Aluminum to Stainless

[FreeBeeTony]

Am thinking of changing from aluminum to stainless to maybe get a bit more mid-range speed.

Currentle running a 17" aluminum getting 30MPH @ 3600RPM and 37MPH at 4500RPM at WOT.

Was thinking of changing to aluminum...........could/should I stay @ 17" pitch? and what type of performence increase would I expect?

 

[Tail_Gunner]

Re: Aluminum to Stainless

Those Grady's are heavy boat's Tony, i seem to remeber another individual posting about a year ago with a similar setup. If i remeber correctly that bow really does some plowing.

Going to SS would more that probably get you a better hole shot since you can reduce the pitch a few inches....But i doubt if you picked a High rake bow lifter it would make a big difference...

You never know until you get it on a run it. If it was me id get the MWC Apollo that WH reviewed in the top of this forum...It seem it was a great pusher prop and very little speed loss.

 

[FreeBeeTony]

Re: Aluminum to Stainless

Thanks TG.....but what about the pitch? Would I stay the same?

Might look for something used on ebay........

 

[Tail_Gunner]

Re: Aluminum to Stainless

1. 17 @ 4500
2. 16 @4700
3. 15@4900
4. going ot ss drop 200
5. 15p @ 4700..
6. add a fouth blade 4600

That be my choice tony... http://boatpropellers.iboats.com/Me.../9595/?**********=444563917&*******=826997102

This would be a 3 blade choice

http://boatpropellers.iboats.com/Me.../9592/?**********=444563917&*******=826997102

I cannot honestly say how this stilletto would work..but it sure would out perform that alum you have..Stilletto's have a lot of cupping for grip they are great props and dirt cheap to right now hard to pass..

http://boatpropellers.iboats.com/Me...17565/?**********=444563917&*******=826997102

 

[FreeBeeTony]

Re: Aluminum to Stainless

Thanks again TG........not really looking to spend that kinda $$$......

Last year I had a 16" 4 blade aluminum........didn't like it at all at the top end, didn't seem to grab above 3500RPM or so.

 

[tmh]

Re: Aluminum to Stainless

Tony, if you're not willing to pay $350 or so for the prop, then you're not looking for a new SS prop. That's what the less expensive ones cost. What do you plan to spend?

You can always try craigslist and eBay for used ones I guess. I've bought props both places and done fine. I also bought a new SS here on iBoats because I couldn't find the model and pitch used.

 

[MikDee]

Re: Aluminum to Stainless

Am thinking of changing from aluminum to stainless to maybe get a bit more mid-range speed.

Currentle running a 17" aluminum getting 30MPH @ 3600RPM and 37MPH at 4500RPM at WOT.

Was thinking of changing to aluminum...........could/should I stay @ 17" pitch? and what type of performence increase would I expect?

IMO, From my experience, a SS prop is harder to spin compared to aluminum, because it is heavier, & pushes more water (due to less flex). Rather then load up your motor with a 17" pitch SS, I suggest a 15" pitch 3 blade SS prop. This should give you more speed, & better performance all around while reaching the same WOT rpm.

 

[steelespike]

Re: Aluminum to Stainless

Take a look at the Turning Point Hustler.Stainless performance at aluminum prices.With that heavy boat you might drop down an inch or two in pitch.
There have been a couple of follow up reports here with good results.
The Turning point prop usually manage an improvement across the board.
Any prop change is a bit of a gamble.Max speed increase could be a couple of tenths or a couple of mph.I believe there is a prop finder at the Turning Point site.

 

[MikDee]

Re: Aluminum to Stainless

This was my boat, a 24' SeaRay cuddy, and with a stock 1979-350/260hp Merc (4000lbs) I got it to do 40mph fully trimmed out, using a 17" pitch black max aluminum prop.
http://smg.photobucket.com/albums/v240/MikDee/My Boats/?action=view&current=24SeaRayCuddy260Merc.jpg
I think your boat is heavier, but you also have a late model 350Mag with vortec heads. That's why I think the only way you're going to free up the torque, & hp of that motor, is by dropping your pitch to a 15" if you're going with a SS prop.

I've heard good things about that Turning Point Hustler aluminum prop that Steelespike mentioned as well!

 

[QC]

Re: Aluminum to Stainless

IMO, From my experience, a SS prop is harder to spin compared to aluminum, because it is heavier, & pushes more water (due to less flex).

The second part of that is correct and why they are more efficient and make boats go faster. The weight difference however is insignificant as far as robbing any power is concerned . . .

