I have a 20' Maxum SR2000 with a Mercruiser 3.0LX and a 19" Mercury High Five SS prop. We don't waterski, so hole shot's not important to me. We do occasionally drag the kids on tubes, but 75% of the boating we do is just cruising the rivers and lakes.
I'd like to get more top-end speed, as well as pick up a spare prop, so I'm thinking about using my high five as a spare most of the time and going with a three blade aluminum prop. I'm changing a lot of parameters, so I'm really unclear as to where to go with the pitch.
WOT for my motor should be about 4400-4800. With a typical load and properly trimmed, I'm running at about 30-32 mph (per gps) on calm lake water at 4800 rpm. Problem is, I can't run full throttle without exceeding my rpms by another 600 or so, so I have to keep it backed off.
I've read that for each 2" of pitch increase, rpms should drop 200-400, but I've also read that increases in the number of blades will also drop rpms. In my case, I want to shave off at least 600 rpms AND I want to drop two blades.
Off the top of my head, I'm thinking a 23" pitch might get me in the ball-park, but I'm relatively new to boats, so I'm hoping to get input from more knowledgeable people (which pretty much means anyone reading this).
Thanks.
I should add that my current gear ratio is 1.98:1 (or 1.94:1?) and I'm well aware that my slip is VERY high, like 20-25%. My High Five is pretty nicked up, so that's probably the main reason.
I'd like to get more top-end speed, as well as pick up a spare prop, so I'm thinking about using my high five as a spare most of the time and going with a three blade aluminum prop. I'm changing a lot of parameters, so I'm really unclear as to where to go with the pitch.
WOT for my motor should be about 4400-4800. With a typical load and properly trimmed, I'm running at about 30-32 mph (per gps) on calm lake water at 4800 rpm. Problem is, I can't run full throttle without exceeding my rpms by another 600 or so, so I have to keep it backed off.
I've read that for each 2" of pitch increase, rpms should drop 200-400, but I've also read that increases in the number of blades will also drop rpms. In my case, I want to shave off at least 600 rpms AND I want to drop two blades.
Off the top of my head, I'm thinking a 23" pitch might get me in the ball-park, but I'm relatively new to boats, so I'm hoping to get input from more knowledgeable people (which pretty much means anyone reading this).
Thanks.
I should add that my current gear ratio is 1.98:1 (or 1.94:1?) and I'm well aware that my slip is VERY high, like 20-25%. My High Five is pretty nicked up, so that's probably the main reason.
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