Question about right propeller for Crownline 19 SS 4.3 mpi 220 hp

[Maleaw]

Hello everyone,
I would like to ask you a question about appropriate prop selection - I'm a new boat owner and couldn't find it anywhere, so please be kind.
I have got the Crownline 19 SS 2007 year of production, 5.81m long, 2.33m beam and 1750kg BMT with Mercruiser engine 4.3 MPI 220 HP V6 with Alpha One Gen II drive Serial No 1A111812. Currently the prop is 3 blade Mercury Vengeance 48 16318 21P.
The reason why I decided to post my question is that the boat can not exceed 4000 rpm (for this engine WOT should be 4400 - 4800 rpm).
Is this prop properly selected? Could you please also help me with identification of gear ratio? I wanted to select prop on mercruiser webpage but I can't find this parameter.
Best, Mike from Poland

 

[Sea Rider]

Welcome to Iboats,

Any prop can be properly selected accoring to a given load and wot rpm range factory stated. When buying second hand boats can't tell if previous owner proped it right or not, his application could be much different than yours. So it's a good thing going fine tuning dialing a correct prop for your application and load.

If engine is in excellent running condition going say 2 less prop pitches to a 19 prop while maintaining a 3 blade one should increase engine's rpm towards + 400-600 wot revs, only checkable on a wot test on flat calm water cond.

Happy Boating

 

[Scott Danforth]

first, check to see if you dropped an exhaust flapper down the y-pipe. also check to see that all 6 cylinders are firing (balance test - pull a spark plug wire off each cylinder one at a time to make sure they are all firing.)

you should be able to hit 4800RPM or more with a 21P prop

gear ratio should be on side of drive.

 

[samuelahickman]

Hello--Agree with the earlier comments. It really depends on what you are looking for out of the boat. For example, if you want to be able to pull up a skier, tube, etc., a four blade prop with lower pitch would help. But, that'll lower your top end speed. If you're looking for greater top end speed, a higher pitch might deliver it for you.

Bottom line, decide what you want the boat to deliver and come back (or to your local prop shop) for more guidance. I'll tell you that I have a Sea Ray with nearly the same specs and put on a four blade 18 last summer and, at WOT, the RPMs are at 4800. Ontop of that, it'll pull up a skier real quick. BUT, I now can't get much faster than ~38 MPH.

Also, there are a lot of prop shops that'll let you try out different props and, so long as you bring them back undamaged, return for different ones to try until you've found the perfect one.

 

[QBhoy]

Hi

Scott is spot on here. IF your data given is accurate, there is something wrong.
The standard 4.3mpi and drive ratio (1.62) for a boat like that should turn a 21” right to the limiter. Would happily turn a 23” too and likely push on by 50mph. Maclin will tell you.
Get it checked out.
Also, your boat weight seems very heavy for that boat.

 

[porscheguy]

It’s hit or miss on the drive ratio. Some are 1.62, some are 1.81.

A lot of boat manufacturers want to talk “speed, speed, speed” but once a boat touches 50mph, they all get scared and do things to cripple the boat.

Whenever I reply to posts here I try to do as much homework on the boat in question as I reasonably can. Fortunately late model boats made in this century have a lot of info available.

Ive seen tests on other 19’ runabouts with the 4.3 MPI and 1.62 ratio. The best they can do is 48/49 on a 19P prop. Mercury should have come up with a 1.70 ratio for engines in the 200-225hp range.

Rant over with, I’m gonna go with those who said check to see if your exhaust flaps are intact. The ratio should be on the side of the outdrive.

my guess is overpropped and possibly an obrstruction.

check post #12 in this thread to see where to look for your gear ratio.

https://forums.iboats.com/forum/gen...questions-and-topics/10518908-merc-v8-re-prop

 

[Maleaw]

Thanks a lot guys for your replies. Honestly I thought the same that there might be something wrong with the exhaust system. I asked a manufacturer and recieved information that my drive has 1.62 gear ratio and originally had stainless steel prop with 21 pitch so the same as it currently has. Still I consider than even if overpropped it should reach above 4000 rpms without any problem - at the end of the previous season it stucked on 3500 rpms. I ordered Techmate Pro diagnostic tool and should have it to the end of the week- will it show what might cause the problem? Do you guys have some tutorial how to proceed balance test mentioned above? Thanks for your advices - I'd simply take my boat to service but trust me - here in Poland it's quality is very poor and probably I would lose my money.

