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prov1900

Calling all Mercury Opti owners...HELP

Question

prov1900

I have a 05 225 Optimax. Have had on-going probs with the prop issue. Settled in (recently) on a Mercury Laser II. 21P, 16 Dia. My dealer says I shouldnt have to put the plugs in, i.e., the ones that close up the exhaust holes. I am not getting $#%p for performance and am pegging my tac. (no alarms and no spin outs like before) Do I need, per the instructional, to plug the exhaust holes in the prop?, Or is there some other issue? Any quick help appreciated, heading to that one country north of Minnesota next Friday, going to Lac Seul.

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Valv

21pitch and 16" diameter ? That's a HUGE prop, it doesn't even show on Mercury application chart.

Are you sure that's the correct reading ? With a prop like that you should barely move the boat and lug motor down so much it should kill. It would be like taking off at a stoplight in 4th gear

I've seen props like that on Mercruiser Bravo son 34feet cigarette boats, try to read the numbers again and confirm it's a 16dia 21 pitch

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prov1900

Valv, the numbers stamped on the side are: 48-16546 21P. Am I reading that right? As far as 16 diameter? The performance you described is about what I am getting, except for the killing the motor thing. Also, when I am trimming up from bare bottom when I am getting on plane, I am creating a monster rooster tail, at @ 25 to 30 mph per GPS. By the way, at 25 to 30 mph, I am at @5800 rpms and am only at not quite 3/4 throttle. Is my problem way more than the prop?? Is it possible that my tac is off its rocker, because I am not spinning out and it doesnt sound like I am over revving, but even when I shut my motor off, my tac is reading 2000 rpms. Obviously something is messed up.

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prov1900

Valv, lets try 13 instead of 16. Definately 13. Right now the plugs have never been in the prop.

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PierBridge

I used to run a 21 on my 115 Merc Outboard....I would imagine the 21 would peg your tach easily "not good", I would have thought a 23 or 24 would be a better prop for that Engine and boat.......

What are looking get out of the new prop.... hole shot, top end?

What were the RPM's on your old prop at WOT....?

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prov1900

My old prop was an aluminum one that would spin out more often than I cared. I am looking for overall performance. Really I dont care about any one thing in particular, I just want a comfortable, stress free ride that saves on engine wear and gas (somewhat). (My old prop would be somewhere in the 5600-5700 bracket, and my question to you, per your first sentence..youre saying that it is OK to peg your tac?

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PierBridge

No! you want to operate in the manufacturers recommended Range not sure on your Engine but Probably right around what your old prop was turning....

What are the RPM's on the New Prop and what was the problem with the old Prop?

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Valv

You have to find out exactly what you have, you cannot go from 16" diameter down to 13", that's 3 inches of diameter which is way too much.

I believe a standard size for your motor would be around 14" 14 1/2" x 21" pitch, then you can go up a little toward 23 and 24 pitch. You have to run your motor at full factory RPM when at full throttle, no more or no less.

Where did you get current prop ?

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delmuts

if your tach is reading 2000 with the motor off! you need to get it calibrated, or a new one first. you need to know what your rpms actually are. then play with different props.

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Surface Tension

48-16546 21P. looks like a 13.75 X 21.

If your tach is correct and your running 5800 RPMs at 28 mpg with a rooster tail I'm wondering if your trimming up to far, especially when you say your spinning out.

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randallt

I have an 02 optimax 135 that performs awesome. I couldn't be happier with it. My suggestion is to get a mechanic on board. He can calibrate the tach and also tell you which direction to move with the prop pitch.

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Scenic

First off I agree in that it sounds like the tach needs to be either replaced or calibrated. I also run the Optimax 225 in the Salt Water Edition and according to Mercury it should never be ran over 5500 RPMs.

As for mileage, at least with mine, at 5500 RPMs I will be burning approx. 48.8 Gph. or more. But if backed down to 4400 RPMs she only burns 11.7 – 11.9 GPH. With gas at near $3.00/gallon I run it a bit lower! When running at 4400 – 4600 I am still running right around GPS speed of 45–50 mph with three people in the boat. I have no or very little roaster tail.

