This boat was originally powered, or I should say underpowered, by a pair of 6.2L Mercruiser smallblocks. The factory props were 17 inch diameter by 19 inch pitch 3 blades with these engines, with a 2:1 reduction in the transmissions. The optional 8.1L engines were available for this boat at the time, and used the very same shafts and 2:1 transmission ratio, but the prop diameter was increased to 18 inches, with a 22 inch pitch, and 3 blades.
As many of you know, I have been taking great pains to reduce drag, improve the weight balance, and increase the efficiency of this vessel. The hull has been faired and smoothed, the struts and rudders have been profiled for reduced drag, the trim tabs have been modified, etc. etc. A big player in this effort is the propeller selection, and I have been researching the available options for many months before coming to a decision. The debate between the merits of 3, 4, even 5 bladed props will never end, and I don't expect to settle it here. But for the type of boating I engage in, my final prop selection is 4 blades. I have no interest in top speed performance. Instead, my goal is utmost midrange and cruise efficiency, along with secondary goals of smooth performance, low vibration, and good performance around the docks at very low RPM. These parameters led me to ACME Propellers - http://www.acmemarine.com/
Briefly, these props are not made like conventional wheels. They are fully CNC machined. This manufacturing method yields precise control over the blade shape, not only of individual blades, but between blades themselves. The result is an extremely balanced, smooth running propeller. For all intents and purposes, the blades are effectively identical. These are props with optimized blade thickness and profile, that maximize efficiency, minimize drag, and run with minimal vibration.
I'll have more prop install details in the next post, and also some other information about shaft alignment.