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I'm trying to get a handle on propellers and their design properties but I've become confused (not a difficult thing to do in my case).

In everything I've found the concern is how to accomplish max speed and sometimes hole shot.

My concern is fuel efficiency for Great Lake cruising & camping/fishing with my kids. Waterskiing will be done but they're only little kids!

It's a 1984 Outrage 22', 1990 225 V6 Evinrude VRO, specs say Gear ratio is 14:36 (.538) The current aluminum prop has no markings except SP on it. I also carry extra weight, 9.9 Evinrude, stern seat, lots of canvas & junk for a family of 4 to weekend camp aboard, and I'm on a diet.;)

Ideas are greatly appreciated even it's not propeller related. Tips are good! Or what to look out for. Anything guys ! These pump prices are scaring me:(
You should also know that this boat is new to me. Only managed to use it 2 days in the late fall so my current data is not very good but in those 2 days it did seem a tad excessive.

Regards,

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What speed do you get with your current prop and what rpms at WOT?

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Unfortunately due to my newness with the boat I have not recorded these stats. Considering the 2 hail storms and 3 brief snow storms today that statiscal survey gathering may be a few more days / weeks.:(

Your response is good though because I really didn't know what information to gather and provide to answer my query.

Which brings to mind that I may have an opportunity to dunk the boat this coming weekend.( snow or no snow) I do not have a GPS, yet, but I do have an older fishfinder installed that records speed/mileage. etc

What do I need to record to help this topic? So if someone can tell me what to record with my limited gauges by Thursday, I can post more qualifying information Monday.

Thanks.

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Peter,

Let me start with the basics here as I know them. Speed is not important at this time, this will come later in the fine tuning.

1. Most important factor is having a tachometer. The prop selected should perform within the range of what the engine manual states for the Maximum RPM's.
Example: If your engine books states that your engine should run at max RPM's between 4500 and 5500 RPM, then your choice for a prop would let the engine run in those ranges.
If you are using a 19 pitch (forget about the diameter for now), and you are getting only 4500 RPM's, then you need to drop down to a smaller pitch prop like a 17 pitch or a 15 pitch.
On the other hand, if you are running a 19 pitch prop and your tach shows 6000 RPM's, then you need to move up to a 21 pitch prop.

Those are the basics. You need to get the right pitch prop so your engine will run very close to the recommended max RPM's. Next, fine tuning and what you want in performance.

Here is another example from my personal past experience with a 70hp Evinrude.
1. I used a 17 pitch prop which would give me a little faster top end speed but it was slower out of the hole. The Max RPM's fell within the recommendations from the manual. Both of these were around 5200 to 5400 RPM's.

2. I used a 15 pitch prop which was much faster out of the whole for water skiing etc., but was about a mile an hour or 2 slower than the 17 pitch. This prop also fell within the recommendations from the manual for max RPM's.

So, now I could use either prop for whatever my intentions were for the day. Water skiing I would use the 15 pitch, and for top end speed I could use the 17 pitch. Usually I just left the 15 pitch on as I never was concerned about top speed.

That's about it for the basics... If you want to get fancier and race your boat, then you need to start looking at cupped props, double cupped props, 4 bladed props, etc., etc... and, you would have to talk to someone else besides me.... :)

So, start with the basics and make sure your engine RPM's fall between what your manual says. Good Luck..

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You were posting as I was editing Joe.
I have what I believe to be the original OMC "text book/manual" for this motor so I if can make it to to the lake this weekend (snow or no snow) I'll try to document all the readings at all speeds and rpm's etc.

I have a speedo, I have a tach, and I have the Fishfinder with transducer? I just hope they are all reasonably accurate.

It would be nice to figure out what exactly is on there now too. And the spare that came with it.

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Okay, so the kids are looking at me strangely for crawling around in the dark and rain under the canvas outside. But...

The spare prop that came with boat has 14-1/2 X 19 on it. it also has MN216 on another location. The prop on the motor still only has the SP I mentioned previously. Nothing else.

May I assume this spare prop is 14 1/2 inches witha 19 degree pitch?

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Peter,

Speedometers are very seldom accurate and speed is not important at this time. Only RPM's of an accurate tach are important.

Props are usually marked in one or two of 3 places.
1. On the outside between 2 of the blades
2. On the back of the hub around the area of the retaining nut
3. On the front of the prop hub. (you must remove the prop to see the markings)

Look at your spare prop closely. It should have the diameter, pitch and part number somewhere as mentioned above.

