Prop size

[tsubaki]

Normally when they repitch a prop, they heat and bend the blades causing the need to rehub. Actually, if I'm not mistaken they have to remove the hub to fit their presses.
Lets say you repitch from a 15 to a 17, you will lose diameter. If you repitch from say a 17 to a 15 you may need grinding to fit beneath the cavitation plate or miss the steering torque.
When buying new, there are numerous changes that can be made toward performance with subtle changes of the prop, this is where the pro's come into place.
Depending on the circumstance, keeping a certain pitch but changing the diameter or even the blade design cup or lack there of can make a huge difference in performance. The same can be said for keeping a certain diameter and changing the pitch, having a cupped or regular blade.
The diameter basically dictates how much water the prop grabs BUT there is almost always a relationship with the pitch.
What I do is find a normal manufacturer of a prop (Michigan Wheel preferred) and work within the perimeters of their props. Easier to replace with the same if damaged.
Lets say I've got an engine not turning up enough rpms and have verified the engine is running correctly and at the correct height. I'd decrease the pitch a couple of numbers, test and go from there. You will see the average manufacturer does not carry the same diameter while also changing pitches.
Now, problematically, different prop materials will change your prop designations. Stainless, aluminum or composite materials perform differently even if you have the same exact pitch, diameter and blade design between the three.
Sorry this is not a good definition but about the best I can muster.

[Joker2]

It's helpfull, thanx

[Joker2]

I checked all the cylinders pulling the wires one at a time didn't really notice the Tach move, but I did hear a drop in the engine with each one. Also on the lower Starboard plug there was a little build up of black. This happened once before when I was running double oil on break in, just thought it was the extra oil fouling the plug, should I be conceerned?

[reelapeelin]

Originally Posted by Joker2

I checked all the cylinders pulling the wires one at a time didn't really notice the Tach move, but I did hear a drop in the engine with each one. Also on the lower Starboard plug there was a little build up of black. This happened once before when I was running double oil on break in, just thought it was the extra oil fouling the plug, should I be conceerned?

Joker, these are deep V hulls, which means there is a lot of planing surface on the water which means resistance...IMO they need a large diameter prop to get all the push against that resistance...I used a 15 1/4" x 17 for that reason and was completely satisfied that my motor was getting all the prefomance possible on that hull...The only reason I didn't use a 15 1/2" diameter was that it was a little too heavy and caused a rattle in the lower unit, but your motor should handle it...you didn't mention SS or alum...use SS for best performance...hope this helps you find the right prop...sometimes it's not easy...

[Joker2]

Originally Posted by reelapeelin

Joker, these are deep V hulls, which means there is a lot of planing surface on the water which means resistance...IMO they need a large diameter prop to get all the push against that resistance...I used a 15 1/4" x 17 for that reason and was completely satisfied that my motor was getting all the prefomance possible on that hull...The only reason I didn't use a 15 1/2" diameter was that it was a little too heavy and caused a rattle in the lower unit, but your motor should handle it...you didn't mention SS or alum...use SS for best performance...hope this helps you find the right prop...sometimes it's not easy...

the prop on there is a 15- 1/2 X 15 aluminum. She really jumps onto plane, since I had it repitched I can get 5000 on Tach ( if Tach is correct ) but doesn't feel that powerfull only 30 mph. on GPS. Last year I got 30 mph at 4000 RPM. I will do a compression test on all cylinders, if that is good I will research if doing a seafoam treatment that everyone talks about on this forum will be safe to do to my engine. maybe that is all it needs.

[awthacker]

Originally Posted by Joker2

I checked all the cylinders pulling the wires one at a time didn't really notice the Tach move, but I did hear a drop in the engine with each one. Also on the lower Starboard plug there was a little build up of black. This happened once before when I was running double oil on break in, just thought it was the extra oil fouling the plug, should I be conceerned?

]

I don't know too much, but maybe you should run some seafoam through it to clean out the cylinders/plugs. However the fact that one plug is fouling may mean that cylinder is not firing and the unused oil is causing the residue.

[Joker2]

I have a 1995 150 HP Ocean Pro. Is the seafoam safe to do on this engine ? I only have ten hours running double oil ( break in ) that was last year. This year about 4 - 5 hours on motor, that doesn't seem like a lot, should I have to do a treatment already ? By the way my marina is a 20 minute in and out no wake zone, so I am going very slow a lot, could that be reason for some extra fouling of plugs ?

[Destroyer]

Actually, I think that I'd try a 14 1/2 x 17 prop for that engine. (The smaller dia. will let your RPM's come up a little, and the extra pitch should help with your top end once they get there). As to the fouling, is it really fouling, (as in not firing) or does it just have some black residue on it from the break-in? I use Seafoam as a preventitive measure, not as a corrective. And even then I only use it about every 6 tankfuls or so. (When I remember to add it)

[reelapeelin]

Originally Posted by Destroyer

Actually, I think that I'd try a 14 1/2 x 17 prop for that engine. (The smaller dia. will let your RPM's come up a little...

My Honda spun up to redline (6gs) as fast as you could ask it to w/both the 15 1/4 & 15 1/2 props...the extra diameter didn't slow it a bit...

As for the suspicion of idling causing the cyls to load up...it may very well be...a trick to prevent that at idle is to TILT the motor UP a little PAST LEVEL...that prevents unburned oil from building up in the top of the cyl and fouling the plug...a marine tech told me that years ago and it worked on the 150 Evinrude I had at the time...