Water to Grist Ratio

[ADDLED]

Hi all. I have a limited space in my mash tun, i think its 36 litres, and want to do a quite high gravity beer such as a Rochefort 10 or an Imperial Stout, but if i use 2.5/1 ratio of water and grist i wont have room for anything over 7.5%. Can anyone help me with a way to get around this pls?
I was wondering whats the reason for the usual ratio of 2.5 to 1 water to grain? If i use less water to get more grain in the tun will it have adverse effects on my beer at all and what possible problems will i encounter.
thanks in advance
ADDLED

[mysterio]

You'll be fine going lower, the only real drawbacks are a)harder to stir and more chance of doughballs, b)slightly lower efficiency, c)possibly slightly more dextrinous wort (maybe mash half a degree lower to compensate). Not really anything to worry about imo.

A couple of get-arounds:

Get a new mash tun

Conduct two mashes, one in a spare unmodified coolbox, add the second mash to your lauter tun when you're draining off first runnings.

[adm]

I've done a 2:1 water/grist ration in my coolbox mash tun when I did my Crazy Ivan Imperial Stout. I used 2 additional batches for the batch sparge and ended up with 75% efficiency - so it's quite doable. The tun was really full, so i had to take it slowly and carefully to avoid wort all over the floor.

As Mysty says, it's a thicker mix, so you need to make sure you really stir it well and get it nicely mixed together.

[ADDLED]

Hey thanks lads, much appreciated. I will go careful with the 2/1 ratio and see how i get along.
Hey Chris why does fly sparge make a difference in this case?
tks
ADDLED

[ADDLED]

With batch sparging, you add a large amount of sparge water to the mash tun before you drain it so you need spare capacity to accomadate it.

With fly sparging you drain the mash tun as you sparge so you don't need any extra space in the tun.

Oh yes, the second lot of batch #1. I forgot
Is it possible to go lower than 2/1 ratio or am i making Scotts Porridge gloopiness?

[ADDLED]

Possibly but I wouldn't want to try it. I suspect it would put a dent in your efficiency if you did and you may have problems with incomplete conversion.

Can i fly sparge with a watering can rose on a hose? I ask cos i have an oblong tun and so the sparge arm I dont think will work too well.

[brewzone]

Quite a few people use a sheet of baking foil with lots of holes placed onto the mash to prevent disturbing the grain bed.