Help with new (used) prop

[nixdorf]

Hello all,

I bought a used prop today for my 2004 Tracker Pro Team 190TX with a 90 HP Mercury 2 stroke.  I picked up a used Quicksilver stainless prop for less than $100.  It is replacing an aftermarket aluminum prop that is in poor shape.  The new prop appears to be in good condition.  I checked that this model does fit using Mercury's prop selector on their website before buying it. 

Now that I have it home, I wanted to check the condition of the hub, but I can't seem to break the hub free from the prop.  It appears I should be able to gently tap on the thrust-washer/gear case side of the hub to force it out.  I tried it with both a brass punch (alternating sides that I hit) and a 22mm socket, but was unable to break it free.  See the second pic below to see the side I was banging on.

To be blunt, I understand enough about marine props to be dangerous.  Before I do any damage, I thought I'd ask for advice here.  Any thoughts?  Should I just use it without checking the hub?  Hit it harder?  Use a bigger hammer?

Thoughts?

[Jig-Man]

Put it on the motor and use it.  I've only ever had one spun hub in my life.

[fishnkamp]

The older models had a press in hub. They have held up well. mercury changed it to the new style just so it can be changed easier.  If you do have a problem any prop shop can replace it.  Go run it.  Watch what your hole shot, wide open throttle rpm , and top speed is.  You may need to make some engine height adjustments. Also if your boat does not have a water pressure gauge add one and watch it.

[iabass8]

Get it balanced first and foremost. Wont br expensive. You can tap a mark on the housing of the hub and then on the hub itself to check for prop slip after usage. The lines will move a little but not too far. 

[nixdorf]

Thanks for the replies. They are really helpful. 

One more question: I'm worried if this hub will give out before damaging my lower unit if I hit something.  Any idea if Mercury installed "breakaway" type pressed in hubs on older Laser II props?

I do have a Flo Torq II hub from an older prop. I don't know if it would be useful here.

Thanks again.

[fishnkamp]

Find a good prop shop near you and talk to them  They will know if that prop can be changed over to the new style hub.  Before I spent a dime changing anything on the prop I would install it and take it to the water and run it.  Lets see how it works first.  If the performance is good and you get all of your numbers than you can talk to the prop shop about the hub and any little changes you might want.  I run an aluminum bass boat with a performance aluminum Hustler prop. I was prop testing and found they make a 17, 19 , and 21 inch pitch in the correct diameter. The 21 was too much and the 19 was not enough so I had my local prop shop add both an inch of pitch and some cup to the 19 pitch prop. Now I have a perfect match for my rig.  By doing this the prop cost $100 the hub cost $50 and the rework cost $77. I choose to run an aluminum prop because I run a lot of shallow water with underwater junk like crab traps. old boats etc. and a tide that is constantly changing.  A prop is cheaper than a lower unit.   By knowing my boat/ engine performance numbers my prop shop knew just what to do. I improved my hole shot, improved time to plane and gained 4 mph on the top end.

[iabass8]

2 hours ago, nixdorf said:

Thanks for the replies. They are really helpful. 

One more question: I'm worried if this hub will give out before damaging my lower unit if I hit something.  Any idea if Mercury installed "breakaway" type pressed in hubs on older Laser II props?

I do have a Flo Torq II hub from an older prop. I don't know if it would be useful here.

Thanks again.

I don't know if the hub will work on that prop. Make sure you are using the correct washer and components though. 

If you're worried about the damaging the lower unit when hitting something /w the prop you may want to run an aluminium prop so there's more "give" on impact. If you hit something on the water with such force that the prop slips off the hub /w a stainless, you more than likely did quite a bit of damage to both the prop and the LU/drive and prop shaft. It should take a ridiculous amount of force on impact to rip a prop off the hub. All props are easy to get nicks and small gouges in but if you hit something hard enough /w a stalness steel prop to mangle it, the prop is the last thing I'm worried about at that point. I'm not an expert on props but the ones I've used have a gasket in between the hub and the prop. When I get my prop balanced, I always inquire about the hub and am always told it takes so much force to pop them out that I should only worry about it if it starts slipping. I have 2 marks tapped on mine to show any slippage. 

Again, I would have your prop balanced and then drive it. It most likely will show any signs of slippage on the water and then you get have them replace it. I wouldn't worry about the hub unless it is indeed slipping. It's pretty inexpensive to repair.

[WIGuide]

You're really over thinking this. Put the prop on and run it. If it's slipping you'll know since when you spin a hub you don't usually sort of spin it, it's spun so it'll slip when the most torque is applied to the prop and that's at takeoff. A lot of times if the hub is spun you can't pop the boat up on plane. The reason Mercury went to the flo-torque hub insert wasn't so they'll break in the event you hit something, it was to make Mercury props interchangeable with other brand motors. Previous props were designed around a Mercury prop shaft so if you had a different brand motor it wouldn't necessarily match up spline wise. 

