Logo
Results 1 to 3 of 3

Thread: Prop madness

  1. #1

    Default Prop madness

    I need a new prop for my boat, a 1978 Sea Ray with a pre alpha 260 outdrive. The prop I was running came with the boat and has no markings on it other then the hub which is stamped with 48-79576-21 and across from that the letter U. But I can't find anything online other then more unanswered questions.

    Anyone familiar with this stuff? There's got to be other options out there that will fit.
    Last edited by 805HD; 08-20-2017 at 11:56 AM.

  2. #2
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,806

    Default Re: Prop madness

    the last two digits give you the pitch - 21" for the prop you have. the other variable left is diameter and there isn't much choice there due to the outdrive design....the splines are fixed. the other variables are material and blade count. for those outdrives, three blade props are standard....and most opt for aluminum due to $$...stainless holds up pretty well but costs more $$$.

    one typically selects the prop's pitch to allow the engine to get to the WOT rpm band specified....and due it with a 'full and normal' load in the boat. if you are 'in the band' then the prop's pitch is acceptable. If the rpm band is exceeded, you need more pitch to load the engine more; if it wont get into the WOR rpm band, there's too much load on the engine (lugging) and a smaller pitched prop is in order. due all of this with the engine in proper working order.

    Finally, any decent dealer or prop shop can answer all your questions - they are usually worth a visit just for that...

    PS the owner's manual and the shop manual both have decent discussions on prop selection....may be worth the read.....
    Last edited by makomark; 08-20-2017 at 02:46 PM.

  3. #3
    Join Date
    Sep 2008
    Location
    Hague, Virginia, USA
    Posts
    3,700

    Default Re: Prop madness

    If the current prop was 21 pitch, you can get a close approximation of the diameter by placing the prop on a piece of cardboard and tracing the outer edge of one of the blades as you turn it through 360 degrees.

    Be careful - many of the Volvo props are left turning, long hub props. For comparison, on a previous C-Hawk I owned with the pre-alpha drive powered by a Crusader 220 (which was basically a GM 305.) The WOT band was 4400 - 4800 rpm. This was a 6000 lb boat when fully loaded. I experimented with several props. The best setup was a 15 X 17. So, in addition to Makomark's good advice, you need to consider the engine horsepower and the weight of the boat. And, as he said, a good prop shop will likely get you what you need.

    There are also several Sea Ray forums out there. If you find someone that has the same setup as you have, they may know the prop size and pitch that works for them.
    CHawk 25 DLX

Similar Threads

  1. 2002 Mercury 4-Stroke 40Hp Motor w/Steel Prop & Sq-Lok Hub System -Prop Nut Torque Help
    By bpoulson in forum Propeller Selection and Replacement
    Replies: 1
    Last Post: 08-29-2017, 09:10 AM
  2. DAMMIT!! I bent my prop shaft and chewed up my prop 1980 Johnson 25 hp J25RCSA
    By Jhanratt in forum Johnson Evinrude Outboard Forum
    Replies: 23
    Last Post: 09-02-2016, 11:31 PM
  3. e15rcde prop bushing bad? prop spins on prop shaft while in gear
    By rockfisher805 in forum Johnson Evinrude Outboard Forum
    Replies: 2
    Last Post: 08-15-2014, 02:09 PM
  4. Prop size question and off shore style prop on a through hub exhaust?
    By H2oallyear in forum Propeller Selection and Replacement
    Replies: 0
    Last Post: 07-25-2014, 08:07 PM
  5. Trying to determine diameter and pitch of prop on 85HP Johnson from number stamped on prop
    By Bob Padowicz in forum Johnson Evinrude Outboard Archive
    Replies: 3
    Last Post: 07-30-2006, 12:27 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •