Switching from AL to Stainless Steel Prop

[CptCrunchie]

Since I've dinged the crap out of 3 props in 3 years, I'm thinking about changing from an AL to a stainless steel prop. Has anyone else done this? And will the clutch dogs have an issue with the harder prop?

And if I were to go that way, is there a good, better best? I've been looking at the Solas HR 3 blade, and the Solas Titan HR 3 .....in a 14.75 x 17.

[smitty477]

Sorry I cannot help with you exact boat as I have not had one.

But I have had 5 Solas Titan 4 blade SS props and they were great in quality,performance and finish.

I would definitely buy a Sola SS prop again if the need arose.

[Nauti_Mike]

Well if you are hitting bottom that regularly a SS may fair better but that energy will get transferred into the drive and may cause damage to it over time. IMO props are cheaper than buying a outdrive.

[itsabowtime2]

Switching to a harder material will, more than likely, cause damage to the drive as the stainless is not as forgiving.

If you are boating in shallow waters I would most certainly stay with aluminum. Must less expensive to replace a prop yearly versus a drive.

[CptCrunchie]

That's just it, I'm not boating anywhere near the bottom. In fact, the closest I get to the bottom is when I launch and retrieve. I boat in the Strait of Juan de Fuca in very deep water. Yet, every time I return to the dock, there are more and more pieces missing from the leading edges of the blades. I hit one deadhead a while back, but it missed the prop. This is all damage from small floating crap.

[Guest]

In salt water with tidal flow and current, I find the SS to bite better. But in fresh water with more obstructions I use aluminum. As said better to chip the prop than damage gears.

[CptCrunchie]

"pjumper" post=827974 wrote:
....better to chip the prop than damage gears.

I absolutely agree, ...IF I was hitting ground or some other immovable object. But I'm having difficulty with the difference between the force of the impact versus the strength of the blade. Whether it is AL or SS, the gears are basically taking the same impact, the only difference I can see is that the AL isn't holding up like a SS prop would.

I'm thinking of the difference between a cheap hammer and a good one, when they both have wood handles. Both drive nails with the same impact, but one will last far longer than the other. Even still, longevity has to do with the size and hardness of the nails I'm driving. As long as the nails are smaller, the wood handles never really come into play.

If I ever did hit something hard with the prop that took out the OD, that will be an insurance claim.

This is what I'm getting to. If I was hitting the ground - or something that doesn't give - I can see where I would want the prop to be the weakest point. The stuff dinging the prop is small. What am I missing?

Please know, I have no desire to pick fight; I'm seriously wanting to understand this, but my background in physics seems to be getting in the way.

[bal734]

On my 3058 I switched from aluminum three blade to stainless four blade and it was a great move. Less vibration and noise, up on a plane at lower rpm, and a mid range increase in speed of three knots. Only trade off was slightly less top end speed. Never chewed up the prop tips.

[TPONZ]

Hi, Just read this old post of yours, Are you able to tell me what props you changed from, and changed to ? Cheers

[smitty477]

[attachment]42111 wrote:
IMG_5228.JPG[/attachment]

"bal734" post=827985 wrote:
On my 3058 I switched from aluminum three blade to stainless four blade and it was a great move. Less vibration and noise, up on a plane at lower rpm, and a mid range increase in speed of three knots. Only trade off was slightly less top end speed. Never chewed up the prop tips.

n our case it is exactly as said above - switching from a 3 blade Al to 4 blade SS Props added lower planning speed, better efficiency, lower blowout in turns and in our case a faster top speed - likely due to the extra lift.


Attached files

[CptCrunchie]

Excellent info. But that brings up a question that has been debated extensively on BOC - 3 blades or 4. I know the 4 blade gives a better hole shot, which lessens the top speed (as long as your AL 3-blade was propped correctly to begin with), but what gives it better fuel efficiency? Better grip means more needed torque. More torque mean more power. More power needs more fuel.

Since I rarely take it anywhere near WOT, I'm far more interested in fuel economy than speed. Can anyone explain how a 4-blade saves more fuel than a comparable 3-blade?

That said, to me, there is a huge difference between fuel efficiency and fuel economy. While I like fuel efficiency, I'm all about fuel economy. In my brain, fuel efficiency means the best fuel economy at a given speed, where fuel economy means the least fuel used at any speed to get from one place to another ....that is, while on plane.

This brings up another question. At what RPM do the secondaries typically open on my 4-barrel carb? Would keeping these as closed as possible save fuel without compromising too much power? I realize I could have switched to a 2-barrel, but I like the idea of having more power available. I did a speed/fuel consumption graph, and my best fuel economy (2.4MPG with close to flat seas, minimal current and no wind) is at 21kts with almost full trim tabs, at 3500RPM. I have no idea what the carb is doing, but those are my numbers. I'm only asking to gain a greater understanding of the details of how this all works.

[88fourwinns]

A few things...

1) aluminum is much softer than stainless steel, so it does cushion the impact to the prop shaft and fwd/pinion gears.

