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Author Topic:   Prop Question
whalersman posted 01-19-2003 09:06 PM ET (US)   Profile for whalersman   Send Email to whalersman  
I am looking to purchase a new prop. I have a 1985 150 HP Evinrude. I am using a 15 1/2 x 15 Pitch Prop. My Evinrude book says I can use many different props that they have listed in my parts manual. From what I have heard and read though, a 15 x 17 pitch prop is the best choice for this engine.

Now here is my question. What will the 15 x 17 give me that the 15 1/2 x 15 won't?? A faster hole shot? Higher top speed?? Or about the same? Or less?

To me they are basically the same. One prop is a 1/2" larger in diameter but 2 less in pitch. To me it seems that the diameter would almost offset the pitch of the 17...

I am running about 5250 RPM WOT with light load. This boat explodes out of the hole. You can't even count to 1 and it is on Plane with minimal (if any) bow lift..

I have never been able to understand the difference between this small amount of prop difference between diameter and pitch..

I'm sure all you experts have an opinion and I am looking forward to hearing from you.

Bthom posted 01-19-2003 10:36 PM ET (US)     Profile for Bthom  Send Email to Bthom     
Hi, I'm by no means an expert but my understanding is that one inch in diameter is roughly equal to two inches of pitch.
That said, by changing to the 15"x17" you would probably be gaining about an inch more pitch, which would make your boat a little slower to get up on step but would give you a little faster top speed and lower WOT RPM.

That would be my guess.

Sal DiMercurio posted 01-19-2003 11:40 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
First of all, why are you running so much diameter ?
What type & make of boat is it on, [ size ] ?
Stay away from the 17 pitch, as your already to low on rpms with the 15-1/2 x 15.
By going from a 15 pitch to a 17, your going to drop your rpms by 400 rpms, to 4,850 rpms, "FAR" to low for that engine, will loose more with a bigger load.
My suggestion to you is, go with a 14.25 x 15 just to see what gives.
Unless your running that engine on a 22 ft boat [ to big for the engine ]to be so low on rpms, you might think about doing a compression check or a leakdown test.
That engine needs to be able to get to 5,600 rpms at wot, trimmed out with a normal load.
If she can't get past 5,250 rpms, with the 15 pitch, the engine is very sick, tired, or mounted to low.
15-12 inches of diameter is insane for that engine, thats a prop for an i/o.
For every inch of pitch taken out of the prop, you gain 200 rpms & just the reverse when adding pitch, .going from a 15 pitch up to a 17 will not help your hole shot, plus reduce your wot rpms by 400 rpms for which your already to low.
Who even gave you the idea to go up in pitch or the 15-1/2 diameter ? they sure don't know what their talking about.
weekendwarrior posted 01-20-2003 09:59 AM ET (US)     Profile for weekendwarrior  Send Email to weekendwarrior     
Did you get your WOT RPM with the motor trimmed up a little, or down all the way? This can make a significant difference.
Tom W Clark posted 01-20-2003 10:40 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

Something is wrong here. Is your 15 1/2" x 15" prop an OMC prop? If we are talking about your Outrage, I would think you should be running 19” pitch prop. That is what I ran on my nearly identical to yours Outrage 18. I used an OMC SST II 14.5” x 19” with both the 1983 Johnson 150 (powerhead rated) and the 1990 Johnson 150 (prop shaft rated) that I repowered with. Both engines reached the upper end of their RPM ranges with that prop and speeds in the high 40’s trimmed out all the way. Motor was one hole up.

A 15" x 17" prop would be OK for heavy loads or for water skiing, but a 15.5" x 15"? That sounds way to low a pitch.

As far as the diameter vs. pitch is concerned, that's pretty much a given within a given line of propellers. If you want an OMC prop, then a given pitch is going to have a given diameter. You don't really get to choose. If you were to buy an OMC prop with 17" pitch and a diameter of only 14", it will be a prop designed for the V-4's and their smaller gearcases.

There's no way your motor should be turning only 5250 with a 15.5' x 15" prop. Are you sure your tach is operating correctly? What is top speed as measured with GPS?

