# Power tech prop testing-Charleston SC



## NealXB2003 (Jun 8, 2020)

I think the rpms between the RED3 and the scd3 will be miles apart if the pitch is the same. Granted, my 70 is a 4 stroke. But I usually run a 16 scd3 at 6350 rpms. I have a 13 pitch RED3 and it'll usually pull about 6250 rpms. It's got more cup and it's much harder to turn. Red3 does have more bow lift, if your boat likes bow lift. Scd is a stern lifter.


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## NealXB2003 (Jun 8, 2020)

PS.... if you really can turn a 17", a Yamaha black stainless like the one I posted for sale yesterday would be a good option. The fast duck boat crowd claims they're 2-3mph faster than the SCD3 (which is a copy of the Yamaha prop) and they'll retain bite higher on the jackplate. I didn't have the power to turn it to really see what it would do, but I can vouch that it doesn't ventilate as much as an SCD3 Even at 1"+ higher on the jackplate. Pushed my slug 38 mph, but I could only get 5800 rpms out of it. On a lighter boat, I have no doubt it would run 40. Wish you were closer.... I'd let you give it a run.


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## whoislang (Jul 29, 2020)

NealXB2003 said:


> PS.... if you really can turn a 17", a Yamaha black stainless like the one I posted for sale yesterday would be a good option. The fast duck boat crowd claims they're 2-3mph faster than the SCD3 (which is a copy of the Yamaha prop) and they'll retain bite higher on the jackplate. I didn't have the power to turn it to really see what it would do, but I can vouch that it doesn't ventilate as much as an SCD3 Even at 1"+ higher on the jackplate. Pushed my slug 38 mph, but I could only get 5800 rpms out of it. On a lighter boat, I have no doubt it would run 40. Wish you were closer.... I'd let you give it a run.


What boat are you running the Yamaha black on?


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## NealXB2003 (Jun 8, 2020)

I've got an 18' aluminum Excel. It's a .125ga hull that weighs in excess of 600 lbs. Not exactly a performance craft.


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## NativeBone (Aug 16, 2017)

whoislang said:


> Talked to Michelle at Powertech and this is what she recommended for my rig:
> 
> RED 3 17, best bet for two stroke
> 
> ...


I have ran all three on my 70 2s. Wasn't thrilled with the Red or SCD models. Hole shot and turning was an issue. 
I currently run the NRS model and satisfied with the performance. Good hole shot and turning. The NRS has more cup than the RED series.

I do not run a jackplate and motor cavitation plate is set 1-1.25" from bottom. 
Cruise @ 33mph @ 5000rpm. WOT 38-39mph @ 5800rpm. Hope that helps.


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## NealXB2003 (Jun 8, 2020)

NativeBone said:


> Hole shot and turning was an issue.


I had to have my prop guy add cup to my SCD3 to give it bite in turns. 

RED3 had too much bow lift for a flat bottom (induced porpoise) but may be the ticket for a pad v.


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## whoislang (Jul 29, 2020)

NativeBone said:


> I have ran all three on my 70 2s. Wasn't thrilled with the Red or SCD models. Hole shot and turning was an issue.
> I currently run the NRS model and satisfied with the performance. Good hole shot and turning. The NRS has more cup than the RED series.
> 
> I do not run a jackplate and motor cavitation plate is set 1-1.25" from bottom.
> Cruise @ 33mph @ 5000rpm. WOT 38-39mph @ 5800rpm. Hope that helps.


What boat ?


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## whoislang (Jul 29, 2020)

Found a SCD3 16p locally for 250. Figured it’s a pretty good deal so I’ll try it


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## NativeBone (Aug 16, 2017)

whoislang said:


> What boat ?


Copperhead


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## whoislang (Jul 29, 2020)

So, I tried out the SCD 16p last night.

