Trub/Chiller Loss - I think the default messed me up...

Did my first AG today, an Oktoberfest.  I took care to enter what I knew how to enter into BeerSmith, e.g. I did a one-hour water boil last week to measure boil off, I measured dead space in my tun and kettle (accounting for some tipping), etc.  And because of that, I pretty much nailed what BeerSmith said I should hit for the mash:  about 7.25 gal to boil, with a preboil SG measured @ 1.046 vs. calculated 1.048.  Pretty darn close, so I was expecting a perfect brew!  My post-boil size was right at 6 gallons, just as BeerSmith predicted.  This should have set my red flags off when I generated the recipe I suppose, since my target batch size was only 5 gallons...

So when I drained the wort into the carboy, and found myself with 5.5 gallons (and I could have kept going for a little more), I realized something was wrong.  Measured the gravity, and it was only 1.038 vs. a target of 1.06.  Obviously too much water.  Since I had everything pretty much nailed up until boil time, am I on track thinking that the trub/chiller loss is a culprit here?  I left it at the default .75 gal, more for lack of knowing what a good value was or how to measure it...I figured BS would pick a "typical" default.  But in my head now, I just don't see losing three quarts of water to trub, and I honestly don't even know how I would lose water to an immersion chiller. 

For giggles, I lowered this number by a half gallon in BS and reapplied to the recipe, and sure enough it just tells me to add about that much less water during the batch sparge.  Seems like that would have gotten me closer to my 5 gallon batch size right there.

So am I on or off track here? 

(Even worse, with 5.5 gal in the carboy, I didn't have enough room for my entire 2L starter!  I only got about 2/3 of it in, but I don't think it's an underpitch given the lower gravity.  I just saved the rest for next time.)

Since your pre-boil gravity reading was 1.046, I would suspect that your post-boil gravity measurement is off.  At 7.25 gal preboil with a gravity of 1.046, your post boil volume of 6 gallons would give you a gravity of around 1.057 to 1.058. 

Next, if you are planning on leaving 0.75 gal for trub with a target batch size of 5 gal, it appears as though you pretty much achieved that volume, but added too much to the fermentor with the result that you did not have the head room for your full starter.  If you want to pour the whole kettle into the fermentor, then you should set your trub and chiller loss to zero. 

Another helpful point:  I usually cold crash my starters and then decant most of the wort.  This minimizes adding too much of a wort I really did not want in my fermentor.  If you want to test the effect, save and taste some of the starter wort versus the wort from the recipe you just produced.  With a 2 liter starter in a 5-gal batch, this is almost a 10% dilution of your recipe!

Personally, I design for a 10 liter batch with 1 liter of trub.  Knowing this, I stop somewhere around 10 liters in the fermentor and measure the remaining liquid to confirm the post boil volume.

Okay thanks, that helps.  I guess the bad news is that, if you're right and I just horribly misread my gravity, then I did underpitch.  The remainder of the yeast has been in the fridge for several hours now, maybe I'll decant off the wort and pitch the remaining yeast...there should be room for that much smaller amount.

And sometimes I cold crash and decant, sometimes I don't.  Probably should have with a 2L, you're right;  I should have started the process a day earlier.