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Discussion Starter · #1 ·
Backstory: Original owner had a 2003 25hp Merc 2 Stroke with modification to make it a 30hp.  Came with 10x15 Solas 4 blade aluminum.  I had the suspicion that it was well over propped.  I bought a Tiny Tach to find out. (I know the deal with them.) Tiny Tach said 4400rpm average no matter the load.  Average 23-25mph depending on load.

I worked with PowerTech who were a great help. Ron there was great.  We decided to start with a SRA-4 11 pitch.  Tested today with TT and I am seeing 5850-5960 rpm and average of 26.5 mph up and down current with one and two people on board. Max was 28mph alone. Hole shot is freaking incredible! Turns are very sharp for this skiff with very little loss of bite.  I have the engine pretty darn high too.

Mercury says safe operating rage is 5000-6000 rpm on this motor.  I would think optimum rpm is 5400-5600. I think I should go from 11p to 12p. I am guessing I would gain 1-2 mph also.  I know TT can be +- 300rpm.

Opinions from anyone?
 

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devilray snob
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I wouldn't say that the merc on the shadowcast has an optimum 'rpm' as much as it does a 'best speed'. If you can achieve what you feel is the best holeshot to speed ratio without looking at your RPM, you would be surprised what it would say.

With that motor, you should be running at least 28MPH like I was on mine. I had a solas 3blade SS 15p with a custom cup added. My RPM's were also 5350-5400.

Just because you are in the upper echelon of the RPM range does not mean you are in the best spot as far as performance.

Are you going for hole shot or top end? You will need to find a balance of the two, which is going to be a slight trade-off of the opposing one.
 

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Cert. Yamaha technician
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Theres a fine line between spinning a motor at 6k rpm with said prop and getting said mph, versus 5600rpm with different said prop and different mph. (If that makes any sense..)
Basically some boats will run faster turning a slightly higher pitch and getting a lower rpm, while some run faster with a lower pitch screaming at a higher rpm. It really comes down to hull weight and design, engine powerband etc.
Ide say your pretty happy and in the sweet spot between the two radical opposing ends of slow-all out race
 

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Discussion Starter · #4 ·
I think I am going to go up one pitch. Hole shot should not suffer. It wasn't bad even over propped. Should put rpm where I want it.
 

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Stripper in my own Mind!
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Just out of curiosity, is the performance gain going to be that crucial to justify spending the money on another powertech? I've dealt with them before and their advice has been excellent to say the least. Those props aren't cheap and it seems like a waste unless your planning on keeping another as a spare.
 

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Discussion Starter · #6 ·
PT has a return policy. You just pay a restock fee. Tiny Tach is reading 5950 with a load. I have read they can be off +- 300 rpm. The engine is screaming at wot. I would like to drop that down about 250rpm-300rpm. It will give me better peace of mind. Performance will most like remain the same. My main concern is do any damage to the engine. Before I make my decision I am removing the fin on the cavitation plate the engine came with and playing with the jack plate height some.
 

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Stripper in my own Mind!
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Was not aware of the return policy. That's a good thing. I was always under the assumption that many people were spending thousands of dollars in testing unless they resold the prop. Carry on, I'm sure the restock fee is not that much.
 

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Discussion Starter · #9 ·
I thought of that too. Wonder which would be less? $50 restock fee I imagine. Never had an custom prop work done so I don't know.
 

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Brandon, FL
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If the restocking fee is $50 than that is the least costly method - but add in shipping and it could be more than an aluminum redo - still less costly than stainless.
 

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Discussion Starter · #11 ·
Removal of the plastic compression plate fin thingy the engine came with now gives 6200rpm and 28-29 mph. I like the speed and holt shot.

A bit more cavitation on hole shot but not much.

Torn on whether to up one pitch or two now.
 

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6200 rpm is way to high for your motor.
x2
Sounds too high on the rpms. Check your owners manual to verify the RPM range. Your going to screw up your motor trying to gain a couple mph. The shadowcast wasn't made to run fast. Everyone tries to squeeze the last bit of speed out of these hulls. In my opinion the 4 blade grips a lot better with the pocket tunnel and doesn't sacrifice too much speed.
I have tested a pt 4 blade sra and a pt 3 blade sra and only see 2 mph gain out of the 3 blade. I kept the 4 blade because of handling and holeshot are way better. Can deal with the loss of a couple mph. Still running 25 - 26 mph which is just fine in my book.
 

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Discussion Starter · #14 ·
That why I say I think I should go up 2 inches in pitch. As stated max rpm for my motor is 6000. Speed was not my main concern. Longevity of my engine and being propped right is. My only real question here is whether to go up one or two inches before I get a RA from PowerTech... The stats are there. :D
 

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devilray snob
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You could be running 5999 RPM and not blowing out, but still not be performing as well as you could at 5400 RPM. That's what we're trying to say here...

My Shadowcast, setup almost exactly like yours, with the exact same engine and mods, was running at 5450RPM average and I had the highest speed of any shadowcast on this board.
 

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Discussion Starter · #16 ·
Totally agree with you. I will see how the 13 pitch performs and post my results. Sending the 11 back after the weekend. Will just have to hold off the throttle until then. I believe the 13 will be the perfect prop for my set up.
 

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904 Redfish
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You could be running 5999 RPM and not blowing out, but still not be performing as well as you could at 5400 RPM. That's what we're trying to say here...

My Shadowcast, setup almost exactly like yours, with the exact same engine and mods, was running at 5450RPM average and I had the highest speed of any shadowcast on this board.
Not calling you out lol but Just lowered my motor on my boat so I can trim the bow a little higher and right now I'm getting 30 constant and fastest Ive seen running today in 20 mph winds was 30.8 But I'm still doing a little testing and tuning because Just lowered my motor today.... But I'm pretty sure I got the fastest shadowcast on here lol but who gives a chit its only a few mph, next thing I'm getting is a 30 hp Carb from Creek Runner for my motor should be seeing 33 or so
 
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