Underpropping is good!!

O come on boys - easy..... some good points are being made.
I had several different props for my Gambler 206SS with Merc 225.
17 pitch was for skiing and tubing; it would pull your arm sockets out coming out of the hole. But if you didn't watch it the rev limiter would hit at 50 MPH.
26 pitch was a dog out of the hole but could propel that boat into the triple digits. It would not allow the motor to hit the limiter. At least not that I could hear.
26 Pitch in action -
I had an air entrapment hull on a Hydrostream ski boat with a 220 Merc which resumed accelerating at 60 mph as the hull lifted but I always backed off. The water would break your neck for sure. The Seafair races used to be Gladitorial when a driver would die every other year. Less exciting with the canopies and helicopter engines. Somehow our Chip H. escaped.
 
Ohhhhh how I soooo long for the 1960's. They had buildings called libraries with books that told you how to be a boater. The old codgers back then actually knew what they were talking about and if you followed the guidelines all was good. Even today the stuff they talked about back then still works today.

The problem today is that the youngins don't know crap and the codgers are all senile.

How I wish Bill Ruger and Ole Evinrude were still alive.
 
You can tell Bill Ruger my LCP2 doesn’t properly eject multiple different cartridges and also has soft primer strikes and failure to fire. He will turn in his grave.
 
You can tell Bill Ruger my LCP2 doesn’t properly eject multiple different cartridges and also has soft primer strikes and failure to fire. He will turn in his grave.
I have heard similar complaints. Mine works 100%. In fact, most reliable semi I ever owned.

Send it back to Ruger and they will make it OK.
 
Good thread, I'm glad you posted it. And timely for me. I just discovered my (new to me) '98 185 has a 14.5x17P 3-blade AL on it. (I also discovered I had fishing line wrapped around the prop shaft... Glad I decided to take it off yesterday!).

I have an incredible hole shot with this prop but was also touching 5100 RPMs at WOT at about 43 MPH. I actually installed a GPS speedo because I thought the stock one wasn't showing the speed properly, since the specs say it should be running at 52 MPH. It turns out the OEM prop was a 14x23P AL 3 blade, which would lower the RPMs and raise the top end speed significantly.

I'm thinking of buying a 4 blade 14x19P SpitFire to meet in the middle between the OEM spec & the better overall performance I seek. I especially don't like running higher than the 4400-4800 RPM WOT as per the engine spec, as much as I like the awesome hole shot & low end performance of this 17 pitch prop. I'm hoping the conversion to a 4 blade prop will help me retain some low end performance, despite raising the prop pitch to 19P.

PS - for those of you who haven't used Mercury Marine's Online Prop Selector yet, you're missing out!
 
I started playing around on the Mercury Prop selector... I'm surprised to see it recommends either a 21 or 23 pitch prop, based on how I enter the info into the site. No manipulation of the data leads to a lower pitched prop than that. Maybe Mercury is recommending a prop sized based on what would be 'least taxing' on their engines?
 
Maybe Mercury is recommending a prop sized based on what would be 'least taxing' on their engines?
Despite how some companies want their products to have a short life, Mercury Marine actually wants your engine to last long, so you'll come back and buy another one for your next boat. Following all the requirements in the owner's manual is simply common sense.

Underpropping and exceeding the max rpm (that the engine was designed for) will provide excessive wear. Overpropping causes the engine to lug and thus taxes all the component parts. Running where the engine was designed to run not only prolongs its life, but utilizes the full HP, gives best speed and lowest fuel consumption.

Regardless, everything is a compromise. "Optimum" is not an absolute, but rather the best of all worlds.
 
Update: I bought a Merc SpitFire 4-blade 14x21P in place of the 3-blade 14.5x17P the primary owner installed before he sold it to me (and apparently never used).

I'm taking a gamble that this new 4-blade 21-pitch prop will give me a better hole shot and overall 'mileage' than the stock 3-blade 14x23P Sea Ray recommends. It's going to be hard to tell. I've never had the OEM prop on this 185BR. Most folks in these forums say that going to a 4-blade prop (and/or pitching down) is going to be better for hole-shot perf, handling and acceleration.

