Andrew,
I would definitely list them separately.
More photos, both clear shots of boats interior and staged shots of them in hunting situations will help. People like pictures.
In the listing for the scull boat you might consider either a link to the old sculling website with some basic info or copy and paste the info in to your ad (if Steve is ok with it). Tell a story of a successful scull on ducks when nobody could get them to decoy.
This may get somebody who doesn’t know much about scull hunting pumped up and want to try it. You will likely get more for the scull separately if you can sell it with its own trailer as well, as it is too big of a boat to car top or fit in a pickup bed.
Open water gray type paint jobs are more traditional for scull boats but you probably wouldn’t be able to recover the cost of a repaint when selling.
For the scaup listing more photos, talk up how well the boat hides, how well it handles in snotty weather, how much better than the average john boat it is. Again get somebody excited and wanting to upgrade.
Keep relisting through September, all you need is one guy who gets frustrated with his current boat to want to make the upgrade. Once you get past mid October people are probably going to be locked in their current boats and will have already made their major hunting purchases for the year. After that you will get guys who are looking for a deal and will have a hard time getting what you want.
As someone else mentioned above advertise as much as you can. Put flyers on the bulletin boards at sporting goods stores, boat launches, anywhere a duck hunter may be found and post on the web as well. craigslist.com; hunting sites, etc.
Good Luck!
