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Author Topic:   Conquest 23 prop question/suggestions pls
Justcurious posted 06-02-2005 10:56 AM ET (US)   Profile for Justcurious   Send Email to Justcurious  
Just replaced my stolen prop w/ what I thought was same model.

Conquest 23 Merc 225 efi

New prop is Mirage Plus 15x15 pitch

Old stats

WOT 4700 rpm @ 32 knts, good accelaration, plane @3000


WOT 4000 rpm @ 27 knts, sugglish, plane @3200

Nothing else has changed.

Any suggestions or comments would be appreciated.

Thank you.

Whalerider posted 06-02-2005 12:04 PM ET (US)     Profile for Whalerider  Send Email to Whalerider     
I think something is terribly wrong. If it really is a Mirage 15.25x15 prop then something is not right with your engine.. 4700 rpm is way too low and 4000 rpm is WAY wrong. Even on a heavy boat you should easily turn around 5500 rpm (give or take 100).

Mercury's prop selector says you should turn 5700 rpm with an 15.25x18 Mirage on a similar boat. IMHO, running a WOT of 4000 rpm is a powerhead "blow up" waiting to happen. I would check with a dealer.

As a side note...I can turn a 15.25x17 Mirage at 5725 rpm on my Merc 150.


bsmotril posted 06-02-2005 12:28 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
There are two families of Mirage props, Original Mirage, and Mirage-Plus. the latter has a bit more cup, and act as if they have a couple inches more pitch than an earlier Mirage. Is you new prop the same Mirage family as the original? Also, is the diameter the same as the original? BillS
LHG posted 06-02-2005 12:34 PM ET (US)     Profile for LHG    
For what it's worth, here are the load numbers for a Merc 225 EFI: (gear ratio 1.76)

15" pitch prop: 6000-8000#, speed range 38-43
17" pitch prop: 4200-6700#, speed range 42-50
19" pitch prop: 3600-5500#, speed range 51-56

Sounds like the engine needs a check up, as you should be able to turn the 15 all the way up, and then some. The load figures indicate to me that a 17" is your pitch?

Even before the prop was stolen, your engine was not getting adequate RPM. There is definitely a problem with it. Remember, that's about a 242 HP engine, hands down the most powerful 225 on the market. It has a lot more grunt than than a 225 Optimax. Did you buy this boat new, and has it always performed this way? Seems hard to believe the factory would prop it for only 4700 RPM.

Keep us posted

handn posted 06-02-2005 06:28 PM ET (US)     Profile for handn  Send Email to handn     
Just Curious,
The specs on your original prop are pretty close to what I got with the same labled prop on a 23 Conquest with a single 225 Optimax.
Obviously, the thief of your prop didn't steal the performance of your engine so you didn't get the same prop as you had before.
As long as your are swapping props, try a Mirage 16 diameter 13P three blade.
I got 200 more rpm across the power band and 5300 rpm at wot. In addition, I got much less cavitation going up big rollers at minimum planing speed. Fuel economy was the same.
You don't want to use the prop you have now because you are way under the minimum recomended 5000 rpm at wot.
BW23 posted 06-02-2005 11:13 PM ET (US)     Profile for BW23  Send Email to BW23     
I have a 97 225EFI on my 23 CON turning a MIRAGE 15P.

4000 RPM's = 25 knots
WOT 5400 RPM's = 36 knots

Your motor is defenitly not running properly. I bet it is not running on all 6 cyls.
I experienced 2 intermittent CDM's(spark plug coils) a few seasons ago.

Justcurious posted 06-03-2005 10:22 AM ET (US)     Profile for Justcurious  Send Email to Justcurious     
Thanks for the quick replys. After reviewing an old picture of the boat, I do think the current prop 15 3/4 is a larger diameter than the old. Don't know if this ould make such a drastic difference.

I am going to have the engine checked this week and go from there.

I'll let you know what happens.


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