Taking the day off to brew

I've been struggling to find the time to get round to brewing as of late so did the logical thing and took a day off work to brew. And what I will be brewing is Tasty McDole's "Janets Brown". Recipe below adjusted to what I had available:


Batch Size (Gal): 6.00 Wort Size (Gal): 6.00
Total Grain (Lbs): 16.00
Anticipated OG: 1.066 Plato: 16.20
Anticipated SRM: 19.3
Anticipated IBU: 63.2
Brewhouse Efficiency: 70 %
Wort Boil Time: 90 Minutes

Grain/Extract/Sugar

% Amount Name Origin Potential SRM
-----------------------------------------------------------------------------
75.0 12.00 lbs. Pale Malt(2-row) America 1.036 2
7.8 1.25 lbs. Cara-Pils Dextrine Malt 1.033 2
7.8 1.25 lbs. Crystal 40L America 1.034 40
6.3 1.00 lbs. Wheat Malt America 1.038 2
3.1 0.50 lbs. Chocolate Malt America 1.029 350

Hops

Amount Name Form Alpha IBU Boil Time
-----------------------------------------------------------------------------
1.00 oz. Northern Brewer Pellet 6.50 19.0 Mash H
1.25 oz. Northern Brewer Pellet 6.50 30.8 60 min.
1.00 oz. Northern Brewer Pellet 6.50 6.6 15 min.
1.50 oz. Cascade Pellet 6.00 6.8 10 min.
1.50 oz. Cascade Pellet 6.00 0.0 0 min.
2.00 oz. Centennial Pellet 9.00 0.0 Dry Hop

Yeast
-----
Fermentis US-05

Mash Schedule
-------------
Mashed in at 154*F or 68*C if you will.

As I am a BIAB brewer I've made some slight adjustments i.e took into account no sparging.

This is my first attempt on the electric water urn brew kettle my friends and I chipped in to buy and brew day is off to a bad start. With a beer this big you need a lot of grains and alot of water. This is probably one of the biggest problems with BIAB brewing. Let me explain.
The electric kettle I use is 40L and I want 23L in the fermenter. For this happen I need calculate how much water I need. So....
If i want 23L I need to add 23L to the kettle
The malt bill for is about 7.5kg. I assume for every kg of grain, I lose 1L of water + 7.5L
On the this kettle I can assume 2L lost to evaporation per hour. This is a 90min boil. +3L
So to start I need 23L + 7.5L + 3L which gives me 33.5L of water needed. Plenty of room in a 40L kettle for that.
Except i haven't eally taken into account the displacement of the 7.5kg og grains. Now 40L isn't quite big enough and I got a bit of an overflow.

Balls.

Still, rather be doing this than working.