5000' ft and higher which prop should I use?

[Derric]

I was told it would be easier to change the pitch on the prop than the jets. If so can anyone suggest the right prop for the elevation. I have a 16' open bow with Mercury 90hp L6 1984 2 stroke with a 17" 3 blade right now.

 

[rndn]

Re: 5000' ft and higher which prop should I use?

Change the jets. With a different prop the motor will still run like crap.

 

[Tail_Gunner]

Re: 5000' ft and higher which prop should I use?

Come's with good Illustration..........

Notice she's a 4 blade probably not SS but some dang fangled composite.....

 

[Frank Acampora]

Re: 5000' ft and higher which prop should I use?

Change the jets! At 5,000 feet, the air is less dense and you will be running rich no matter what prop you use.

 

[Wotam]

Re: 5000' ft and higher which prop should I use?

Depending on what you're doing with the boat, you may have to change both prop and jets.

1) Jets to make it run properly.
2) Lower pitch prop to compensate for the power loss at altitude.

#1 is a 'given'
#2 depends on what you're doing with the boat... tubing, skiing, fishing etc?

 

[Bill Adkins]

Re: 5000' ft and higher which prop should I use?

I have a older glasspar Avalon that I bought from a neighbor with a way large Merc 135 on it. Its a 1971 1350. It had a 13-19 prop on it that it wouldnt run with at 7000 ft. I took it to the local boat shop and he had his way with me so to speek. He did put a used 15 pitch prop on it that is small as the motor will rev much higher than the 5200 recomended but it planes almost instantly and although it isnt maximized for performance it will hit 42 mph without issue. I have been considering doing a rental or try out to determine the correct prop in a 4 blade. It sounds like a better prop if absolute maximum speed isnt a real issue. From reading the posts it seems there is a max prop speed that is efficient in a 4 blade and the effective efficiency decays beyond that speed. When I was a teenager we had a neighbor that had a SK flatbottom with a 450 inch hemi puffer motor. I got to ride in it once at above 100 mph. That resolved any speed issues I might have otherwise had at least on water. The motor made a tad over 1000 hp if my memory serves me correctly.
I did find a Mercury prop finder that recomended a 16 pitch prop once but I havnt been able to find it again.
Bill

 

[Derric]

Re: 5000' ft and higher which prop should I use?

Well, at the 5000' ft lake we were gonna fish and ski. The 7000' ft lake just fish trolling. So I might want to try a 15" pitch 3 blade at those elevations?

 

[jaxnjil]

Re: 5000' ft and higher which prop should I use?

derric; i live at 6500 ft and boat from 8000 ft to 4500 or what ever lake powell is. i have a 165 hp merc i/o so i get by pretty good not having to jet when i change elevation which can be every week.
that said your 2 stroke is much more sensitive to elevation and trying to troll at 7000 ft with to rich jets will be more of a problem than running hard as you will end up fouling plugs.
rndn is right unless this is a one time trip you are going to have to re-jet. the good news is you should be able to jet for 7000 and over lap down to 5000

 

[Bill Adkins]

Re: 5000' ft and higher which prop should I use?

Deric, I have a Merc manual that I bought from I boats that gives the factory recomended jet sizes for altitudes and if memory serves me right the recomended change is only a couple of thousanths of an inch. It is in the mountains and I wont be up there this weekend. The book is worth buying as there is tons of info supplied. My neighbor in the mountains has a pontoon with a Merc 80 on it that came from sea level and wouldnt idle in gear at all. He took it to the local shop and they re-propped it and it runs really well now. Not sure how much effect is really noticed, my motor was a sea level motor and a re-prop got it performing quite well. If you are still checking in a couple of weels I can look your motor up in the book but as I said its well worth the price.
Bill

 

[Derric]

Re: 5000' ft and higher which prop should I use?

Thanks for the good info. You are all giving me some things to think about. After Labor Day I will be using my boat primarily for fishing at Shaver, Huntington, Courtright, and Wishon. all above 5000' and mostly trolling so if I dont want to be fouling my plugs then I should re jet the carbs. I probably wont use my boat again down in the valley until next june 2008. Not much water in the lakes this year.

 

[Bill Adkins]

Re: 5000' ft and higher which prop should I use?

I just read a thread here that indicated a reduction in main jet size of .002 for every 2500 ft above sea level. Dont know if that will help but what I could find.
Bill

 

[jaxnjil]

Re: 5000' ft and higher which prop should I use?

i should have told you before i can run a 15"x19" at powell,i think its 3800 or a little less and at flaming gorge a 15"x17" at around 6000 ft. at steam boat lake around 8000 ft. i have a little trouble getting on plane and loose 300 or so off wot with with the 15x17 i dont go up there that much so i havent tried to change for that high.
there have been some get by with sea level set up but more that dont.
allso what elevation you are jetted for now will make a difference in how well you can get by.
2500 ft. per jet size sounds about right so if you jet for 6000 you would be good for 5 and 7 .
my boat is a 1974 18.5' jamaica 1950 bayliner 2250lb empty with motor

 

[Bill Adkins]

Re: 5000' ft and higher which prop should I use?

I might be way off base here but the oil for lubrication is a part of the fuel delivery in a 2 stroke. If you lean it out too much dont you risk detonation along with a lower lubricant level for the motor. Just a thought.
Bill

 

[jaxnjil]

Re: 5000' ft and higher which prop should I use?

bill if you do lean a 2 stroke to much it is very easy to melt a piston and burn it down. this can happen when a crank seal gives up and you suck more air in to the crank case or any number of other mechanical failures.
if you jet for higher altitude and go to a lot lower you also run this risk.
trust me i'v lived at 5200 ft and higher all my life. the air is enough thinner that you have to cut down the fuel mixture to maintain the proper fuel air mix or you run wayyyy rich and on a 2 stroke motor this can be just as bad as burning down. all manufactures i know of error on the rich side so you are safe with ther reccomendation and if you want more performeance you can work down leaner but thats another story.
you dont change you oil ratio mix-that stays the same what ever your elevation and in fact if you dont lean down thats part of the problem because along with to much gas your also getting to much oil in the crank case.

 

[Tail_Gunner]

Re: 5000' ft and higher which prop should I use?

In all seriousness go to outboard's and learn hot jet that motor, then come back with your result's at altitude with your current prop........

 

[Derric]

Re: 5000' ft and higher which prop should I use?

Thanks for all the helpful information really appreciate it. I have ordered a new prop with 15" pitch and have different size jets coming. I will let you know how it ran we are going for our Labor Day weekend hoo rah up to Shaver Lake so with any luck everything will go well.