Aluminum to Stainless

[This_lil_fishy]

On my boat (in sig below) I've got a 4.3 TKS Merc with Alpha 1 out drive. It currently has the stock aluminum prop. My merc manual says I should not exceed 4800rpm at wot but I sit at, or very close to, 5000rpm and close to 50mph. I was thinking about getting a stainless prop for improved performance, and was wondering if I should pitch up one, or down when changing to stainless to get my RPM down to the recommended max.

I'm not really looking to increase performance per se, as I may do some tubing or wake boarding...maybe..but mostly I'm looking at efficiency, and keeping the motor in the proper range. So any suggestions for number and blade style would be apprciated as well.

Ian

 

[Tail_Gunner]

Re: Aluminum to Stainless

On my boat (in sig below) I've got a 4.3 TKS Merc with Alpha 1 out drive. It currently has the stock aluminum prop. My merc manual says I should not exceed 4800rpm at wot but I sit at, or very close to, 5000rpm and close to 50mph. I was thinking about getting a stainless prop for improved performance, and was wondering if I should pitch up one, or down when changing to stainless to get my RPM down to the recommended max.

I'm not really looking to increase performance per se, as I may do some tubing or wake boarding...maybe..but mostly I'm looking at efficiency, and keeping the motor in the proper range. So any suggestions for number and blade style would be apprciated as well.

Ian

Down one..you should be happy BowLifter Solas HR titan series 3 blades.....SternLifter Stilletto Bay Pro 11..For I/O's that is about the extent you can do and both of those prop's are very good props...Or the the stilletto advantage series in a 3 blade..If you go to a 4 blade you may want to post your current pitch

 

[This_lil_fishy]

Re: Aluminum to Stainless

Stock is 832832A45P21 Merc Prop.

14 1/4" X 21 pitch



Ian

 

[Tail_Gunner]

Re: Aluminum to Stainless

http://boatpropellers.iboats.com/Me.../9534/?**********=334253683&*******=297506917

http://boatpropellers.iboats.com/Me.../9586/?**********=334253683&*******=297506917


http://boatpropellers.iboats.com/Me...17657/?**********=334253683&*******=297506917

1. Top speed
2. lower planing speeds more midrange overall smoothness
3. I just cant help plugging Bay Pro's tons of grip extremely smooth and midrange that pulls like a tractor.. but you will lose top end speed..

It's to bad they dont make a odd pitched 4 blade(Stilletto)...Solas made a good move be so universal. You could try a 20 and it may work, but i do know it will grip like a 21p ss. (BayPro 11 ) that is..maybe call i-boats and see if they still give you a right of exchange.

 

[This_lil_fishy]

Re: Aluminum to Stainless

Yeah I might do that, I think cruising is more important to me, to be honest, it'll spend more time at idle speeds then anything else. So going down one pitch will reduce rpm? I had it in my head it was the other way around.

PS: Those measurements were with 3 people (lightwieghts all of us) and a full tank of fuel. She seems to plane a bit low in the bow too, would not a "sternlift" prop increase this tendency?

Ian

 

[Tail_Gunner]

Re: Aluminum to Stainless

Yeah I might do that, I think cruising is more important to me, to be honest, it'll spend more time at idle speeds then anything else. So going down one pitch will reduce rpm? I had it in my head it was the other way around.

PS: Those measurements were with 3 people (lightwieghts all of us) and a full tank of fuel. She seems to plane a bit low in the bow too, would not a "sternlift" prop increase this tendency?

Ian

The Stilletto's would greatly improve your lower planing speed's and if i-boat's will allow you to try a 20 and it if thats to much prop for the boat... amd exchange it for a 18 id say go for it.

You going from alum to SS that is a 200 drop in rpm...so a 20p ss will or should keep you at 4900...ad a 4 blade and drop another 100. Now The Bay Pro 11 are different animal's they have quite a bit of cupping..that is the reason for my hesitation on there 20..One might think you could get away with a 20 aka 200 for ss and 100 for the 4th blade gets you 4800 but the cupping will make it act like a 21 pitch netting you out to 4600..not good for today's engines and gas.

What you will experience is a much smoother feel in the boat...lower planing speed's....at 18 mph when you nail it it there is enough grip it feels like a 4 barrel carb kicking in..fun stuff.

 

[wca_tim]

Re: Aluminum to Stainless

No disrespect intended, but you did have it right with going up in pitch drops rpms... going to stainless typically drops rpm a little as well. I bet if you go with a 21 4 blade it will put your rpms right where you want them about 4800, you'll pick up a little top end and it'll pull smoother overall. I like the Solas titan 4 for a bargain 4 bladed stainless prop. but there are a ton of other choices as well...

 

[Tail_Gunner]

Re: Aluminum to Stainless

No disrespect intended, but you did have it right with going up in pitch drops rpms... going to stainless typically drops rpm a little as well. I bet if you go with a 21 4 blade it will put your rpms right where you want them about 4800, you'll pick up a little top end and it'll pull smoother overall. I like the Solas titan 4 for a bargain 4 bladed stainless prop. but there are a ton of other choices as well...

None taken WCA i have watched your posts for a great deal of time they seem well informed and to the point. It has been my experieince that going going from a 21 pitch alum to a ss with some if any cupping will drop the rpm 200 rpm...aka 21p 3bl alum @ 4950 to ss should convert to a 20p 3bl @ the same rpm..4950

Now Baypro 11 have quite a bit of cupping which creates a tremendous amount of stern lft. No matter how you define things energy in energy out.but and i say but if your hull balances on its hiny there is a lot less drag...resulting in enhanced or less drag and higher speeds.

Put these numbers into a slip calc....20p gear ratio 1.66... rpm 4950...speed 55mph..5% slip...not on a production hull...but add cupping and reduced drag...they work very well.

There only draw back is 18 and 20 pitch avaiblity.. Solas does not lift like a stilletto..i have them both.

Your into performance..if your boat falls within there limited range try one...you will be very surprised..

 

[This_lil_fishy]

Re: Aluminum to Stainless

Thanks guys, your info is stellar. Iboats doesn't allow for returns from Canada (we ship to the US regularly, it's a lot of red tape, so I can understand). I'll have to see what I can find locally...that will let me exchange a prop.

Ian