Prop size

  • August 22, 2018 7:48 AM
    Message # 6634019
    Deleted user

    I would like information regarding the correct prop size for my W32 which has a Beta 1308 37.5hp engine with a 2:1 gear ratio. The prop currently in use is a 16R11 (diameter:pitch) three bladed prop, but I am not able to attain the 3000rpm under load suggested by Beta Marine. The engine reaches 3300rpm with no load.

  • August 22, 2018 4:55 PM
    Reply # 6634817 on 6634019
    Deleted user

    Mark I believe you are over pitched (slower and less noise motoring), should have be down in the 9" to 10 pitch for max RPM, noise and speed? not 11

    Here is an ok site to do the #'s

    Victory prop cal

    you could go with something like a 2 blade 16 x 10 ? or an 16 x 9 on the three blade thing ? or a max prop would allow adjustments to get it exact.

    Hope this helps.


    I am assuming the prop is super clean (just launched) and the bottom is spotless, else you are never going to get full RPMS if stuff is stuck to the prop.

    p.s. use 7kt as desired speed to run #'s  in calculator, on the other hand if you are getting 6.5kt out of your current setup you are about as good as it gets.

    pps. mark if you could use the current prop as a backup and get a 2 blade 16x10. That way you would be set for anything.

    a second option is to have a prop shop depitch the blades back to a 16x10 and you would be pretty close to getting the 3K 

    I myself enjoy 1800 to 2000 RPM, with less noise, less fuel and less likely to be on time.

    Last modified: August 22, 2018 5:43 PM | Deleted user
  • August 23, 2018 4:06 AM
    Reply # 6635319 on 6634019
    Deleted user

    Norm,  Thanks for your insight. It supports my suspicion. I totally agree with your preference for lower rpm operation but want the prop sized correctly so as not to load the engine unnecessarily. Also, a recent total lapse of attention resulted in a bent blade on the current prop so it is time to address this concern. Thanks again for your help.


  • August 23, 2018 8:23 AM
    Reply # 6635704 on 6634019
    Deleted user


    How did you bend a blade? they are tucked way up, and away from almost everything?

    Second if you buy your new prop from a prop shop, bring your torque curve for the bata, it could be that the larger pitch may be correct a little lower down the RPM curve?? in any case, if you can, use a good propeller repair shop (with good tech skill = not just a sales person) you will be ahead.

    just a FYI most bad things happen from missing obvious signs (i.e planning and prepping for ? as much as you can, will reduce these) but learning from a screwup will stick with you for a long long time. For me, I have yet to repeat any stupid mistakes = once is enough. One of those is; if I am getting rushed, I look to see is there a way to back off, even if it is not tward my goal or in a forward direction, if so, it could be the best plan, one can regroup and then make it to a better and happier end.

    With a sail boat sailing, you can pick a destination, or a time to dock, just not both. So go out knowing that you may will need to change plans, and that is OK, if not, you will missing much of the joy of sailing. Also a check list is a good thing to use.