Now that is a water heater!
I see an issue if indeed this is a water heater with the stove stuck into the tank.
Now I have zero engineering background as well minimal education 12th grade:>)
So take my thoughts with a grain of salt.
If water surrounds the stove it will rob the stoves ability to keep consistent high temps reducing efficiency in combustion.
Now if I am viewing this incorrectly never mind my thoughts.
So here is what I see, if indeed it is inset and surrounded by water it will struggle to maintain an efficient burn as the loads are spent and temps start to come down.
The water temps as well are going to fluctuate causing a tug of war on the system.
Again if I am getting this wrong how you have built this and its function pay no attention.
If it is my understanding it is inset and surrounded by the water, what I would do would be to have the main stove body outside the tank, insulate that, have the stove exhaust into another box that is set inside the tank.
This is quite an impressive scale you fellas have done this in.
By having the stove outside the tank well insulated you can maintain consistent temps needed to keep it running efficiently.
You could build a flue box that is inset into the tank with heat sink fins like you did on your original design.
That box could be designed in a way to create the natural drafting needed.
I would put heat sink fins inside the secondary box and outside it that the flue gases pass through.
I can see where you could have the flames exiting into the secondary box and done in such a way it does not rob the high temps needed to keep the stove running efficiently.
If done right you could have a roaring flame passing through the entire heat exchanger box.
I can do a simple drawing up if you think what I have presented is worth considering.
Think of having the stove outside the tank and the flames and flue gases pass through the heat exchanger that is inside the tank.
Now if I just did not get what you are doing with this design I apologize.
I can see where you could attach a suction fan at the end of the chimney to produce high velocities of air for initial start up, the Japanese and Koreans are doing this.
They have come up with a flue suction fan that does not impede the natural flow when turned off.
Or one could just add a fan inline something like an upside down Y where the fan would push the gases up the flue pipe when opened up and turned on creating much higher velocities in the intake of the stove.
This should in theory generate much higher temps and get the system heated up more quickly.
I am betting one could use a 12 volt car heater fan and run it in a off grid system.
No doubt would need a substantial solar power system and battery bank to handle the demand you would need.
I can do a drawing up on the fan idea if you think this would be helpful.
Not saying I have anything here on the idea nor tooting any horn but I have been following a bio mass company for about four years.
After putting out my pellet burner basket design I found a few months later they had redesigned their biomass basket and looked like to me they either came up with a twist of the same idea or saw one of my videos.
I have also given some thought to the way the fire wood load would behave when loading large quantities of wood for long burn times.
By loading numerous large logs onto each other if there is not some sort of spacing between them, this as well could cause them to burn inefficiently.
I thought about creating some sort of lattice a grid system that would allow you to load logs into a lattice that would look like how wine bottles are stored.
You could create a rack with spacing so the logs could be slid into the lattice spacing creating open air gaps allowing the flow of air to flow between the logs.
As they burn and break down they will naturally crumble and fall down between the lattice still providing air gaps.
One should be able to load new fuel at intervals once the cycle is figured out for its maximum efficiency.
Just random general thoughts for now, no specifics.
Sorry if I was not able to convey what I am describing well enough for you to understand.
I probably should have put this in your original post showing the build.
I have not been on the forum for quite sometime now due to a lot of irons I have in the fire, no pun intended.