It does take a lot to spin a hub, but it can happen. It's not a fail safe of protecting your lower unit, but lower units are pretty robust. I've seen some pretty mangled stainless props that had no lower unit issues. That's not saying it doesn't happen, but I've never considered that a reason not to run stainless. The performance difference alone is night and day

[nixdorf]

Great feedback, guys.  Thank you.

I went ahead and put the prop on the boat last weekend, but didn't get on the water until yesterday.  Right out of the gate, the new (used) prop performed well.  Holeshot wasn't as good as before, but I'm told that is to be expected going from a 21P to a 22P prop.  My top end speed didn't change much (~41 MPH by GPS), but the winds were around 10-15 MPH on a wide open lake so there was considerable chop.

The one thing that caught my attention was my wide open throttle.  The WOT with the old 21P prop was steady at 5400 RPM.  The WOT with the new prop topped out around 5600-5700 RPM, although this was when the engine was trimmed up a little more than normal.  As noted in the OP, my engine is a 2004 Mercury 90HP 2-stroke.  Specs for the engine indicate WOT of 5000-5400 RPM.

Should I be concerned about the WOT with the new prop?

[iabass8]

I'm a little more OCD about that stuff than others and would, personally, have the pitch adjusted to cater to the correct RPM range (assuming your tach is correct of course). You stated that your engine was trimmed up a little more than normal and that will make your RPMS rise a bit as you are aware. If you are trimmed level at WOT and getting 5500 I wouldn't worry about it but I would still have the pitch adjusted back to 21. It's really cheap to have that done. I'm sure Way2Slow can give you a much better answer.

 

[fishnkamp]

Talk to a good prop shop. Since you said you lost a little hole shot and your top end was a little higher I would talk to them about adding a little cup instead of changing the pitch. By adding a bit of cup the prop will "bite" a little more which might help the hole shot and the rpms might fall right in the correct window. Adding cup is not that expensive but running the wot rpm can be. I have just finished reworking my prop. I tested a few Hustler props for my 75 Merc. I found a 19 pitch was a little to small and the 21 a bit to much. I purchased the 19 pitch and had my prop shop add 1 inch pitch and some cup. Man they hit it perfect. The wot was right in the window and both top end and hole shot were vastly improved.  

[WIGuide]

On 7/9/2016 at 8:04 AM, nixdorf said:

Great feedback, guys.  Thank you.

I went ahead and put the prop on the boat last weekend, but didn't get on the water until yesterday.  Right out of the gate, the new (used) prop performed well.  Holeshot wasn't as good as before, but I'm told that is to be expected going from a 21P to a 22P prop.  My top end speed didn't change much (~41 MPH by GPS), but the winds were around 10-15 MPH on a wide open lake so there was considerable chop.

The one thing that caught my attention was my wide open throttle.  The WOT with the old 21P prop was steady at 5400 RPM.  The WOT with the new prop topped out around 5600-5700 RPM, although this was when the engine was trimmed up a little more than normal.  As noted in the OP, my engine is a 2004 Mercury 90HP 2-stroke.  Specs for the engine indicate WOT of 5000-5400 RPM.

Should I be concerned about the WOT with the new prop?

Being that you were coming from an aluminum prop to begin with, it's kind of like comparing apples to oranges. They're both fruit but they are completely different. Being that the aluminum prop was in bad shape just adds to the differences. 

First with the basics, the bigger the pitch the faster the top end (to an extent), but the more torque it requires to get it moving, so your whole shot isn't going to be as quick as you get a larger and larger diameter prop. A smaller pitch prop is going to get you out of the hole quicker, but not have the top end. 

Your stainless prop should have more grip than your aluminum, and that should allow you to trim more than you could with your aluminum prop. I'd take your boat out again and try to find optimal trim for your rig and prop. Keep your eye on gps speed and slowly keep bumping it up. Your speed should increase to a point, and then either not gain anymore, or actually slow down if you keep going. You want to see where your RPM's are at that point. Keep in mind you probably want your boat loaded how you fish with it most often. If you fish with 2 people, add the second person. Recheck your speed and RPM's. Once you know that, you can take it to a prop shop and have them tune it the way you want. Usually you'll have a performance goal in mind whether it's hole shot, top end, or best handling. Once you give them your information they can tweak it a bit to work. 

As far as the RPM deal, I wouldn't run it over if I could help it. If you want best top end performance and you normally fish with 2 people, they're going to tweak it to be close to the top of the max with two people. If you run it with one then, you'll have to back out of it a little when you're running solo so you don't over-rev.