Originally Posted by smurphny
If you are going to live with a Yanmar, I highly recommend spending the bucks to get the service manual. It has more info, than you'll ever need and EVERYTHING that you will someday be looking for. All the torque curves are in there and good instructions on how to fix everything. I have found it essential on many occasions. The 3GM reaches peak torque between 2200 to 2800 rpm at 13-17 hp. The 2gm reaches peak at 2800 as well at 11 hp. The trick is to size the wheel so that when you are at hull speed, the engine is at the low end of that rpm spec. Fuel
consumption for the 2GM looks like it's most efficient at 2800, which is also the peak torque. The 3GM is the same. The only issue is whether the 2GM can get the boat to hull speed at an efficient rpm. I doubt it. You would need to spin the 2GM at 3300 to get to only 13 hp. The 3GM on my boat does get the boat to hull speed at 16-18 hp/27-2800 rpm. They run very comfortably at this rpm. Hope this helps with your comparison.
The motor in the A35 in the OP is a Beta Marine.
However, I have a Yammar 2GM20 in my current boat. 16hp/18hp at 2800. Cruise at 3000 and it hums. Not to go off topic, but how can the 3GM only be 13-17?