Sal DiMercurio posted 01-20-2003 12:17 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Tom, 14.25 diameter is for the V6 gear case, i'm running one on my 200 hp FICHT.
Theres absolutly no reason for him to be running a 15-1/2 diameter, none what so ever.
If he's running an 18' outrage, with a 150, he should be running either a 14.25 x 17 or 19.
whalersman posted 01-20-2003 01:40 PM ET (US)     Profile for whalersman  Send Email to whalersman     
Thanks Everyone..

I just purchased the Outrage 18 late this summer. It came with two OMC Props. One of them was the Aluminum 15 1/ 2 x 15 part #391535 and the other is 14 1/ 2 x 19 SST part #389924. I have not had a chance to try the SST as yet.

My Evinrude parts books gives for many different props to choose from beginning with :

15 1/2 x 13
15 1/2 x15 (This one was on the engine)
15 x 17
14 1/2 x 19
14 1/4 x 21
14 1/4 x 23
15 x 16 SST
14 12 x 19 SST (I haven't tried this one)
14 1/4 x 21 SST
14 1/4 x 23 SST

Plus a few other props with the Suffix of SRX, SST II, and SST R, which I have no idea what these props do.

My Evinrude is mounted all the way down. I may raise it up a hole or two this season. The times I have had the boat out, I may not have had the engine trimmed up properly as I am still getting used to the boat.

It seemed to me from what everyone has said that the 15 1/2 x 15 is too small in pitch and too large in diameter. I can only assume that this prop was used to pull water skiers as that is what the original owner did with this boat mostly.

This boat jumps right on plane with this prop. I am not a top end speed freak but thought about trying a different prop to get a little more top end speed but not to lose to much of the hole shot either.

I relaize that using the same diameter prop with different pitches will change the way the boat jumps out of the hole and reduce or increase the top end speed.

I also realize a certain motor can only throw a certain diameter prop due to clearance. 15 1/2 diameter seems to be the largest diameter for this engine.

I realize there is a relationship between diameter and pitch but wasn't sure how it worked. Why throwing a 15 1/2 x 15 as opposed to a 14 /12 x 19 would make much difference. It seems to me that the diameter of one would almost offset the pitch of the other so that is my dilemma and my question.

I think I will try the 14 1/2 x 19 as soon as possible..

Thanks again,

Tom W Clark posted 01-20-2003 02:23 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

That 19" SST is what you want. It is what I had. Actually I had the SST II, the difference being that the SST II is "double cupped" instead of merely "cupped".

Your motor should be one hole up for starters as that is what Whaler recommended way back then. If you want to try experimenting with high performance set ups you might even try more, but one hole up is the "standard” position”


Perhaps you misunderstood what I was saying. I agree that Joe shouldn't be using the 15.5" x 15" prop. But if you DO want a 15" pitch OMC prop, then it's going to have a 15.5" diameter. You don't get to mix and match pitches and diameters within a given line of props. As a general statement, as pitch goes up, diameter goes down.

Sal DiMercurio posted 01-20-2003 10:30 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Tom, omc makes the worst props on the market, they belong on electric motors in the bedroom on hot nights.
For half the price of an omc prop, he can get a Stiletto with 14.25 x 15 or 17 or 19 or whatever.
It's absolutly nuts for him to run a 15-1/2 diameter on an 18 ft outrage.
It's not true as you say, when pitch gos up, so does diameter, theres many bass boats running 14.25 x 25 & 27.
He can even use a 140 hp prop which is 13 diameter all the way up in pitch to 29.
The stiletto will make that boat dance, it will lift the whole boat for a completely different ride & less wet surface means more speed.
I wouldn't even think of running an omc prop on my 200 Evinrude for the simple reason they are not good props, Merc props are eons ahead of omc props, nice thin blades with plenty of cup.
If he wants more cup, [ which will also bring his rpms lower ] nothing to adding cup to a s/s prop, but removing pitch from a s/s prop is not the best idea, as they can only bend the tips of the prop & the rake & pitch starts at the hub.
If he's only twisting a 15 pitch prop & his rpms are way down, how do you figure a 19 pitch will be right for him?
A 19 pitch from a 15 will drag his rpms " DOWN" another 800 rpms.
Tom W Clark posted 01-20-2003 11:19 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

You’re not quite following along, are you? I think we have established that Joe is not well served by his 15.5” x 15” prop. We all agree on this. OK?

