Moderated Discussion Areas
  ContinuousWave: Whaler Performance
  Propeller: 23 CONQUEST Single 225 EFI

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   Propeller: 23 CONQUEST Single 225 EFI
BW23 posted 04-19-2004 03:36 PM ET (US)   Profile for BW23   Send Email to BW23  
I have a 97 225 EFI 30" on my 23 Conquest. This past offseason I replaced the lower gearcase.
While testing it this past weekend, it is apparent that the gear ratio is different(old 1.87, new1.75) and I'll have to re-prop.

The prop I was using is a MERC Vengeance, 14 1/2 17P.

Motor statistics with 17P
original gearcase, 4000rpm 25.5 knot cruise, WOT 5200-5300 36knot cruise

new gearcase , 4000rpm 18.5 knot cruise, WOT numbers not available.

Bottom line...I lost 7 knots at 4000rpm.

Thoughts on moving to a 19 or 21 P or check WOT numbers and write back?


Peter posted 04-19-2004 05:50 PM ET (US)     Profile for Peter  Send Email to Peter     
Something doesn't make sense here. Your new ratio means that for every 1.75 flywheel revolutions you get one propeller revolution and the old ratio meant 1.87 flywheel revolutions for every propeller revolution. So for any given crankcase speed your propeller is now turning faster than it did with the old gearcase. Accordingly, your speed for any given RPM (within reason) should go up not down with a 1.75 ratio rather than a 1.87 ratio. Alternatively, your cruise RPM should go down for a given speed.
BW23 posted 04-19-2004 08:20 PM ET (US)     Profile for BW23  Send Email to BW23     

I based my ratio numbers on some resaerch that I have done since the problem

The new case is a "new" non-oem and the distributor I purchased it from did not question which ratio I needed. (I didn't know what I needed)

The cast aluminum case is slightly different than the old. I questioned this and was told it was a newer version. I checked with a MERC dealer today and he mentioned that the ratio was changed to 1.75.

Based on your opinion, I need to reduce the pitch rather than increase it??

If we leave the ratio numbers out of it, I need a pitch that bites the water more to bring my speed back up. Hence the 19 or 21.
I plan to check WOT with the current 17 this weekend and have borrowed a 19 and 21 to test.


Sal DiMercurio posted 04-19-2004 09:02 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
The difference in the gear ratio is so small, you really shouldn't notice much difference at all.
It's "NOT" what prop you "WANT" to put on, it's which prop "CAN" the engine twist, you don't get to pick any pitch you want, the engine does.
According to your post,you can't go to a 19p & a 21p is totally out of the question, because the 17p isn't allowing you to spin up to reasonable rpms as it is & more pitch will just end the engines life.
If I'm not mistaken, that engines maximum rpm range is like 5600, by putting a 19p in place of the 17p your automaticly going to loose 400 rpms right now & a 21p is really going to put that engine in the mid 4000 range which is pure poison for that engine & totaly UN -acceptable.
You better prop her to reach it's maximum rpms, or you will be looking for a new power head to match the new lower unit.
Peter posted 04-19-2004 09:05 PM ET (US)     Profile for Peter  Send Email to Peter     

New 225 EFIs come with a 1.75:1 ratio. Assuming your new gearcase has a 1.75:1 ratio and the old had a 1.87:1 ratio, then in theory you would need to reduce your pitch, not increase it, to get comparable performance. So instead of using a 17 P, you might need to drop to a 15 P, everything else being equal.

Before you do any repropping, run your motor up to WOT or maximum speed of 5800 RPM, which ever comes first, and see where your speed and RPM are (in case WOT reached first). If its a 1.75 ratio, your engine should have a hard time reaching 5000 RPM at WOT based on the old data you provided. If that happens, then switch to a 15 P which should put WOT operation at 5400+ RPM.

BW23 posted 04-20-2004 08:52 AM ET (US)     Profile for BW23  Send Email to BW23     
Sorry guys I really appreciate your input but now I'm really confused.

When I check this site, it calculates to move "up" to a 19.


So my plan is to check WOT this weekend and test the other props. Based on you opinions I should go get a 15 instead of the 21.

