Prop Question!

[Weksos]

I have a 1998 Mercury Tracker Pro Series 90HP (2 stroke). At wot in at 5200-5300 RPM @ about 41-46 mph depending on weight I'm carrying & water currents. My current prop is a Mercury 77348A45P21. My question is if I were to go with a SS Prop, what would be the best size for gaining top speed.

[KJMinion]

Weksos, I'm sure others can chime in on this and have a better answer for your question than I do but I was under the impression that going to a stainless steel prop on a 90 won't do much for the performance. I've been told that the SS props are usually for higher hp motors (115 and higher) and for pushing heavier boats. I might be wrong but I think you might only gain a mph or two at the top end but probably not as much as you were probably hoping for.

I've got a 2000 90hp two stroke motor on a 1700 Lund Angler and I get about the same speeds that you had mentioned with the standard mercury prop that it came with. I've thought about getting a SS prop in the past myself but I've heard that it probably would not make that big of a difference.

[leech~~]

Stainless weigh a little more but it has to do more with pitch not what they prop is made of. As far as big motor's only I have a SS on my 75HP Merc and it moves along just fine. It's faster then the old 90HP Force I use to have on the boat.

[BoxMN]

Used to have a 87 Merc 90, which I think is about the same inards as the motor in question. We had an 18" Merc SS prop on it, and it spun about 5700, a bit above recommended, but we often had three people and gear, so it revved about right then.

SS will give you better hole shot for sure, even with a 90. It will resist dings, and bite the water better for better control. It probably won't give you much extra in terms of speed.

I would guess that a 19" three blade would be a good fit, just don't get a Laser - they are horrible for the that motor. (edit - the Laser was horrible for our boat with that motor, but it was a walleye style alum boat, not a sleek glass boat) Tried one, and it went FAST but horrible hole shot.

You might even be able to raise the motor a hole with a good SS prop, and the would help your top end. I think we did that, but it was long time ago now but think we were on middle hole, and it handled great, could waterski great. Good luck.

[hydro]

Stainless is a stronger material than aluminum and as such the blades are usually made thinner. That equals less resistance to turn the prop and a little more "push" available with the same horsepower input. Usually when going from aluminum to stainless you need to drop down an inch or so in pitch to carry the same RPM.

That said, with 5300 RPM, assuming a 1.86:1 gear ratio and 21" pitch, and a true 45 MPH, you have over 20% slip which is too much. That wastes power (gas!)and can be improved. A stainless prop at 19" to 21" pitch should net you a couple of MPH if you can stomach the price. Be sure to know your recommended RPM range and shoot for the top 1/3 with your normal load when evaluation a new prop. Check with a reputable propeller shop for a recommendation on the best design prop for your boat and see if you can work a "Trial" kind of deal to test the new wheel.