Hi Ryoma!...Greetings from Georgia, USA!
It is so nice to have someone representing Italy to join us here at SMF!...Welcome!...
I will try to answers your questions as best as i am able. There are others here that can fill in any answers that I leave out in the event that I missed something..
Let's look at the questions now....
A-1) If built properly, water can be used in BOTH a horizontal and/or a vertical smoker.
A-2) Yes and no, dependent upon the way the smoker is constructed. I will explain more about this after question 3 since the answer to both questions are relative to each other.
A-3) The 'bulkhead' in the photo is actually a series of 'Tuning Plates'. These are used to 'tune' the heat distribution inside the cooking/smoking chamber.
Another, and quite different 'bulkhead' is illustrated and explained in Post #21 of this thread which deals with the Reverse Flow Horizontal Smoker-Cooker.
To help explain this as well as my answer to question 2, let's look at the the photo below which illustrates the Tuning Plates and the Baffle Plate.
I also created a graphic which will help you visualize those things which are not visible in the photo.
The Horizontal Smoker-Cooker w/ Offset Firebox
To help orient us to what we are seeing in the photo, keep in mind the following:
The firebox is located to the right and below the 'Baffle Plate' and is not visible in the photo.
The opening from the firebox into the cooking/smoking chamber is just beneath the Baffle Plate and is hidden
from view.
The heat/smoke exits the cooking/smoking chamber through the exhaust flue (smoke stack, chimney, etc.)
which is located at the end of the smoker opposite the firebox and would be just outside the left edge of the
photo and is not visible.
In the photo below you can see the Baffle Plate and the Tuning Plates (TP-1, TP-3 through TP-6) with
TP-2 hidden from view under the metal grid just to the right of TP-3, and TP-6 is only partially visible to the
left of TP-5.
Notice also the Baffle Plate tilts or slopes gently downward from the right towards the left as you can see from the shadow of the cooking grid above it.
Now I will try to explain how this all works.
As the heat/smoke flows into the cooking/smoking chamber, the downward sloping Baffle Plate directs the flow gently downwards and under the Tuning Plates as it flows from right to left towards the exhaust flue.
The Tuning Plates are adjustable and are positioned such that there is an open space between TP-1 and
TP-2. The width of the open spaces between TP-2 and TP-3, TP-3 and TP-4, TP-4 and TP-5, as well as
TP-5 and TP-6, are increased in width progressively as we proceed from right to left.
By making the spaces between the Tuning Plates wider, the amount of heat passing between the plates
will increase and make that area of the cooking/smoking chamber hotter.
By making the spaces between the Tuning Plates narrower, the amount of heat passing between
the plates will decrease and make that area of the cooking/smoking chamber cooler.
Through a trial and error process of adjusting the width of the spaces between the Tuning Plates, it is
possible to 'Tune' the cooking/smoking chamber to have an even temperature across the length of the
smoker from the firebox to the exhaust flue.
It must be noted however, that each individual smoker/cooker will have its own unique personality
and therefore will require its T.P.'s to be adjusted to its own individual characteristics...
Because of this, the adjustments outlined above are intended as a
starting point only!...
For best performance the TP's should have a thickness of 1/4 to 1/2 inch (0.6 cm to 1.3 cm), with most
builders opting for a thickness range of 1/4 to 3/8 inch (0.6 cm to 0.9 cm), and should be made of iron
or steel in order to have the thermal mass necessary to moderate temperature fluctuations in the chamber.
Aluminum is not a suitable material for use in TP's since it lacks the thermal mass that is necessary.
Additionally, there is no set number of TP's to use in a smoker, nor is there a particular width of TP that must be used.
This is something you will have to decide based on the length of the chamber that you will be working with.
A greater length would require more TP's, a lesser length would require fewer TP's.
I created the graphics to reflect exactly what was shown in your photo, and this is the reason only 6 TP's are shown in them.
So...To complete my answer to to your second question:
Without the Baffle Plate and the Tuning Plates, Yes. The heat/smoke will enter directly into the cooking/smoking chamber, causing hot spots and cold spots.
In other words, the heat/smoke would begin almost immediately to rise towards the top of the cooking/smoking chamber where it would traverse the length of the chamber on its way to the exhaust flue.
Because of this, the end opposite the firebox would remain relatively cool at cooking grid level.
With the Baffle Plate and Tuning Plates, No. The heat/smoke will enter the cooking/smoking chamber indirectly, resulting in an even temperature throughout.
In this case, the Baffle plate, by sloping the heat/smoke downward, will in effect tuck the heat/smoke under the tuning plates, which will tend to act as a duct carrying the heat/smoke to the end opposite the firebox.
In the process of doing this, the tuning plates will be heated, which will then be able to release their stored heat under the cooking grid.
In addition, the heat/smoke which leaks upward through the progressively wider spaces (slots, gaps, etc.) between the tuning plates, will tend to surround any food items placed on the cooking grid, as well as even out the temperature from end to end in the chamber when adjusted properly.
Referring to your first question, a container of water may be placed on the Tuning Plates nearest the
firebox to produce steam to help regulate the temperature and to provide moisture in the cooking/smoking
chamber.
A steam table pan, or tray, such as those used in a cafeteria or restaurant, works exceptionally
well for this task.
These pans and trays are made of food grade stainless steel, are rectangular in shape, and are available
in several sizes and depths, and they will withstand the heat in the event of boiling dry.
Here is a photo example of them:
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Here are links to the websites of two different companies that build Horizontal Smoker Cookers w/ Offset Fireboxes...both are located in the state of Texas, in southern USA.
These websites have lots of photos that may be of help in planning the building of your smoker-cooker...sometimes a picture truly is worth a thousand words.
BBQ Pits by Klose located in Houston, Texas.
Gator Pit of Texas located in Houston, Texas.
The
'Pit Builders List' has links to many other Smoker-Cooker builders.
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Next: The 'Reverse Flow Horizontal Smoker-Cooker'
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I hope this has helped in some way...Good Luck in the building of your new Smoker-Cooker!...
Until Later...