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I have 17' Montauk. Its been under propped for as long as I have had the motor on this boat. 13 x 15 SS. I picked up a 13" x 19" SS for $50.00 I see some guys on this forum running them on the 90 HP motors but they are the 4 cylinder 90's Is this prop too tall for my 3 cylinder 90 Yamaha set up?

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On a good day... Low humidity I can squeeze 5200 out it on a 17 fT super sport LTD. I am mounted flush on the transom. Raising the engine a hole or two may improve that.

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Do you have a Tach? Wide open, how many r.p.m. with one person in the boat? About 5,400 is supposed to be right. I am using the 19" on a 16' 1967 Whaler and it is only allowing about 5,000 r.p.m. with a 90 h.p. 2 stroke. I may go down to 17 inches soon. However, the choice of pitch has to do with how high you mount the motor on the transom and whether you are using a cupped prop. Overall, the Tach will allow you to choose the best prop.

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5500 RPM's is 33 MPH max on GPS One person on boat. The engine is mounted flush down on transom.

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I am going to bet you may not be able to turn that prop on the motor to 5000 rpm or anything above.

That said, since you've bought the prop, why not run it and see what you end up with? It is not going to hurt anything.

If nothing else you got a good deal on a prop you will likely be able to trade on or sell and make a couple dollars.

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Jeff, Last week I ran my 17 for last time for the season with 2 grown men and about 10 gallons of fuel... 5100 rpm's As I noted above if properly set up and the hull is dry you could see 5400. In the right conditions I squeeze 5200 out it now mounted flush with bottom paint.

Below is performance bulletin for a K series 19 inch prop on a boat about the same size an weight as older 17. It hits 5500 RPM but only 42 MPH. I see 42MPH at 5100 using a GPS... I use the same prop. Naturally conditions like humidity, wind, prop slip, and a light chop will effect numbers.

http://www.yamaha-motor.com/assets/pr...-90tlr.pdf

Mark, maybe the hull could be wet? but looking at you page she seems to sit in the water perfectly. 5500 with a 15 does not sound quite right. Was this a Yamaha prop as well? When I use my spare 17in Yamaha SS I hit 5700 RPMs 2 people and fuel... When I experiment with another prop years ago, Michigan wheel Ballistic 19 inch.. I could only see 4900 with a light load, that was not the right prop for a 17ft Whaler.

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Let me clarify. I get 5400-5500 at 33 MPH with a lot a throttle left over. I just don't want to over rev motor

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Now it's making more sense...:-) with a 19 K series you should see results like mine. I would very interested in how it works out for you.

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I talked to a prop guy today he said he can take some pitch out of the 19" if I want. he said it would be close to 17"

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What is the redline of your motor?
It sounds like you need more pitch, not less. Or a different style/brand of prop.

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5500 RPM max recommended by mfg'er

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Then you are under propped...
You need more pitch or a more aggressive or cupped prop.

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Right. I was curious if the 19" was to tall. Seems most guys have 17"

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A 17 pitch is shorter... Less Pitch...

You need more pitch or a different style of prop that acts taller than the one you have now..

The prop you have now is not big enough...
What brand and model is it?

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.....the 13 x 15 is unknown the 13 x19 I picked up is a Michigan Wheel

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17 sounds right. But you need to use a Tach and figure it out.

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It would wise to state the manufacturer of a prop since prop size is not universal across brands.