The mystery of a proper prop and terrible performance.

Discussion in 'Props' started by missinginaction, Jan 25, 2020.

  1. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    Just a quick update to this thread. First Gonzo, I thought supercavatating props were primarily for boats with speeds over 35 knots. I've never looked into them but will ask the question.

    I had a nice conversation with the people at Michigan Wheel today. They don't use the "Beta roh - delta" prop calculation that I used but they were nevertheless very polite and more importantly very good listeners. I explained my situation to them and we discussed gearing, blade loading, cavatation and how these concepts could apply to my particular boat. I did get some confirmation on my thinking. They felt that a 17 x 18 prop was appropriate but were concerned that 2" clearance between the propeller and the hull was too little. We agreed that it would be easier to shave a 17" prop down to 16" rather than try to add material to a 16" and go wider.

    I had a second conversation with Walter gear and based on the serial number of the drive I have it was indeed made in 1973. It must be OE. Surprised at this but it is what it is.

    So this is going to be a $4,000 experiment, although it's a well calculated risk. For the time being I'll amuse myself getting the old v-drive out and getting ready to install the new unit.

    I will get back to you all and let you know how this works out.

    MIA
     
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  2. DogCavalry
    Joined: Sep 2019
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    Good luck!
     
  3. missinginaction
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    missinginaction Senior Member

    Just an update to this thread. My plan was to get started on this project now. Over the last couple of weeks though everything's changed. Most businesses closed. We're not even sure what we're doing at the boat club I belong to. So many of you took time and made the effort to get me pointed in the right direction. I hope I can get this job done this year but it may not happen depending on how this virus situation plays out. I'll resurrect this thread when I can get this done but I'm beginning to think it may be 2021 the way things are going. I hope not but we'll see.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Plenty of things are on hold with the virus about, main job is not to get the thing ! :eek: You are methodical, and will get it done.
     
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  5. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    v-drive.jpg Well, the old 1.46 : 1 v-drive is finally out and in the workshop. Next stop is Walter Gear. I'll have to see if they want to change the ratio on this one to 2.05 : 1 or sell me a new unit. I'll let them make the call. BTW, I found a way to get this out of the boat all by myself! I didn't tear up the seal either. Thanks to all who contributed to this thread, I just wanted you to know that I'm moving forward with this project. MIA
     
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  6. Cajunpockettunnel
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    Location: Franklin, LA

    Cajunpockettunnel Senior Member

    You guys amaze me with the knowledge you have. I wish you the best with this project and will be keeping an eye out. Great boat you have also. Keep us posted
     
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  7. missinginaction
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    missinginaction Senior Member

    What a nice thing to say. Thank you.
     
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  8. Cajunpockettunnel
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    Cajunpockettunnel Senior Member

    Just giving credit where it's due.
     
  9. Cajunpockettunnel
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    Cajunpockettunnel Senior Member

    Bo's Propeller http://www.bospropeller.com/

    MIA, check these guys out. I just got off the phone with them. They will send props to you to try, if you don't like them send them back as long as they are not damaged. Sounds like a pretty good deal to me.
     
  10. missinginaction
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    missinginaction Senior Member

    Old prop.........and new prop. If, as I determined, my problem was insufficient blade area I've solved it. Still a number of things to do in the engine compartment, not the least of which is moving the entire engine/drive line aft 1-3/4 inches and installing a new 2:1 ratio v-drive to match the prop. Time will tell. Thanks again to everyone who helped with this.

    old prop new prop.jpg
     
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  11. 7228sedan
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    7228sedan Senior Member

    WOW, that's a nice wheel... Can't wait to hear the result!
     
  12. missinginaction
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    missinginaction Senior Member

    Yesterday, Sunday May 9th, my brother in law helped me get the new Walter RV-26D V-drive into the boat. A two man lift for sure.

    There was no one around today so I tackled the installation myself. I won't go into all the details but let's just say it was a challenge. The Rv-26 is slightly larger and 20 lbs or so heavier than the RV-20 that it replaced. There is still a lot to do but day by day the list keeps getting a little shorter.

    So far so good.

    MIA
     
  13. cracked_ribs
    Joined: Nov 2018
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    cracked_ribs Senior Member

    Curious to see how it turns out.

    I have a heavy 20 foot deep V with a 215hp 302. It moves along pretty well but is barely more than half the weight of your Silverton. And I wouldn't want any less power, that's for sure. I get on to plane by running her at 3500, sometimes a little more.

    Planing a boat that big with that little engine is definitely going to be work! I can see why setup would be critical.
     
  14. missinginaction
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    missinginaction Senior Member

    Well, you have to keep in mind that for the vast majority of the time my boat operates at 7 or 8 knots. The objective of this project is to enable her to carry modest speed into ocean inlets or running from weather when necessary. I'm hoping for a cruising speed of around 20 knots. We will know in a month or so.
     

  15. cracked_ribs
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    cracked_ribs Senior Member

    Might be possible, for sure. If I had to guess I'd say you will have to flog that motor pretty hard to get out of the hole; I can't even think about planing below 2800, and that's under perfect conditions, having backed down from 3500 or so.

    I've never seen a Silverton 26, but a 31 flybridge followed me out of a rough rivermouth one day; we were talking at the gas dock beforehand. IIRC he had twin 360s but that's a bigger boat, obviously. I mostly couldn't see him once it got rough, he just disappeared between the waves. But I could hear him barking his props and then once we got out into open water I could look back and see him again, still in the thick of it, hull launching out of the water on the way up and props barking at the peak...it was pretty gnarly for that mile or so. But he did fine.

    Anyway I wouldn't be that surprised if you could get her to 20. I think it'll take a while to plane, though, and you will probably have to wind her right up. Cruising RPM on my 302 is 3500. I think if it's geared right you could sustain 20 knots at 3500 and keep her on plane.
     
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