Getting new prop, couple questions

[redneck joe]

Matching 1982 merc 50, 18 f cc starcraft. Normally just me only occasionally an extra person. Boat and motor and gear and my fat a.. Maybe 2000 lbs.

Question one... Currently has solaris that i put on but somehow got nicked up a small bit last trip out so just going to file down and store for spare. I has same brand in stainless on the carver never a problem, but is that considered a decent brand? Amazon has a Jason Marine for only $55 and for that price point I'd buy a couple each year.


Question two... Im not quite hitting WOT rpms but that may be related to the sparky box we are replacing but cant test until a shift cable actuator thingie get put on next week and get back to all four cylinders. I know i should down pitch but what i havent been able to learn from the interwebs is how/if diameter affects performance. I can upsize half inch and of course can downsize. Thoughts?

And I'm sticking with aluminum from now on so no discussion needed.

 

[jimmbo]

You mention Rpms are low. Is this a new thing, as you also mention what might be misfires?
Keep in mid that propping this time of Year usually results in a prop that is too high in Pitch during the summer. Unless you are south of the Equator.
I believe your engines WOT Rpm Range is 5000-5500. Those 4 cylinder 44cu inch 50s, are Sweet Motors. Basically two 20s stacked together, as they share the same Bore and Stroke

 

[redneck joe]

Rpms are seperate, maybe. It went bonkers one day and could only keep running in idle. Mechanic put his tester on and only showed three sparking, with that one being shiny and clean so may not have been sparking since i got it. When i dragged home the prop on it was bad enough i didnt run except on muffs until i got new one on and just copied what was on there, other than going 4 blade. I'm at 4900 at WOT.

Never heard about propping for different seasons. What is the correlation?

So far love that little motor. Boat is rated for a 115 so definitely not a speed demon, but at my age dont need speed anymore. Slow cruising and enjoying the day is what its about for me. All cylinders at 120, pressure test after impeller change good. New sparky box with some new linkage should last another 40 years.

 

[jimmbo]

Temperature and Air Density. The Air in the Spring and Fall is cooler and more Dense, thereby the Engine can produce more power. So if proppeed in the Spring or Autumn, the Owner is wondering why his motor in the Hot Summer isn't getting the Rpms it did in the Spring. Mercury even mentions this in their Service Manuals, and their older Prop Books

 

[redneck joe]

Thanks, good info. So with that, in summer just remember to check rpms if desired first thing in the morning when its cooler. I only WOT to check.

Back to question two on diameter. How does that math factor in?

 

[jimmbo]

A change in Diameter can affect loading, however, so does Blade Shape, Blade Area, Rake, and Cupping, so it isn't as cut and dry as a lot of people may think

 

[redneck joe]

Ok so sounds like since I'm at the lower end on summer mornings, I'll downside to a 12p for year round use. Should put me in the range overall.

Any concerns on the Solas brand?

 

[jimmbo]

Solas, never owned one, and my experience is limited to being in my cousins Boat that had one. Seemed to perform okay, and looked very similar to an OEM prop. But Solas offers more than one Line...
My dealer sold another 3rd Party Brand, and I was not impressed with the QC. I had opened up several boxes and found the Sesame Street 'One of these Things is not like the Others...' Song playing my head. That brand did had some odd Props that would have 2 nicely Raked Blades and 2 Elephant Ear Blades on one Hub, but this was a 3 Blade

 

[redneck joe]

Great thanks for all the help.

 

[Texasmark]

Solas, never owned one, and my experience is limited to being in my cousins Boat that had one. Seemed to perform okay, and looked very similar to an OEM prop. But Solas offers more than one Line...
My dealer sold another 3rd Party Brand, and I was not impressed with the QC. I had opened up several boxes and found the Sesame Street 'One of these Things is not like the Others...' Song playing my head. That brand did had some odd Props that would have 2 nicely Raked Blades and 2 Elephant Ear Blades on one Hub, but this was a 3 Blade

Those dual 4 blade (aluminum black) props were probably Turning Point brand Hustlers and I have a couple of them and some of their 3 blade aluminum props. The brand advertises to put SS high performance functions in a rigid aluminum prop saving the buyer some money over SS. 3 blades have the rake, cupping, porting (and high strength aluminum thinner blades than normal aluminum props) mimicking a SS props attributes.

 

[jimmbo]

Yes they were, and the QC of their Product is Abysmal, Putting 2 different designs of Blades, doesn't result in an Increase, but rather a Decrease in designs performance. But some people will lap up the Marketing Hype

 

[Texasmark]

Yes they were, and the QC of their Product is Abysmal, Putting 2 different designs of Blades, doesn't result in an Increase, but rather a Decrease in designs performance. But some people will lap up the Marketing Hype

Agree and that's why they are sitting on the shelf, not mounted on the engine. I had purchased a 20 year old boat and was trying to understand where I was with engine condition and boat performance. Since the props were cheap was no biggie to experiment.

 

[redneck joe]

Final update with some good news . Two good news....

First good news is i think i found a new and reliable mechanic. Talking to a guy at the ramp and he spoke highly of him. Left the very good local boat place about ten years ago, works out of his house. The local place doesnt work on old motors anymore. New sparky box, some sort of oem linkage, impeller, etc all in for $800. Very happy.

Second good news is with the new sparky box it is now consistently running all four cylinders is is at 5200 WOT, 27 mph. (The motor is less than 50% rated hp for the boat so mph is fine). Still going to get new prop and use this one as spare since it dinged up.

Be well, off to the driveway for final Christmas parade on my float.