I think I'll be happy with the new 4 blade prop.
 
Lots of things make us happy. Hole shot and bow rise are subjective. WOT rpm and top speed are hard data. Collect all the data and let us know the results.

Just remember its aluminum, so take good care of it.
 
Ohhhhh how I soooo long for the 1960's. They had buildings called libraries with books that told you how to be a boater. The old codgers back then actually knew what they were talking about and if you followed the guidelines all was good. Even today the stuff they talked about back then still works today.

The problem today is that the youngins don't know crap and the codgers are all senile.

How I wish Bill Ruger and Ole Evinrude were still alive.
And Carl Kiekhaefer. Libraries now are daytime home to homeless watching porn on computers funded by libraries. Carl dazzled us all by underrating his Mercury 2-strokes. Thus, all 2-strokes had underrated HP. New 4-stroke outboards are dogs because the were rated by engineers who thought the truth would excuse comparative poor performance.
 
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On speed data, Android cells have a free GPS app which utilizes their high end screens to be very visible when dash mounted. Apple still only allows apps sold by their company store.
 
On speed data, Android cells have a free GPS app which utilizes their high end screens to be very visible when dash mounted. Apple still only allows apps sold by their company store.

I just counted 7 free GPS speed app's on the Apple app store...one of which I've used for years. You may want to double check your sources for what Apple has to offer :)
 
Android used to, and still may, have a side load option where you could directly install apps. This was intended for development and soon proved insecure. Apple requires all developers to register and are issued certificates that become baked into their final app. Without this certificate, and it’s chain of trust, you can’t upload your app to the store. This protects the whole ecosystem from malicious software. It is true that apple takes a % of your sale for using the store, but then again you are gaining the advantage of a secure infrastructure.
 
And Carl Kiekhaefer. Libraries now are daytime home to homeless watching porn on computers funded by libraries. Carl dazzled us all by underrating his Mercury 2-strokes. Thus, all 2-strokes had underrated HP. New 4-stroke outboards are dogs because the were rated by engineers who thought the truth would excuse comparative poor performance.
I'm glad I don't live where these libraries are located. My 4-strokes must have something wrong with them. Their performance beats all else.
 
...Now engines have electronic rev limiters so, why worry?
Hopefully you're not talking about letting the rpm slam off the rev limiter indefinitely because:

If it's a newer rev limiter that cuts fuel and spark you are still changing the harmonics that the engine produces due to constant misfiring and the balance of the engine will be thrown off resulting in excessive and most likely abnormal wear.
If it's and old school rev limiter that only cuts the spark you're doing the above plus dumping raw fuel in to the exhaust and then in to the water.

Many things in life come under the heading of "just because you can doesn't mean you should".
 
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I'm glad I don't live where these libraries are located. My 4-strokes must have something wrong with them. Their performance beats all else.
Rape is way down, all the perps are exhausted by library visits.
 
Underpropping may produce sporty performance including instant planing and happy slalom skiers. I would not underprop if my primary intended use was cruising where mpg counts. My point here is that you can now underprop w/o fear of blowing an engine. The prop is no longer the rev limiter. As you note, modern electronic rev limiters are sophisticated and reliable. Don't know if you made up that harmonic stuff but I agree that it would not seem to be bad practice to be bouncing off rev limiter. I've just trimmed down a bit, the boat slows, the revs come down, the boat bounces less, everyone is happy.
 
Rape is way down, all the perps are exhausted by library visits.
I apologize. It went over my head. I thought it was a serious comment, not facebook blather.
 
We fear over-reving because the engine may blow up. Used to be that some of the components weren't up to the stresses of turning fast. Now the issue is whether you have an "interference" engine whose valve train is turned by a chain or by a belt. An interference engine is one where the valves and pistons try to occupy the same space with disastrous results. Maybe valve float could cause this but usually the disaster happens on a higher performance OHC engine whose non-metal timing belt broke as a result of the owner's failure to change, as recommended. This Suzuki I was propping for revs has a timing chain so I am comfortable but a Yamaha has a belt!
 

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