Re: prop for 19.5 bowrider with 4.3 mercruiser mpi
You've got the right idea for enhancing low end performance: 4 blades instead of 3, stainless steel, lower pitch. I think it's smart to move from a 21" pitch to a 19" pitch, and if that's still not enough to "yank" your skiers out of the water, go down in pitch even further, maybe another inch or two, at most. Just be careful when using a prop with a really low pitch, not to over-rev the engine when you're cruising.
I expect that you'll be pleased with the performance of your new 19" four blade SS prop, but let us know.