good market for used airboats in the areas that use them.

or buy a replica cannon. I'm sure somebody makes them it can't be that EVERY civil war recreationist who has a cannon has an original.

I'd have to agree with Silver, I don't think buying a cannon is remotely practical. The cheapest full sized guns I can find start at around $6000 for something that *might* be in working condition and is in any case of smaller calibre than Old Moses. This price doesn't include shipping.

That just isn't practical, either as something they could afford to destroy or as something they could keep on the off chance they might want to use it again - apart from anything else a full sized cannon is simply to larger and heavy for them to keep in storage.

So the practical options would be to hire a gun, in which case they will need to go overboard (so to speak) to reassure the owner that their gun is not going to be damaged. Or they would have to make their own - which may run into problems of time needed for the construction as well as legal hurdles to overcome. I don't know why, but I have a feeling that they may feel that making their own cannon is not a good idea given the mishap they had not long ago - or their insurance company may be telling them that they should use something they didn't knock up in the shop.

Having said that there is a type of cannon they might be able to make, or be willing to buy, to run some tests;

www.pdhsc.com/cannons.htm

These miniature cannons (or something like them) would be perfect for small scale testing - allowing them to test out ways to secure the gun on a full scale boat as well as proof of concept testing indoors. The examples in the link still cost around $2000, but I'm sure they could either find cheaper versions or make their own. I'm guessing that more than one MB would LOVE to have their own desk-cannon as a paper weight.

an alternative would be military surplus. the military MIGHT be willing to lend the mythbusters working ordnance (along with the accompanying expert) and depending on the vintage, it would be at least minimally scalable in weight of projectile and power of charge.

for that matter, I am in possession of a .50 cal brass replica of a naval cannon - which they could get much more cheaply than even your golf ball cannons. (meaning get their own - it's not an offer to sell it) it's the one I threatened to put on a cookie sheet in a wheelbarrow full of water earlier in the thread.

www.cabelas.com/product/Traditions8482-Mini-Old-Ironsides-50-Cal-Cannon/706191.uts?Ntk=AllProducts&searchPath=%2Fcatalog%2Fsearch.cmd%3Fform_state%3DsearchForm%26N%3D0%26fsch%3Dtrue%26Ntk%3DAllProducts%26Ntt%3Dblack%2Bpowder%2Bcannon%26x%3D0%26y%3D0%26WTz_l%3DHeader%253BSearch-All%2BProducts&Ntt=black+powder+cannon&WTz_l=Header%3BSearch-All+Products

'Small craft' is relative, the navy would consider something 150 feet long to be a small boat - but that size is well beyond what MB themselves would be capable of dealing with.

Ideal what we want here is something that is small and light enough for Mythbusters to be able to transport themselves, possibly build themselves and which would allow them to build the 'trench' quickly and easily. We also want something that they could use to test both small and large guns - meaning in this context probably a punt gun upwards. If the boat is too large however then any force that is produced by the smaller guns is unlikely to be able to overcome the mass and move it, making the use of such guns rather pointless.

A small airboat hull or similar design would be ideal. They are long enough to handle any major type of gun MB are likely to be able to use. Wide enough that it is unlikely that it would roll over if the gun isn't directly on the centreline or if the water is in any motion - which even in a trench is probable since loading the boat will cause waves. Their shallow draft means they don't have to dig a trench that is too deep to jump into, or would cause major problems if they have to recover something from the water.
Last of all this is a design that could either be picked up fairly cheaply ($750 was the figure I saw for a hull, although that would not include transport costs), or which MB could make themselves in the shop if they decide that is cheaper, faster or more convenient (in terms of reinforcing the structure).

The guns themselves are an area where a lot would depend in the sort of restrictions MB have placed on them. As I said, I suspect that their insurance company if not MB may be wary of using guns made by the MB's themselves. Getting experts from outside to make a cannon for them might be an option, but it might also have problems of cost and a desire not to turn the entire show over to the experts*.

(*Note that even when experts or special guests appear they very rarely do any of the builds themselves.)

funny, West Coast Choppers got a similar reputation after they were on Discovery channel.

I see a trend - people on Discovery reality shows can afford to be jackleg operators. the ones who aren't quickly lose interest in having cameras around all the time (or the cameras lose interest in them)