2120 SC prop

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Well-known member
Sep 17, 2006
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Hi folks. I have a 2006 2120SC with a F150. The boat came with a 141/4 by 16 polished ss prop. I checked the Yamaha performance bulletins and found that they had tested the boat in June 2003 but with a 133/4 by 17 prop. Results at 4500 rpm were 30.4mph and 3.75 mpg.....not bad.

I called Jeff at Parker and learned that they are now using the 141/4 by 16 prop on that boat. Apparently it wasn't available in earlier years. Jeff was kind enough to send me the Yamaha test bulletin he had. I guess everthing doesn't appear on the Yamaha site.

I was expecting to see better performance. No way. In fact the performance was much worse. At 4500rpm speed was 29.6 mph but only 3.02 mpg. Best mpg was 3.28 at 4000 rpm at 25.6 mph. This is about 25% more consumption at 30mph. Similar results were noted at other rpms. Top speed essentially the same.

Weight of boats were almost identical as was wind. The only difference was water and air temperature......75F and 85F for the June test with the 133/4 and 48F and 38F for the Feb test. Can't believe that explains it.

Sent Jeff an Email asking what is going on. Hope to hear from him. With the cost of gas a correct prop will quickly pay for itself.

Any comments greatly appreciated.

Thanks in advance.
With that motor you should be getting approx 5,500 at wide open throttle (WOT).

Only getting 4,500 means that the prop is too aggressive. This means your engine is probably working too hard, which will cause increased wear and tear. Recommend you move to a less aggressive prop and get the WOT rpms up to somewhere between 5,300 and 5,700.
Also check the mounting height of your OB. While on plane, your ventilation plate (erroneously called the cavitation plate) above your prop should just be skimming the surface of the water. Cupped and 4-blade props can run higher, less performance props need to be a touch lower to stay hooked up.

If your OB is mounted "too deep", it robs you of RPMs, MPH, and performance. I also think most dealers sell the boats with too high a pitched prop.

What Prokchunker advise it correct. Determine YOUR maximum WOT RPM of that motor (I don't know whether it's a 5.5K or 6K MAX RPM outboard) and prop it to be within a few hundred of that, with clean bottom, 1/2+ tank fuel and a normal load. That usually gives you the best all-around performance.
Thanks guys
The rpms I was referring to was from the yamaha bulletins. For the 133/4 prop the gas consumption at cruse ( about 30 mph )is about 25% less than the 141/4 prop that Parker is now using on the 2120sc f150. Makes no sense to me.
According to the bulletins the mounting height was the same. Wot rpms were 5500 and 5600 respectively with top speed almost identical.

On my boat with the 141/4 prop at wot and trimmed i can get 5500 Rpm which is exactly what it should be. My concern is the gas consumption. The only other difference is the 141/4 prop was polished ss performance series while the 133/4 was black steel. Called yamaha and they were also surprised at the difference but couldn't explain it.

Thanks again

rplas48":1ayz4xr8 said:
My concern is the gas consumption ...
Called yamaha and they were also surprised at the difference but couldn't explain it.
Ray, FWIW I've yet to see any boat match any performance bulletin put out by Yummieha or any other OB maker. I still would look into your mounting height, as I was alble to raise my rig (OB on bracket) 2 holes higher than the factory setup, though I am using an agreesively cupped prop which will stay hooked up better.

You might want to consider a fuel management transducer/computer, like the many Navman models out there. They interface to your GPS, all give readout in GPH, but other models do the calc's for you and show instant miles-per-gallon info. Lowrance is also making some fuel systems too, they can be had as low as $100.
How do the "Time to plane" figures compare?
Some have noted the 21 Parker with 150 is a little sluggish. Do you ever have a hard time on the back side of a swell?
Maybe the different prop helps out?

