Now, I have a prop question! I have a Lowe Stinger 190 with a Mercury 90hp 2 stroke engine. I am looking at replacing the aluminum prop with a stainless steel. The alum. prop is 13.5dia. and a 19p. Can I install a 13 1/4 and 21p? Your help is appreciated since I am clueless on the subject 
You can use that prop, it will give more top speed but you will lose a lot of power out of the hole.
At wide open throttle and average load what rpms do you run with the aluminum prop on? That would tell you if you should be changing pitch or not…
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At wide open throttle and average load what rpms do you run with the aluminum prop on? That would tell you if you should be changing pitch or not…
5500. I really don’t know if I should go to stainless, or just get a spare alum. 
We run run a Mer 90 2 stroke on a 17 foot Lund and we run aluminum props. We run everything from a 19 through a 23 depending on the situation and which one I haven’t destroyed at the moment. A 23 is our tournament prop and with two guys and no breakfast we get top speed but motor only turns 5100 RPM or so. 21 pitch works OK for same porpose only turns a few more RPM’s. The 19 works great for a boatload of people or playing but the top end is off some and I have to watch to make sure and not over rev. I have never played with stainless so that part I couldn’t help you with.
Going to a stainless will improve your overall performance, hands down. However, you have to be careful. Higher the pitch(to a certain extent anyway) the more top end, but less peak RPM. At the same time, your hole shot will suffer. If you want both, then you may also consider the bigger pitch with a hydroplane device. See Jame’s recent post about his new skeeter in the skeeter boat forum.
If the price is right I would say put it on. It’s not going to hurt anything.
With your wot at 5500 rmps u are right in the range of most two stroke motors I beleive.
Going to a 19″ pitch prop is probably going to drop you to around 5100 rpms. That’s getting pretty low.
I would contact a boat shop that sells your brand of outboard and ask them where your motor should be running at wot. A general rule of thumb is changing pitch by 2″ is going to lower or raise the rpm at wot by 500 rpms in the respective direction + or -. Increase pitch, loose rpm, decrease pitch and the rpms raise.
You don’t want to over rev your motor, and you don’t want it overworking either.
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Going to a stainless will improve your overall performance, hands down. However, you have to be careful. Higher the pitch(to a certain extent anyway) the more top end, but less peak RPM. At the same time, your hole shot will suffer. If you want both, then you may also consider the bigger pitch with a hydroplane device. See Jame’s recent post about his new skeeter in the skeeter boat forum.
Kooty, sorry to ask a dumb question, but would less rpm on the engine mean it isnt working so hard?
For overall performance I’d try a Merc Lazer II 20p. Very common prop with good bite and bow lift. You should find a loaner prop to try out at any Merc dealer.
Good Luck,
-J.
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With your wot at 5500 rmps u are right in the range of most two stroke motors I beleive.
Going to a 19″ pitch prop is probably going to drop you to around 5100 rpms. That’s getting pretty low.
He is getting the 5500 on the 19p aluminum.
-J.
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sorry to ask a dumb question, but would less rpm on the engine mean it isnt working so hard?
Less RPM = Less HP. Your motor will work harder to push the same load.
-J.
Thank you Jon, I KNEW my thinking was off somewhere… 
You are going to lose a few hundred RPM’s when going to the 21 from the 19. The posts on here are also correct about hole shot, which will suffer a bit depending if the prop is vented, has PVS holes or not (relieves exhaust gas in front of blades to make it easier to turn prop at take off) Alot also depends on the style of prop you are going to run, every brand offers something different as there is much more to props than just pitch. To win at the prop game you want to get as close as possible to your motors max rpm’s at wide open throttle without exceeding.
There are only two real ways to find out what will happen. Find someone who has run the exact same thing on the exact same boat or do it. If the prop fits from a hub design standpoint no harm can be done except for running above max RPM’s, make sure you know that for your engine before you do anything.
It’s also important to have good baseline data before you start such as time to get on plane, or seconds to 30mph and top speed. Don’t forget to test with full livewells, full fuel or a full crew on board. Having good data is key to making decisions on next steps.
Keep us informed on how you do.
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sorry to ask a dumb question, but would less rpm on the engine mean it isnt working so hard?
Less RPM = Less HP. Your motor will work harder to push the same load.
-J.
Think of it this way.
Consider pitch the same as gears on a 10 speed bike. And RPM’s the same as pedal speed. The higher the gear the faster the bike will travel. The faster you pedal, the faster you go. But as you know, there are many variables to riding your 10 speed bike. You can’t put it 10th gear and pedal fast unless you increase strength (Horse Power – HP).
So in a scenario where you are in 5th gear pedaling comfortably along and come to a hill. You either need to increase strength (HP) or decrease gear (Pitch). If you kept it in 10th gear, you would exert a lot of force on your legs. (Or in the case of a motor, work harder)
Since boats don’t have gears and you can’t change pitch without changing props, you need to find a nice middle ground that works well in all situations. The right combination of diameter and pitch, combined with the available horsepower to push the average load is what you need to find. Go to high on the pitch, you over work your motor. Go to low of a pitch and you never get any kind of speed. (Like pedaling fast in 1st gear.)
The 2 main things you gain with a SS prop is durability and bite. An SS prop can take hits that will destroy an aluminum prop. Bite is the ability for the prop to hold in turns and take off. A prop that loses bite blows out in turns or when you are trying to get on plane.
-J.
Man, you guys are great! That is all excellent info, and I now feel I can make an intelligent decision. Thank you all for your input, and for taking the time to answer! 
From the post above
The 2 main things you gain with a SS prop is durability and bite. An SS prop can take hits that will destroy an aluminum prop. Bite is the ability for the prop to hold in turns and take off. A prop that loses bite blows out in turns or when you are trying to get on plane
So take into consderation, if you do hit something with a SS prop, it does not give, the force is absorbed throughout the lower end, ie twisting prop shafts, breaking gears etc which could end up costing a whole lot more to repair than an alluminum prop. Something else to consider.
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So take into consderation, if you do hit something with a SS prop, it does not give, the force is absorbed throughout the lower end, ie twisting prop shafts, breaking gears etc which could end up costing a whole lot more to repair than an alluminum prop. Something else to consider.
I have not seen one claim to where this statement is true. For the most part, I believe that this is an old wives tale
I would love to hear from guys where this actually happened too.
Ron
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So take into consderation, if you do hit something with a SS prop, it does not give, the force is absorbed throughout the lower end, ie twisting prop shafts, breaking gears etc which could end up costing a whole lot more to repair than an alluminum prop. Something else to consider.
I have not seen one claim to where this statement is true. For the most part, I believe that this is an old wives tale
I would love to hear from guys where this actually happened too.Ron
I agree with Ron. They put rubber/urethane hubs in SS props just for that reason.
I think that your speed makes a difference if you’re idolling along and hit a pile of rocks with a alum prop you will trash your prop real good but w a stainless you won’t be to happy about the bill to repair said prop but at least you will be able to run around quite well,also I lost RPM’s w ss props of the same size but gained speed becauce you have less flex and better bite
Stan 
0Yuo wont see much performance change in a 90 hp motor with stainless. I have 90 hp and it barely changed. Mark at marks prop shop told me you wont see much untill you get to at least a 115hp. I think the suggestions above where good choices but for the money you will be a bit disapointed. just change the pitch to get to around 6000rpms 
ACTUALLY YOU’LL RUN ABOUT THE SAME RPM WITH THE 21 SS AS THE 19″ ALUM. YOUR BOAT WILL PERFORM WAAAAAAAAY BETTER!
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