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Best prop for a 115hp mercury

SrA Eason

SrA Eason

Member
I was wondering if anyone could tell me what they have on the same or near the same motor. Mine has a stainless steel 3 prop 21p on it right now. just wondering if there's any other better one i could put on it.

thanks in advance.

ryan.:banana:
 
justincase said:
All depends on what your rpm is at wide open throttle and what your current speed is and how good of holeshot you have.
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I should have mentioned that I am a newbe to boating. also my boat doesn't have a rpm gauge. and I don't know what holeshot is. so I'm f'ed:brickwall:
 
yeah buy the tach first i have a inline 6 115 and motor came with a cheap ole never installed alum 21P and two others 19p and not sure what the other was but on my boat the 21 spun way over 6000rpm at 3/4 WOT now running a laser II 22P stainless turning around 5400 at 60PMH no prop acts the same on any boat thats why you see so many people wanting to try props before spending the bg bucks on one my motor came off a 16' glastron family ski boat and the old junk alum props turned up fine but when put on my little mx-15 spun way fast never even got boat WOT So you need the tach to find out what your turning at WOT and could be as simple as motor set up also that will make a differance i drop my motor 1/2" and lost 5-6 MPh top end and now taching less but rides better with little women in it. Not sure why she doesn't like flying at 60+????:eyecrazy::eyecrazy:
 
Also careful who you get advice from some people like to talk but dont exactly know what they are talking about Im a newbie also, and have alot of great help from a very special friend in here. He is a quite man and sits back and watchs and listens to alot of the BS but he has forgotten more than some of these guys know. He raced boats in the 70's and 80's ran trial's for checkmate and mercury out boards helped in some of the designs sold both checks and hydros In my opinion and most of the guys don't even know it But he is the BOATING GOD. He is the nicest man you will ever meet. Not to mention he has built some very sick boats.
 
chrisMX-15 said:
Also careful who you get advice from some people like to talk but dont exactly know what they are talking about Im a newbie also, and have alot of great help from a very special friend in here. He is a quite man and sits back and watchs and listens to alot of the BS but he has forgotten more than some of these guys know. He raced boats in the 70's and 80's ran trial's for checkmate and mercury out boards helped in some of the designs sold both checks and hydros In my opinion and most of the guys don't even know it But he is the BOATING GOD. He is the nicest man you will ever meet. Not to mention he has built some very sick boats.
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i'm guessing your talking about Kip? thanks for all the advice. How hard would it be to install a tach?:thumb:
 
what year is motor mine pluged into controls. Never manually wired one. Im a car guy just recently got bit by the boat thing. cars are not hard to wire cant believe the boat is any worst should be only few wires Get a manual its worth the money. search the threads i know there was a diagram someplace on tachs. I swapped motors on my boat and wasnt sure mine was right. If i find it i will send it to you.

No I wasnt talking about Kip he may to be an awsome guy but I was referring to Viper 1. :cheers: he could answer most issues over the phone and was always right. he nailed my fuel pump issue right on the nose adn the marina i brought it to couldn't even fix it the first time. The argued with me about how the gas was screwing it up. they replaced the diaphram and not the checkvalves they put 20 yr old parts back in with new ones Bunch of idiots. Not sure who was dumber them for being a so called speed shop or me for being stupid and bringing my boat there.
 
If you have the controls that originally came with the motor, you can buy a cable that will plug into the front (bow side) and can be run to your tach. You only really need three wires- +12V (switched), tach signal, and ground. I wired mine without the cable and it works great.
As far as the prop, I'd guess you'll need either a 20 or 22p Laser II... it'll depend on the specifics of your boat. Don't prop it so the engine lugs though (overpropped)... you want the engine to be able to hit 5800 when it's wide open.
Where do you live? There may be someone around who can let you borrow a prop to try.
 
ToP_Enticer said:
If you have the controls that originally came with the motor, you can buy a cable that will plug into the front (bow side) and can be run to your tach. You only really need three wires- +12V (switched), tach signal, and ground. I wired mine without the cable and it works great.
As far as the prop, I'd guess you'll need either a 20 or 22p Laser II... it'll depend on the specifics of your boat. Don't prop it so the engine lugs though (overpropped)... you want the engine to be able to hit 5800 when it's wide open.
Where do you live? There may be someone around who can let you borrow a prop to try.
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I live in dayton. I'm going to put the tach in maybe this weekend or next. I'm planning on going out to Ceasers creek on friday. So we will see.
 
i'm runing a 21P laser II and just lifted motor one hole today and broke the 60 mark hit 65 speedo and 62 GPS Sweet thing it is going anything bigger may lug it down some my motor is 2 1/2 above transom and WOT turning 5400 Make few passes with tach and like i said before set up is just as important as prop what boat is it on i can get some answers for you from my friend. I dont even have to trim so far out as to shoot rooster tails my mtor is just barely trimed and my boat is still running on the tabs let me know how it went :cheers:
 
Here's a link to check out:

http://www.go-fast.com/Prop_Slip_Calculator.htm

You either have a bad tach, a bad GPS reading, or it's not a 21p prop (I'd lean towards prop). I'm 99% sure your gearcase is 2:1 unless you modded it, so that gearcase with a 21p at 5400 will get you to 54 mph with ZERO slip (which never happens).
On the other hand, if I work backwards from your GPS reading assuming 4% slip (what mine is), that works out to 6500 RPM, which should be impossible on an inline. If I assume the GPS and tach reading are right, that suggests your prop is actually a 25p. I can't tell you for sure where the issue is, but there definitely is one.
 
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