4 Blade Alum to 4 Blade SS ?

[tahoejag]

Currently running Mich Vortex 14x20 4 blade alum. #'s are WOT- 4800 rpm, Top Speed 45 mph (gps), boat with average load and weight/fuel. I am running at the higher recommendation for WOT 4400-4800, possible bit for concern; however would like to go with SS. Here's where my question comes in. I ran the numbers thru the mercury prop selector and they came up with recommend..of a 14x21 pitch 4 blade SS. I am looking for mid range/fuel econ cruising and also maybe lowering the WOT rpms a bit. Now, would not a 14x20 SS give me same numbers as the alum? Or would the 14x21 SS put me at about 4600 rpm, where I'd like to be? I chose to go with the Solas HR Titan 4 I hear its a hell of a prop for the price. Stay with the 14x20 or go into the 14x21? comments/opinions please!

 

[steelespike]

Your numbers look good. Your over all performance should be stronger staying in the upper rpm.If your not comfortable at 4800 throttle back a little.
Usually assuming your numbers are good it is suggested you reduce pitch one inch when going to a ss prop.
It is also suggested to drop 1" when going to a 4 blade.
While the 4 blades do a great job your ss prop should improve performance over the al prop throughout the various conditions.
If your not comfortable at 4800 if you go for a 4 blade skip the pitch reduction.
​ Just keep in mind the motors are usually happier being allowed to rev freely within the wot rpm range.
Hole shot is easier,planing at reduced throttle is easier, speed holds up better with added weight.
​ Just did a little calculation your present numbers are just about perfect.
Prop results aren't carved in stone.

 

[tahoejag]

Steelespike, don't mean to sound redundant but I'm running 4 blade alum now 14x20. I desire to go to the Solas HR Titan 4 blade SS. However, a bit confused on which pitch to go with. Unwritten rule would be go to a 14x19 (dropping down an inch for SS). I'd like to point out that I ran my present numbers thru the mercury prop selector guide and their suggestion was to go to a 14x21 pitch. I personally was thinking of staying with the same pitch as what I have (14x20) ??? so confusing......lol.​

 

[steelespike]

I would replace the prop based on the results with your present prop. Normally you would drop an inch for going to a 4 blade you
also would drop an inch going to a ss prop. So that would put you at 18"
You definitely wouldn't increase pitch going from al to ss And you wouldn't increase pitch going from 3 to 4 blade.
Any prop change can be a bit of a gamble. You want to change brands,material and design.
To keep it a little simpler I would suggest a 19" ss prop forget the 4 blade.Or go to a al 4 blade 19"
If you boat where the prop might make hard contact (rocks) the ss costs more to repair.
If you boat where soft contact(mud/sand) is likely the ss may hold up better but will cost more to repair when the time comes.
The 4 blade al prop can definitely improve your performance all but top end which usually will be a couple mph less.
You might check out the Mercury Spitfire prop. Said to do all the 4 blade stuff at the same pitch as your existing 3 blade prop
while maintaining speed.

 

[tahoejag]

Steelepike...not sure if your missing something here, but I am running a 4 blade alum now; not a 3 blade. 14x20. In theory to go to a 4 blade SS just drop 1 inch in pitch for similar result (#'s that is). I got away from the 3 blade for very good reasons due to handling. I know a SS will outperform an Alum, just not sure which pitch to go with seeing I do have very good #'s currently.

 

[littlerayray]

The only reason for your boat to go to stainless is the look your boat is not spinning the aluminum prop fast enough to distort it's shape you need 250hp or more to spin a prop fast enough to distort shape I wouldn't change the prop if I were you your bets are great if you don't like running at 4800rpm then throttle back a bit just cuz it's here doesn't mean you have to use it