Put your boat just on a plane, back the throttle down to about ½ - ¾ and then begin trimming it up while watching both your tach and your speed on your gps. You will reach a point where the tach will climb but your speed will either drop or not increase. At that point trim it back down just a bit or back the throttle off a bit. Depending on what boat you have this on you may have to trim it down when turning some corners or in very rough water. I know that I have to do that on mine or it will spin out no matter what prop I put on it. A good trim gauge is also helpful. I hope that makes sense as it is harder to explain this then I thought.

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prov1900

Valv, I got my "16" idea from the set of numbers on the prop, but was mistaken, it is 13 7/8 from the box. I got the prop from my dealer. I had like I explained earlier, an aluminum prop and was not getting any performance out of at all. Always spinning out, etc. This issue has been a real pain in the @$$/ Thanks for the help. Back to the dealer tomorrow to look at my tac.

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Valv

Ok, 13 7/8" is a reasonable size, you had me puzzled for a while.

Follow the suggestions above, especially regarding trim of motor when taking off and during plane, Jeff and Frank have good points.

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Kevin Turner

Quote:

my tac is reading 2000 rpms


I'm not much of a prop guy, so I can't help ya there....But, as long as your tach drops to zero with key on / eng off, that's normal....

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sparkyaber

sounds like the motor is running fine, You just had performance issues with the previous prop?

It sounds like you may still not have the right prop for your application. The P.V.S. holes are to help with holeshot, they allow gases to escape and let the motor "breath" easier. with all of them out, the motor willl breath the best, but you have a larger chance of having blow outs, or cavitation as some call it. I tried 5 different props before I found the best one for me. Don't try just one, try a bunch. If your tach says 5800 and your only supposed to be at 5500 max you should be getting a warning saying you are overreving. I would definatly make sure you are not trimming to far out of the water. Does you boat have a water pressure gauge? I would make sure you have at least 15 psi when trimmed all the way up. Gotta keep the water flowing through the motor, Also, If you are trimmed up to far that would explain the rooster tail and the high rpm on the tach. Go to your dealer and try a few different props and pitches. Merc's new Enertia is supposed to be a great prop for bigger deeper boats like the prov. The largest they make is 22". I have a bass style fish and ski and a 4 blade was the answer for my blow our problems.

Good Luck

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prov1900

Update. OK, I ran my boat today, although limited, but it seemed to run better. Still no blow outs, but I think my Tac is messed up. My rpms are at 2500 in neutral/idle. Is that right? I swear my engine is not overrevving. On my other prop, no question about it, it was overrevving. You could hear it. Since I obviously pegged my tac on the old prop, is it going to do that until I get it re-calibrated? I think I have the right prop, because my hole shot is good, but when the tac is showing the high numbers at low throttle, it is hard for me to push it without stressing me out. I will be on the horn tomorrow with my mechanic and will provide you with updates. Thanks everyone so far. Boat ownership shouldnt be such a hassle. Why is that???

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Whoaru99

2500 at idle or neutral is not right.

Don't know what your big engine should be for sure, but almost certainly under 1000 RPM at idle/neutral.

Sounds like your tach is either defective, or not set properly. Some have settings to match them to the type of signal provided by the engine.

On the prop, it's hard to say until the tach is working properly. But, as other guys have said, 21P sure sounds small for that engine.

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Surface Tension

Jeff's description of trimming up and throttling back after getting on plane is is right on. I like his comparison of gallons per hour also. Running across the water with your hair on fire will cost you much more then if you picked a good cruising speed.

Looks like your on the right track by getting the tach checked out.

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Black_Bay

I would try a Tempest Plus or the new Enertia in 21 pitch. The Laser 2 doesn't have enough lift for that boat. Supreme Marine has demo props.

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Capt. Don*

I run twin 225 optimax w/smart craft instruments, both engines at idle in neutral are 550-600 rpm. If your tach is reading correctly, which I'm thinking not, have it serviced.

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prov1900

I replaced my tac today, so hopefully my woes are over and I can try that boating thing yet this year! Going to Lac Seul tomorrow, so will post how it worked when I get back next week. Thanks for all the input. Now I just hope I have the right prop.

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prov1900

Sorry to drag up this old post, but it was the tac after all. I finally have a boat!!! Thing runs great and the Lazer prop is awesome. Maybe something different might be better, but my boat has a great hole shot and great top end. 5200-5300 rpms equals 55 mph. I dont think that is too bad. Drinks the gas though.

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