I have a 1977 Grew (slickcraft) SS215 with a Mercruiser 165 inline 6. A heavy boat with a deep vee hull. I also have a Doelfin attached to the outdrive. Nobody believes me when I tell them that I plane at 2,500 rpm at 9.8 mph! I've checked it many times in salt water and in the lake and every time it just pops up onto plane. Best speed and economy is at 3,500 rpm and 28 - 30mph. I think the combination of the hull shape, doelfin, propeller and low end torque of the inline six is perfectly matched in my boat. I'm just the operator!
i don't know what speed i plane at as i don't have a speedo. but 2k-2100 is about as low as i can get and still be planing. 165 L6, no tabs, no tail, my normal load of 2 w/ gear. max cap. is 6..
A lot of the answer depends on your definition of planing. Here's what most people call "planing":
When the boat begins to plane, the formula becomes irrelevant since the boat is climbing its own bow-wave. The bow rises slightly as it starts by mounting its own bow wave. When it reaches the speed where it overtakes the bow wave, the bow resumes its normal attitude. The boat can often be seen to leave its stern-wave some distance behind it. The hull is now planing.
