I'm attempting to brew a high gravity stout, OG 1088. Its been in the primary for two weeks. I assumed it had completed fermentation since it feremented extremely vigorously, so much so I had to use a blowoff tube (for a bucket fermenter). Once that calmed down I replaced with bubbler and it went consistently for over a week. I checked the gravity today and it is between 1032-1034, which is still rather high. Visually it appears that fermentation has complete. I used Wyeast NB NeoBritannia 1945, and think b/c of the high gravity it is just spent. I have another package of this available should I consider adding this fresh yeast to it? What kind of results can I expect if I add another entire smack pack of yeast?
Like so many things in beer, a multitude of factors could be at work.
Is this an all-grain or partial mash? It's possible that you ended up with a lot of unfermentable sugars and the yeast are just done. More yeast will have nothing to eat. In which case your beer is just done. 7.35% ABV and ~63% apparent attenuation. Not terrible.
If the yeast has pooped out, adding more yeast may or may not help. I haven't done a lot of research into it, but a friend was explaining how the enzymes that cause the current yeast to flocculate will also cause new yeast to just flocc out to the bottom and go dormant.
What temps are you keeping it at? The first thing I would try is raise the temp up a bit - since most of primary fermentation is done, I'd raise it up to ~70-72 - and gently swirl the fermenter to rouse the yeast.
No matter what, I'd definitely give a beer that big another 2-3 weeks in the fermenter.
Did you make a starter initially? If not, you seriously underpitched for a beer of that gravity. If you want to try adding more yeast, keep in mind that it takes a LOT of yeast to restart a stuck fermentation. 2-3 qt. of yeast slurry is what's usually needed. if you have a brewpub nearby where you can get some yeast, that would be your best bet. Or do you have another batch of beer around that you could use the yeast from?