Re: Anchor weight for 1650 Ib boat...
I am sure many people will chime in with get the biggest anchor you can get, but in reality it also depends on what your anchoring needs are going to be. Lake, Coastal, Overnight, Lunchtime anchoring, Daysailing, Crusing, etc.
They are rated by length because a lot of the forces on your anchor are going to be wind and current and as such the weight of the boat is not as significant as length/windage/etc unless it is already moving.
If you think your anchoring needs are relatively light, then you can certainly get away with the 11lb anchor. If you think your needs are going to be more significant, I'd say you need a heavier anchor, not to mention I'd probably spring for a newer spoon type anchor (Rocna, Mantus, etc.).