I have an 18'6" Xpress aluminum bass boat with an f115 on the back with a PowerTech 13x19 prop. I have installed Mobster Tabs to fix a porpoising problem I had (which worked beautifully) and was just plinking around on the net looking at boat topics and came across a prop pitch calculator. It is the same algebraic formula that everyone uses but it is automated and will do the math for you. I plugged in the pitch (19 plus 1 for cupped prop), engine rpms (5850), gear ratio (2.15), and speed (50 mph per gps) at the given rpms and it computed a slip of 5%. Is that about right? I have read that the slip is usually between 6-10%. So I would guess that with the current setup with the help of the trim tabs, I am getting about the best I can expect from this setup, right?
As a side note, the addition of the Mobster Tabs was probably the best thing I did for my boat and my pocket book. Before, the most speed I could get out of the boat was 40-42 mph at about 5400 rpms and the motor was just chugging the gas down costing me a fortune. Now with the boat running out right and apparently under less strain (evident from the higher rpms and higher speed) the fuel economy is probably double what it was before the tabs. I used to have to worry about how long we would be able to run on the tank. Now, we can do our normal fishing routine, running from hole to hole or reef to reef and at the end of the day, I have to worry about what to do with the other 1/3 to 1/2 tank of gas I have left. Definitely a satisfied customer.
As a side note, the addition of the Mobster Tabs was probably the best thing I did for my boat and my pocket book. Before, the most speed I could get out of the boat was 40-42 mph at about 5400 rpms and the motor was just chugging the gas down costing me a fortune. Now with the boat running out right and apparently under less strain (evident from the higher rpms and higher speed) the fuel economy is probably double what it was before the tabs. I used to have to worry about how long we would be able to run on the tank. Now, we can do our normal fishing routine, running from hole to hole or reef to reef and at the end of the day, I have to worry about what to do with the other 1/3 to 1/2 tank of gas I have left. Definitely a satisfied customer.
