Name:	MrHodja -	Reply
Subject:	Prop Recommendation
Date:	4/5/2022 9:21:23 PM

Just bought a 21 foot bowrider with a Mercruiser 5.0 engine.  Boat dry weight is 3,150 lbs.  Current prop is 21 pitch aluminum three blade.  Engine WOT range is 4400-4800 rpm.  Current prop condition is OK, but has a few dings that need to be smoothed out.  Considering a four blade prop and soliciting others' experience with four blades and whether the extra blade might change the optimum pitch.  Not looking for a racer, but something that will balance fuel efficiency and a decent top end.

Name:	wix -	Reply
Subject:	Prop Recommendation
Date:	4/6/2022 4:53:40 PM

Hodj, I’m certainly no authority in I/O’s but a couple of things to check/know about 5.0 L Merc’s.  5.0’s are not known to have a good high torgue, which sounds like what you want.  If yours is fuel injected, you are much better equipped, if not Merc raised the out drive ratio to 1.62 to help the motor build rpms quicker….which will lower top speed.  You’ve gotta have good torque to get the effectiveness out of a 4 blade prop.  Your aluminum prop may not be cupped.  Cupping could increase take off and help increase top speed some, but it will also reduce max rpm and needs good torque.

Name:	MrHodja -	Reply
Subject:	Prop Recommendation
Date:	4/6/2022 10:11:20 PM

Downside is it is not EFI, so we may be limited there unless it can be upgraded from two to four barrel or maybe to throttle body injection.  I believe it is ok just as-is, but one always looks for a little tweak here or there.  No, the aluminum prop is not cupped, and it may well be that a quality stainless prop, same diameter and pitch, would be all we need.  The seller gave me a nice stainless 19 pitch prop, but said the engine over-revved when he used it.  Aluminum one is 21 pitch and has no problem reaching max RPM.  Interesting info about torque, though.  Maybe four blades would be a waste of money. 

At the moment there might be a clogged low speed jet, as pushing straight to full throttle from idle chokes down the engine, while a gradual advance of the throttle sees no hesitation at all.  May be that the effect of starting out with last year's gas hasn't been overcome.  Filled up with almost 20 gallons fresh gas in a 37 gallon tank at Kowaliga Marina and motored from there to Anchor Bay and back to Parker Creek, but the hesitation is still there.  My older son is a gearhead an has some recommendations that I can try.

Thanks for the feedback.

Name:	wix -	Reply
Subject:	Prop Recommendation
Date:	4/7/2022 11:05:39 AM

Might try cupping aluminum prop.  I have had very good lock cupping to accomplish 2 things at once.  Reduce rpm’s to low end of max (4400) while increasing acceleration.  Good Prop shop can cup stainless, as well.  Rebuild 2 barrel carb wouldn’t cost much and very well may solve problem.  Good luck.

Name:	GoneFishin -	Reply
Subject:	Prop Recommendation
Date:	4/7/2022 3:58:54 PM

Here is some info on  the engine. The reference is to a 1989 but what is important is it's a card engine like yours. Enjoy your boat.

https://www.justanswer.com/boat/diw4q-1989-mercruiser-4-3l-gmc-two-barrel-carb-starts.html

I have never used a 4 blade....I assume you have a 14x21. I suspect since you want to pull a 240lb  skier a 3 blade gives you more  low  end. A 4 blade will give you more top end.

Have you  checked the Merc Cruiser table  for   correct prop?

Name:	GoneFishin -	Reply
Subject:	Watch This
Date:	4/7/2022 4:03:45 PM

https://www.youtube.com/watch?v=AO5pT-MgU-k

Name:	MrHodja -	Reply
Subject:	Watch This
Date:	4/7/2022 5:06:32 PM

Interesting, thanks.  Looks like I keep the stainless 19 pitch the guy gave me and use it if I want to pull a heavy skier, but for all-around daily use stay with a 21 pitch, stainless if I dig up another tin can from the back yard.  Otherwise maybe find a prop shop to cup and otherwise smooth out the aluminum 21 pitch.

Name:	GoneFishin -	Reply
Subject:	Try This
Date:	4/8/2022 6:13:00 AM

ttps://www.mercurymarine.com/en/us/landing/propellers/

Name:	MrHodja -	Reply
Subject:	Try This
Date:	4/8/2022 1:45:38 PM

Link to the video on prop selection doesn work ????‍??

Name:	GoneFishin -	Reply
Subject:	Try This
Date:	4/8/2022 6:34:10 PM (updated 4/8/2022 6:37:33 PM)

It is not a link. It is copy and paste...(black and white).  I just copied and pasted it into Google and it worked. I can't get the Forum to accept using the link feature.

https://www.youtube.com/watch?v=AO5pT-MgU-k