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Hello,
Just purchased a 1997 Dauntless 15 with a bad Merc 4-stroke 50 Carb. Replaced the Merc with a Yamaha F50 EFI(same powerhead), engine came with an 11 pitch Yammi aluminum High Trust Prop.

I ran it briefly and got a bit nervous as my tach was at 5500 at partial throttle, was aware of where the limiter kicked in.

Wondering what prop would be good all-around - Aluminum or SS?

Any help would be appreciated.

Thx!


(Please follow the guidelines at the top of this page and use the full 4 digit year)

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A stainless steel prop will improve every aspect of performance compared to aluminum - the only downside is the higher price. Did you buy the motor new? Then don't devalue your investment by installing a cheap prop.

I'm a little confused by your comment about the rev limiter. It should not be kicking in at 5500. Your owner's manual will tell you, but my guess is it should start to limit around 6100 RPM.

To get a feel for the right pitch, check out Yamaha's performance bulletins for that motor on similar boats. From a quick look, 11 would seem underpropped. However, please clarify whether you bought the F50 or the high thrust T50 - they have different gear ratios and so would require different pitches.

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Thanks for the info.

This is the High Thrust F50. The motor is a 2007 with 130 fresh water hour - came from a pontoon boat.

Would prefer a stainless prop, figured a Yamaha 13 pitch would be a good start if I stayed aluminum.

The tach was reading 5500 when I ran it, it was not on the limiter - so din't go further.

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Interesting. Not sure if that is the same motor Yamaha now calls the T50? I'm guessing yes - is it a 13" diameter prop?

In any case, to start finding the right pitch, take it out and run it up to 6000 RPM, with a light load in the boat, making sure it's trimmed to get the best speed at that RPM. Then post back RPM, top speed, and the top speed you hit with the old motor and we can do some math and make a good guess at the prop and pitch that will work for you. It's not an exact science.

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Snow -

Keep in mind that prop sizing and performance are not standardized across same make, different model or even across makes.

To dial it in, you should select the make and model of prop and then adjust the pitch to meet your WOT range based on your load 80% of the time.

Having said that with a WOT range of 5000 to 6000, gear ratio of 2.33 and an expected top speed of ~35, the pitch recommendation is 15" of pitch.

The Yamaha Painted Stainless Steel is a good prop.
https://www.simyamaha.com/category_s/...s/1767.htm

While the engine may have been rigged for a pontoon, you don't need that for the Dauntless.