Design help

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towtruck

Newbie
Original poster
Jul 11, 2018
26
3
I was given two 6' pieces of 8" x 12" x 1/2" box beam. I want to build a custom smoker on a trailer to do mainly ribs with. With an internal dimension of 7" x 11" air flow over the food my get slowed down a bit. I do have a system of racks designed already.


Edit.........I edited out my original post and design to avoid confusion...see new design below.
 
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I should have mentioned this second plan as well.......my second plan is to lay both 6' pieces horizontal, one on top of the other. The bottom tube will house a long charcoal tray (or two shorter one's) Air flow into the fire box will be regulated along the long edge. The heated air and smoke will be regulated into the top tube where the food will be. An exit stack would be placed near the center of the top tube. The heat from the charcoal would heat the cooking chamber from below and the smoke would enter from the ends and travel over the food and out the stack in the center. Control of air would allow you to cook in half of the chamber for smaller cooks.
 
I have scrapped plans for the "h" design and I have been playing with this second idea a bit on paper. What I have come up with is this will end up basically being two 3' reverse flow smokers built back to back with a fire box under the cooking chamber. The material is 1/2" thick and if I stack them with the fire box tube on edge and the cook tube flat I can get good air flow under the coals and across the tube into the cook chamber. I ran the numbers through the calculators for each half to get opening sizes. I would do a plenum and stack in the center at the top. All my openings will be over sized a tad to help air flow in the long narrow cook chamber. I may regulate them with dampers as well...just tossing out ideas so far.

Since each half of the cook chamber will be 3' long the two fire hoppers will be 1' long placed in the center to allow the heat to travel under the cook chamber for another 2' before entering the chamber. The one unknown I still have is how much extra heat is going to be transferred into the cook chamber with the fire box's directly underneath the cooking chamber. I could always space the two chambers out but by how much? I am going to stack the chambers and do a test burn through them without cutting them yet. I will put some bricks in the cook chamber as "food" and see how well it flows and probe the heck out of it to see how hot it's going to get. That little experiment should make or break my idea as a working one or wishful thinking.

Some of the down sides are.......massive weight of steel to cook 8 racks of ribs laid flat, only able to cook meats that will fit and flow air in a 7"h x 11"w cook chamber, and a completely unproven design.

Upsides.....massive chunk of steel to cook 8 racks of ribs :-), a heavy wall cooker that should retain an even heat for a long time, Simple to build the way I envision it.
 
Drawings would definitely help. I’m lost in the high weeds trying to understand what your design looks like. Sounds like a lot of thermal mass that yes it would “retain even heat for a long time”. The down side to that is that it would take a long time to heat up, especially in cold weather. Don’t see where your located in your profile but if your in the cold NE that could be an issue.

Put your thoughts and dimensions on paper and I’m sure you will get more assistance and responses.

Edited- I hate Spell Check

Weedeater
 
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Okay.....two pieces of 8" x 12" x 1/2" thick box tube. Each piece is 6' long. Fire box is bottom piece.. that box tube is on edge ( 8" wide 12" tall) On top of that tube is the cooking chamber tube and it's sideways (12" wide and 8" tall). They form a fat "T" shape looking from the end view. Air intake in center of fire box, each fire box is 1' long (1/3 of each side of the cooking chamber.) Smoke travels to ends and up into cooking chamber. Smoke travels around food and out a central stack with plenum at base. I used all the calculation numbers for each side. basically two reverse flow smokers end to end.....The thickness of metal will end up being 1" between fire box and cook chamber. The ends of the smoker will be capped tight with removable end caps to remove food and fire trays. I plan on using charcoal for heat.
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A little background............I'm in the far northern reaches of California.....more a southern Oregon thing. Temps are not wild here and cooking in the winter when it's freezing out won't be happening anyway. I apologize for the vague drawings as I am used to building things in my head without ever putting them to paper. I have built entire one off cars out of my head without writing anything down...it's a sickness I have. I want this cooker for ribs mainly. I will be able to fit other meats in there but the main focus is a dedicated rib smoker. I will be able to fit 8 racks of baby backs in. This will be a trailer build as the two pieces of steel currently weigh 749 pounds.
 
I did a little test today and lit a fire in one end of the fire box and had the smoke travel the entire length of the 6' box then built a temporary transition from fire box to cook chamber and had the smoke run back the entire 6' out the other end of the top tube. It flowed pretty well and the entire thing took about 1 hour (small fire) to heat all the metal up evenly.
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With a smokey piece of wood in there I could see the smoke better to determine how it worked. Now, I know this did not really help me much for knowing how the temps will be but after one hour the temp in the CC right above the fire was the same as the smoke temp on the other end 6' away. Also if it will flow air the entire length then it will be much better when it only has to go half way. I only built a very small fire with twenty briquettes and a small split of oak and two hours later the thing is still hot and getting hotter. I may just go ahead as planned and build this thing.
 
Well, it's done and smoking away......temps hold even for 6-8 hours on tests burns at 225 degrees. It's a double reverse flow center feed smoker. I can fit 8 racks of ribs in it and other meats will be tried too.

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I bite the bullet today and for my first cook I tossed in four racks of ribs and a 12# brisket. Pretty big learning curve being the first time cooking on it. Already I am going to have to switch to lump charcoal just to get up to temp faster. My goal was to not have to add fuel during a 6 hour rib cook. That idea is out the window. I started with 15# of charcoal and at the 3 hour mark I added 7# to the fire box. That will get me to the end of the ribs then I will top it off again and keep going with the brisket. Starting the fire correctly and getting air flow even is key. The brisket side of the cooker has less air flow restriction than the rib side so that is where the heat and smoke wanted to go. I played around with the level of each end and figured out how to compensate for the difference in air flow by dropping the hotter end down more. I'm 5 hours into it and about ready to unwrap from the crutch.
 
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Ribs came out tasting good and very moist. They are a little tougher than I like though. That toughness is from my pit temps not being high enough....first time use learning curve. The brisket is still in there and at five hours it was at 160* so I wrapped it in foil and put it back on the pit to see if I can finish it out with the charcoal I have left. I dumped the last 7# into the coal basket at five hours into the burn. I am going to switch to lump charcoal for the next cook.
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A little update on the smoker.....it has evolved into a split system where the fire box and cook chamber are split into two separate halves that can cook independently of each other. That solved the air flow problem over each end. I have smoked a bunch of meat so far and it all has done very well. The trailer rig has evolved too.....it now has a tool box, work surfaces, a BBQ, a propane stove, and a water tank with soapy water.
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Built a baby smoker too...it holds and cook two brats and works perfectly for a low and slow smoke...
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