I've been hatching Marans for 3 years, and until last year, had dismal hatches, even with a Sportsman.
Then I tried dry hatching, and have much better hatches now.
I also started putting the eggs in a styrofoam incubator for the last 3 days and the chicks practicially pop out of the shells.
Yes, I do get an occasional slow one, and have to help out, but my success rate is much higher. Trying to hatch in the Sportsman was impossible, I could never get the humidity over 50%. Now, I get it up to 80 the last 3 days and it works great. I also put my Wyandottes in with the Marans and they are hatching better than before.