Propeller for Merc. 50 HP 4 stroke

[briangeorge]

I have a new smoker craft 16 foot fishing boat with a 50 HP 4 stroke outboard. It has a 10 and 3/8 diameter by 13 pitch propeller. It is very slow out of the hole and even slower with 3 Adults on board. Maximum RPM is around the 5000 to 5100 mark. I have been told by some other boaters that I should be running a 10.5 to 12 pitch propeller to get the full RPM out of this engine. Mercury specs say top RPM on this engine is 5500 to 6000 RPM which I have never seen. Anyone know if the lower pitch prop is going to help?
Thanks and regards:
briangeorge

 

[usskydvr]

Re: Propeller for Merc. 50 HP 4 stroke

Short answer is Yes. Each 2" of pitch change will change RPM about 300-400 RPM and you need to increase about 700 RPM which would mean going from your current 13 pitch down to a 9.

 

[Reloder]

Re: Propeller for Merc. 50 HP 4 stroke

Hmmm . . . I have the exact same setup on a smokercraft 16 pro alaskan and wonder the same. What is your speed at 5,100 rpm with just you in the boat and a quarter tank of gas?

If you decide to go to a smaller prop, please post the results.

 

[briangeorge]

Re: Propeller for Merc. 50 HP 4 stroke

Reloder:
My Smoker craft is a Pro Angler XL. I have only had the boat about 6 weeks. It is all new. Boat and Mercury 50 H.P. 4 Stroke. With just myself and fuel tank almost full the Max. RPM is approx. 5000-5100 and top speed is around 28 to 30 mph. depending on water conditions. With 2 people in the boat it is still doable but it takes forever to get up on plane. With 3 adults on board with a child you are lucky if it gets up on plane. I had the smart tabs (planing tabs) installed and that helped somewhat.
The existing prop that came on boat is 10 and 3/8" diameter with a 13 pitch. The dealer has ordered me a 12" diameter with a 10.5 pitch. Hopefully I have it on in the next couple of days and I will let everyone know the results. That engine should give 5600-5800 RPM. at WOT. If I had it to do over again I would have put the Mercury 75 H.P. on the boat. May do it next year if this propeller doesn't work out.
briangeorge

 

[Reloder]

Re: Propeller for Merc. 50 HP 4 stroke

Assuming you have a 1.83 gearbox: (5,100 x 13 x 60)/(1.83 x 12 x 6080) = 29.79 KPH. That would indicate that you are not slipping the prop or churning water.

I would guess a change to 12" would make enough difference to get to 5,600-5,800. Changing a couple inches on the pitch in this range is a big change. A 10.5 pitch prop should get you to 27 kph, but I anticipate that you will be able to wrap the engine above 6,000 which post facto indicates you are still not propped correctly.

If you are concerned about the hole factor I would look at the trim, the cavitation plate height in the water on plane, or switching to a four blade or stainless prop. I run a four blade 10.5 x 13P and never have any problems getting up and can stay on top doing just 14 knots. With the three blade 10 3/8 x 13P that mine came with I had to do at least 16.5. I assume my boat may be a little lighter than yours (1,300 w/ motor). At what speed does your boat begin to plane out?

I run by myself at 5,600 to 29 KPH. Those numbers go out the window if I run with a canopy in anything other than glass calm.

 

[steelespike]

Re: Propeller for Merc. 50 HP 4 stroke

Generally they reccomend proping a 4 stroke near the top of the rpm range.
Just because its a new setup don't assume the throttle opens all the way.
Also you should be able to see the antivent plate(just above the prop) at speed if you can't the motor needs to be raised This could improve hole shot slightly and improve top speed.A 4 blade prop will improve hole shot and ability to stay on plane.
Generally reccomend dropping 0ne inch pitch when going to a 4 blade. 11" in your case.Sometimes the 4 blade will lose a little top end.

