SuperPickle1967
Recruit
- Joined
- Jul 13, 2010
- Messages
- 3
In really have a fine running boat. She's a 502 Mercruiser MPI in a Formula (Bravo One 1.5) and pushes along at about 4500 RPMs on a 25 pitch prop at WOT. She is crisp and sharp and never lets me down. Tuned up. Runs like a top.
The boat was surveyed and the surveyor advised me to 'get a more modern prop'. He mentioned better raking and cupping found on modern props will do more to lift the bow and prevent blowout in turns.
I also need a smaller prop, because I've found other owners of this boat and they are on 23p props spinning from 4800 to 5100 depending on load. One guy runs a 24p 4-blade. Time and time again, the stock setup I find is the 23p prop. Since the boats are all mid 90's models, the stock was non-cupped 23p prop.
If I drop from a 25p non-cupped prop to a 23p cupped prop, what's the overall effect on RPM going to be? Doesn't adding cupping add bite (resistance) and knock down some RPM? I don't want to go from an old 25p non-cupped to a modern 23p cupped and find the drop in pitch (which should yield more RPM) was countered by the cupping.
(The reason she has a 25p prop now is that the original 23p prop was stolen and the previous owner got by with the 25p prop he already had. He sold the boat because it [replacing the prop] was just one more expense he couldn't manage).
The boat was surveyed and the surveyor advised me to 'get a more modern prop'. He mentioned better raking and cupping found on modern props will do more to lift the bow and prevent blowout in turns.
I also need a smaller prop, because I've found other owners of this boat and they are on 23p props spinning from 4800 to 5100 depending on load. One guy runs a 24p 4-blade. Time and time again, the stock setup I find is the 23p prop. Since the boats are all mid 90's models, the stock was non-cupped 23p prop.
If I drop from a 25p non-cupped prop to a 23p cupped prop, what's the overall effect on RPM going to be? Doesn't adding cupping add bite (resistance) and knock down some RPM? I don't want to go from an old 25p non-cupped to a modern 23p cupped and find the drop in pitch (which should yield more RPM) was countered by the cupping.
(The reason she has a 25p prop now is that the original 23p prop was stolen and the previous owner got by with the 25p prop he already had. He sold the boat because it [replacing the prop] was just one more expense he couldn't manage).
