[dmtaylor]

Is there an equation to figure how much of a higher gravity to expect over a longer boil? I'm doing a Barleywine with 100% ESB Malt and I do not see that BeerSmith really helps calculating the OG over a long boil time. Also, planning to mash low around 148-150? Shooting for 1.110-1.112 and possibly 1.020-1.022 FG.

This is actually very simple to figure out.  Changes in gravity and volume are inversely proportional, i.e., as volume goes down, gravity must always go up, as the dissolved solids don't go away during the boil but are preserved.  It's a simple scientific and mathematical law.  So:

GravityA x VolumeA = GravityB x VolumeB

For this equation, you can dump the 1.0 from the specific gravity and just use the last couple of digits which are also known as "gravity units".  For example, for 6 gallons of wort at 1.040, if you boil down to 4 gallons, you'll end up with a wort at 1.060, because 6 x 40 = 4 x 60.

Simple as that, really.  So, if you know what you want for GravityB and the only unknown is VolumeB, you can rearrange the above equation to look like:

VolumeB = (GravityA x VolumeA) / GravityB

So, for example, if you have that same 6 gallons at 1.040 but you want to get it down to 1.110, then you can figure out exactly how far to boil to get there by doing this math:

VolumeB = (40 x 6) / 110 = 240/110 = 2.18

So, you need to boil off 6 - 2.18 = 3.82 gallons of the water.

Boiloff rates for most people are somewhere around 1 gallon per hour.  So, for this example, this might take around 3.8 hours to get down that low.  If your GravityA is a lot higher then obviously you won't need to boil for as long.

Cheers.