I have had 3 Parkers, the Yamaha performance bulletins have been "dead on" for all three. You sure there's not a little anti-Yamaha sentiment being displayed here? :wink:
With the engine trim down ...about 2 on the indicator....the boat comes up on plane pretty well. The tests indicated 5.95 for the 133/4 and 5.69 seconds for the 141/4. I also in the past have found the yamaha bulletins to be pretty accurate. In this case I think something is wrong between the two test. Increasing the diameter by half an inch while decreasing the pitch by 1 should be a wash. And the bulletins indicate that to be the case at wot 39.3 and 39.4mph for the 141/4 and 133/4 props respectively. The fuel consumption comparison is what is driving me nuts. A 25% difference can add up to big $.

Still waiting a call from Parker. Will look into the Navman gauge.

I have posted previously on this boat and motor combination. The factory 14-1/4 X 16 did not work well for my situation and I have since switched to a 15-1/4 X 15 Black Steel and also have a 13-3/4 X 17 Black Steel as a spare. I find the Black Steel props give me much better performance with the F150 and 2120 than the polished stainless. Top rpm around 5700 (black) vs. 5200 (polished) respectively. Major difference in mid rpm range handling and control. Your results may vary. Buy some extra props from eBay (or trade with a friend) and test them yourself. It's the only way to be sure. You need a spare onboard anyway. I got mine for around $75, new in the box.

See my web page for a discussion of my experience. At some point I will try other brands as well. As it is, I barely have enough time to fish. :x
Ranger Tim
Thanks for the reply. I have some black props the same size as yours and plan to test in the spring. Also hope to add on some fuel, monitoring so I can get to the bottom of this. I am surprised that you are able to get the higher rpm with the 151/4 prop. Do you have any fuel consumption data and is the boat bottom painted?

In any event the fuel consumption is of a concern to me . With the 141/4 polished prop I can get 5500 rpms but according to the Yamaha test bulletins the fuel consumption is 25% greater at 30mph than with the 133/4 black steel prop. Through the entire rpms the 133/4 looks like a much better prop then what Parker is now putting on the boat.
Still hope to hear from Jeff. Parker must have a good reason. The polished ss looks nice but it also costs. I go through about 400gal a year when I had a 202 Scout. If I do the same with the Parker, 25% means 100gal and at $3 bucks, $300 per year savings.

Thanks again
Sorry, I do not have any fuel management equipment. I only know how much I pump in at the stations. Most of my time on the water is spent trolling or fishing off of structure, so I am idling mostly. I notice the prop performance particularly when there is a mild to severe chop in the bay or with rolling swells. The backs of waves can be dangerous places unless you are propped correctly and have the power to overcome it. The black steel series gets a lot of bad press because folks worry about rust and appearance. They are excellent props and are not cheap (except on eBay!). What people prefer when they see the boat out of the water actually may not be the best for in-water performance. We can reap the benefit of this by taking advantage of lower resale prices on these props.

The 15-1/4 X 15 performance is very close to the 13-3/4 X 17, except the former seems to have more positive control of the boat in mid range speeds. The latter seems to have a bit more top end speed, but not a really noticeable gain. I do not have a feel for fuel economy differences at all. I would appreciate some hard data on these set ups, if you ever get to test them. I am basing my comments on very subjective opinions.
Thanks again Ranger Tim. Still awaiting a reply from Parker. I am interested in what they have to say. If I can easily adapt some fuel measurement I will run the tests. I agree the black steel are fine props and that is what I used on my 202 Scout. That boat very closely matched the Yamaha test data on speed at tested rpm.

With that motor you should be getting approx 5,500 at wide open throttle (WOT).

Actually, you want the F150 to spin up to 6000 RPMs at WOT with a typical load.

Yamaha does not recommend 15.25" diameter props for use with the F150, I would not go that route.
If Yamaha does not recommend 15-1/4 inch props with the F150 why are they listed on Yammie's F150 specific web page as options? Or why are they listed in the F150 service manual table of available props for that motor? Where did you hear this?

