Reduces hop utilization in concentrated boils

I really want to max out my 15g mash tun. So bad. I'm planning to do a double batch of an ipa. I'm calculating a gravity for 11 gallons of beer with 35 lbs of grain of about 1.080, given my expected efficiency.

My question is just how heavily should I hop this thing to try and hit 70 IBU or so. I think I can average a 7 gallon boil.

My calculator (beer calculus at hopville.com) says my hop schedule will produce a wort of 75 IBU. However, will this then get further diluted when I add un-boiled wort to make 11 gallons?

I'm defininitely planning on dry-hopping the crap out of it (2 oz per 5g batch) either way!

Here's the recipe:

http://hopville.com/recipe/687555/imperial-ipa-recipes/double-double

Any comments on this recipe or method, other than "wasting" money on hops, is very welcome!

Unboiled wort what what? Don't add unboiled wort to your fermentor. Grain is silly with lactobacillus.

In any case, the various hop formulas scale linearly...so if you calculate 70 IBU in 5 gallons, you'd get 35 IBUs if you then diluted those 5 gallons to 10 gallons.

75 IBUs in 7 gallons should be about 48 IBUs in 11. If you want 70 IBUs in your full 11 gallons, you should shoot for about 110 IBUs in your 7 gallon boil.

Is there any way you could boil the rest of the wort on your stove or something and add some hops too that? Adding unboiled wort is a bad idea, but if you can boil the last 3-4 gallons on your stove then it will be a lot easier to hit your 70 IBUs.

Another idea would be to boil 6 gallons, put it into the fermenter, then boil the last 5 gallons and add it to the 6 already in the fermenter and pitch your yeast. I don't think the extra couple hours in the fermenter before you actually pitch the yeast will hurt anything as long as you make sure everything is sanitized.

Great advice. I guess I didn't even think about the sterilization of the un-boiled wort (other than keeping it's containers sterile).

I'll probably just bring the "second" wort to a boil after my initial boil just to sterilize it.

Thanks for the help! I'll scale the ibu's by volume.

Starting to wonder if it's worth it