I also sent both of you an e-amil with some RPM/speed numbers.


Peter posted 04-20-2004 09:33 AM ET (US)     Profile for Peter  Send Email to Peter     

The numbers don't make any sense to me. I'm wondering whether your propeller has a spun hub? You can check this by scratching a line on the outer and inner parts of the hub that are separated by the rubber filler. If the lines don't line up after use, then the hub is "spun" and a new hub needs to be pressed in. You could also check this by borrowing another identical propeller and see if you get the same results.

The only other thought is that there is something wrong with the tachometer. Does the engine sound the same at 4000 RPM now and then?

The 23 Conquest is a relatively heavy boat and there is no way that the 225 EFI can turn a 21 inch pitch propeller on that boat with an ordinary gear case. My gut instinct tells me that a 17 P is the most that you should be using.

BW23 posted 04-20-2004 11:54 AM ET (US)     Profile for BW23  Send Email to BW23     

Spoke in length with distributor and mfg.

Ratio is and always has been 1.75 for that engine. 1.87 is for 2.5 liter, 1.62 is for high altitude.

Mfg. say to breifly check numbers at WOT. 17P SS prop might have been damaged over the winter(I stored it off the motor) causing some ventilation.

Plan to test this weekend(boat is 3 hours away) and write back.


jimh posted 04-22-2004 06:17 PM ET (US)     Profile for jimh  Send Email to jimh     
Let me try to recap the information presented here.

Boat=1997 23 CONQUEST
Engine=Mercury 225-HP 2-stroke EFI
Propeller=Vengance 3-blade 17-inch pitch
Ignore all talk about gear ratios; nothing changed. The gear ratio is 1.75:1.

Previously the boat ran at 4000 RPM at 25.5 Knots. This calculates to a SLIP of 20%.

The lower unit was replaced with a non-Mercury gearcase.
The propeller was damaged.

Now the boat runs at 4000 RPM and only 18.5 Knots. This calculates to a SLIP of 42%.

Looks like the problem must be either:

--new non-Mercury gearcase
--damaged propeller

BW23 posted 04-23-2004 08:52 AM ET (US)     Profile for BW23  Send Email to BW23     
That is it.

PLan to run some more numbers with the SS 17P then switch to a ALUM 19P and even 21P.

I also plan to have the SS 17P evaluated professionally.
I post what I find Sunday eve.


BW23 posted 04-24-2004 11:25 PM ET (US)     Profile for BW23  Send Email to BW23     
Latest is,

Pulled 17P SS off and istalled a new hub. Tested WOT, 5300 RPM 35 knots. 4000 RPM still delivered 18-19 knots.

Installed a 19P aluminum and my numbers are much improved.
WOT 5300 34 knots. Felt like the rev limiter might have started to kick in.
4000 RPM delivered 26 knots which I'm happy with.

Looks like I'll be shopping for a 19P SS. Are MERC brands props worth the difference? Any thoughts if I should even think of going to a 4 blade?

Thanks to everyone that offered advice.


Sal DiMercurio posted 04-25-2004 01:12 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Whoa ! hang on just a minute.
Something is really screwed up here.
If you were running a 17p & getting 5300 rpms at wot, there's no way your still going to get 5300 rpms with a 19p at wot.
The best you will get with the 19p is 4900 maybe 5000.
Why are you saying your going to try a 19p or a 21p ?
Obviously you don't understand prop math.
Your rpms are already marginal on the low end of your max rpm rating with a 17p prop at 5300, if you even dream that that engine can twist a 21p prop, your really dreaming.
A 21p will bring your rpms down to 4500 rpms at wot & that will be a death sentence for that engine.
I think your going in the wrong direction, I feel you need to drop down to a 15p.
Peter posted 04-25-2004 08:20 AM ET (US)     Profile for Peter  Send Email to Peter     
I agree with Sal. Something still doesn't make sense here. With the 19P propeller, your WOT slip is 28 percent, which is very high. With the 17P, your WOT slip is over 17 percent, also significantly higher than the 6 to 10 percent norm for a single engine configuration.

