Prop question for T-Mac

[Timber]

I have a 2002 Lund Alaskan 20 with dual consoles, and have a 90 hp. Yamaha 4-stroke on it. The prop on my Yamaha is a 13 1/2 x 15. A friend told me I have the wrong prop, that it should be a 13 x 19. As proof, he refered me to Yamaha's performance bulletin on the internet where they tested a 1675 Pro Sport with a 100 hp Yamaha 4-stroke (same engine as my 90 hp, right?) and used a 13 1/2 x 19 prop. He says there could be a RPM problem. Is he right?

[Dave in Mpls]

Any motor will be able to turn a larger prop on a smaller/lighter boat. I assume the 20 Alaskan is a heavier boat than the 1675 Sport; therefore, the 20 Alaskan will require a smaller prop than that used on the 1675 to turn the same RPMs. The only way to tell for sure is to install a tach.

Regards

[chris]

Hey sorry to interrupt, but how do you like that motor so far Timber? Lookin at the same one myself for a 1675 Explorer.
Thanks!

[Timber]

I really like the motor! I had a 90 Honda before, which I liked. But I prefer the Yamaha.

[John Gildersleeve]

You need to go by the rpm of the motor to get the right prop.That motor should run close to 5500 rpm for proper rpm range to run in.Every boat can be propped alittle different then the next and still perform well.The bullitens are just a starting point.dont go by them as the golden rule.Pay close attention to gps and rpm.

[T-Mac]

Well... no way to really know until you run her out and see what rpms you get @ w.o.t. and best trim. You are looking for 5500-6000.
Props vary.
What 15p prop is it?

[T-Mac]

Yamaha - white, aluminum? or ? Makes a difference.

[Timber]

The 13 1/2 x 15 is a white aluminum prop by Yamaha. A friend of mine has a new Mercury "Black Max" 13 x 19 prop with a Flo-Torq. II kit that he will let me have. I tried it, and it fits on my 90 hp Yamaha, but the nut is a different size. Can I use that prop?