SS prop vs same size alum ?

[zenoahphobic]

Boscoe, panasonic....in my boat, fully loaded, WOT, i can reach btwn 4800-4900, light load 5000-5100. Spec for my engine is 4500-5500. 21" pitch.

I should decrease. And i know propping is an art form, but what's yall's best guess to decrease...down to 19" or 17"? Consider i run the boat majority of the time loaded. Speed isn't a concern, whether i gain or lose a few mph, optimum engine performance is.

Shame we lost that thread. If your prop (21in) is a s/s then it would be regarded as above average into the "performance" category - so you are not upgrading as such.
I would say either a drop to 19 or 17, the later may be a touch high Reving but at weight load pretty near. You will get a better up and go, although you don,t care loosing a mph or two, you still will be speculating on efficiency. That is your miles per gallon. Car brained people will argue reducing rpm,s but maintaining speed is more efficient. You,ll need to trial and error and do exact measurements to compare. It would be lovely to have an array of props handed to us and spend the day playing lab scientists. A library of props should be attached to this forum as a privelage being a member. Dreaming again, to most we must pay $$$$ to do this.
See what others come up with.

[zenoahphobic]

I must add, said much before, boat/ motor sellers take advantage of this manufacturer's WOT rev range. It gives an excuse to not go to much effort in providing the correct (customer specified needs) setup.
Think, if the manufacturer said WOT revs should be within a few hundred revs (no reason not to from an engineering point of view) , then deals would lead more to the seller providing a better match in order for the sale to go ahead.

[boscoe99]

I must add, said much before, boat/ motor sellers take advantage of this manufacturer's WOT rev range. It gives an excuse to not go to much effort in providing the correct (customer specified needs) setup.
Think, if the manufacturer said WOT revs should be within a few hundred revs (no reason not to from an engineering point of view) , then deals would lead more to the seller providing a better match in order for the sale to go ahead.

Methinks boat builders/boat sellers are more interested in a quick and easy sell for them than they are interested in the satisfaction of the customer. Plus, selling motors that are over propped results in increased sales of propellers.

Damn I hate being cynical.

[panasonic]

Boscoe, panasonic....in my boat, fully loaded, WOT, i can reach btwn 4800-4900, light load 5000-5100. Spec for my engine is 4500-5500. 21" pitch.

I should decrease. And i know propping is an art form, but what's yall's best guess to decrease...down to 19" or 17"? Consider i run the boat majority of the time loaded. Speed isn't a concern, whether i gain or lose a few mph, optimum engine performance is.

Flip a coin Jason. Heads for 19...tails for 17. Lol

Is there no 18"?

But going by the info Boscoe presented, by Yamaha, it seems to be a better choice to be under propped slightly and have some wiggle room right at the very top of your engine rpm. Go for the 17" and see what happens....

[boscoe99]

Flip a coin Jason. Heads for 19...tails for 17. Lol

Is there no 18"?

But going by the info Boscoe presented, by Yamaha, it seems to be a better choice to be under propped slightly and have some wiggle room right at the very top of your engine rpm. Go for the 17" and see what happens....

If a motor is a bit under propped the operator can see it on the tachometer. If the operator does not see it then the motor has an over rev protection motor to protect the motor from an over speed. Most folks don't drive around at WOT where over speed would be an issue.

If the motor is over propped it can be hard to know. Only if someone is sensitive to a bit of slugishness might they sense the motor being over propped. Long term it is not conducive to the health of the motor.

But then we here on boats.net are the very few. Most boat owner's/operator's either don't know or don't care about such matters. They just want to get in the boat and go.

So much easier in an airplane where at each annual the mechanic will apply the brakes and run the motor at WOT. The motor has to be turning at X RPM plus or minus a few. If too few or too many he can check the propeller for good condition. If the propeller checks good but there are too few RPM then he knows that the health of the motor might not be what it is supposed to be. So he knows a few things. One, the propeller is doing what it is supposed to be doing, the propeller won't be harming the motor and the motor is or is not in good condition from a power output standpoint.

[panasonic]

I don't work on piston aircraft much, but what you say is correct for fixed pitched props on piston engines.

I work on turbine driven prop aircraft mostly DHC-8. So anytime we change an engine, prop, or any other major power plant component we run the aircraft to ensure proper operation. The Dash 8 100 series has variable pitch prop 13 feet in diameter. Engine HP is 1850 with power up trim to 2150 Hp(single engine operation)

Max prop RPM is 1200 RPM +\- 50 at a certain engine torque (approx 90%) which we figure out depending on air pressure and air temp. Min prop is 900 rpm. Constant speed 4 bladed prop.


So if you don't get 1200 rpm you have to determine if it is the engine not producing power or the prop control may need adjusting.

Thought you prop guys might be interested in that bit of information.

[99yam40]

we need those variable props on outboards.

can you imagine what putting that stuff on a boat with inexperienced operators would do to everything

[Jason2tpa]

Flip a coin Jason. Heads for 19...tails for 17. Lol

Is there no 18"?

But going by the info Boscoe presented, by Yamaha, it seems to be a better choice to be under propped slightly and have some wiggle room right at the very top of your engine rpm. Go for the 17" and see what happens....

