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Author Topic:   SUPER SPORT 15, Yamaha F70, PowerTech SCD3 Propeller
tedious posted 08-10-2015 09:55 AM ET (US)   Profile for tedious   Send Email to tedious  
On my SUPER SPORT 15 with an F70, I’ve been running for a number of years a Stiletto Advantage in size 13.25 x 15 and generally been happy with the performance, good grip, super mileage, and a reasonable turn of speed. I boat mainly on the Maine coast, so opportunities to go flat-out are few and far between. But while not unhappy, I had a nagging question in my mind as to whether the large, grippy Advantage was really a good match for the F70, which wants to spin to make power.

With the Advantage, I could hit 6000 RPM and about 40 MPH, but it required a lot of trim to do so. And the combination didn’t really have that midrange punch that my old OMC 70 had. I missed that instant acceleration, although I did not miss the smoke and noise. In my early prop testing I did try an Advantage in the 13 pitch; it did improve acceleration, and let me hit 6300 RPM with some trim, but top speed was only about 38 MPH.

So after thinking about it for a long time--years--I had a hunch that a prop with smaller blade area, allowing it to spin easier in the mid-RPMs but still hook up at the high end, might work. Based on the experience I read here about another individual getting good advice from PowerTech, I contacted them and asked for their recommendation. After some back and forth, they recommended the Power Tech SCD3 in size 13 x 16 – they said that prop is similar to the Yamaha semi-cleaver, if that means anything to you.

So I bought the SCD3 and just got back from a week in Maine using it – it’s absolutely a great match for the F70 on a 15. It’s better in every aspect of performance – acceleration, top speed, ability to hold plane at low speeds, you name it. Mileage did not change at all.

With this change of prop, I feel I’ve really unlocked the power of the F70 such that the performance is very close to my old OMC. I did not get a full set of numbers, but one early morning speed run gave 41.4 MPH at the 6300 RPM redline, at 25% trim. I did trim up more and got up to 6400, but did not get a speed reading – I mention that because if you’re a real speed demon, you might find yourself underpropped with the 16 and want to bump up to 17 or even an 18 pitch. I’m very happy with the 16-pitch for my usage model – I’m frequently running with very little trim to keep the boat on the water and the 16 gets me almost 40 MPH with no trim.

I want to thank Power Tech for their advice and generally excellent customer support.


dgoodhue posted 08-12-2015 12:57 PM ET (US)     Profile for dgoodhue  Send Email to dgoodhue     
Good to know. I will store that away for when I repower my 15' which will highly likely be repowered with a F70.

Tim, do you still have a jackplate on your 15?

tedious posted 08-12-2015 03:20 PM ET (US)     Profile for tedious  Send Email to tedious     
No, I took it off - I didn't see a lot of difference in performance in my usage model, and it made the boat more challenging to store. It also made the motor a lot noisier at idle - you could hear exhaust noise, while on the transom you just heard parts moving.

Your boat has always seemed faster than mine - maybe because I'm a chicken. I'd be intrigued to see what you'd be able to do with an F70 and a 17 or 18-pitch SCD3 - I'm sure you're enthusiastic about me spending your money.

I always missed the pop of my old Johnson 70 - with the new prop, feels like it's back!


Peter posted 08-12-2015 04:03 PM ET (US)     Profile for Peter  Send Email to Peter     
I had a Yamaha 70 2-stroke on my 15 Supersport with rough bottom paint. Motor was mounted all the way down on the transom with the bottom bolts into the blind holes. It would consistently hit 42 MPH with me and a full 6 gallon tank of fuel spinning 5900 RPM turning an aluminum Yamaha K-series 19 inch pitch prop. Sometimes I'd see 43 MPH. Scary fast in that boat.