“OMC props are the worst props made”. Hardly. I can think of worse, and there may be better. But the fact is an OMC prop will serve his needs quite nicely.

Joe can buy a Stiletto prop for several hundred dollars. Or he can try his 19” SST which will cost him zero dollars. Of these two choices, which do you think he might try first?

It is true that, as a general statement and within a given line of props, as pitch increases, diameter decreases. This is true of the OMC props as Joe has demonstrated in his post above, it is true of Stiletto props and it is true of Rapture props.

Sure some bass boat are running a 14.25” x 25” prop, but that’s not the kind of boat we are talking about here, is it? You can’t compare apples and oranges in any meaningful way.

It is also true, as a general statement, that as pitch increases, RPM’s decrease. If Joe’s boat is already low on RPM’s then an increase in pitch would not seem to be warranted. But I happen to think there is more to this issue than just the prop on his motor. I can say this because for ten years I owned the very same boat with the very same motor, which is something you cannot say.

Sal, If I were trying to milk the last bit of speed out of my boat by selecting the right prop, believe me, with your years of boating and racing experience, you’d be the first person I would consult. But I know that Joe’s 19” prop is right for his boat so long as his motor is sound. It might not be the absolute fastest prop in the world, but I think it will serve his needs quite nicely.

It may well be that his motor is a little tired after all these years as you have suggested. He might be well served by doing a compression test. It will certainly help if he raises his motor one hole. It’s also important when maximizing one’s top speed to trim the motor out. I am sure Joe will have fun the next time he gets the boat in the water and begins experimenting with his props and I look forward to hearing the results.

fester posted 01-21-2003 01:04 AM ET (US)     Profile for fester  Send Email to fester     
One of the best things I did was to go to a prop shop when I bought my new motor a year ago. The owner of the shop was very knowledgeable and lent me a prop to make some test runs. I then ended up with a 15x19 which was a bit much for my boat. I exchanged it for a 15x17 which was a bit easy for my motor so the prop shop repitched it to an 18. The prop is great. I ended up with a stainless prop and paid about $350. There was no charge for the exchanges and the repitching cost very little. The shop I went to was Valley Propellar in Ventura California.

I think there are too many variables to enable one to select the best prop by talking about it over the internet. Go to a prop shop and you will probably save money in the long run.

lhg posted 01-21-2003 06:55 PM ET (US)     Profile for lhg    
I think the boat should be running an OMC Raker, Mercury Laser II or other aftermarket SS performance prop, since it has a top speed capability of 45-50. All this assumes the engine is running strong. My experience is that 18 Outrages are strongly in need of a bow lifting prop like these.

My Mercury prop charts indicate that an older Merc 150 (2.0 liter block) on an 18 Outrage would easily turn a 19 inch prop, with a 2:1 gear ratio. A 21 would be a light load alternative. A current 150 EFI, with 2.5 liter block and 1.87:1 gearcase, would also turn a 19, but give a faster top speed.

Props are picked by PITCH, PITCH & PITCH, plus prop design. Leave the diameter to the engineers.

whalersman posted 01-22-2003 07:26 PM ET (US)     Profile for whalersman  Send Email to whalersman     
Thanks everyone for all the input....

You don't have to hit me in the head more then a couple of times before I most likely will get the point...

I have used the 15 pitch before, so I will put on the 19 pitch that I already have and will try that. If it is too much of a prop then I will try out a 17 pitch (15 x 17).

I will post what I find out here once I can get my boat back into the water for the season.