I am interested to know your source so that I may know whether or not I am doing something to mine I may regret. I like how the motor performs with this size prop, but I don't want to do any damage.
Hey guys I finally got to the bottom of the props for the 2120SC F150. It all started because the published numbers from Yamaha's site indicated very high fuel performance numbers for the 133/4 by 17 black steel prop......@4500rpm, 30.4 mph at 3.75 mpg. Top rpms were 5500.

My boat came with a polished ss 141/4 by 16 prop yet there were no published reports from Yamaha for that prop. I went to Parker and found they had a Yamaha test for that prop. The results at 4500 and 29.6 mph was 3.02 mpg ...25%poorer fuel performance at about the same speed. Top end was 5600rpm.

Parker also provided their own test data run on the same day on the same boat with the same sea condtions. Some of the data

133/4 by 17black ss...4500rpm, 28.1 mph, 2.87 mpg ...top end 5500 rpm,34.4mph,2.29mpg

141/4 by 16 polished ss....4500rpm, 28.8 mph, 2.91mpg.. top end 5500,36.75mph, 2.39mpg

151/4 by 15 ....4500rpm,27.3mph, 2.97 mpg.. top end 5600rpm,35.2 mph,2.27gph

In speaking with Parker it appears the Yamaha test data for the 133/4 by 17 is wrong and yet the Yamaha tests with the 141/4 by 16 is close to Parker's.

In short Parker is now using the 141/4 by 17 because it gives a little better top speed and mpg. But really any of the props noted are fine as they allow the engine to develope its max hp at 5500rpm (page 41 owners manual )

Hope this helps.

For what its worth, Yamaha's site now has the test results for both the 133/4 and 141/4 inch props and still shows a 25 % difference in fuel consumption at about 30mph.
Ranger Tim":289hgu82 said:
If Yamaha does not recommend 15-1/4 inch props with the F150 why are they listed on Yammie's F150 specific web page as options? Or why are they listed in the F150 service manual table of available props for that motor? Where did you hear this?

The Yamaha Saltwater Series 15.25" props do not appear as accessories for the F150 on the Yamaha web site.

http://www.yamaha-motor.com/outboard/ac ... all/1.aspx

Apparently the Standard Black Steel Series are still listed.

You can check with Yamaha to confirm, however, it is my understanding that the 15.25" wheels are for the V6 engines only.
For what it is worth the service manual for the F150 lists on page 1-21 the 15 1/4 by 15 stainless prop as well as 14 other sizes. This is because that engine can be placed on a very wide selection of hulls.

I think one of the main concerns in prop selection is that the prop should allow the engine at WOT to turn as close to max rpm as possible which for the F150 is 6000. However any prop that allows 5000 to 6000 is fine. Remember the F150 develops the max horse power at 5500...qwner's manual page 41.

If you have been following this thread my main concern is the efficiency of the various props in terms of mpg for the 2120SC. At the same 30mph cruise different props varry by 25% in efficiency according to Yamaha tests under almost identical test conditions. See Yamaha's site under performance bullitins. When I spoke to both Yamaha and Parker about this I just didn't get a satisfactory answer to explain the difference.

I have a variety of props and have bought a fuel flow gauge and hope to run my own tests in the spring.


My F150 runs the best with the 15-1/4 black steel. I'll have to check with Yamaha and find out the scoop. If there is any problem with the engine I'll post. So far it is the best prop I've found. I get 34-38 mph at 5700 rpm and can maintain plane longer than other smaller props. BTW, my top speed keeps edging up slightly all the time; At 350 hours I would have expected any break-in to be over with.

I'm interested in finding out more info on why they would not recommend this prop. Maybe Andy at SIM has the lowdown?
I will be looking forward to those fuel efficiency tests in the spring with baited breath, Ray! Actually, the fuel economy is so good with this motor I am continually amazed by how little I spend on gas. I have been four trips to the bay and still don't have to stop at the filling station. What a boat! It easily costs me twice as much to trailer to the water (100 miles each way) than it does to run the boat.

So far this motor has lived up to its reputation; Economical, reliable, easy to maintain, and powerful. Did I say quiet? Quiet as a mouse blowing bubbles in a feather bed!