Again, try not to concern yourself with speed... Only the Tach RPM's.... This will keep things a little easier for the time being.

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Again we were crossing posts.
But, although the current prop only shows what I mentioned on the outside, I did find on the spare, sitting here on my desk, where to look on the hub for the info when I remove the current prop. And remove the grunge.

Seems odd the spare has all the obvious marking between the blades on the outside but not the current installed prop.

Thanks

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Now you are getting somewhere...
14 1/2 x 19 pitch is correct... Generally the pitch is given last.

That seems to be the same prop that my V6 150 hp uses.
If your other prop says nothing, I would put the 19 pitch on and see what you get for RPM's. Then we know where to go from there.

On my Evinrude 150, I dropped down in pitch to 17 because I prefer the hole shot and not top end speed. My RPM's still fall within the range called for in the manual...

Are we crossing post again........ ????? :)

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I would check and see what Jeff is running since they have almost the same engine and the same boat

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I mentioned above I would try to dunk the boat this weekend - not so.
It's the 100th anniverssary of my alma mater high school Corps and my business partner's son is the CO, Lt. Colonel. My presence is expected. Plus it's the year end grad for my nephew at RMC. Royal Military College. And Sunday is Mothers Day!

My disappearing to the lake for boat trials may not be appreciated;) What was I thinking?!

I'll pull the current prop to check it's numbers and I'll Hail Jeff in the meantime.

On a good note, all the gauges are very new Teleflex so I'll have to assume the tach is accurate.

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Peter I run a standard Stainless OMC prop with a 14 or a 14 1/2 x 19 pitch on the 235. I have a pretty good hole shot and a GPS measured top speed of 43mph. My WOT rpms at 5500 - 5700. It is a pretty good prop all around but it will ventilate in hard turns.

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Thanks Jeff, except for the stainless part it sounds indentical to my spare. Now I need to pull what's on there. See if it's the same or different. I'll let you know. See if anyone has an opinion of which one to try first.

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Peter,

The 14 1/2 x 19 still sounds like the correct prop and Jeff uses the same thing as I mentioned above for my V6 150hp.

The part number for the Aluminum 14 1/2 x 19 is #391201

The part number for the SST 14 1/2 x 19 is #389924

A size up would be 14 1/4 x 21 pitch
A size down would be 15 x 17 pitch

The props mentioned above are all OMC (now Bombardier) props and the numbers may have been superceded.

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Joe,
The current prop is also 14 1/2 x 19 and they both have # 391201 on them, matching your indicated OMC aluminum part number.

Maybe I should find find another 225 to go with the prop. I certainly wouldn't have to worry about WOT.:o

Next step - - water.

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Something is a little odd. At WOT the rpms are 4600. Seems low from what other folks say.

From the manual:
Full throttle operating range should be 5000 to 6000 rpm.
Power rated at 5500 rpm
Test propellor OMC P/N 387388
Miniumum Test rpm 5700 rpm

I fail to see how this will effect anything but I should mention that at WOT there seemed to be an unusally high rooster tail. Since I was alone I decided not to crawl over the transom to see if the doel fin was below or above water. Also, this boat came with those "Smart tabs". Not "real" trim tabs like Bennett or Lenco.

So from what Joe stated earlier I should be trying 17 pitch prop instead of the 19 I currently have on it?

Any ideas on achieving my desired cruising fuel economy anyone?

Pete

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Okay,
I'll try a 14.5 X 17, 15 X 17 or what ever is the next one down, and see what happens when I get the chance.

Peter

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Peter the 4600 rpm WOT seems low. I would check the stops on the throttle linkage in the motor housing to make sure that they really are opening up all the way. Also the tabs that are on your boat....I take it you do not like them? I saw them and wondered about how good they work. I also would say remove either the doel fin or the tabs. They are both doing the same thing so you really do not need them both.

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Jeff, it does appear to me the tabs AND doel fin are redundant. It's not that I don't like the tabs, just that I wish they were Lenco or Benetts. At lower speeds the tabs do very little except increase drag. I think I'll get rid of them, not the doel fin.

Didn't think about the linkage. I'm going to the lake this afternoon. I'll see what I can determine.

Thanks

Peter

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I didn't have time to take your advice in the heavy rain yesterday Jeff, But it was turning 5,000 rpms. Maybe it just needed an extra few miles after the long winter hibernation ?

I'd still like to get it to 5500 though so I think a 14 1/2 X 17 may be the one to try.

