Altitude and Prop Pitch

[Artsy72]

Does anyone know if you increase or decrease the pitch for increases in Altitude? I'm currently using a 19 Pitch Prop, but seem to have a helluva time getting on plane when fishing in high altitude lakes.

Should I decrease the size of pitch? To maybe a 17 or 15?

 

[mike343]

Re: Altitude and Prop Pitch

Yes, but try one before you buy.

 

[lowkee]

Re: Altitude and Prop Pitch

What kind of boat do you fly?

Oh, like nobody else was thinking that!

 

[fishrdan]

Re: Altitude and Prop Pitch

Decrease pitch

what altitude are you fishing at?

 

[Texasmark]

Re: Altitude and Prop Pitch

I am a rolling hills lowlander. Our altitude is around 600'. Couple of years ago I went to NM and AZ where I encountered mountains to 8500'. I have a Ram 1500 with the 4.7 liter engine.

At home that engine is very peppy and responsive; a good match for the truck. However, when I was going across the 8500' mountain near Alamogordo, NM (spelling?) the truck performance was absolute PUKE!

So, relating this to your question, I'd say that if you were boating at that altitude, a decrease in pitch of possibly 4 inches may be in order....but I agree with Mike, and as I have said many times, try before you buy; well worth the extra bucks you probably will have to pay to get a cooperating dealer.

Best I can do.

Mark

 

[ArcadianStar]

Re: Altitude and Prop Pitch

Old RULE of THUMB was 10% drop per thousand feet. But that didn't make sense because at 10,000 feet you still had some horsepower.

Dealing with people for years, I've learned that big diameter and low pitch is the best of high altitudes.

Generally 2 inches of pitch is 400 RPM....For places like Lake Powell, big diameter, many blades and low pitch seem to work well.

Without knowing you boat and where you boat, it is difficult to know what you REALLY need. Sometimes going to an over the hub, like an outboard prop works great at places like Big Bear and Rocky Mountain Lakes...

Working with a prop shop that knows your area, maybe best, but testing new props might be the only answers.......but you can always sell you old props on E-Bay!

ADD;

In the OLD DAYS re-Jetting the motor helped a ton, but today's EFI's don't need it...I think! WIth outboards, we ran less oil in High Elevations, as less oil is leaner air to furl ratio....that was with fixed jets.

 

[trendsetter240]

Re: Altitude and Prop Pitch

Old RULE of THUMB was 10% drop per thousand feet. But that didn't make sense because at 10,000 feet you still had some horsepower.

I'm not even sure that rule of thumb is accurate, but let me tell you how it might have worked!

If the rule is to drop 10% per thousand feet then if you have a 200 HP motor then you will have 70hp at 10,000 ft.

You drop 10% of the remaining hp at each 1000ft interval. 200hp at 0 feet, 180hp at 1000ft, 162hp at 2000 and so on. 180 hp is 10% off 200, 162 is 10%off 180, 162 is 10% off 180...


See below:

HP FEET
200 0
180 1000
162 2000
146 3000
131 4000
118 5000
106 6000
96 7000
86 8000
77 9000
70 10000


Might be worthless but hey...

 

[fishrdan]

Re: Altitude and Prop Pitch

I've heard it's more like 3% power loss per 1000'

200HP @ sealevel
194 @ 1000
188 @ 2000
182 @ 3000
177 @ 4000
171 @ 5000
166 @ 6000
161 @ 7000
156 @ 8000
152 @ 9000
147 @ 10000

I run a 140Hp up at 9000' and the power loss is quite noticeable, probably 30-40HP down.

 

[hwsiii]

Re: Altitude and Prop Pitch

Artsy, 3% loss of power per thousand feet is a lot closer than 10%, but even that does not take into account the vapor pressure difference at higher elevations, especially above 5,000 feet. cavitation is a whole new ballgame at those elevations, so I would recommend the same thing as Arcadian, larger diameter or more blades so there is less HP per each square inch of surface area of the prop and a drop in pitch as well, just depending on what altitude you are at.


H