# Another Shadowcast 16 Prop Thread



## Dillusion (May 21, 2012)

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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## cutrunner (Jun 8, 2010)

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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## kamakuras (Feb 23, 2012)

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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## AfterHours2 (Aug 2, 2010)

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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## kamakuras (Feb 23, 2012)

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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## AfterHours2 (Aug 2, 2010)

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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## blondmonkey777 (Oct 18, 2012)

you can always have a prop shop re pitch your prop up 1 or 2


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## kamakuras (Feb 23, 2012)

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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## DuckNut (Apr 3, 2009)

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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## kamakuras (Feb 23, 2012)

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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## Dillusion (May 21, 2012)

6200 rpm is way to high for your motor.


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## el9surf (Dec 23, 2008)

> 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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## kamakuras (Feb 23, 2012)

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.


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## Dillusion (May 21, 2012)

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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## kamakuras (Feb 23, 2012)

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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## blondmonkey777 (Oct 18, 2012)

> 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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## blondmonkey777 (Oct 18, 2012)

Quick screen shot from today cant wait to get that 5 extra hp


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## edmiears (Oct 16, 2012)

@Blackmantis, any word on that 13 pitch yet? I'm seriously considering the same prop.


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## disporks (Jan 19, 2011)

Adding cup to the prop will also lower the engine rpms some.


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## kamakuras (Feb 23, 2012)

> @Blackmantis, any word on that 13 pitch yet? I'm seriously considering the same prop.


Prop is ordered and should be in next week. As soon as it is here I will drag the skiff across the street to the New River for testing.


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## blondmonkey777 (Oct 18, 2012)

Little update on my setup tuned around a few other things and getting a good cruse speed around 22 and fastest I seen on GPS was 32.8 still waiting on the bob machine shop cav plate to come in and also the 30 hp carb for my motor


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## kamakuras (Feb 23, 2012)

Update:
New prop is SRA4 13p. Without Permatrim I saw 5600-5700 rpm and 29 mph.
With Permatrim installed 5500 rpm and 27-28 mph.
Tested with two people and gear.
Cruise 22-24mph.
Going to play with engine height now. It looks like I can raise it quite a bit more with the Permatrim.


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