Boil volumes?

[Gdog]

I'm about to brew up BierMuncher's cream of 3 crops recipe. It calls for a 90 minute boil, I'm assuming to get rid of dms. I need my 8 gallon brew kettle near capacity to do a 60 minute boil and still hit my numbers. Is it ok to boil the wort for 30 minutes, then top off the kettle with more boiling water to complete the full 90 minute boil?

 

[phuff7129]

You can just use the same amount of water that you would use for a 60 minute boil and then just top up your volume after it cools. The numbers should work out the same because you are just boiling off water and not sugar.