First mash - double batch - am I thinking this right?

Hello all! I am moving from extract brewing to my first partial mash brew. I am sure someone has done what I am about to do but I have found no info on it so I wanted to make sure I was not overlooking anything or forgetting anything!

The recipe is for a 5.5 gallon all grain batch, what I am doing is doing the full mash, batch sparging and collecting the wort in a bucket, then splitting the wort into two 3 1/2 gallon boils in my two 5 gallon brew pots. I am adding extract to each at flameout to make 11 gallons total and then I'll ferment these in two separate vessels. The rational for this is: I don't have the equipment to do a full 5 gallon boil + I don't have a wort cooler. Mainly, though, I want to brew two exact batches with one variable different. In this case I will be using two different yeasts to find out what the differences might be. In the future I might try substituting hops, and different fermentation temps and/or times etc.

So with all this in mind... remembering that I have never done any mash before!... here is what I'll do brew day:

1. Heat the cooler up with boiling water.
2. Put the grains (16 lbs of Pale 2 row malt + 1 lb of Victory malt) in the cooler and add 20-22 quarts of 170 f water to mash at 154 f for 1 hour.
3. Drain the mash then add 3 gallons of 168 f water, mix & drain (do I need to let this sit for 15 mins?)
5. Split the wort into my two 5 gallon pots and add water to make 3.5 gallons in each (will I need to add water at this point? What if there is more than 7 gallons collected?) I guess I'll take a hydrometer reading at this point right?
6. Boil, add hops etc. and then add 3 lbs of DME (depending on the gravity) in each at flame out.
7. Cool, add remaining water to make 5.5 gallons in each fermentation vessel, pitch, & ferment.

Have I forgotten anything or not thought of something significant?

FWIW here is the full recipe, a slight variation on the DFH 60 minute IPA recipe by YooperBrew from this thread https://www.homebrewtalk.com/f69/dogfish-head-60-minute-clone-ag-extract-25709/ I'll be doing continuous additions of hops instead of the schedule below.

Recipe Specifications
--------------------------
Batch Size: 11.00 gal
Boil Size: 7.00 gal
Estimated OG: 1.066 SG
Estimated Color: 5.6 SRM
Estimated IBU: 70.4 IBU
Brewhouse Efficiency: 75.00 %
Boil Time: 60 Minutes

Ingredients:
------------
Amount Item Type % or IBU
6.00 lb Extra Light Dry Extract (3.0 SRM) Dry Extract 26.09 %
16.00 lb Pale Malt (2 Row) US (2.0 SRM) Grain 69.57 %
1.00 lb Victory Malt (25.0 SRM) Grain 4.35 %
2.50 oz Chinook [11.50 %] (60 min) Hops 27.9 IBU
1.00 oz Simcoe [12.20 %] (Dry Hop 10 days) Hops -
2.00 oz Amarillo [7.50 %] (Dry Hop 10 days) Hops -
1.50 oz Amarillo [7.50 %] (35 min) Hops 9.0 IBU
1.50 oz Simcoe [12.20 %] (30 min) Hops 13.6 IBU
2 Pkgs Nottingham (Danstar #-) Yeast-Ale


Mash Schedule: Single Infusion, Medium Body, Batch Sparge
Total Grain Weight: 17.00 lb
----------------------------
Single Infusion, Medium Body, Batch Sparge
Step Time Name Description Step Temp
60 min Mash In Add 21.25 qt of water at 170.1 F 154.0 F


Thanks for any and all comments!!

Sounds like a decent approach...I would however change the following:

Rather than heating the cooler w/ boiling water, just add your strike water hottter at say 180 - 185. Let it sit for 20 min and then carefully stir or temper down to strike temp w/ cool water or a few ice cubes.

Coolers aren't really meant for boiling temps and the addition of boiling water to a cooler can shock it and stress it unnecesarily.

Your sparge water can be hotter than 168. Likely around 185 - 190. Point is that you don't want the actual temp of the mash to exceed 170, the sparge water will need to be hotter to raise you from mash temps.

Stir the sparge water in well to rinse the grain. No waiting is really required, but a 5 or ten minutes might help settle the grain bed and improve clarity of runoff.

Rather than add water preboil, I think your goal should be to sparge more to acchieve the desired preboil voluume.

Oh, I admire your enthusiasm going for a double first batch...that being said I'll let someone else try and talk you out of it.

I gotta say, for this being your first time mashing, doing a double batch is leaving a lot more room for error. A lot of people on HBT have so many efficiency issues to work through when they begin mashing - I would hate for your brew session to throw you for a huge loop because of the unexpected. But it sounds really fun so I don't want to discourage you too much! Just expect low efficiency - maybe do your calculations for 65% or less? And make sure that the mash runoff is evenly split between kettles. Whether that means using a Y-splitter to evenly distribute, or thoroughly stirring up your runnings before splitting, just do whatever you can to keep it even - I've had trouble with sugar distribution when splitting wort.

And +1 to what wilserbrewer said about adding preboil water. If you find you're under your target volume, continue to use sparge water to rinse the sugars from the grain.

If you are set on doing this for your first mash (not recommended as said above), make sure to use more mash water. I calculate 1.25qt/lb to be 5.3gal. This is the bare minimum I would use on a first mash, but you can otherwise mash much longer.

The rest of your process looks less than optimal, but you knew that going in. It looks to be the best you could do with your equipment.

Thanks for the responses! I was actually considering a test batch all grtain APA with 10 lbs of grain to check out what might happen, so this mighty be my second batch. I think! It was, actually, this idea - the recipe, and doing two identical brews with one variable different - that motivated me buy the cooler and the hardware (and a grain mill,) so I may just bit the bullet and go for broke.

wilserbrewer I am printing out your advise for my brew day notes!

"Just expect low efficiency - maybe do your calculations for 65% or less?" Yes I'll do that for sure.

More mash water, OK! I am quite interested in how this process will work for me. I have read and re-read the Palmer book so I have a decent idea, but of course, like my first several extract brews, there are so many bits that might not look the same from my perspective the day of...!