I have SM 243. When I was having problems with low rpm with my old 78HP VolvoTMD22 (with both the Amel-supplied AutoProp and spare fixed prop), I called Brunton's (AutoProp) who said mine was sized and pitched for a SM with 100 HP Yanmar. I had the fixed prop checked by a highly recommended propeller shop in Annapolis. They said the fixed Prop was also over pitched for my boat and engine. I had the spare fixed Prop repitched to their recommendations, and voila!...3100rpm.
With your new Yanmar, your props shouldn't be overpitched, if anything, maybe slightly underpitched. I suspect you have a problem with the Yanmar but if everything checks out you might have the fixed Prop checked at a reputable propeller shop. If you give them your boat's specs, they can tell you if the Prop is right for your boat with the Yanmar 110.
I'd check the exhaust elbow and turbo first. It is recommended that you run your diesel hard (over 3000rpms for10-15min) every 6-8 hours to help delay problems with soot buildup in the elbow and turbo.
I have lost one wing of the Auto-Prop Propeller, Now I am traveling with the fix-Propeller, Amel had suplied with the boat. I am surprised, that I canot increase the tours/ min higher than 2400. With the Auto-Prop it has gone up to 3500. I have the Yanmar 110HP Engin. Is this normal or is eventually the Turbo not working anymore ?
Any experience ?
AMEL SM200 SAMANTHA