RPM's & Prop Size

[retsey]

Hello Guys,

Operating a 21.2' HydraSport / walk-a-round with 150 Yamaha, 4 Stroke.

I believe the range for this motor is 5000 - 5500 rpm

The boat came with an Alum 14.5" dia X 17" pitch alum., 3 blade prop.

I do plan on buying a stainless prop.

 

Loaded up as I would typically fish I am hitting...

1) 4900 - 5000 rpm with slight chop (maybe 1' ers) and tabs set .

2) 5000 rpm calm with everything trimmed.

I did pick up 2-3 mph being able to operate at 5000 rpm...but it was at calm conditions

 

My question is should I drop to a 16" or 15" pitch.

I'm afraid to drop to 15" and hit to close to 5500 rpm.

 

Suggestions?

Thank you in advance

[High Bidder]

Its always best to get a prop where you can return it after you try it. Different brands of props and types(SS vs Aluminum) will give different results even if they are the same pitch. I wanted to get closer to the high limit of my RPM's on my IO and changed from a 19 to a 18 pitch. Instead of the expected 200 RPM change I got a 600 RPM increase which put me a little over the max limit. It did give me a better trolling speed so I just make sure I don't open the throttle all the way.

[Sk8man]

I guess the question becomes is 2 or 3 mph faster worth the possibility of over revving my engine and the potential damage associated with it. I did it (went wth faster prop) with a previous boat and couldn't figure out why my engine got so hot .....until I realized what the problem was....luckily no major damage...and I didn't have a tach on that one....

Edited June 18, 2013 by Sk8man

[CaptSpike]

I was told it is better to be over reved than under. Under you are lugging the motor and will reduce the life of the engine. That stated when I was told over it was by a couple hundread rpm above the motor spec at WOT. So if your motor is rated at 5000-5500 you wouldn't want to be over 5700 on your rpm at WOT a nd due to lugging the engine you wouldn't want to be under your reccomended WOT range at all.

just what I was told.

 

Spike

Edited June 18, 2013 by CaptSpike

[Roughrider IV]

Drop an inch pitch at the most. You may be at your sweet spot if your full fishing set up included other passengers. I dropped 3 in pitch and gained about 1000 rpm. Also went with a 4 blade for holding plane.

[Nemesis]

Contact Propgod.com in Florida. He has the answers. Also has props he can mail you to try first.

[Chas0218]

I have 2 props for my boat.  15.5x15 and 15.5x17 both aluminum.  I can squeak out 2 more mph with the 17' pitch but with 5 guys and full load (fuel, and all my gear) my motor drops the WOT rpm by 200.  I have it set up so with me and the usual light gear it will be near the middle of the recommended peak rpm. This should give you an idea of what I mean:

 

Recommended rpm 4500-5500

 

Prop: 15.5x17

Boat heavily loaded - 5000

Boat Usual loaded - 5200

Boat light loaded -5300

 

Prop: 15.5x15

Boat heavily loaded - 5200

Boat Usual loaded - 5300

Boat light loaded -5500

[rolmops]

A 1

Edited June 20, 2013 by rolmops

[rolmops]

The yamaha 150 has a WOT range that is between 5000 and 6000 rpm. so in theory you can go up a 1000 RPMs. that would mean going from 17 to 12 pitch. But Stainless has less relative water resistance than Aluminum. So it is a good idea to slightly increase your propeller size and go down a bit less in pitch.

If you have an F150 you should look into a 15x14.87 stainless, if it is a regular you are better of with 15x14.37. these are Mitchel Appollo stainless props.

[Fish Hunter]

Hey, you guys are hot-rodders...lol.

I never have my ourboard or  I/O much over 4000.

[Sk8man]

I guess at least they don't go through a bunch of tires peeling out in the parking lots....

Edited June 21, 2013 by Sk8man

[Kuba]

Hehe.......donuts???

[Chas0218]

I don't run my motor at WOT all the time just when I fish a tourney getting to a spot or when I want to skip waves.  Other than that it is generally around 4000.

 

Although I have been known to do a couple donuts when driving motor vehicles, I don't seem to get the same satisfaction when doing them in the boat.

Edited June 21, 2013 by Chas0218

[rolmops]

Hey, you guys are hot-rodders...lol.

I never have my ourboard or  I/O much over 4000.

That is really where you save fuel. By running your engine at 2/3s of its capacity your fuel consumption goes way down per mile traveled.

[Adk1]

same here. I do like to "clean her out" at least once each trip out though