Using the high end of the normal slip range at WOT, at 35 Knots, your motor should only be turning 4800 RPM with the 17P propeller, too low. With the 19 P propeller at 34 Knots, it would be turning 4200 RPM at WOT. With a 15 P propeller, assuming 35 Knots, at WOT you should see 5500 RPM.

The fact that the engine achieves the same WOT crankcase speed, as indicated by the tachometer, with propellers having different pitches but achieving nearly the same top boat speed suggests to me that there may be something wrong with the tachometer. Before you lay out good money on a 19P stainless steel propeller, have someone check your tachometer accuracy.

If I were you I would also call Whaler and ask what size pitch they recommend for the 23 Conquest pushed by your motor since its all in the Brunswick family. As they must have set a few of these up at the factory, they ought to be able to give you a very good guess on the correct pitch.

BW23 posted 04-25-2004 08:27 PM ET (US)     Profile for BW23  Send Email to BW23     
Based on the numbers I also wondered about the tach.

It felt and sounded like the rev limiter kicked in early.
It started to miss/retard at 5300 using both the 17P SS and 19P aluminum. I never tried the 21P.
An idea at what rpm the rev limiter kicks in?

Not sure what to do now except attach a test tach and run the props again. From other posts I have read, guys with 23 Cons and 225 EFI's were running 17P's.

Hope you had a better boating weekend.

Sal DiMercurio posted 04-26-2004 12:02 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
The over rev limiter dosen't make the engine miss or sputter, it either shuts it off or puts it in slow mode.
I'd say the limiter on that engine is 6,000 rpms or even 6,200.
There's no way that engine can twist either the 19 or the 21p on that boat.
If anyone tells you it can at an acceptable rpm, tell them I said they don't know what they are talking about.
There's either something wrong with the tach or the engine.
BW23 posted 04-26-2004 02:12 PM ET (US)     Profile for BW23  Send Email to BW23     
Thanks for the thoughts guys.

Looks like I need to get the motor able to run 5500-6000rpms before I can make any conclusions. Can I carefully try to make it ventilate on purpose?

I hear ya that the motor needs to turn RPM's or the head will be toast. Plan is to de-carbon in 2 weeks, install 17P SS and run it.

Others mention that is could be detonation at 5300rpm and not missing. Now if we all could agree on how to de-carb....I know ..that is another story.

We'll get this fixed.


LHG posted 04-26-2004 02:32 PM ET (US)     Profile for LHG    
First of all, the engine should be running the 1.75:1 gearcase. If not, you have the wrong gearing in your aftermarket case. The 1.87:1 gearcase is for the 2.5 liter engines only.

Assuming the gearcase is the correct one, the 17" pitch prop sounds correct according to Merc's prop charts, which for the 225 EFI show 4500-6300 loading, at 39-49 speeds. The proper prop should be a Mirage Plus 3-blade, 15 1/2 x 17" pitch. A Revolution 4 4-blade would also be a solution, but they cost about $50 more each. You need a prop with large blade surface to carry a large, heavy boat like the 23 Conquest single powered, and a Merc Laser II, Stiletto or Rapture would be less than acceptable. Same for the "elephant ear" Vengeance.

I just spent some very valuable time with a Mercury technical expert, testing out various Merc performance props on my own Whaler, and he was complaining about Merc Vengeance props on a 240 Outrage with twin 150 Optimax's he was running.

You can get new Merc performance props for $400 each, and I would imagine the Mirage Plus models are plentiful on the used market also. Are these Mercury props worth the extra $100 cost? You bet, every penny of it.

BW23 posted 04-26-2004 02:46 PM ET (US)     Profile for BW23  Send Email to BW23     
Thanks LHG,

Your not the first person to mention the 15 1/4 15P Mirage.

My analytical mind is still trying to figure out what changed. (I know...get over it )

The 17P Vengeance was probably the wrong prop but it can with the boat when I purchased it 3 seasons ago.

All I'm trying to get back is good overall performance and half decent economy at 3800 to 4500rpms.

Thanks for your input.

bbrunner posted 05-10-2004 12:03 PM ET (US)     Profile for bbrunner  Send Email to bbrunner     
any update on this BW23?

