Kettle Design for Rolling Boil

[NailCreek1]

We are fabricating a Boil Kettle and I am trying to assemble as much information as I can on kettle design. I am shooting for a 3.5 barrel system and it will be direct fired, stainless steel. I have an excellent local fabricator to work with and an interested welder that will work at night at a well discounted rate. Although I have tons of questions about many design facets, I am wondering, at the moment about the best way to achieve a rolling boil with a direct fired kettle. I have read about the general methods of heating one side of a jacketed tank to higher temperatures to achieve this effect, and read about how breweries use internal heating to channel wort up to a splash plate above the boil with a percolating effect. The only mention I have heard for direct fired kettles was, I believe, to offset the heat source (burner), so that one section of the bottom of the kettle is hotter than the other and a rolling boil may be achieved as a result of the difference in temperature. That does not sound very likely to work well, but may be an idea. We plan to insulate our kettle with 2" of rockwool and have an enclosed burner box beneath the kettle. Exhaust gas will be direct up an uninsulated potion of the outer jacket space to a chimney at some poin on the side of the kettle. It was my thinking that I may baffle this exhaust and create a hot side to promote a rolling boil. Any thoughts on this?

The other idea was to build a partial percolator which would perhaps be designed like an inverted funnel. The thinking is that the widest part of the funnel would be a bit narrower than the bottom of the kettle and be a few inches above the heated kettle bottom. Presumably, the hottest of the heated wort would be below the funnel and be forced to rise up into the narrower portion via convection. I would hope that this action could force the wort up against a splash plate just above the boil. The theory seems OK, but maybe I am over-thinking this or maybe it would be a pain to clean. Any advice on this?

[canyon]

You don't need to worry about it for a kettle your size. As long as you have an adequately sized burner with correct distance from the bottom for the burner design you will get a rolling boil. If you complicate matters you will have more complicated issues to deal with. I built a 3.5 bbl direct fire kettle (more forgiving with the B.O. issues brewing 3) that has over 4500 brews on it and now I am replacing the bottom and converting it to wood. PM me if you need more help. :)