Numbers don't add up for a Dubbel

[BroomVikin]

I found this recipe online and it looked great to me. However, when I put it in BS it comes out as a LOT bigger beer than the original recipe says. There's no OG listed on the recipe but it says the target ABV is 8.1%. When I put it in Beer Smith though I get an estimated ABV of 9.9% for a 5.5g batch and 11.0% for a 5g batch! Am I doing something wrong? The original recipe is here.

Malts

14 lbs Belgian Pale Malt
1 lb Malted Wheat
12 oz. Special B
8 oz. English Medium Crystal
4 oz. Chocolate Malt
12 oz. Amber Candi syrup

Hops

1/2 oz. Magnum 14%a, 60 minutes
1 oz. Tettnanger 4%a, 20 minutes

Yeast: Wyeast 1762 Belgian Abbey II

 

[xben]

Lower the efficiency... my experience tells me to reduce brewhouse efficiency when brewing big beers as there is more losses.

 

[m00ps]

Yeah, there's an article somewhere on bigger beers you should expect a efficiency drop of up to 10%

 

[BroomVikin]

I've got to bring it down to 56% to hit 8.1%. Would it be that big of a difference?

 

[chickypad]

I think the person writing the recipe must be getting very bad efficiency. It doesn't list target OG but I'm thinking it can't be much over 1.075? And 5 pts or so will come from the sugar, so that doesn't leave that big a mash. I would probably count on my usual 78-79% for something like that. When doing big beers say in the 1.090 range I've had to adjust down to like 71% or so, but 56% sounds pretty low.