She's a 30' O'day shoal draft w/ the 2qm15 and is certainly underpowered. "Stock" displacement is 10500 but actual at least 12000.
I'm not looking for anything special - just hull speed w/ a bit of reserve for storms in Lake Pontchartrain/Gulf. My guess is I'm in the Beta20-Beta25 arena? Any input's appreciated. Thanks.
I think that your boat is underpowered because of the engine. It was a nominal 14 HP when new and now that it is 25 years old it is no longer at its best and possibly only giving out about 75% of its rated output if you run it at maximum. The 2QM15 was not Yanmar's finest hour because, although it was reliable, it made too much noise and vibration to be acceptable.
I have run propeller calculations for you using the Beta 16 and the Beta 20 and the Beta 25. The Beta 16 will give you about 6.5Knots and the 20 should get you close to 7. The 25 will give you no appreciable improvement over the 20 so I suggest using the difference in price between the 20 and 25 to pay for part of the repower.
The first call from the prop calc is a 14"x8" three blade propeller. This should give you quiet and very economical cruising with lots of reserve power.
