I have a Ranger RT178 with a 4-stroke Mercury outboard.  I have a factory 4-bladed aluminum prop.  When I have 2 people and gear loaded up (plus one stern mounted talon), I can get about 35-36 mph out of it in good conditions.  I'm wondering what kind of increased performance/speed I could get if I upgraded to a 3-bladed stainless steel prop?  If you have a similar size boat/motor and have experienced this, please let me know what kind of speed increase you have.

 

It would be worth it if I could get another 5-6 mph out of a stainless prop but if only got 1-2 mph increase then there's not much incentive.

 

Thanks

What is the HP and what are you pulling for RPM'S?

 

Given apple to Apple comparisons going the other way, 3 blade aluminum to 4 blade aluminum, there is usually a decrease of 3ish MPH on the top for better  hole-shot.

 

Introducing the variable of a stainless 3, may grab you 5MPH

Probably get you a few on the top end. 4 blades are good for bite 3 blade will be better for speed plus, an aluminum blade can flex causing a loss of performance

All things being equal, a S/S screw is almost always a better performer than aluminum.

However, the first thing I'd recommend is to check your U S Coast Guard Maximum capacity plate numbers.

An accurate calculation that includes the total weight of you, your passengers, your gear (meaning motor, batteries, fuel as well as any & ALL gear on the boat) will allow you to recognize where you stand as it relates to what type of performance you can expect - regardless of your prop type.

Additionally, according to Ranger, the RT178 is rated for 75 hp - you may have something else.

Either way, the closer your numbers are to 'maximum capacity', the less performance improvement you can expect.

If you are close to or over loaded, I'd address that first.  

If you're weight looks well with in parameters, you're too underpowered, and you're motor's getting to the recommended RPM's at WOT, as mentioned above, you might get a few more mph out of the top end.

If nothing else, you'll probably improve the vessels ability to get on plane.

A-Jay