 

[MikDee]

Re: Aluminum to Stainless

The second part of that is correct and why they are more efficient and make boats go faster. The weight difference however is insignificant as far as robbing any power is concerned . . .

Say what you will QC, but IMO, I think simple physics would conclude that spinning a much heavier weight on a shaft would require more power to get to 3000 + prop rpm, and hold it there. They are no featherweight. Hence one reason for decreasing pitch when going to stainless.

 

[QC]

Re: Aluminum to Stainless

Mik, Mik, Mik . . . the reason that sometimes SS props require a decrease in pitch is the lack of flex . . .

Yes, they are heavier, but for anyone to conclude that this weight difference results in a need for less pitch would be simply wrong. I am not trying to start a debate on the infinitesimal amount of power needed to turn the increased reciprocating mass. I am only trying to insure that someone does not conclude incorrectly that the increased weight means that Stainless Steel props are less efficient. Properly designed and matched SS props are more efficient than Aluminum propellers, period, end of story.

 

[MikDee]

Re: Aluminum to Stainless

They are no Featherweight. Hence one reason for decreasing pitch when going to stainless.

I know it's also a combination of factors, including design, but you can't say weight does not figure in the equation. IMO

 

[wca_tim]

Re: Aluminum to Stainless

I don't really have a dog in this hunt... and I hate to be the bearer of bad news... but if you consider that torque for an engine and after accounting for the gear ratio, represents the force available to spin the prop. Torqe for marine engines is expressed in foot pounds... 1 foot pound of torque represents a pound acting at a distance of one foot. Most of the mass for a prop is much closer than a foot, so even though it weights more than a pound, the average amount of torque required to accellerate a prop is going to be on the order of a foot pound or less. Now consider that if your engine is putting out over 300 ft pounds of torque, and is coupled through a 1.5:1 gear ratio outdrive... we're looking at 450 - 500 foot pounds of torque at the prop...

So you're both right! it does figure into the equation... however it can be neglected because it is trivial compared to the amount of torque required to accellerate the prop against the resistance of the water.

 

[MikDee]

Re: Aluminum to Stainless

Okay, QC & Tim, you've made some very good points, I don't want to debate the issue because I like you guys, & consider you both very knowledgable

To sum it up, I usually go by the general rule of dropping one pitch size when going from Alum. to SS, like when going from a 17" pitch Alum. prop, to a 15" pitch SS prop (for whatever the reasons) and I found it works for me.

 

[wca_tim]

Re: Aluminum to Stainless

Thanks for letting me off the hook on this one!

and thanks for the rule of thumb. Isn't it funny how sometimes the closer you look the more complicated something becomes, but more often than not, the "simpler" approach worlks best in the end? I very much appreciate the many things i've learned from your posts (and others).

 

[Tail_Gunner]

Re: Aluminum to Stainless

Okay, QC & Tim, you've made some very good points, I don't want to debate the issue because I like you guys, & consider you both very knowledgable

To sum it up, I usually go by the general rule of dropping one pitch size when going from Alum. to SS, like when going from a 17" pitch Alum. prop, to a 15" pitch SS prop (for whatever the reasons) and I found it works for me.

Tip Toe's in and very gaurdeiningly say's..QC is spot on....You cannot confuse the people who watch these post's. SS is vastly superior to alum.

 

[MikDee]

Re: Aluminum to Stainless

Tip Toe's in and very gaurdeiningly say's..QC is spot on....You cannot confuse the people who watch these post's. SS is vastly superior to alum.

gaurdeiningly? Is that a word TG? By the way, there's no disputing SS is superior to Alum? For those who can afford it.

 

[Tail_Gunner]

Re: Aluminum to Stainless

gaurdeiningly? Is that a word TG? By the way, there's no disputing SS is superior to Alum? For those who can afford it.

...Nope next time i will try some along these lines...It is with some apprehension that i come into this conversation and side along with QC. The inherent qualities of SS are vastly superior to that of alum and yes there is a cost.

As to cost i could not agree with you more and taking a closer look at the entire subject matter i can see where a alum prop could actually out perform a SS in a given situation.

That is my apprehension, performance is subjective in that there is a cost for top overall performance and sometimes those gain's do not merit the investment.

Hmmm gaurdingly....now that was a doosey err deusy

 

[wca_tim]

Re: Aluminum to Stainless

Another point in favor of aluminum is that it is easier on the outdrive - especially when you hit things. The flex in the aluminum serves to dampen the blow on the rest of the drive train relative to stainless...