Because the F70 turns the prop though the same 2.33:1 gear ratio but has a 6300 RPM limit, I would think that a 17 inch K-series prop would do well on the F70 15 Supersport combination and would give similar acceleration due to the fact that it has a wider operating range which allows it to take advantage of the lower pitch propeller.

tedious posted 08-13-2015 10:57 AM ET (US)     Profile for tedious  Send Email to tedious     
I am not familiar with the K-series, but as far as I can tell, it's the smaller blade area of the SCD3 that makes the difference, so if the K is also smaller than the Advantage, it might be a good fit.

I agree with you on the speed. Although I have an academic interest in seeing how fast my 15 could go with an inch or two more pitch, I really don't want to be the one driving it. Just over 40 is plenty fast for me - you're so close to the water it feels a lot faster.

One of the nicest aspects of the new prop is flexibility at slow plane - my wife and I went on a long cruise, and you could pretty much dial in any speed you wanted. With the Advantage, I always felt at risk of dropping off plane.


Tom W Clark posted 08-14-2015 10:23 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
"K-series" is not a model of propeller, it just means a 4.25" Yamaha prop.

Yamaha offers nine different Yamaha branded models of propeller that are K-series is addition to the Turbo branded propellers, some of which are unique to that brand

tedious posted 08-14-2015 11:12 AM ET (US)     Profile for tedious  Send Email to tedious     
Thanks Tom, good to know what the K means. Good thing this prop terminology is so standardized!

I came across the page whose link follows - it gives a good sense of the number of parameters that can be varied in prop design.

Keeper posted 08-20-2015 12:49 PM ET (US)     Profile for Keeper  Send Email to Keeper     
I have a 1988 15 I restored .... Powered w/ a Yamaha F70. I run a Turbo Flats X 4- Blade 13 1/4" x 14" stainless prop. I'm VERY happy with it. I do have the Bobs 5" manual jack plate installed as well.
My boat is a bit heavier w/ a trolling motor 3 batteries etc. But I've had me, my Lady, & 3 kids with an inflatable 'Tow-behind" and it worked awesome!

I really noticed improved 'stability' & stern lift with the 4-blade over the 3. Low speed maneuvering is also greatly improved.

Thanks to Tom Clark for his advise & patients, helping me with propeller selection. He saved me a TON of time & money. Good Stuff.

crbenny posted 08-20-2015 05:06 PM ET (US)     Profile for crbenny  Send Email to crbenny     
Tom's a doctor?..
jimh posted 08-20-2015 10:56 PM ET (US)     Profile for jimh  Send Email to jimh     
He was, but he found he could make more money as a carpenter and selling propellers as a sideline.
tedious posted 08-21-2015 08:00 AM ET (US)     Profile for tedious  Send Email to tedious     
Keeper, that's interesting. What is your WOT speed and RPM?

In looking at the Turbo props website, I see they particularly recommend their Quest prop for the F70 - they mention is specifically, by name.

I'll insert their writeup here: "...helps allow the outboard to achieve and sustain proper RPM throughout the power band. Quest™ propellers are very well suited for 15’ - 18’ utility/work boats and various applications using Yamaha’s F70 outboard, due to their lower rake angle and advanced blade design. Available with 3 or 4 blades. Excellent for 3 and 4 cylinder outboard applications using an intermediate (4.25”) gearcase. Very well suited for smaller utility/ work boats and Yamaha F70 applications."

Interesting they call out the lower rake angle as being a characteristic particularly suited to the F70 - that certainly matches my experience, but I wonder why that is so? In any case, it looks like the Quest might also be worth trying.


Keeper posted 08-21-2015 12:26 PM ET (US)     Profile for Keeper  Send Email to Keeper     
Ha . . . 'patience' . . . my bad.

As far as the 4-Blade, I'm running it pretty high on the jack plate. It will rev up all the way to redline. I saw the tach show 6400 once, so Immediately backed out of it.

I haven't had a gps on board yet, so I can't offer a number. I will say that I can definitely notice a bit less top end than with my yamaha performance series 16" pitch 3-blade. But the boat handles so much better with the 4-Blade, I haven't put the 3-Blade back on.

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