Here's my notes

*SCD 3 Blade 16" pitch 13" diameter*










2 people on board, 10gal fuel, flood tide load (12 pack, 1 rod, one flybox)
6000rpm 37.3mph = 4% slip *rev limiter*
5600rpm 34.9mph = 4% slip
4700rpm 29.2mph = 4% slip
2000rpm 6.56mph = 50% slip

Hole shot seemed better, but didn't get a great feel for it yet.
---------------------------------------------------------------------------
Compared to
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Chewed up Quiksilver aluminum QA2036x










*3 blade 17" pitch 13.25" diameter*

2ppl on board 15gal fuel, tarpon load (6 rods, full 20qt soft cooler, camera gear, food, tackle boxes and misc weights)

4300rpm 30.3mph = -2% slip
4300rpm 29.6mph = 0% slip
1700rpm 6.5mph = 45% slip

No Gear, one person

5800rpm 38mph = 5% slip


So, the questions I have are: 

1. What gives with the aluminum prop calculating negative slip?

2. The SCD was all over the rev limiter at 6000-6100 rpm, and then the tach was acting weird, reading random values all over from 0rpm -4500rpm.

3. Could I bring the RPM down by going up to a 17" pitch SCD and gain some mph?

4. Is it safe to be able to get that high of RPM on my two stroke? I didn't even have the throttle pinned to the dash. More like 7/8 of the way down.



I will try the SCD again tonight by myself to try to see if my top end gets better with one less person and also test hole shot.


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## NealXB2003 (Jun 8, 2020)

What kind of tach do you have? Tiny tach with a wire wrapped around a spark plug wire? Mine gives crazy readings when I get into the rev limiter, because the spark is cut by tube computer.


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## DBStoots (Jul 9, 2011)

How do you measure the prop slip?


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## NativeBone (Aug 16, 2017)

DBStoots said:


> How do you measure the prop slip?


Here is one way....


BBLADES - Prop Slip Calculator



OR



https://www.getaprop.com/blog/propeller%20slip,%20boat,%20horsepower,%20rpm,%20blade,%20slip,%20gear,%20ratio


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## DBStoots (Jul 9, 2011)

NativeBone said:


> Here is one way....
> 
> 
> BBLADES - Prop Slip Calculator
> ...


Thank you!


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## DBStoots (Jul 9, 2011)

Learned this today also:

*Prop Slip*. Slip is the difference between actual and theoretical travel through the water. For example, if a 10-inch pitch prop actually advances 8-1/2 inches per revolution through water, it is said to have 15-percent slip (8-1/2 inches is 85% of 10-inches).

What is normal prop slip? The number we will find is the difference between the theoretical and the actual boat speed, which is actually the *slip* value of our *propeller* if we convert it into a percentage. We should know that, as far as the ribs are concerned, most ideal *slip*percentages *range* between 4-8%.


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## whoislang (Jul 29, 2020)

NealXB2003 said:


> What kind of tach do you have? Tiny tach with a wire wrapped around a spark plug wire? Mine gives crazy readings when I get into the rev limiter, because the spark is cut by tube computer.


No, it’s a Yamaha 6y5 gauge


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## whoislang (Jul 29, 2020)

NealXB2003 said:


> PS.... if you really can turn a 17", a Yamaha black stainless like the one I posted for sale yesterday would be a good option. The fast duck boat crowd claims they're 2-3mph faster than the SCD3 (which is a copy of the Yamaha prop) and they'll retain bite higher on the jackplate. I didn't have the power to turn it to really see what it would do, but I can vouch that it doesn't ventilate as much as an SCD3 Even at 1"+ higher on the jackplate. Pushed my slug 38 mph, but I could only get 5800 rpms out of it. On a lighter boat, I have no doubt it would run 40. Wish you were closer.... I'd let you give it a run.


Just threw on a 17” SCD after trying the 16” and getting into the rev limiter. Will update this thread tomrorow hopefully


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## No Bait / Lures Only (Apr 10, 2011)

whoislang said:


> Talked to Michelle at Powertech and this is what she recommended for my rig:
> 
> RED 3 17, best bet for two stroke
> 
> ...


Get the black yamaha ss prop


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## whoislang (Jul 29, 2020)

No Bait / Lures Only said:


> Get the black yamaha ss prop


Running a 17p RED that somebody ported out, maybe 1/4" holes behind the base of the blades. Runs nicely on top end, 37-38 at 5300 with two people. Maybe the 16p RED would be the ticket. The 17p SCD was too slippy I think.


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