Not your usual prop

Discussion in 'Props' started by maxmini, Nov 21, 2017.

  1. maxmini
    Joined: Aug 2017
    Posts: 23
    Likes: 7, Points: 3
    Location: Northridge CA

    maxmini Junior Member

    I am putting together a little fun toy for the summer and have uprated the power plant from a 1987 Nissan 40 to a 1993 Johnson 50. We really weren't looking for more HP but the power tilt option is going to be very helpful where we will be using the boat. The price of the motor was ridiculously low and we spent a small bit of time and money on refreshing the internals and making it look a lot better on the exterior. My issue is as you can see the boat is not what you would normally put a 50 HP motor on even though the hull is built to take it . I have two new props for it which are the recommended type on the charts but of course that recommendation was most likely for a much larger and heavier boat. At a going out of business sale I picked up a pair of Mercury Vortex units one 12 1/4 - 15 and a 11 3/4 - 17 for a total of $40 just to give us a base line . The original prop on the motor was a bit dinged up so we wanted to start fresh.
    As I mentioned the boat is just for fun and it will spend much more time cruising and perhaps towing the grand kids on a tube than at full throttle. I would like it to be reasonably fast but getting the last few MPH out of it is not my main goal.
    We are presently modifying the transom to take the longer shaft motor and hope to end up with the cavitation plate slightly above the bottom line of the boat for starters.
    IMG_7457.JPG IMG_8526.JPG IMG_8545.JPG
    I thank any of you that may have some advice in this area. IMG_7444.JPG IMG_7456.JPG
     
  2. kapnD
    Joined: Jan 2003
    Posts: 1,293
    Likes: 408, Points: 83, Legacy Rep: 40
    Location: hawaii, usa

    kapnD Senior Member

    Is that Johnston 50 a 20” long shaft?
    They made them in a 15” length, would look better and help keep CG lower , and save you a bunch of work.
     
  3. maxmini
    Joined: Aug 2017
    Posts: 23
    Likes: 7, Points: 3
    Location: Northridge CA

    maxmini Junior Member

    I agree with you and those short shafts are quite rare from what I have been able to find out. I will keep my eye out for one and would make the switch . I am aware of the CG issue and would make the change for that reason alone but at this point all we have is the 20 inch shaft. Where would some good places be to look for a short shaft ? Thanks for the input.
     
  4. kapnD
    Joined: Jan 2003
    Posts: 1,293
    Likes: 408, Points: 83, Legacy Rep: 40
    Location: hawaii, usa

    kapnD Senior Member

    You might get some results by posting an ad or inquiry on THT forum, mostly outboard guys over there.
    All you need is a mid housing and a shaft, your motor looks immaculate.
    I had a 60 hp Evinrude short at one time, think it was early 1980s. It sure made my 13’ Boston Whaler a rocket Ship!
     
  5. maxmini
    Joined: Aug 2017
    Posts: 23
    Likes: 7, Points: 3
    Location: Northridge CA

    maxmini Junior Member

    Thanks for the nice words . I am not familiar with the THT forum. Could you provide a link perhaps ?
     
  6. kapnD
    Joined: Jan 2003
    Posts: 1,293
    Likes: 408, Points: 83, Legacy Rep: 40
    Location: hawaii, usa

    kapnD Senior Member

    The Hull Truth Forum, it’s pretty popular with east coast outboard people, you can easily get there via Google.
    Be forewarned that it is not a forum populated by knowledgeable practioners, but it does reach a lot of people.
     
  7. maxmini
    Joined: Aug 2017
    Posts: 23
    Likes: 7, Points: 3
    Location: Northridge CA

    maxmini Junior Member

    Thank you. The boat will be kept in CT so perhaps I can find some events that might be fun to attend as well . I've been very active on sailboat racing and auto forums for way too many years and I know you have to take the good with the bad.
     

  8. PAR
    Joined: Nov 2003
    Posts: 19,126
    Likes: 497, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    THT is a bit understated by KapnD. There's a fairly large percentage of professionals, from different arenas within the industry here, but over there it's mostly JimBob and his half brother/uncle JoeLarry, taking about what they did to their BassTracker last year.

    Given your project, the best advice you can get is to try what you have and see where she runs out at WOT and if it's pulling the rated RPM. If not, you have a good idea which way to go. Behavior at speed will also provide some information about prop selection (rake, cup, etc.), I don't think you'll need to worry much about the hole short, unless racing similar rigs.
     
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