2) you have a Cobra drive, the parts are not that easy to get, I'd make the sacrifice of using an alu prop (and that's what I do) to put off as long as you can having to rebuild the lower unit. Yes it would be an ins job but remember you have to have the parts to fix it.

3) as far as fuel economy, it is well known that the Rochester Q-Jet is about as good as it gets, because of the small primary bores. I have found that is I stay under 3600 rpm the secondaries don't even open on mine. A bit less prop pitch to keep the boat on plane at a lower speed might help with this.

[dktool]

"CptCrunchie" post=827966 wrote:
I'm not boating anywhere near the bottom. In fact, the closest I get to the bottom is when I launch and retrieve. I boat in the Strait of Juan de Fuca in very deep water. Yet, every time I return to the dock, there are more and more pieces missing from the leading edges of the blades.This is all damage from small floating crap.

As I recall, you are running one of those "adust-o- matic" props. I would look long and hard as to the quality of the material they use.

Go with a name brand, Michigan Wheel etc. aluminum prop of unquestioned quality and see what your damage factor is after that.

IMO, 3 blade aluminum, 151/2 x 15

As stated, aluminum props are cheaper the Cobra gears.

[CptCrunchie]

"dktool" post=828026 wrote:
As I recall, you are running one of those "adust-o- matic" props. I would look long and hard as to the quality of the material they use.

Go with a name brand, Michigan Wheel etc. aluminum prop of unquestioned quality and see what your damage factor is after that.

IMO, 3 blade aluminum, 151/2 x 15

As stated, aluminum props are cheaper the Cobra gears.

The ProPulse prop? It got the Armstrong Float Test after the third time I used it. The first time it worked admirably. The second time it developed a tremor. The third time it felt like it was trying to shake the boat apart. I replaced the fins and took it crabbing, then took it on a tour of Protection Island. It started out great, but by the time we hit the dock, it had developed that shake again. So, .....it got the Armstrong Float Test. I'm back to using my AL 15x17, though I still have my 15.5x15 with the big dings out of it. Guess I could have them repaired, but for a few dollars more, I may as well buy new.

The comments about sourcing Cobra parts hits home, so guess my best bet is to stick with AL. And considering I can (almost) buy 3 AL props for the price of one SS prop, I'll have three years of service for roughly the same cost.

[Guest]

What are you hitting to damage your prop? In Florida there is offshore boating that I like SS, a lot of bite and nothing to hit (aluminum tended to flex more and didn't give me the control I needed in rough water). In the shallows was mostly sand bars and the SS would cut through minor groundings. In Ontario there are a lot of huge boulders. Hit them with a SS prop you will damage gears. Aluminum will break easily, protecting your gears. Also fresh water doesn't seem to push you around as much as salt. So Aluminum does the job. Just my thoughts, haven't said that, i replaced my outdrive at 750 hours. 1/2 salt 1/2 fresh. And no I don't damage many props.

[smitty477]

"CptCrunchie" post=827996 wrote:
Excellent info. But that brings up a question that has been debated extensively on BOC - 3 blades or 4. I know the 4 blade gives a better hole shot, which lessens the top speed (as long as your AL 3-blade was propped correctly to begin with), but what gives it better fuel efficiency? Better grip means more needed torque. More torque mean more power. More power needs more fuel.

Since I rarely take it anywhere near WOT, I'm far more interested in fuel economy than speed. Can anyone explain how a 4-blade saves more fuel than a comparable 3-blade?

That said, to me, there is a huge difference between fuel efficiency and fuel economy. While I like fuel efficiency, I'm all about fuel economy. In my brain, fuel efficiency means the best fuel economy at a given speed, where fuel economy means the least fuel used at any speed to get from one place to another ....that is, while on plane.

This brings up another question. At what RPM do the secondaries typically open on my 4-barrel carb? Would keeping these as closed as possible save fuel without compromising too much power? I realize I could have switched to a 2-barrel, but I like the idea of having more power available. I did a speed/fuel consumption graph, and my best fuel economy (2.4MPG with close to flat seas, minimal current and no wind) is at 21kts with almost full trim tabs, at 3500RPM. I have no idea what the carb is doing, but those are my numbers. I'm only asking to gain a greater understanding of the details of how this all works.

I cannot speak for your boat or outdrive as I have not owned one. I can compare the 3 blade al vs 4 blade SS props I have had on my 5 outboards.

By efficiency I mean that they burn less fuel to go the exact same speed. They do that by being thinner in their attack profile, more ridged resisting flex and they are made and stay much more accurate. On our boat in the pics above they also added some stern lift at anything above planning speeds and added a measurable fuel use per mile (about 5% or so) over the Al props at the exact same speed. The Yamaha' s on these boats were equipped with the fuel flow readings from the factory so not so hard to make comparisons.

Skiing at lower speeds was pretty amazing as well as pulling wakeboards and tubes.

The reasons we could also reach higher speeds with the 4 blade SS props was the stern lift combined with being able to run higher on the stern with the props - good for about 5mph but not sure as it was a bit scary to reach full WOT at that point.