1) Performance issue you are trying to correct: Get my WOT RPM down to 4400-4800 (Mercruiser maximum), increase my top speed back to 40-45 mph, increase handling and reduce trim sensitivity.
2) Current prop manufacturer, model, aluminum or stainless as a minimum. Turning Point Hustler, aluminum
3) Current prop diameter and pitch (required). 14.25x23P
4) Wide open throttle RPM and speed with an average load (very helpful): 6000 (way too high), fastest GPS speed was 32 mph but average is 23.
5) Engine/drive make, model, year, and HP: 2019 Mercruiser 4.3 with 4 BBL carb but Mercruiser says it's an MPI(?), Alpha One outdrive with 1.81 gear ratio, 220 HP according to Mercruiser
6) Boat make model, year, length and weight: 2011 Bayliner 195 BR, 19', weight: 3870 lbs empty, with my family and gear: ~4500 lbs
Based on the very limited research I have done, increasing the diameter to 15.6 would reduce my RPMs by approximately 700ish, and increasing the pitch would reduce them by an additional +/-200 per inch. My understanding is a 15.6x27P (largest prop diameter that will fit) would put me around 4500-4700 RPM. Is my assumption correct? Also, given my boat weight, would I better suited with a 4-blade over a 3-blade? What my current plan is: replace the current prop with a 15"+ diameter prop and either 25P or 27P, no decision on 3-blade or 4-blade, no decision on material but aluminum is ideal due to living in Hawaii and only using it in salwater. Boat is squeaky clean on the outside of the hull, and before the engine was replaced, it held 4500 RPM at WOT with the current prop.
Backstory (read this if you want to, it's really long but I have some of my research at the end):
Recently had the engine replaced in my boat. Previous engine was a 2011 4.3 Mercruiser TKS, with roughly 195 HP. The prop diameter and pitch was perfect for the boat and it would run at 4500 RPM at WOT and max speed was just north of 45 mph (GPS said 45.6) and it handled like a dream. That engine had a piston that decided it wanted a valve for lunch, so I bought the current engine and my WOT RPM are over 6000 (can't get an exact number since the gauge tops out at 6000 and it blows past that at half throttle), and it will only get to about 25 mph. As soon as I push it past half throttle, the temp gauge shoots up. The boat handles like absolute crap now and if it's not trimmed perfectly (that word is intentional, because there is a very precise position) it will either kick the bow up and hold it high, or it will slide to the left and right, even on glass smooth water. My estimation is that I need to reduce RPMs by at least 1400 to get back within range. I suppose I could spend a ton of money on props, spend the time swapping them out and test running them but the truth is, I would much prefer a well-informed, mathematical decision instead of trial and error, as getting my engine replaced didn't leave very much wiggle room in my budget to do trial and error. Any help would be greatly appreciated.
2) Current prop manufacturer, model, aluminum or stainless as a minimum. Turning Point Hustler, aluminum
3) Current prop diameter and pitch (required). 14.25x23P
4) Wide open throttle RPM and speed with an average load (very helpful): 6000 (way too high), fastest GPS speed was 32 mph but average is 23.
5) Engine/drive make, model, year, and HP: 2019 Mercruiser 4.3 with 4 BBL carb but Mercruiser says it's an MPI(?), Alpha One outdrive with 1.81 gear ratio, 220 HP according to Mercruiser
6) Boat make model, year, length and weight: 2011 Bayliner 195 BR, 19', weight: 3870 lbs empty, with my family and gear: ~4500 lbs
Based on the very limited research I have done, increasing the diameter to 15.6 would reduce my RPMs by approximately 700ish, and increasing the pitch would reduce them by an additional +/-200 per inch. My understanding is a 15.6x27P (largest prop diameter that will fit) would put me around 4500-4700 RPM. Is my assumption correct? Also, given my boat weight, would I better suited with a 4-blade over a 3-blade? What my current plan is: replace the current prop with a 15"+ diameter prop and either 25P or 27P, no decision on 3-blade or 4-blade, no decision on material but aluminum is ideal due to living in Hawaii and only using it in salwater. Boat is squeaky clean on the outside of the hull, and before the engine was replaced, it held 4500 RPM at WOT with the current prop.
Backstory (read this if you want to, it's really long but I have some of my research at the end):
Recently had the engine replaced in my boat. Previous engine was a 2011 4.3 Mercruiser TKS, with roughly 195 HP. The prop diameter and pitch was perfect for the boat and it would run at 4500 RPM at WOT and max speed was just north of 45 mph (GPS said 45.6) and it handled like a dream. That engine had a piston that decided it wanted a valve for lunch, so I bought the current engine and my WOT RPM are over 6000 (can't get an exact number since the gauge tops out at 6000 and it blows past that at half throttle), and it will only get to about 25 mph. As soon as I push it past half throttle, the temp gauge shoots up. The boat handles like absolute crap now and if it's not trimmed perfectly (that word is intentional, because there is a very precise position) it will either kick the bow up and hold it high, or it will slide to the left and right, even on glass smooth water. My estimation is that I need to reduce RPMs by at least 1400 to get back within range. I suppose I could spend a ton of money on props, spend the time swapping them out and test running them but the truth is, I would much prefer a well-informed, mathematical decision instead of trial and error, as getting my engine replaced didn't leave very much wiggle room in my budget to do trial and error. Any help would be greatly appreciated.