 

[briangeorge]

Re: Propeller for Merc. 50 HP 4 stroke

reloder and steelspike:
I just read your posts and I have to run out for a few hours. I will reply when I get back. Thanks for all the info. I do want to reply to both of you.
briangeorge

 

[briangeorge]

Re: Propeller for Merc. 50 HP 4 stroke

reloder:
Yes you are correct about the 1.83 gearbox. According to Smoker Craft brochure my boat weighs in at 1010 pounds and I assume that is with out motor. So with motor you and I are close to same weight I'm thinking.
Once up on plane I can throttle back to about 4000-4200 RPM and still keep on plane aprox. 20 mph. according to boat speedometer.
I am curious have you ever had 3 adults or more in your Smoker Craft? If so did you have trouble getting up on plane?
I hope to get my new propeller on the week-end and will update you to the results. Interesting about the 4 blade. Are you happy with your Smoker Craft?
Thanks and regards:
briangeorge

 

[briangeorge]

Re: Propeller for Merc. 50 HP 4 stroke

steelspike:
I'm new to alot of boating terminology. Could you explain the antivent plate above the prop? Is it the flat plate that has the adjustable steering tab under it? Also you say I should be able to see the antivent plate at speed. Do you mean slow/fast or any speed? Both you and reloder have me interested in the 4 blade now. As I said in my reply to reloder I am hoping to get the 12" diamter X 10.5 pitch prop on by the week-end. I will let you know the results as soon as I can get out.
Thanks and regards:
briangeorge

 

[longshanks]

Re: Propeller for Merc. 50 HP 4 stroke

I had one of those motors and it was a pretty strong 50. It is worth noting though that mine too was a slug with a 10 3/8 by 13 prop. It spun up to about 5200. I eventually went with a stainless vengeance #12 prop which went to 5750. The motor performed completely differently with the correct pitch. I'd try a 12, 11, or 10 pitch prop. My boat and motor weighs in at about 1400lbs total and it had no problem with 4 large adults once it was propped correctly.

good luck

 

[briangeorge]

Re: Propeller for Merc. 50 HP 4 stroke

Hi Longshanks:
Thanks for the info. It seems to be a common problem with the Merc. 50 H.P. 4 stroke. So you found a huge improvement when you changed props? You put on a 12 pitch what diameter? What make and size of boat?
Thanks again:
briangeorge

 

[Reloder]

Re: Propeller for Merc. 50 HP 4 stroke

I wouldn't get too hung up in the diameter. It does come into play but you will be limited in your choice of diameters depending on the pitch you want from a specific manufacturer.

You should not have any trouble getting up. The more you post the more I think your outboard may not be properly mounted. The cavitation or anti-vent plate is the flat piece directly above the prop. That should be as close to level with the bottom of the transom as possible when the outboard is in its lowest position. Are you trimmed all the way down when you start out?

I have had 5 people in my boat and could get up. I had to place two in the bow to start but moved them back to the middle once we were going. It was not a quick process.

Smoker Craft makes a decent boat, but it is too unstable for my preference. I have been impressed with how well the Pro Alaskan model takes waves at the bow, but there is no way I can stand up while drifting in decent chop without getting tossed around. It likes to pitch.

I also don't like that they routed the wire harness in the bilge without a snorkel. I will upgrade to a bigger boat next year. I want a new truck this year.

 

[steelespike]

Re: Propeller for Merc. 50 HP 4 stroke

steelspike:
I'm new to alot of boating terminology. Could you explain the antivent plate above the prop? Is it the flat plate that has the adjustable steering tab under it? Also you say I should be able to see the antivent plate at speed. Do you mean slow/fast or any speed? Both you and reloder have me interested in the 4 blade now. As I said in my reply to reloder I am hoping to get the 12" diamter X 10.5 pitch prop on by the week-end. I will let you know the results as soon as I can get out.
Thanks and regards:
briangeorge

Yes it is the plate with the fin above the prop.It should be visable at top speed
not necessarily totaly visable but bbreaking the surface.Usually ends up about an inch above the bottom of the boat measured with a straight edge along the keel.

 

[longshanks]

Re: Propeller for Merc. 50 HP 4 stroke

I agree with the previous two posters. Make sure your motor isn't mounted too deeply. I think I settled on a Mercury vengeance 12 pitch by 11 diameter. Based on my experience with props on that motor, I can tell you that the closer you get to 6000 RPMs, the better the motor will perform. My boat is not a production model, but it is a wide, heavy aluminum hull and the 50 EFI performed just fine once I had the right prop on it. good luck to you

 

[briangeorge]

Re: Propeller for Merc. 50 HP 4 stroke

Hello Guys:
I have checked the anti-ventilation plate and I believe it is right on the money. With trim completely down the plate is almost flush with the very bottom of the boat.
I am installing the new prop in about 2 hours and will post tonight or tomorrow early a.m. with the results. Thanks reloder, steelespike and longshanks for all the great info.
Regards:
briangeorge

 

[briangeorge]

