better to be at the low end or top end of RPM?

[H20Rat]

2002 Hurricane Fundeck I/O deckboat. She's a bit chunky, lots of fiberglass... 19ft, probably about 4000# or so with 2 people and 40 gallons of fuel on board. 2 barrel 4.3l, 1.81 alpha. Very little water sports, most of it is just cruising, usually under plane or just on plane. I also have smarttabs on it which dramatically improved the handling, but probably cost me a little on the top end.


Merc aluminum 3 blade 21p, I get 40 mph (gps) at 4450 rpm.
SS 3 blade mercury 19p, 38 mph at 4800 rpm or just a hair higher.
(both are right at 20% slip)


2 other untested props
4 blade Solas aluminum, 21p - Definitely not enough engine.
3 blade SS 21p Turning Point Mach 3 express - Would need to be looked at by a prop shop first. Out of the box it was far out of balance it vibrates, bad.

 

[alldodge]

I always shoot for the high side, motor works easier getting there and hardly ever go full WOT

 

[jimmbo]

I'm surprised there was a Drop in speed with the 19, being that the Rpms ae higher.

 

[Texasmark]

Running low (end of the power band) RPMs with a loaded engine puts excess strain on the moving engine parts and on non fuel injected engines, causes more fuel consumption......intake manifold vacuum is high sucking fuel harder. HP is developed with torque and RPMs. 4 strokers usually have adequate cubic inches of displacement so they can tolerate loading up better and with fuel injected engines, depending on the computer, may not notice it as much in MPG. 2 strokers running a HP/CU IN don't have the cubes to get the torque so they need the RPMs to generate HP.

 

[airshot]

I have always propped to the highest rpm when the lightest load is in the boat...then it is easier on things when you add some passengers or other weight. Hardly ever run at wot for any period of time.

 

[QBhoy]

Prefer near the top, personally. Might also say that your results from your stainless 3 blade at 19” pitch…might be letting the side down..might I be right in thinking that it’s maybe something terrible…like a vengeance? Horrible things. Yet to see one of them do better than the ally black max, like for like in pitch. Not to take away from the black max though. Great props.

 

[jlh3rd]

I propped my pontoon for the higher end when not loaded so that I wouldn't lug the motor when tubing and loaded down...
so my 3 blade 16x12 did cost me some speed over my 4 blade 14x14...

 

[jimmbo]

Normally I cheer when a 4 blade is ditched and replaced by a 3, but on a Pontoon, a 4 blade 14 x 12 may have been better when loaded down

 

[jlh3rd]

what I needed was a 4 blade, 14x13....and it has to fit my CT gearcase diameter.......so It seemed at that time two years ago one did not exist...
It does now appear merc has a 13.8x13, 4 blade.....but what I have now works for my purposes....I still have the 4, 14x14.....
The 4, 14x12 maybe would've been fine...I did not want to take a chance on dropping 2 inches........
It's easy to sit on a computer and tell others what to buy as if that person hasn't considered other choices. I have two props sitting on my shelf now....
Propping a boat can be a one step, easy change...or a compromise because a prop may not exist for that 1 inch decrease you need.....even if you know what you're doing,...I do not have bottomless pockets....

 

[H20Rat]

Prefer near the top, personally. Might also say that your results from your stainless 3 blade at 19” pitch…might be letting the side down..might I be right in thinking that it’s maybe something terrible…like a vengeance? Horrible things. Yet to see one of them do better than the ally black max, like for like in pitch. Not to take away from the black max though. Great props.

Very good guess! Yep, 3 blade vengeance. In very good condition, not dinged up/bent. Didn't realize they were that much of a dog.

 

[Texasmark]

what I needed was a 4 blade, 14x13....and it has to fit my CT gearcase diameter.......so It seemed at that time two years ago one did not exist...
It does now appear merc has a 13.8x13, 4 blade.....but what I have now works for my purposes....I still have the 4, 14x14.....
The 4, 14x12 maybe would've been fine...I did not want to take a chance on dropping 2 inches........
It's easy to sit on a computer and tell others what to buy as if that person hasn't considered other choices. I have two props sitting on my shelf now....
Propping a boat can be a one step, easy change...or a compromise because a prop may not exist for that 1 inch decrease you need.....even if you know what you're doing,...I do not have bottomless pockets....