Thanks again,

Sal DiMercurio posted 01-22-2003 09:47 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Joe, your running an 18 outrage, with a 1988 - 150 hp Evinrude right ?
Forget getting an omc prop, go to your nearest West Marine store & get a Michigan Raptor in 14.25 x 17 s/s, try it & see where your rpms go trimmed out & normal load.
If your engine over revs [ i'm confident it won't ] then bring it back to WM & they will allow you to change it,.then try a 14.25 x 19 & see how close she runs to 5,600 rpms.
You certainly do not need a 15 diameter on that boat, you could even run a 13 diameter & you will say, wow, it almost breaks my neck coming out of the hole.
No need for all that diameter on that boat.
If thats the only size you can get it in an omc prop, get an aftermarket prop as wev'e spoke of.
A good omc performance prop is going to cost you very close to $500.00 where a Raptor or Stiletto will run less then half that [ Between 250. & $300 ]for the same performance.
15" diameter on that engine with that boat, is like putting a semi truck tire on a Harley Davidson...................

Bigshot posted 01-23-2003 09:24 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Sal do you read these posts? He ALREADY has the OMC 19".
Sal DiMercurio posted 01-23-2003 11:38 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Bigshot, do you read the posts ?
His engine can't turn whats on there now, the 15 x 19 omc is too much prop.
Yes, I know he owns it, but the wrong prop is the wrong prop.
I'll put money on the 14.25 x 17 .
A new engine might be able to twist the 15 x 19, but not a 15 year old tired 1988 - 150 hp.
We will just have to wait & see what happens , won't we?
Bigshot posted 01-23-2003 01:27 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
OMC prop will be a 14.5x19 not a 15x19. Omc makes the 15x17. He may be able to spin it and considering he has it already, he can spend $40-50 to have it repitched to a 17 or 18". Why spend $250 when you already own a prop? His gear ration is different than newer 150's so it may be perfect, may suck but for free it is me.
Sal DiMercurio posted 01-23-2003 10:50 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
The last time I looked at the omc prop book, they had stopped making, or handling a 15 x 17 & went to a 15 x 16 instead.
I have no idea why, but but I think their still on the 16.
Personally, I feel it's not a good idea to add or subtract pitch on a s/s prop, as they can only bend the very tips of the prop, & the pitch starts farther down the blade, i'v seen pitch added with no ill effects, but some really screwed up props when they try & remove pitch.
Cup yes, as it's at the trailing edges of the blades.
I think Joe needs to get a new engine, as it sounds pretty tired.
Peter posted 01-24-2003 08:21 AM ET (US)     Profile for Peter  Send Email to Peter     
Joe, it sounds to me like your engine is mounted too low. You must raise the motor so that it is one hole up before the 19" prop will work properly. If you do that and it revs to 5250 or more with the 19" then you should be fine.

Barry posted 01-24-2003 11:24 AM ET (US)     Profile for Barry  Send Email to Barry     
whalersman, before you try the other prop I would check the throttle linkage, check the engine compression, check the engine height (anti-ventilation plate level with bottom of hull to 2" above), decarb, and then retest the current prop. Then I would put on the 19" and test with that prop.
whalersman posted 01-24-2003 07:41 PM ET (US)     Profile for whalersman  Send Email to whalersman     
A lot of great recommendations here. Thanks...

I can see the marks on the motor bracket where the engine was once in the 1 hole up position. Why it is now is the lowest position, I don't know.

According to the original owner who has always had the boat maintained, and by the original Hour Meter, there is only 350 hours on the boat and motor. I believe this to be true. I will however get a compression test the next time I take it by my Evinrude mechanic. The engine may be tired (I don't really think so) but it will have to do for awhile.

I will try the 14 1/2 x 19 pitch prop first just to see what it does and then most likely raise the engine a hole and try that too.

Can't wait for the boating season to begin.... In the meantime I am mounting my Fish Finder, VHF Radio and a few other things.

Thanks again everyone,

Sal DiMercurio posted 01-26-2003 01:13 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
You know Bigshot, both of us are way off base on this one.
Were talking about props on a healthy properly mounted engine.
His engine can't even swing a 15 pitch & were taliking about 17s & 19s.
Yes, on a heathly engine up on the right holes, trimmed out the engine could very well twist a 17 or maybe even a 19 pitch, but I don't think his engine is going to get anywhere within 1,000 rpms of it's recommended rpms at wot with more pitch.

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