Double this recipe (help with hop schedule)

[duckredbeard]

A few weeks ago I brewed a very nice ale. My wife agrees. She's drinking it all. I intend to do a double batch of this as my first 10 gallon recipe. Here's what it was for 5 gallons

10 lbs Maris Otter, mashed at 150 until converted, fly sparged for 7.5 gal preboil, 90 minute boil for 5 gallons in primary.

1 oz Willamette 4.7 for 60
1 oz Willamette 4.7 for 10
1 oz Willamette 4.7 for 5
1 oz Willamette 4.7 at whirlpool

I got a 1.065 for an efficiency of 85%, which is around typical for my system. I would like to do a 10 gallon batch, split between two primaries. The original lost some volume due to hops in the kettle. I will use a hop spider/hop sock to reduce losses in the larger batch due to larger quantities of hops.

I don't have beersmith, and I've done some tinkering with online calculators, but I'm not sure of them. Can someone guide me in calculating the hop schedule for a double batch? I need to keep it very close in IBU/flavor for the wife (maybe a little more aroma). She loves the original, so I want to keep it close.

 

[rcsoccer]

I plugged it into BeerSmith and doubled everything and got the same IBUs and gravity, so you should be fine with 20 lbs. of MO and 2 oz. of Willamette at each addition.

Cheers!

 

[duckredbeard]

I expected utilization to increase with volume.

 

[rcsoccer]

I expected utilization to increase with volume.

It shouldn't increase that much if you double the amount of malt. I thunk the IBUs dropped by 0.8