Need Prop Help... 140/Looper on a Bracket

[BigMike]

I have a 1979 V-20 ...I repowered it from an I/O to a Gil Bracket with floatation... Installed a 1988 Johnson 140HP VRO Looper .....It has a 13 1/4" X 17P aluminum prop on it, Cavitation plate is 2 1/2" above the bottom of hull... My V-20 is heavier than most with lots of gear and fishing equiptment and a hard top... Motor runs great but seems to have way to much prop on it the tach was broken. . I just installed a new tach.....I'm wondering if anyone can recomend a starting point for prop size I'm thinking 13 1/4 X 15p or even a 14p.....

[spareparts]

do you have the small V4 style gearcase or do you have the big V6 gear case, they were avbailable both ways

[Skools Out]

how far back is your motor set? the correct height is for every 1 ft back from transom to the lower unit your cav plate should be 1 inch above bottom of the boat. is it a 20 or 25 inch motor? if it's a 20 inch you will have the small gear case, is it a 13 or 15 spline prop shaft? if it's a 13 spline then the 13 1/4 x 15 in stainless would be a good prop. if it's the 15 spline larger v4 lower unit then a 15 x 15 would be a good place to start.

[Destroyer]

Originally Posted by BigMike

I have a 1979 V-20 ...I repowered it from an I/O to a Gil Bracket with floatation... Installed a 1988 Johnson 140HP VRO Looper .....It has a 13 1/4" X 17P aluminum prop on it, Cavitation plate is 2 1/2" above the bottom of hull... My V-20 is heavier than most with lots of gear and fishing equiptment and a hard top... Motor runs great but seems to have way to much prop on it the tach was broken. . I just installed a new tach.....I'm wondering if anyone can recomend a starting point for prop size I'm thinking 13 1/4 X 15p or even a 14p.....

What is your WOT reading on the new tach? By "too much prop" I take it you think the motor is not reaching it's proper RPM @ WOT? If that's the case I'd keep the same dia if possible and drop to a 15p prop for starters.. Dial in the pitch first, then fine tune with different diameters if necessary. IMHO

[THEFERMANATOR]

Being an 88 it is probably a V-4 gearcase regardless of shaft length. A 13 1/4 X 15 stainless would be a good starting point as the 17 is quite a bit of prop for one.