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.
So, are you saying that 20hp might be sufficient for a A35?
Given the A35's handling characteristics under power described earlier in thread (which I expect of a full keel boat), my biggest concern would be in close quarters (i.e., the marina). If the boat isn't doing what I want it to do, I need to change directions now, not 30 seconds from now. I'd also like the motor to have a chance to stop the boat if needed (I can have a stiff tail wind comming into my slip).
How does your A35 respond, having only 18 hp?