Mash/Sparge water volume questions

[Hovik]

Hi gang,
I need some help and have looked around but am not coming up with an answer. I have done Extract and then BIAB for the last few years but just got myself a 10gal cooler mash tun with false bottom for my AG brewing as I was limited to my 7gal boil kettle when mashing BIAB.

So now I've set up the new equipment profile in BeerSmith2 but am scratching my head when looking at water volumes. I took a recipe (https://www.homebrewtalk.com/f66/bison-brewing-company-honey-basil-ale-clone-264689/) that I had previously brewed BIAB and look the mash tab in BS2. For the 11.5# of grain it says to use about 4.5gal mash water and about 1.9gal of sparge water, which should fit fine in my 7 gallon boil kettle but the ratio has me wondering if I did something wrong here. Is less than 2 gallons of sparge water enough to fly sparge with? If you set the input/output rates the same you'll run out of sparge water half way through draining the wort from the mash tun right?

I turned to google to look for answers and I came across Palmer's site and read "What is Sparging" on this page (http://www.howtobrew.com/section3/chapter17.html) where he says

Typically, 1.5 times as much water is used for sparging as for mashing (e.g., 8 lbs. malt at 2 qt./lb. = 4 gallon mash, so 6 gallons of sparge water).

Now am I losing it or does 10gallons of water for a 5gallon batch (I am assuming at 8# of malt this HAS to be a 5gal batch) not add up? or do you leave like 4 gallons behind in the mash tun after sparging? Now I am more confused than before...

I must be missing something here. Can anyone point me in the right direction?

 

[Staylow]

You have to take into account grain absorption, boil off rate, tun loss and kettle trub loss. The amount of loss depends on your system. For example, I typically lose around .13 gal/lb to grain absorption, 1.5 gal to boil off starting with an 8 gal boil, a quart or so to the tun and about a gal to the kettle, leaving me with 5.5 into the carboy.

You'll have to brew a few batches to dial in your system and know what kind of losses to expect.