Re: Propeller for Merc. 50 HP 4 stroke

Hello Guys:
I have checked the anti-ventilation plate and I believe it is right on the money. With trim completely down the plate is almost flush with the very bottom of the boat.
I am installing the new prop in about 2 hours and will post tonight or tomorrow early a.m. with the results. Thanks reloder, steelespike and longshanks for all the great info.
Regards:
briangeorge

Good Morning Everyone:
I was out fishing yesterday afternoon and evening with the new prop on the 50 EFI 4 stroke. What a difference. There was 2 of us in the boat with quite a bit of gear. The most noticeable change is how much faster it jumps up onto plane. MAX RPM at WOT has increased from 5000-5100 range to 5500-5600 range. MAX Speed is about 27-28 mph which is close to what it was with original prop. Once up on plane I can throttle back to 4000-4200 RPM and stay on plane at approx. 16 MPH.
I am hoping to get out again today and would like to get 3 adults in the boat to see how it performs. I will keep everyone updated.

 

[briangeorge]

Re: Propeller for Merc. 50 HP 4 stroke

I WAS OUT LAST NIGHT WITH THE BOAT. THERE WAS 4 OF US IN THE BOAT AND I FIGURED WITH EVERYONE'S WEIGHT AND ALL THE GEAR THAT WE WERE AT OR OVER THE MAXIMUM ALLOWABLE FOR THE BOAT WHICH IS 675 POUNDS. WATER WAS CHOPPY. THE BOAT DID GET UP ON PLANE WITH THE NEW 12" BY 10.5 PITCH BUT IT TOOK A LONG TIME.
WITH THE ORIGINAL PROP 10 & 3/8" BY 13 PITCH IT NEVER WOULD HAVE PLANED. I WOULD LIKE TO TRY ONE MORE PROP SOME TIME. I AM THINKING 10 TO 11" DIAMETER BY 10.5 TO 11 PITCH.
JUST THOUGHT I WOULD GIVE EVERYONE AN UPDATE.
REGARDS:
briangeorge

 

[longshanks]

Re: Propeller for Merc. 50 HP 4 stroke

Hi Brian

glad to hear it is working better. I think you may have your numbers confused, and what you are running is a 12 pitch by 10.5" diameter? I finally settled on a 12 pitch 11" diameter which is very close.

I still have a quicksilver 11 pitch by 12" diameter stainless that sounds as if it might be a good prop for your rig. I sent you a pm as well.


My 50EFI was somewhat finicky and unimpressive until I got the right prop on it. It was most impressive with the 11 pitch stainless prop, but it would occasionally over-rev, and I liked to run it at full throttle

 

[CRFan1]

Re: Propeller for Merc. 50 HP 4 stroke

I am reading this post with great enthusiasm because I have a new Alumacraft 165 CS (16') with a 60 merc 4 stroke efi...so similar. They also put that same 10.38 x 13 prop on my boat but that prop must really stink because although it would would pull 5800 to 5900 on the tach with 3 people and gear, it would only do 29.5 mph and had one hell of a time getting on plane! It basically had too much slip. Went to a Michigan Wheel Apollo 10.5 x 13" SS prop and it was a huge improvement (would do 34.5 with me, 32.5 with 2 adults and 30 with 3 adults)...BUT...depending on conditions...still a chore to get up on plane with 3 people and would only pull 5400 (with three on board). Better but still not great.

Now, my motor may be a bit low as the antivent is slightly below the keel but before I move it I am trying a 10.5 x 13 4 blade aluminum (solas amita) to see where that get's me. I WOULD get a 12" pitch 4 blade but I could not find one for my motor. If this new prop gets me out of the hole good with three people and keeps me in the neighborhood of 30mph, I will be happy. Next move will be to get my motor raised...but I hate the thought of doing that on a new boat. No wait, the next move will be to get a 75 hp Etec or opti which is what I should have done in the first place, LOL.

Anyone want to buy a MINT 60 hp Merc 4 stroke EFI?

 

[longshanks]

Re: Propeller for Merc. 50 HP 4 stroke

when I went through all of this, I remember thinking how sensitive my 50EFI was to being correctly propped. I tried a stilletto 12-pitch prop and found it to be lousy for my application. they have a very good reputation but it didn't give me rpms or performance. I had the best luck with the cleaver-style large blade stainless props, mercury vengeance style.

My hull is heavy, dented, and not overly efficient, but with a #12 pitch stainless my wife and her sister could pull my 220lb self out of the hole on a pair of waterskis. Those motors are very smooth and efficient, and I think you'll be happy with them once you get the correct prop on there. Even correctly propped mine was no speed demon, I think I could top out at about 30-31mph.

good luck