Thanks,
Peter

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Peter,

The next size down OMC aluminum prop is the 15x17 pitch, part number-391200... Don't even concern yourself with the diameter of the prop, let the engineers do that...

I am running the 15x17 pitch prop on my 150hp Evinrude on the Outrage 18 as I mentioned above. I am getting around 5300 rpm WOT with a regular load in the boat, ie., 2 people, full tank of fuel, fishing gear, cooler full of ice, food, beverage, etc...

I don't like trim tabs unless they are absolutely necessary.
I also don't like any fins hanging off my motor. I have never found a need for the fin and have no idea why some people use them except maybe to stay on plane at a lower speed.

Whatever Floats Your Boat..

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Thanks Joe,
Amazes me how you also quote the part numbers for all this stuff.
I'd never seen these fins bolted to our motors before this past year but everyone sure seems to talk about them AND use them. I've even seen them on I/O's now.

Like you did, I've noticed people comment about the load carried in regards to all this and well...I think my typical load could be quite different from the norm and positioned differently too.

I think I'll take a step back and remove both, the tabs and the fin. Then see where the rpms are at and what the ride is like in different conditions.

Start over again with a bare, clean hull & motor shape.

Regards,

Peter

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Peter,

Another suggestion on props... Don't go buying any if you can avoid it... Borrow them first to see if it will work for you. Many people use the Stainless Steel props too. They don't have as much flex as aluminum but they are expensive.

I boat and fish in shallow water most of the time so I am not going to buy a stainless prop. I can buy about 3 aluminum props for the same price as one stainless.

Let us know what prop works for you when you find the right one.

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Removed the smart tabs and doel fin yesterday. I actually like it like this for now, I don't find the bow raises too much when coming out of the hole.

But the point is...after all this I've discovered my AV plate is at least 1.5 inches below the the keel. So this may be part of the problem.

I'll be in touch... after I figure out how to raise a V6 225 a few notches.

Peter

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I'm running out of time these days to move the boat north for the summer and this may be a stupid question but...

So what if the AV plate is 1.5 inches below the keel?

I've read lots of stories that it shouldn't be but I don't recall reading about why. Afterall, it's been like this for the last 15 years I didn't own own it.

Peter

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It was a stupid question. Apologies.
I just wasn't using the appropriate search parameters.:

Peter

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Peter,

My engine was mounted all the way down on my 1978 Montauk for it's entire life.
The only thing that happens is that you lose a little top end speed and you may be throwing a Rooster Tail off the cavitation plate. If your not throwing a rooster tail, I wouldn't worry about it too much if you are not interested in gaining another mile or two faster at top speed.

My Outrage 18 was mounted all the way down and I hated the rooster tail so I moved the engine up one hole. What a difference. I am not concerned about top speed that much but did want to get rid of the rooster tail...

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Well that's interesting. I do have the rooster tail but it's much less now that I've removed the doel fin.

I haven't had time this morning to read all the threads I finally found on CW, but I was getting the initial feeling this could be effecting the extra 500 rpm I'm looking for, therefore performance, therefore the gas mileage effiency which is really why I started this thread.

WOT is still just 5000 but I've noted that 3000 - 3200 is a very comfortable cruising speed for the Great Lake water I'll be on.

Good to know I needn't worry quite so much.
This outboard leaning curve is getting tiring.
Thanks for all the help.

Peter

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So here is a question guys. I have a large V spray coming from my outboard when up on plane and trmmed all the way in. Though it never goes away it does get a little smaller when trimming the bow up. I know this is a sign of it being to low in the water and should be raised however if I take a straight edge off my hull it hits perfectly right at the cavatation plate. my WOT top speed per GPS was 43-45mph. What do you think?

It is mounted in the middle hole BTW.

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Jeff,
You're getting exactly what's happening with my boat.
To recap:
I removed the smart tabs
Removed the doel fin.
Raised the motor one notch to the middle one.

I still couldn't get over 5,000 rpms.

So a 15 x 17 prop was finally tested last week. It only increased the rpms to 5200. Seems hardly worth investing in a new prop for an extra 200 rpms. And is it helping the fuel mileage I'm looking for anyway?

Best fuel mileage is the concern so I think a Navman 2100 fuel meter is the next improvement. At least I'll be able to find the best cruiseing speed and what speeds to avoid.

Thanks for the responses and thanks for the patient lesson Joe.

Peter

I should add that I have a new set of Lenco 12 X12 E's sitting here to be installed. I don't know if these will enhance my engine performance but they are certainly needed up here on the Great Lakes to enhance boat performance.