Prop advice

[snownsand]

Hi all, I've been lurking on this site for about a year and have finally decided to pull the trigger and order a new M. I'll be putting the Yamaha high thrust 50 (gear ratio = 2.33) on it and am looking for some advice on prop size. I live and will be mostly sailing at close to 7,000' altitude. Probably make trips to Tahoe also, it's only a few hours away. After searching the archives I think a four blade 14d x 10p prop would work up here but am also thinking maybe I should go with less pitch, possibly 8 or 9p? I realize that I may have to try a few props to get the right one but am hoping you smart folks out there can point me in the right direction.

[argonaut]

Hope you get an EFI model that adjusts fuel/air for altitude.
The EFI's better as far as maintenance goes too.

[snownsand]

According to the Yamaha website the H50 comes standard with EFI and "Microcomputer ignition" that "adjusts timimng to maintain optimum engine performance, economy and durability in all conditions." I'm hoping that means it will run well at high altitudes.

[shehzad]

I have also just bought and installed same engine on my new 26M. It is FT 50 CED. I had just completed its first 10 hours. I have touched 6000 RPM but the maximum speed I acheived with empty ballast and two people on board was only 15 MPH. The proppelllar size was 13 x 11. This is indeed 5 to 7 MPH less than what other people are getting.

I would like to know the maximum speed you could get with this engine.

[Stephen Mooney]

I've got the same motor though carburetted version. It came with a 13 5/8 diam x 13 pitch prop. At max revs, currently 5000 i get about 15knts. Based on another thread & advice from a Yamaha dealer in Australia I am changing to a 14" diam x 11 pitch to get more revs and with luck more speed. We are close to the equator - 7" south and at sea level with average daily temps of 33 C or 90F.
One of the attractions of this version is that is downrated from a 60HP (which are not available here) meaning it is more robust with stronger gear box etc.

[Robert]

Stephen Mooney, I am wondering about engine temperature. I don't have a Yamaha, and I don't think there is a way to measure engine temperature on the boat.
..
Would you expect your Yamaha to run cooler with the 14x11 prop because it will have higher RPM at the impeller to flow more cooling water? Or run hotter because you might be able to get a little more power and speed out of it at the higher RPMs?

[Sloop John B]

I run with the 14x11. The M has more weight. My guess is 14x10 to keep your revs up.

[snownsand]

Thanks John. I seem to remember reading in another post that some of the Colorado guys, at 4,000', are running 14x10 on Mercury bf's. I'm 3,000' higher so maybe I should go 14x9? If the 9p is low what are the consequences? Just a reduction of top speed, which I could live with, or would the engine over-rev at WOT, possibly damaging it?

[Harrison]

Snownsand,

Here in Colorado running my "M" at 5000, using a Merc60 BF, with 3 adults on board, and no mast, Ive seen 18 mph (GPS) and revs in the 5700 rpm range at WOT. Towing an adult on a tube, same lake, same configuration, Im seeing 16-17 mph (GPS). This is with an 14x11 pitch prop. The only problem Id see while spinning a lower pitched prop would be too high of revs at WOT, and poorer economy. (Not that anyone really looks for economy at WOT.)

---Harrison