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TOPIC: Prop Questions

Prop Questions 7 years 2 months ago #25425

  • 64_Express
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So I have 3 props for my motors. One i can get MICHIGAN P6 73. The other two I can't seem to get any numbers off of. Where were the stock casting numbers on the props? I have a fairly heavy boat to push but it does plane out at about 15mph with a load. Would it be benifical to go to a 4-blade prop? I am just going to run a single 55 for now but eventually will be running twins. Has anyone had much experience with the 4-blades and are there different diameters and pitches available?

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Nick

1961 Uniflite 19' Express, Bearcat 55 powered
1975 Chris Craft 25' Tournament Fisherman, Twin 181 FL inboard

Re: Prop Questions 7 years 2 months ago #25433

  • billr
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on the aft face of the hub, see pic, this is a 09 pitch.
for your 19' boat you will likely run a 10 or a 9.
the 4 blade props were made to push a lot of water at lower rpm, and the blade shape is different than the 3 blade props.
I have a few brand new in the box 4 blade 8 pitch props left, but they usually go on houseboats.
The PS73 is an 11 pitch, I think that will be too much prop so you'll likely have max rpm at wot around 4500ish which isn't good for the engine. However, there is no substitute for prop testing with a tach on the water. Most of the 17' boats have been running 10 pitch, sometimes 11 depending on boat weight.
My Skagit 20 ran best with a 9 pitch 3 blade while running a single 55, but I never tried a 4 blade back then, 9 years ago come to think of it.
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Re:Prop Questions 7 years 2 months ago #25439

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Im just going to guess but I think the other two must be a 9 pitch. There are no markings on one and the other is extremely hard to read, almost gone. I am curious if a 4 blade would work the motor too hard at cruise. I know those engines have torque enough for a 4 blade but I dont want to load it too hard. Just hoping for an efficient cruise rpm and speed. Probably going to install smart tabs on her too. I am defineately going to be running a tach on this motor, how much do the 4-blades go for these days?

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Nick

1961 Uniflite 19' Express, Bearcat 55 powered
1975 Chris Craft 25' Tournament Fisherman, Twin 181 FL inboard
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