John,
What was the wot (wide open throttle) rpm?
To select the propeller correctly you need to:
1. Engine is tuned to factory specs, valves adjusted correctly, carbs/idle adjusted correctly, control cables adjusted correctly, i.e. the engine is running properly.
2. With engine not running, push control lever to full throttle. Go back and visually verify both carb butterfly plates are horizontal. I have seen this be NOT the case several times.
3. Run the boat per the attached copy of the factory Propeller Selection guide and record wot rpm.
Your boat looks pretty light, I think you will be able to run a 12 and maybe even a 13. But it depends on if you had 4400rpm at wide open throttle. If you did something is wrong as you have too much pitch now. So, the tachometer tells all.
For reference: On Rick's heavy Skagit 17 with foamed bilges and lots of woodwork, heavy fiberglass stringers, glass windshields etc we could run a 10 or 11, ended up with an 11 for overall use. That boat is undoubtedly a lot heavier than yours.
Did you actually weigh your boat or are you basing weight off the brochures? If you have a dump with a scale nearby most allow you to drive on to get your towing weight. I did that with my Skagit 20 and it was instructive as the brochures said anywhere from 960 to 1100lbs. The scale showed the boat weighed nearly 2200 with no more than 12 gallons of fuel, a Bearcat 85 (279lbs), and not a lot else! Brochure weights are notoriously "optimistic"
Hope this helps. That is a nice looking motor, and it's first year with the voltage regulator. Very nice. Dave has a 62 in Michigan that runs great too, on his big pontoon boat. He's done some wrenching on her and even towed a Merc once as I recall, and now for the past few years he's had smokeless four stroke boating fun.
I have props in stock.