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Author Topic:   Outrage 25 Prop Selection
LarrySherman posted 09-10-2001 10:05 PM ET (US)   Profile for LarrySherman   Send Email to LarrySherman  
Here is another one:

My 2-thirsty-5 runs about 4100 rpm at WOT, speed by GPS is 31.5 knots. Im in general fine with the speed, but I know there is a problem here. From what Ive read here, in the Johnson manual, and other sites, I should be running at about 52-5500 rpm at WOT, top speed of about 38-40.

Now, with all the motor problems Ive been having, I originally was going to get them straightened out before working on the performance issues, but I cant wait. I also think that this rpm is as good as it gets, and that it is because I am over-proped.

Here is why: I put a new tach on the boat, and did select 6P for the pulse count. It seems very accurate when adjusting at slow speeds, so Im fairly sure its working correctly. Now, when I have the boat in forward, the slowest rpm I can run is about 1000, and then I am going a few knots. It seems like over-proping, no?

I used the mercuryonline prop selector last night. Here are the results.

BoatType: Offshore Fishing
Performance Goal: Overall Good Performance
Est Boat Weight: 4965.0
Estimated Top Speed: 44.87
Theoretical Pitch: 16.85

1)Black Max: Durable, econ, all-purpose, 3-blade Alum (48-832828A45) Pitch: 17 (RH)

2) Mirage Plus: blah .(48-18278A46) Pitch: 17 (RH)

3) Offshore: Excellent for twin applications, 4-blade SS (48-825898A46) Pitch: 17 (RH)

I think I have a 19 inch pitch on there now, at least from what I could read on it. Would that make sense with my current data? Im thinking I should get a 17 inch pitch 3 blade to try. At least, once I get the motor straightened out. Then buy a 4 blade.

Out of curiosity, what would be the benefit of over-proping?

As always


lhg posted 09-10-2001 10:18 PM ET (US)     Profile for lhg    
Larry: I assume you might have used the Mercury 3 liter 225HP EFI or Optimax engine in your calculation. That is a VERY strong engine, really putting out more like 245HP, and your old 235 OMC is no match for it at all. Besides it runs a very tall gear ratio, because of it's power output, which would give you wrong results in the calculator.

I would try using the Merc 200HP engine in the calculator and see what you get. Assuming the OMC gear ratio is similar to the Mercury 200 1.87 gear ratio, I would think a 15" prop and 38MPH is more like it.

LarrySherman posted 09-10-2001 11:06 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
Ok, that makes sense, but I don't understand the results.

I lowered the hp from 225 to 200, and then from 200 to 175.

Here is the info from the top of the applet:

Top speed = 42.58
Theoretical Pitch = 17.09
Black Max = 17
Offshore = 17

Top Speed = 39.91
Theoretical Pitch = 16.32
Black Max = 16
Offshore = 17

Top Speed = 36.74
Theoretical Pitch = 15.02
Black Max = 15
Offshore = 17

It always recommends the 17 inch Offshore for a 50 hp range of power, but goes down 1 inch per every 25 hp on the Black Max?

So, either the 4 blade props are much more forgiving to prop/engine mis-match, or... they don't make the Offshore in 16 and 15 inch versions.

Nonetheless, it was a good exercise, and kind of strenghtens my belief that I am over proped.

I'll try and read the prop tomorrow.

thanks, Larry

Peter posted 09-10-2001 11:27 PM ET (US)     Profile for Peter  Send Email to Peter     

Just for comparison purposes, my 3.1 liter Yamaha 225 is turning a 15 x 17 to 5200 on a 22 Revenge. The dry weight is 2350 lbs. A friend with a Yamaha 250 on an 24' 7" Aquasport (dry weight is about 4000 lbs) is turning a 15 x 15. I agree with LHG, your 235 should probably be turning no more than a 15 inch pitch prop.

lhg posted 09-10-2001 11:54 PM ET (US)     Profile for lhg    
The lowest pitch 4-bladed Mercury Offshore Prop is 17"! The gear ratio differences are why the same prop is shown for the lesser HP engine.

If you're only getting 4100rpm out of a 19" prop, you're only going to get about 4900 rpm out of 15" prop. My guess is your engine is not putting out full rated crankshaft HP.
I remember when those 235's were offered. They weren't any faster than a 200HP Merc, if they could even keep up. I would agree it probably compares with a 175Hp engine of today. So I wouldn't expect too much out of the old thing, probably about 36-38mph.

I once had a ride in a notched transom 25 with a single OMC V-8 275HP (remember those!), and the boat had a top speed of about 42 mph. Mercury used to advertize that their (then new) 225HP 3.0 litre was faster, so that's why their prop calculator for the 225 is showing 44mph.

LarrySherman posted 09-10-2001 11:55 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
I assume that this prop has been on the boat for some time. So the question now is, will the motor handle going up to 5k rpm when it proably has not been there in years?

Oh boy, it always get darkest before the dawn, right?

Thanks Larry, thanks Peter.

Peter posted 09-11-2001 07:42 AM ET (US)     Profile for Peter  Send Email to Peter     
Your motor should have no problem running at 5000 RPM with the correct prop. In any case, you probably won't run it there most of the time and you wouldn't want to run it there for long in any case or it really will show you how thirsty a "two-thirsty-five" can be.

