Parti-gyle brewing questions

Hey everyone, I am going to try a parti-gyle brew this weekend. I understand the whole process (first runnings the big beer with 1/2 the sugars, 1/3 the total wort, second runnings the small beer, 1/2 the sugars, 2/3 the total wort, etc.) I plan on brewing an Imperial Stout/Dry Stout combo.

I'd like to yield 5 gallons big beer (1.09 OG), 10 gallons small beer (1.045 OG). based on some equations from Randy Mosher http://www.brewingtechniques.com/library/backissues/issue2.2/mosher.html It looks like I need an entire batch gravity of around 1.060. So here's the question: does that mean I have to buy enough grains for a 15 gallon batch at 1.060? How does this 1.060 gravity apply to amount of grains to be purchased? How many pounds of grains are needed for this brew?!

I've been batch sparging, getting around 70% efficiency on my equipment.

Thanks,

Greg

This was a method my homebrew club came up with that used partigyle theories for collaborative mashing. Some of the calculations and theories may be useful for you.

Recipe Calculations

Explanation write up of our background calculations and some of the results.

Write up

If you have enough kettles, you don't even have to get into the heavy calculations. Shoot for 15 gallons at your gravity. Collect your runnings in the three pots, and swap volumes between the pots until you hit your gravities (or close enough). You'll probably have to adjust your target if you don't hit your efficiency, which you probably won't if the grain bill is large. I BIAB so the efficiency wasn't an issue with me, actually ended up overshooting it because I underestimated it.

One thing you can try is doing a no sparge method for the first runnings, which if you follow this:

http://***********/stories/techniques/article/indices/9-all-grain-brewing/1407-skip-the-sparge

You should be able to hit your target OG and calculate how much water you will needs for the two infusions.

For the barleywine i plan on doing, the recipe is built at 56% eff.

I should be able to then top off some 2 row and remash and batch sparge and get a decent OG for a second beer.

This thread of mine; https://www.homebrewtalk.com/f36/lets-partyyyy-gyle-pumpkin-porter-ale-one-mash-74927/ is a real time thread of me getting the hang of figuring out partigyle recipes.