I have half a dozen sitting around, Laser, Ballistic 22 and 24P, Solace, all 3 blade SS, and a pile of 3 and 4 blade Hustler high performance aluminum in 3 and 4 blade. Since I gave my 90 and rig to the local fire-rescue that had no boat to police a local town lake, I had props left over from that boat and then a few years ago bought a larger boat (I thought I was getting too old to boat any more......brain fart) with a Merc 115, more power and gear change dropping 0.33 off the gear reduction....115 has 2:1, I added some new and played with the old that I kept. I guess I keep changing the props I have just to have a different experience when I go out.

 

[QBhoy]

Very good guess! Yep, 3 blade vengeance. In very good condition, not dinged up/bent. Didn't realize they were that much of a dog.

Thought it might be the case. Honestly…they are just a shiny and heavier version of a standard ally prop…made worse, by then being heavy and harder to turn, in comparison. Terrible things, I think. Quite sure they are the cheapest, nastiest budget prop that merc make or made.

 

[Scott06]

Thought it might be the case. Honestly…they are just a shiny and heavier version of a standard ally prop…made worse, by then being heavy and harder to turn, in comparison. Terrible things, I think. Quite sure they are the cheapest, nastiest budget prop that merc make or made.

They are just shinny to get new boats off the lot.…

 

[QBhoy]

They are just shinny to get new boats off the lot.…

Terrible things. No cut or shape to them at all, over a black max. Honestly I’d rather have a black max over one. Yet to see one better perform an identical pitch black max.

 

[Scott06]

Terrible things. No cut or shape to them at all, over a black max. Honestly I’d rather have a black max over one. Yet to see one better perform an identical pitch black max.

I never ran one side by side. A 19” vengence was on my boat when i got it, but when i repowered from a 4.3 to 5.0 and kept the V6 drive ratio i needed more pitch… so i only ran it once but was way over reving. Sold it for $180…

 

[QBhoy]

I never ran one side by side. A 19” vengence was on my boat when i got it, but when i repowered from a 4.3 to 5.0 and kept the V6 drive ratio i needed more pitch… so i only ran it once but was way over reving. Sold it for $180…

You did well. Does the guy you sold it too, still speak to you these days

 

[H20Rat]

So my testing shows the vengeance is a really bad prop, what is the group's recommendation for a good stainless steel? I'm running the alum 21" from my first test at the moment, and the engine just seems much happier with that vs the SS veng.

 

[velociraptorfarmer]

Bringing this back from the dead, but maybe giving a 19p Quicksilver Nemesis a shot? Should give you more lift, less slip, etc, which could be extremely helpful on such a heavy boat.

I went from a 21p Vengence to a 21p Nemesis and didn't lose any speed because I could trim up higher without blowing out.

 

[QBhoy]

Normally I cheer when a 4 blade is ditched and replaced by a 3, but on a Pontoon, a 4 blade 14 x 12 may have been better when loaded down

Agree…only exception might be for this use…or maybe a fast light v shaped (no pad) outboard hull…that a 4 blade might make behave better…meaning it can be held full throttle without trying to kill you ! Maybe then. Just maybe…it might offset the terrible prop slip they have wot…compared to a 3 blade…that might otherwise not let you keep the throttle open.

 

[Stinnett21]

Thought it might be the case. Honestly…they are just a shiny and heavier version of a standard ally prop…made worse, by then being heavy and harder to turn, in comparison. Terrible things, I think. Quite sure they are the cheapest, nastiest budget prop that merc make or made.

I've always heard, when it comes to props, weight doesn't matter. Once it's spinning that's probably true but I've wondered, for example, if putting a heavy 4 blade stainless on an alpha 2 would cause more stress on the shift mechanisms especially lower shift cable coming in and out of gear.