Prop size

[Joker2]

I have a 75' V20 1995 150 Ocean Pro ( rebuilt completely in 2010 ) The boat has a 15/12 X 15 Prop on it. After breakin it in last season, able to open it up this year Ifound out I was only getting 4500 RPM's, had the Prop reconditioned for more RPM's, not sure why but now when idling along or going below 2000 RPM engine vibrates I even feel it at the wheel when I bring it up I can't notice anything, I might be crazy but could the prop be out of balance or something like that. Also I have my doubts about the mechanic who sent out the prop, it came back painted but they just went right over all the old peeling paint, no sanding or anything, thought that was lame. Makes me wonder what kind of job they did on the prop. The prop guys are a major prop house in this area. Is there any way to find out what I need to know without using a known good prop?

[Joker2]

From what I read on this site is 15-1/2 X 15 the wrong size should I have a 17 ?

[bradford]

Most folks run a 15 x 17 or 14 1/2 x 19 prop. MJ used to run a 15 x 15 to get added torque for carrying heavy loads. :zip:
You should be getting more RPM's with the 15 x 15. Are you sure she's firing on all cylinders? Makes me think a cylinder or two are not with the low rpms and the low speed vibration.

[Joker2]

I can check that out, she's not stalling though.

[tsubaki]

Good call bradford on the low rpm's and vibration, could likely be a bad plug or two.
And I agree, a 17" stainless or a 15" aluminum should be about right.
Joker, did they rehub the prop (if applicable) too and restamp the numbers?

[Joker2]

not sure about the rehub, but I did not see any stamping. I almost think the #*$%hole mechanic just polished up the blades and charged me for it, because on the main housing the paint was peeling from when he originally gave me the boat last year ( he resprayed a used prop ) Then when I brought him the boat recently to replace my fried Ignition system do to a direct short caused by the metal clip that holds the big red plug together, I asked him to send out my prop to be reconditioned for more RPM's. When I looked at it all the blades were nice but the main housing had all the old chipping paint still there underneath new paint. I never had it done before but for 82.00 you think they would wheel it out and respray. maybe it's me.

[Joker2]

How does the diameter work, can I go from a 15 to 14, not sure what changing the diameter does. I never had to mess with props before, trying to learn. Thanks

[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]

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...

[awthacker]

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]

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.

[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) :head:

[reelapeelin]

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...

[tsubaki]

Joker, I reread some stuff and edited a portion I posted earlier about a 17" stainless or a 19" aluminum should be about right. It was supposed to be a 17" stainless or 15" aluminum.
I ran a 14.8x17 aluminum and a 14x19 stainless on mine and got almost the same exact numbers fuel, speed and rpm wise. I need to go to a 17" stainless.
http://www.wellcraftv20.com/community/showthread.php?t=12543

And get you a gallon of Seafoam, mix to what they suggest. Think it's 1oz per gallon.