How well will a double shell row as a single?

I've got my eye on two shells, a single 24' and a double 24'

double....http://sfbay.craigslist.org/pen/boa/1411868833.html


single....http://sfbay.craigslist.org/nby/boa/1411103222.html


I'd be mostly rowing single, but I figure the option would be nice and I'd rather have a slightly bigger boat.

My guess is I'd need to carry at least some ballast when rowing single so the bow isn't underwater. Maybe some a water tank or bag more towards the stern to it sits lower than the seating area(for additional anti-rolling stability), and has more leverage for counter-balancing my 250lbs?

Does it matter if you row a double from either seat?

 

There are some shells set for both. I've rowed on them. You set the outriggers in the middle and they have the slides for the seat in the middle too. If you have a second person you just change the outriggers.