How do I calculate my hop utilization with my new huge kettle?

[lateralex]

I stepped up to a much larger kettle about a year ago, and have not really figured out how to recalibrate recipes around hop utilization. I've found that some beers are a tad bit too bitter, so I think some adjustment is in order. Rather that just continue to wing it (doubling batches and then rounding down the hops), I thought I'd let the experts shed some advice. I also use beersmith, but am not that great with it.

Old kettle: 44 quart bayou classic http://www.amazon.com/Bayou-Classic-1144-44-Quart-Stainless/dp/B000FTLY1K
New kettle: 120 quart bayou classic http://www.amazon.com/gp/product/B0009JXYMS/

When using the new kettle, I am doing 10 gallon batches, full boil. So I tend to start with about 18 gallons, after biab we are down to about 14 (when the hops are added).

Dimensions:
Old: 15 x 15 x 19 inches
New: 24 x 24 x 22 inches

[brewfun]

Surface area and boil vigor are going to be the main considerations. I find that the bigger the batch size, the more accurate Tinseth's formula becomes. If you're using Rager, then just switch. After that, just add a little more utilization to the equipment profile.

The main thing is to make sure that you compare two versions of a recipe you've made a lot. Like a pale ale that doesn't have more than 50 IBUs. It's simply easier to taste 5 IBU differences when you stay between 20 and 50 IBU.

If your hopping is mostly burst or whirlpool, then the main difference is heat carryover, post boil. In that case, you're detecting more CoHumulone isomerization because that's the first AA to isomerize and has the coarsest texture on the palate.