The 17" is also what I would first go with. As far as an 18", yes there are prop manufacturers that produce an 18" pitch compatible with my hub. Quicksilver comes to mind. Though since Im pleased with the durability and performance of my michigan wheel prop, and dont have the opportunity to test every prop available, I'll likely stick with same brand. They produce only odd number pitch inches, or at least for my model/year engine.

[zenoahphobic]

we need those variable props on outboards.

can you imagine what putting that stuff on a boat with inexperienced operators would do to everything

Perhaps some sort of auto transmission , non operator input. It would not take up much room because you'll regulate say within 80% of the range - like a car overdrive attachment of the past.
Always viewed a "one" gear only vehicle as must having room for performance improvement. Like early auto's were two speed; now what is common? 6 or 8 speed. Even my Radio Control truggy has 3.
Never seen or heard it done, restriction and complicated cowling probably the biggest deterrent for some amateur modification.

[panasonic]

I guess there was a variable pitch prop made for outboards, it was called "Land and Sea Torque Shift" It didn't work so well and had reliability problems as far as can see. There are a few videos on YouTube showing it in operation. Very crude device.

[Zara Spook]

I had the same boat (Cobia 194CC) for a while, with a 2003 Yamaha 150HP carbed 2-stroke, and would regularly hit 44 MPH at 5800-5900 RPM (WOT), and with a tremendous hole shot. I used a three-blade 17-pitch SS prop.

You have a 115HP engine on the other hand. I would think then that you'd need a 15-pitch SS prop to get up into the recommended RPM range at WOT.

[Zara Spook]

...on the other hand, here is the Performance Bulletin for your boat and engine, with a 17-pitch SS prop:

http://yamahaoutboards.com/sites/def...-202-COB-B.pdf

They hit nearly 40 MPH at 6000 RPM at WOT.

So, perhaps it's your brand of prop and the other variables involved (cup, rake, diameter, etc.).

[Jason2tpa]

...on the other hand, here is the Performance Bulletin for your boat and engine, with a 17-pitch SS prop:

http://yamahaoutboards.com/sites/def...-202-COB-B.pdf

They hit nearly 40 MPH at 6000 RPM at WOT.

So, perhaps it's your brand of prop and the other variables involved (cup, rake, diameter, etc.).

Appreciate you looking this up. But unfortunately this bulletin, along with all others I've come across, does not align close enough to my boat/motor to be considered as valuable information. This bulletin tests a 4 stroke on a hull weighing 2,150 lbs. Mine is 2 stroke on a hull weighing half as much.

I can reach 40mph with the 21" pitch, topping out at 5k rpm, which meets the middle of the engines spec range. And if it jumped out of a hole any quicker I may need a neck brace. From a performance standpoint I'm very happy with the 21". From a technical standpoint I should the lower pitch in order for the engine to reach the top of rpm spec.

My guess is the 15" would turn well over 6k, too much. The max amount of rpms I would want to increase by is 500-600. Theoretically, dropping pitch by 4" to a 17" would add 800 rpms.

You bring up a good point. Every brand and style of prop will perform differently, even when the comparison is made using the same pitch across brands. And this is one of the many reasons why correctly propping the motor to the boat is an art form.

I've run this boat with only this prop, michigan wheel apollo B 13x21. But I'm open to switching brands if thats what it takes.

[Hokie 59]

SS prop vs same size alum?

Thanks folks.

You have all been very helpful. My trouble now is that I'm stuck with a big, beautiful, stainless propeller that my on-line dealer won't take back because I bought it in Nov 2016 and I didn't get to test it 'til April 2017 - 5 months later. I can see their point, but it doesn't help me sitting here with more prop than I need.

I'll see what I can do by visiting some of the local prop shops to see what they'll give me on a trade. I'll have my Apollo prop in the box it came in. Apollo makes a 15" pitch SS prop, but with a bit larger diameter @ 13 3/8 x 15. It's the one I think I'll try next with hopes of getting a top WOT of about 6000rpm.

Maybe I can also post it For Sale on the Yamaha Outboard Parts Forum with some pictures. Think I'll try that first.

[Jason2tpa]

Thanks folks.

You have all been very helpful. My trouble now is that I'm stuck with a big, beautiful, stainless propeller that my on-line dealer won't take back because I bought it in Nov 2016 and I didn't get to test it 'til April 2017 - 5 months later. I can see their point, but it doesn't help me sitting here with more prop than I need.

I'll see what I can do by visiting some of the local prop shops to see what they'll give me on a trade. I'll have my Apollo prop in the box it came in. Apollo makes a 15" pitch SS prop, but with a bit larger diameter @ 13 3/8 x 15. It's the one I think I'll try next with hopes of getting a top WOT of about 6000rpm.

Maybe I can also post it For Sale on the Yamaha Outboard Parts Forum with some pictures. Think I'll try that first.

Im in the same situation, same brand and make prop too. What I've discovered from talking with my local prop shops is the resale value of our good used prop is just under the value of our prop sold new. So it really doesn't make cents to buy it used when you can buy it new for only $40-60 more. This scenario only applies to excellent condition used, of course. Once you've talked with your prop shops, PM me if you wanna discuss a price for your prop.