Prop Diameter

Discussion in 'Bubba's Outboards' started by Cattracker16, Oct 15, 2006.

  1. Cattracker16

    Cattracker16 New Member

    Wilton Iowa
    I recently changed my prop, on a 50 hp merc, it had a 10.38 diameter prop on it, 13 pitch, the new prop i bought is a 13 pitch and is 10.5. how much of a diffrence is that1/8 of an inch going to make on the speed/ get up outta the hole? also is the rpm going to differ between the two?
  2. samh

    samh New Member

    New props a little bigger, so your hole shot should not be as good and the top end should be faster, shouldn't turn as many RPMs, but just how much difference 1/8 th will make I don't know, just have to run it and see. I haven't ever messed with different prop diameters, but it doesn't thake much difference in pitch to tell a difference. I've got a 25 pitch on my old 150 for running deep lakes and when I'm alone in the boat, but if I'm carry'n a load or in the river or shallow lake where I want out of the hole fast I switch to a 23 pitch, makes a world of difference, but I can run about 55 (light load) with the 25 and around 45 (same load) with the 23. Great hole shot with the 23, if I've got a big guy with me and a full tank of gas I have trouble get'n out of the hole with the 25.

  3. duxsrus

    duxsrus New Member

    SW Ohio
    I don't see how that new prop would be noticably different. I used to have a 60 Merc that I had a 12, 13 & a 14 pitch prop for. The pitch change was noticable and they were slightly different diameters. But to keep the same pitch should be seamless.
  4. peewee williams

    peewee williams New Member

    Many of us have run small portable and fishing motors for years in sandy conditions.It slowly and steadily ate my props be it my 2,4,6,9.9,20,40 hp. 2 cycles or 9 hp.4 cycle Go Devil.You seldom notice the performance until the erosion is very bad.Now the evidence is extremely noticeable.The steady widening of the distance between your prop and the cavitation plate is also obvious.When you set a new prop of the same pitch and diameter on your old one,the difference is amazing.You will normally notice a difference in the new prop if you notice one at all.I think pitch will make a noticeable difference much quicker than small differences in diameter.As your motor ages and wears,the slight loss in size may keep your RPM's the same,which keeps you from noticing anything.If the performance suits you,I see no problem.If it don;t,I see one.Now 1/8 to 1/4 inch off of the outside of a large prop is a lot more metal and surface area than off of a small prop.peewee-williams