Each 2 inch drop in pitch should add about 200 to 300 RPM to WOT so I would estimate that you'd get about 4700 RPM with a 15 inch, which is still below the 5200 RPM minimum for WOT. The low RPM leads me to believe that the motor really needs a good tune up including a carb rebuild by a good OMC mechanic.

bigz posted 09-11-2001 08:46 AM ET (US)     Profile for bigz    
Larry -- Peter is 100% correct you are just fishing at this point until the engine is tuned and the other problems straightened out.

That 225 should swing a 15x17 and give you about 5000 - 5100 rpms -- your running roughly about 36/37mph at 4100 as you state (31.5/32 knots), this leads me to think your tach is off which is a common situation! Have to keep knots and mph defined here. I think your actually pulling in the area of 4400-4600 rpms not 4100 at that speed, droping to a 17 will get you up around 5000 or so and maybe in the lower 40 mph range for WOT. Until you have it tuned properly (read OMC mechanic) this excecise is a waste,it will just have to repeated again!

John from Madison CT posted 09-11-2001 12:26 PM ET (US)     Profile for John from Madison CT  Send Email to John from Madison CT     

How are things going with the project? Seems the recent outboard problems have been fixed? Keep me up to date, I'm quite curious.


Bigshot posted 09-12-2001 09:49 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Larry, this could have something tio do with your 100psi compression test. I think she might be tired. Before you start spending all kinds of $$ on props, find out what you are running. Then have the tach checked. 1000 at idle is fast. Once you have that narrowed down, procede further with a prop or a carb job. I think carbs are in order.
LarrySherman posted 09-12-2001 11:04 AM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
I put another new powerpack on for the other side. I ordered carb rebuild kits, and will rebuild the carbs as soon as they come in. I also ordered therostat kits and water pump kits. Total cost of less than $400, so I think its worth it if I can get it running. I'm going to do all the work myself, which should give me a good education in outboard maintainience.

They I think the tach is reading incorrectly as well. I'm going to take a good look at the wiring tonight. I know I set the switch correctly, so it must be something else.

The motor continues to run when the key is turrened off, but only when it is warm. When cold, it shuts right down. I do think its related to the new powerpack they put on. A mechanic at NorWest marine told me that the black wire with the yellow stripe comming out of the powerpack is the kill ckt. I have to trace it.

A new wire harness for the engine is $134, for the instrument harness, $120. I held off.



Bigshot posted 09-12-2001 11:40 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Try 12p on the tach. before you mess with the rest. On rebuilding the carbs...if you do not have an air compressor to blow them out with, a shop might let you use theirs(takes 1 minute). Since you also do not have the little "jet files", soak the carbs in Berryman's B-129(At least overnight). Get it at Wallmart in automotive section. Best stuff made.
Bigshot posted 09-12-2001 11:42 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
That is Berryman's B-12. In a white, red & blue can. Available in spray and liquid. Get both. 1 to spray out jets, etc with and 1 to soak in.
LarrySherman posted 09-12-2001 12:07 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
Thanks Bigshot. Will do. What do you think equivalent would be if I can not find it up here?

Bigshot posted 09-13-2001 12:37 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
"carb medic". Do not know if it comes in liquid. If not buy an extra and squirt into container I guess. Gunk and the rest are a waste of time.
Dr T posted 09-14-2001 12:41 AM ET (US)     Profile for Dr T  Send Email to Dr T     
On your "continuing to run" problem.

Since it shuts down when cold, and continues to run while hot, it sounds like you have a heating "short" in the wiring.

This problem is particularly odd since usually this type of problem usually causes circuits to break (at least, in solid state electronics).

When the engine is hot, it is causing something in the ignition system wiring to expand so that contact is maintained evem though power is removed. As strange as this is behaving, I would start checking around the solenoid.

Here it begins to sound almost like science fiction: If the solenoid is staying engaged after the engine starts, the additional drag from the starter could be dragging down the rest of the engine.

Or, as Bigshot said, the engine may just be tired (as well as thirsty).

Good luck.

LarrySherman posted 09-16-2001 10:06 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
Well, things are on the mend, but still no performance improvment.

I replaced the 2nd powerpack, and my starting problems are gone. I founf a thread on iboats stating that these motors are tradidionally hard to start. I don't believe it. With the new powerpacks, it's one turn of the key.

I also rewired the ignition switch, by cutting each connection, stripping and re-criping it. That, and re-installing power-pack #1, and viola! She turns off correctly.

I also made up and installed a new set of OMC plug wires.

And I installed an OMC priming bulb. MUCH better the the merc ones I tried previously. MUCH better.

But the engine still stumbles a bit. I am waiting for the carb-rebuild kits to come in, but I think I'm still having an ignition problem. I'm going to test the ignition coils next, while I wait for the rebuild kits to show up.

John from Madison CT posted 09-17-2001 05:45 PM ET (US)     Profile for John from Madison CT  Send Email to John from Madison CT     

Wow, good for you. You're becoming quite the outboard mechanic. I'm happy to hear about the "run on" problem being fixed.
Good luck with the rest. Keep us posted.