I had the lower unit replaced on my 1999 225 Optimax (1999 23' Conquest) over the off season. I am also seeing slower performance. Before the lower unit was replaced I hit 43 mph on the GPS. I am now seeing 38mph max. I did put 60 more gallons of gas in the engine and a 15hp kicker on the back, but not sure if that should have that much of an impact. I am hitting 5800 RPMs at WOT.

I am also having a hard time keeping it on plane under 4000 RPMs. It cruises around 22 mph at 4600RPMs, but that seems a little high for "crusing".

I am considering getting a second prop that will give me higher speed at lower RPMs. Any suggestions/experience?

bbrunner posted 05-10-2004 12:04 PM ET (US)     Profile for bbrunner  Send Email to bbrunner     
Sorry, prop info is probably important: 14 pitch, 17.5 fourblade mercury offshore, i think.
LHG posted 05-10-2004 02:05 PM ET (US)     Profile for LHG    
A four-blade "Vensure/Offshore" would be the wrong prop for a 225 engine from what I have been told. It is only made in pitch ranges from 17-23, and recommended only for engines 135-175 on less than 22 foot boats. See prop section for descriptions of applications. For larger boats or higher HP engines (such as a 225), this prop has been superceded by the entirely different Revolution 4 series, and are now being seen on the new, larger Whalers.

To the best of my information, a gearcase repair/replacement should have NO effect on performance. All this assumes you replaced in like kind, which should be done

bbrunner posted 05-10-2004 03:25 PM ET (US)     Profile for bbrunner  Send Email to bbrunner     
My gearcase was replaced with a refurbished case. I agree that it should have no affect, i just thought it was funny how BW23 and I had a similar experience. I did add ~500lbs to the boat, so that should have some effect.

I will confirm exactly what prop I have so that this is a meaningful discusssion. I am sure I got the numbers mixed up.

BW23 posted 05-11-2004 12:07 AM ET (US)     Profile for BW23  Send Email to BW23     

I fixed the over 5000 rpm miss. Turned out to be a marginal CDM( spark plug coil). I'll post some numbers tomorrow morning as the spreadsheet is on my office computer.

Does your new lower gearcase have lower water pickups on the frontal area of the cone ?

aquaman posted 05-11-2004 12:45 AM ET (US)     Profile for aquaman  Send Email to aquaman     
I agree with the rest of you, somethings got to be wrong because the numbers don't make sense. The 23 Conquest is not much different then my boat a 24' Outrage. Same hull shape, the 23 is a foot shorter on the waterline and a couple hundred pounds lighter. My 250EFI Yamaha turns a 17" pitch Saltwater Series Yamaha blade @ 5500 at 47MPH with half tank of fuel. At 4000 rpm I'm running 31-32mph. I doubt the 225hp can turn a 19" on a 23 Conquest but maybe??? I'll be interested to hear the outcome.


BW23 posted 05-11-2004 08:54 AM ET (US)     Profile for BW23  Send Email to BW23     
Old gearcase #'s versus new gearcase(w/low water pickups,latest and greatest)

23' Conquest w/ 225EFI , MERC Vengeance 14 1/2 17P prop.
Speed verified using Garmin 2006C GPS, Std Horizon Fuel flow meter.

knots MPH MPG
old new
3800 24.2 27.8 2.0 18.5 21.27 1.53
4000 25.5 29.3 1.95 20.6 23.69 1.57
4200 22.7 26.10 1.65
4400 24.7 28.4 1.67
4500 29.0 33.35 1.91
4600 26.9 30.9 1.75
4800 30.7 35.3 1.82
5000 33.0 37.95 1.74 32.2 37.03 1.71
5200 35.2 40.1 1.57
5400 37.0 42.5 1.51
5450WOT 37.6 43.2 1.48

Holeshot performance was fine. Old/new performance was nearly identical at 5000 rpm. We lost midrange perfomance.
The only thing it could be , would be the low water pickup causing water flow disturbance at these rpms. I spoke with a prop shop in Delaware and he thought this was the problem.