 

[Scott Danforth]

Pull the exhaust elbows and check your flappers. It is common for them to fail and drop down the y-pipe, blocking exhaust. Personally seen it too many times

 

[Scott Danforth]

As for balance test. With boat at idle at the dock, pull one plug wire at a time. If you pill one and tge RPM does not drop by 75-100 RPM, then you found the dead cylinder. From there you can check for spark, fuel, etc

 

[Maclin]

When was last time the cap and rotor were changed out?

My boat has the 4.3MPI with 1.62 ratio, does not ever get to 50mph, can overrev with a 19p and can just get to 4800rpm with a 21p. Somewhere between 46-48 I would say. It accelerates noticeably faster with the 19p, and hits about the same top speed as the 21p just before the rev beeper nazi kills the power.

 

[Scott Danforth]

When was last time the cap and rotor were changed out?

good point. if you have the crab cap change it every 2 years. they fail internally

 

[porscheguy]

Mercury really should have come up with a 1.70 ratio for the alpha drive.

 

[Maclin]

I tend to agree with the 1.7 ratio comments. My boat is a little heavier than some. It is not as quick out of the hole as I was expecting, does "feel" like the wrong ratio to me I guess. Just seems like the bottom end torque does not really manifest the way you would expect a 220HP rated engine to behave, like compared to a 5.0 220HP carbed. Other things are different with this boat that may affect my seat of the pants observations on acceleration though.... It has the fuel tank up front, so it does not have bow rise like some, but also does not ride bow up "on the pad" so much either, long running surface or something at play.

By way of comparison, my just previous 22 foot Cuddy I/O was way heavier, had the 5.7 VP DuoProp 275HP and was much quicker and had higher top speed. Loaded.

My 16' outboard bowrider with 90hp was very quick with just me in it, hit about 40 or so with a 17p SS prop.

 

[porscheguy]

1.62 which is standard on the 5.0 and some of the 4.3s seems to be a bit too tall to get good performance. 19p seems to be the pitch limit for this ratio and engines in the 220hp range. At the same time 1.81/4 is a bit too short for the same engines. My 4.3 is a 190hp 2bbl w/1.84 and when I’m light, it can turn most 23p props right up to the red line. For you MPI/4bbl guys you’d probably go up 1 more inch in pitch with this ratio, but it’s not the best way to get speed as overcoming gearing shortfalls with pitch isn’t the most effective method.

 

[QBhoy]

I would have thought a 18/19ft bowrider with the 4.3 mpi would break 50 no bother. There are plenty of old bowriders with the carb 4.3 190hp knocking on the door and just achieving 50gps.

 

[QBhoy]

Oh and the 1.62 drive isn’t standard on a 5.0 mpi. I don’t think.

 

[Maclin]

I have watched many videos of carbed 4.3's hitting 50+, but they were pegging the RPM's pretty good.

 

[porscheguy]

Mine breaks 50 (52 to be precise) with the 190hp 4.3 and 1.84 alpha 1 gen 1. But that’s running very light with just me in it.

You can break 50 w/ a 4.3 and a 1.81 ratio. The problem with the 1.62/4.3 is those boats can’t turn more than a 19 pitch prop. A 19P may just touch 50 at 4850rpm or slightly higher if it’s a low slip setup.

 

[Maclin]

Along those lines, my previous owner claimed it would go over 50. I think they skied a lot as a couple, it had a 19p High Five stainless, 13" diameter when I bought the boat. With full tank and me it did not take long to hit the rev limiter. Maybe it could hit 50 (prop calcer says it would have had to have been about 5% slip to do it), but I hated that prop. I had to give it too much throttle to back it, my opinion anyway, just did not feel right to me. And having to "fear" hitting the rev limiter (very loud and upsetting to me nowadays) was enough to go to a 21p aluminum. Top speed seems the same and gets right up to the 4800 mark on the tach, has not hit the limiter yet. I found a 19p aluminum spare under the seats and had it re-furbed, accelerated quicker but hit the limiter, and same top speed.

Nobody I boat with cares anything about the speed, so I just need to go with that flow for now

 

[Maclin]

To the original poster, seems like that prop on your boat is too aggressive and that you need to go down in pitch, or change to a less aggressive 21p prop brand/type.

You may also have an engine that is down on power for some reason, may need to have it tuned up.