LarrySherman posted 09-20-2001 03:00 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
Well, good news in CT anyway.

Met my new mechanic. Tony rizzo from Rizzo marine in Greenwich. We went over the motor fairly carfully, and the dianisis:

Its a new OMC powerhead, which runs great, that is, once we changed the prop.

After chaecking compression (perfect), ignition (fine) and fuel, we started discussinf props.

We changed down to a 14x17" he had, and went for a ride. WOT = 5k on the tach, flying through a 2-3 foot chop on the sound. It was fantastic. He said that as the motor broke in, it should idle up a bit, but that a 15" prop would put me closer to 5500 on the tach at WOT, but perhaps over. I decided to stay on the 17 for now.

And he offered to buy it from me. Wow.

And so, all my fears seem to be invalid. I just did not know much about outboards.

I want to thank each of you for helping me over the last few months, it has been great. And to Peter, Tony was a refferal from Joey, so I owe you big.

Thanks, Larry

John from Madison CT posted 09-20-2001 04:22 PM ET (US)     Profile for John from Madison CT  Send Email to John from Madison CT     

Glad to hear the good news ! I'm afraid that this web site has got me bitten by the Whaler bug.
I'm going out to LI sometime next week to look at a 17' Montauk. A far cry from my 25' Whaler of yesteryears but good for now. I'll let you know if I get it. We'll meet in the LI Sound someday.

Take care,


acseatsri posted 09-20-2001 04:41 PM ET (US)     Profile for acseatsri  Send Email to acseatsri     
John, you may want to look into an 18' Outrage. Saw a nice one in front of Ocean Performance in Old Saybrook today. I believe it's an '85 with a '94 Johnson 150 Ocean Pro.
Asking was 15, but who knows what he'll take this late in the season. The Outrage is a LOT more boat than the Montauk, especially ridewise.
Peter posted 09-20-2001 06:31 PM ET (US)     Profile for Peter  Send Email to Peter     

Glad to hear that it all worked out. I am a bit surprised that when you went from a 19 to a 17 inch pitch, you gained 900 rpm. You must have fixed something else at the same time. The real test is to see what the top speed is.

John from Madison CT posted 09-20-2001 08:22 PM ET (US)     Profile for John from Madison CT  Send Email to John from Madison CT     

Yes, I've seen the 18' Outrage there a few times. The boat seems to have a few miles on it and I wasn't all that impressed really.
The 17' is just right for me right now. A nice easily trailerable boat that can do enough good fishing in the LI Sound. When I go up to the next step it will probably be a 22' Whaler with a single 200HP Yammie or similar.

Thanks for the head up though. Keep me in mind if you see a 22' in CT.



LarrySherman posted 09-20-2001 10:29 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
Your right Peter, I may have spoke to soon. I got soaked today, but I could not resist going out to take some test runs with the GPS on board.

I made several runs around Greenwich Harbor today, and measured WOT at 5050 rpm, best speed 31.2 knots. That works out to be 36 mph (1 knot = 1.17 miles, right?). That is about the same top speed I measured with the 19" prop, but at 4100 rpm.

The motor has run smoother since the sencond power pack and new plug wires went on. I don't know that that can account for the 900 rpm gain, but it is what it is. In fact it sounds really cool now at WOT. I just got the carb rebuild kits, but I'm considering doing that over the winter at this point. I think if I got the right prop, I'd be happy. I don't need to go fast, but would like to get up on plane earlier.

I get up on plane at about 19-20 knots, I can then trim up the motor, and keep her on plane at about 18 knots. Less then that and she falls off plane.

Would you stick a doelfin on an engine this big, of go for trim tabs? If its trim tabs, then I have to remove or remount my kicker.

John, I just saw a mint 22 CCC at Rex in norwalk go for 15. I almost bought it myself. Its name was Moon Shadow, and she was 100% origional and immaculate. I'll certianly look for you.

PS: are any of you going to the Norwalk boat show this weekend?

John from Madison CT posted 09-21-2001 07:39 AM ET (US)     Profile for John from Madison CT  Send Email to John from Madison CT     

Thanks for keeping an eye out for me on a 22' Outrage. I'm a few years away from that committment and for now the 17' Montauk is all I need. In time though, maybe I'll hunt down a 25' myself.
I can't make the boat show this weekend. I've got to fly to Texas (eeckk fly !!) for business.

Keep in touch. I'll let you know about the Whaler in L.I..



Peter posted 09-21-2001 08:44 AM ET (US)     Profile for Peter  Send Email to Peter     

For experimentation sake, you might try a 15 inch prop. I doubt you'll gain much speed but if the "two-thirsty-five" has a WOT operating range between 5200 and 5500 rpm, then you are still technically "lugging" the motor at 5000 rpm, assuming the tach is reading properly.

At 5000 rpm, you are still below the WOT range you state. Assuming that is the right range, which I believe it is, you are not developing the maximum rated HP yet.

Doelfin will probably help the hole shot and lower planing speed, but I don't think it will help with lateral trimming to reduce any tendency to lean

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