I received a Mirage 15 1/2 15 P to test this weekend. I also have a Rev 4 14 1/2 17 P on order.


bbrunner posted 05-12-2004 10:51 AM ET (US)     Profile for bbrunner  Send Email to bbrunner     
I checked the prop and lower unit last night and: The prop is a 17p Mercury OffShore series. I do not know the length, but I am thinking that its 14. It was recently re-honed with the replacement of the lower unit. The lower unit does have the water intake on the front of the nose in front of the prop.

I am going to get some measurements similar to BW23 and post to see what the comparisons are. Either way I am in the market for a prop that would provide a higher crusing and top end. The WOT for the 225 Optimax is 5000 - 5750, so I am at the top end of the WOT with the current prop.

That prop is not listed with the merc manual, so I am unsure of the expected performance. I will check the merc site to see what I should be seeing.

Are the 225 EFI and 225 Opti similar in performance? Its my understanding the the Opti may be a little more sluggish, but cleaner burning and better on the MPG.

bbrunner posted 05-12-2004 01:46 PM ET (US)     Profile for bbrunner  Send Email to bbrunner     
When looking on the Merc prop selector, I see 3 props recomended when I input my info(Offshore or Cuddy - Single Outdrive - 5000 lb weight - 2000 225 HP Optimax Outboard - Perf Goal: Top Speed - Gear Ratio 1.75)

The three are: Mirage Plus 17p, Vensura Offshore 17p, and Revolution 4 17p.

I have the Vensura Offshore and am not seeing the Estimated Top Speed of 44.7 mph.

LHG, you recommended the Mirage Plus, why?

What do the last 2 numbers in a serial number stand for? I saw a prop on eBay that had all the same numbers except the last 2: 48-18278A46

LHG posted 05-12-2004 03:22 PM ET (US)     Profile for LHG    
The A46 suffix stands for the hub style and prop design.

An A46 prop has the newer Performance Venting System (PVS) and interchangeable Flo-Torque hub design. This is waht you want. An A45 prop has this hub also, but is not a vented prop, such as alum or Vengeance. Older style V-6 props are A40 or A41.

A Mirage Plus prop is recommend by Mercury for pushing heavier boats (such as a 23 Outrage) in relationship to lower HP (such as a single 225). They have the large diameter blades and blade surface needed to carry the larger boat. A Rev 4 prop will also do this. The Offshore/Vensura line are definitely not recommended for 225 HP engines. I recently learned this from a Mercury performance expert, while testing out a series of props on my 200 EFI's, and confirms this.

I have noticed that for several years now, most Whaler Outrages/Conquests are coming factory equipped with either the Mirage or Revoution 4 series props

bbrunner posted 05-12-2004 03:49 PM ET (US)     Profile for bbrunner  Send Email to bbrunner     
Thanks LHG for the info.

Where does not recommend the offshore/vensura prop? It came back as recommended when I put in my information.

Anyways, What pitch will be best for the 1999 Conquest/199 225 Optimax for the Mirage Plus? Mercury Prop Selector is recommending 17p.

Looking forward to BW23's test results with the 15p this weekend. This should give me a good idea what to get with the only other difference being the opti vs. efi.

Is anyone else running a Mirage on a single 200+ HP on an outrage or conquest?

LHG posted 05-12-2004 06:00 PM ET (US)     Profile for LHG    
See my post dated 05/10/04 above.
bbrunner posted 05-12-2004 06:15 PM ET (US)     Profile for bbrunner  Send Email to bbrunner     
Thanks LHG,

I was looking at the prop calculator and was confused when it recommended the Offshore. But you are right in the prop section: it clearly states that the Offshore is not for the larger outboards.

Swellmonster posted 05-13-2004 08:35 AM ET (US)     Profile for Swellmonster  Send Email to Swellmonster     
On my 1998 20 Outrage,I have the 225 EFI motor. I had the 17" Mirage plus and I was able to reach 6000 RPM at WOT when the boat was very light and trimmed out. Performance was excellent! However, as the engine got 2-3 years older, an annoying lower unit noise would occur when the engine was in gear below 1000 RPM's or so. Under warranty, of course they could find no problem. The term that MarineMax, Mercury factor hotline and an independant garage came up with was "clutch rattle" which doesnt hurt anything.

