Recoil impulse on 3 and 4 inch shells

[PyroKing31]

Going to be launching on the water from a floating platform built with 55 gal plastic barrels as floatation. The surface will be 2x6 or 2x8 boards with cross bars underneath every 16 or 24 inches with some gaps for the barrels.

I want to know if anyone knows the recoil impulse of a 3 or 4 inch shell so that I can ensure that the top surface is not going to buckle bend or break under the lift charge. These shells will be in Racks placed in the center of the platform so that the recoil does not cause too much shift on the axis its floating on and thus changing the firing angle.

[Arclight]

According to the recoil calculator, a 10lb gun firing a 1/2lb projectile at 350fps using 2oz of powder accelerates about 80 fps and generates just under 1,000ft/pounds of energy, This is about the equivalent of a large adult jumping on it from 3-4 feet in the air.

If the whole thing is solidly tied together, I think you could count the weight of the raft as part of the gun, and then it's more like 1/10th that force.

Does that help? If you want to be safe, it sounds like you might want to make it out of things that won't be smashed if you jumped up and down on it as hard as you could

[Mattp]

Also need to consider the absorption from the racks and plugs and plywood ... and also will probably make a difference on how big your raft is!! ... I would think as long as you don?t have them all the way to the left and right... and then intermittently fire left and right you won?t have to much rocking .. they definitely have a hard recoil on there own.. but placed in a rack with solid bottoms.. should be fine

[PyroKing31]

Overall size of it will be 12'x12'

I tend to over engineer things I build, but want to be sure if i step up in size to 6" shells or so in the future I dont need to rebuild the whole thing.

And I dont think I could break it by jumping on it with 2x lumber. Its quite sturdy stuff especially with floor type joists underneath.

[displayfireworks1]

Is this also going to include a finale with multiple shells firing at the same time? If so, that may need to be factored in.

[yamiacaveman]

Last year my son and I built a 10x 10 out 0f 2 x 6 frame 16 on center -regular decking boards, 4 plastice 55 gal barrels one on each corner, braced up a rack of (10)-3inch and a rack of (8)-4inch, I believe each rack had at least 1 salute in it, and had no issues at all, but the lake and weather was calm. This year I plan to have 2 racks of 3 inch and 2 racks of 4 inch (fits the 36 cue with my cobra) but I have a piece of 3/4 advantec flooring left over from a project that I will use underneath the racks this year, rather be safe. Also if you use anything that angles on the dock use two anchors to hold it in place so it doesn't turn towards the audiance.
That's all I have.

[yamiacaveman]

Hey just one more fleeting thought. on another dock - same size same construction, we had consumer mortars and consumer cakes. After the show I did notice that the one cormer of that dock was a little scorched, maybe a square foot. The mortar racks are screwed to he deck of the dock, the cakes are glued to a separate sheet of plywood then screwed to the deck of the dock. I am almost thinking of putting strips of wet rags or wet old rugs on the exposed spots in between the racks and cakes, unless someone has a better idea. The deckispressure treated - also thought maybe watering that down before loading the dock up, but not sure how wet i can get it?
Any other ideas, I would appreciate it.

[tmwjr]

What about that fire resistant fiberglass knit cloth? I don't think that the rolls are too expensive.

Tom

[PyroKing31]

Is this also going to include a finale with multiple shells firing at the same time? If so, that may need to be factored in.

Yes. Present finale plan is 8 3" quick fused for almost simultaneous launch. The racks will be build sturdy, and the cakes will glued on their own boards before going on the platform.

and I do plan to have it anchored on two corners to prevent tilt as I do have some angled effects I will be using.

I am probably going to be moving up to 4" next year and possibly 6" depends on budget.

[Mattp]

using 2x as the decking i think you'll be good... but also there is a very big difference between the recoil of 3,4 and then 6" shells .... the company i work for, their rack system allows for the mortars to sit on the ground/grass... and during cleanup on grass the recoil from 6" tubes get pressed a good 3-4" into the ground while the 3,4" barely make a dent.. but i think this is all overthinking.. yes better to be safe all the time... but if you have very strong flotation under you platform i really think you'll be fine ... i used to shoot at my buddys place on his boat dock float up to 6" shells with no issues at all

[PyroKing31]

using 2x as the decking i think you'll be good... but also there is a very big difference between the recoil of 3,4 and then 6" shells .... the company i work for, their rack system allows for the mortars to sit on the ground/grass... and during cleanup on grass the recoil from 6" tubes get pressed a good 3-4" into the ground while the 3,4" barely make a dent.. but i think this is all overthinking.. yes better to be safe all the time... but if you have very strong flotation under you platform i really think you'll be fine ... i used to shoot at my buddys place on his boat dock float up to 6" shells with no issues at all

Thanks for the real world XP on the dock float. I did some research using a 2.5 pound shell at around 250 feet per second exit velocity and I'm coming up with 1600 ft/lbs of impulse. Which is equivalent to a .308 rifle or so. That said I do think 2X as the platform will be sufficient especially with cross bracing. I will have probably 6 barrels for floatation. The big guns will be center mounted to prevent "tilt" from firing.