So Marine Max put on a different prop, a cheezy performance robbing little 19 vengence, performance was well below my previous prop, plus it slipped, had no bite. I took it back, they double cupped it, it grabs better, now it only gets approx 5200 RPM at WOT. At 52 MPH, you really cant look at the tach for more than a moment! My WOT RPM's are too low. With the new prop, you cant hear the low RPM rattle. The new prop is approximately 2 pounds lighter, and they say that stopped the clutch rattle. I guess I will never be allowed to try a 4 blade prop or any other heavy prop. Pardon the long story, but thats my input on pitches and props with the 225 EFI.

BW23 posted 05-16-2004 10:30 PM ET (US)     Profile for BW23  Send Email to BW23     

I tested a Mirage 15-3/4 X 15 P with 2 adults and 100 gallons of fuel, 23' Conquest MERC 225 EFI.

The minimum speed to remain on plane is about 3200 rpm and 17-18 knots depending on trim and trim tab settings.

I also kept the trim tabs up during all the speed testing. I adjusted the trim(tilt/trim) for optimum speed. Speed would vary 1-2 knots while doing so.

RPM   Knots   MPH  MPG

3400   20.2  23.2  1.88
3600   22.9  26.3  1.95
3800   23.6  27.1  1.91
4000   24.5  28.1  1.78
4200   26.2  30.1  1.80
4400   28.3  32.5  1.80
4600   29.4  33.8  1.75
4800   32.0  36.8  1.61
5000   32.1  36.9  1.60
5200   33.7  38.8  1.63
5400   35.7  41.1  1.45

WOT 5400 28.5 gallons per hour

Overall I was quite happy with the improved performance during testing. The motor responded quickly to changes in trim for optimum performance.

The next day I ran the boat with 90 gallons of fuel and 6 adults on board. Its acceleration was very strong, and the Mirage never cavitated or ventilated in both bay and ocean conditions.
Real water performance with a heavy load has convinced me this Mirage is probably the best prop for my type of boating.

I feel confident enough that I'll probably cancel my order on the Rev 4 blade.


Swellmonster posted 05-16-2004 11:29 PM ET (US)     Profile for Swellmonster  Send Email to Swellmonster     
What instrument measured fuel economy?
Peter posted 05-17-2004 08:03 AM ET (US)     Profile for Peter  Send Email to Peter     
Looks like you nearly got your mid-range cruise back and slip at WOT works out to 6 percent which is right on target. As Larry said, the Vengence isn't the right prop for your boat and your data seems to prove that out.

Assuming the old and new gear ratios were the same, I suspect the low water pickups in the new gearcase have changed the water flow around the gearcase. Perhaps its creating some turbulence or catching some air from the Conquest hull to the point that it was causing the small diameter Vengence propeller to ventilate.

jimh posted 05-17-2004 08:33 AM ET (US)     Profile for jimh  Send Email to jimh     
[Administrative post]
BW23 posted 05-17-2004 08:42 AM ET (US)     Profile for BW23  Send Email to BW23     
I have a Std Hzn FF41 fuel flow monitor. I probably consumed 25 gallons during my test.

Motor idles and runs great!!

Thank you to Peter, Sal, LHG and others that help me achieve these optimum results.


bbrunner posted 05-19-2004 09:26 AM ET (US)     Profile for bbrunner  Send Email to bbrunner     
Last night I also installed a 15p Mirage Prop on my 23 Conquest. The difference was amazing. I saw almost 40mph at 5200 RPMs. The mid rage power was great. I could stay on plane in the low 3000s and cruise at near 30mph without any problem. (sorry for the lack of exact numbers) The engine also seemed much quieter and the boat overall really handled much better. It really threw some water when pushing the throttle to put it on plane.

I guess i need to post the 17p Merc Offshore prop on marketplace.

I was really debating between the 15p and 17p, but decided on the 15p based on BW23's report. The thing I don't get is that they show a 240 Outrage with a Merc Opti 225 using a 17p Mirage. It seems like the 17 would be way to much for my Conquest and that Outrage is a very similar boat.

Another thanks to all for the recommendations. I wouldn't have believed that a lower unit replacement could change that much. I guess I also didn't know what I was missing!

Post New Topic  Post Reply
Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.