Prop pitch vs. elevation

[BURLEY]

Three years ago when BFT did the DAV thing at Strawberry,  I took my boat and joined in. With only one veteran and myself in the boat I had a very hard time getting on plane. I have a 16ft. Tracker with a 60hp motor jetted for 4000ft. elevation. Since then I found out that I needed a different pitch for the elevation. I got a prop from I-boats with the recommended pitch. It has been in my boat's battery compartment ever since. A couple weeks ago I went back up the the Berry to redeem myself after Kent out fished me 110 to 11 a few days before. Well my fishing didn't improve (12 fish) and I forgot to change out the propeller. I did get on plane , but didn't get my full rpm. Last week I changed the prop and went back. I  was able to get on plane like normal and get my recommended full rpm of 5800. 
     Elevation            original prop 11pitch       New prop 9 pitch
CJ Strike 3000ft         6050 rpm (over speed)        ?
Willard   4000ft          5800 rpm (normal               ?
Berry     8000ft          5000 rpm                        5800 rpm
Now I know what a difference in elevation  and pitch can make. 
BTW I did a little trolling after testing the new prop. Pulled a large lipped crankbait on a long line on one pole and 2 colors of leaded line pulling various rapalas on the other. Got many more bites than I caught. I didn't keep count, but I think  about a dozen got netted during the two hours that I was there. The leaded line got most of the action. If I fished there more, I would have to consider downriggers, but I don't often chase slimmers. snicker, snicker

[doitall5000]

Interesting, I have a 16 ft tracker, with a 20 horse. I have no problem getting up on plane, my top speed is 18 mph. If I'm alone I put three sand bags up front and I can plane fast. With another person I have no problem. Elevation don't matter.

[Kent]

My prop works fine everywhere, but I have to watch the RPMs, so that they don't get too high, when I boat on The Snake River (elevation just under 2,500). I used to change to a higher pitch prop whenever I was going sturgeon fishing, but I am getting lazy and just keep the RPMs down. Yes, the pitch makes a huge difference when one changes elevation.

[BURLEY]

Interesting,  I have a 16 ft tracker, with a 20 horse. I have no problem getting up on plane, my top speed is 18 mph. If I'm alone I put three sand bags up front and I can plane fast.  With another person I have no problem. Elevation don't matter.

Mine is the deep V pro guide that weighs 1100lbs. bare bones. Yours must be a lot lighter or a different style.

[doitall5000]

Nor sure how they compare. Yes mine would be lighter.

[Bduck]

I have a Yamaha F150 and had to re-prop for altitude. I had issues getting on plane at Strawberry too. Since, given the standard day condition my rpm can range from 5700-5900. Willard Bay I can get up to near 40mph max throttle, once again depends on standard day condition. Watching those bass tourney guys going full bore max throttle getting the most out of their motors for speed I don't treat my motor in that manner. Coming out of the hole on plane I like to throttle back to cruise 4000-4500rpm. There's no reason to push the boundaries which I need years of service from my motor especially when the cost is like buying a new used car. 

[BURLEY]

Nor sure how they compare.  Yes mine would be lighter.

Yeah, mine is a lot larger. 7'4" beam

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[PBH]

I have a Yamaha F150 ....

Watching those bass tourney guys going full bore max throttle getting the most out of their motors for speed ...

I've got a Mercury 150 Four Stroke on my Ranger.  I can get up to 40mph with glassy water, and light load.

I always notice this when on Lake Powell -- it's crazy when I get up to 37-40mph, and I feel like I'm just flying right along.  There won't be a boat in site either direction.  Then, out of nowhere, I'll have a bass boat zip past me like I'm not moving, and then quickly disappear out ahead of me.  Some of those guys are doing 60+.    Wow!

[Mildog]

Yep, Depending on the set-up, a prop can make a big difference in the performance. Basically changing a prop is akin to changing gears.
I had a buddy with a nice fast Bass boat a few years back, he could not get it on plane with just two of us in the boat at Strawberry, it would run 60 plus and jump up on plane at Lake Powell, and the lower elevation lakes where he fished most of the time. He didn't fish up there enough to switch props so he just lived with it.
I fish out of a 17 foot Gregor Aluminum with a 50 horse 4 stroke merc. I can get it up on plane at the berry with 2 avg people and my dog add another not really. It bogs down and runs much slower. I do have another prop, but it is so seldom that I have issues I havent experimented with it. The one I'm running does well in a variety of situations.
One interesting observation I have made is I can run 3 to 4 miles an hour faster in the morning if it is cool, than in the afternoons. At Jordanelle several mornings I could hit 27 MPH with avg load. But when done fishing and heading back about 23 tops it out. Noticed similar better performance at the berry although not quite as fast. At lake Poweel it will go a bit over 30. Finally figured out it is due to the colder air temps. Runs faster in the cold morning air. Cold air I know is denser so maybe that helps with the fuel air mix not sure? But whenever its a cool/cold morning it definitely runs faster?

[RockyRaab2]

This was my first year with a power boat, so my "know-it" bank balance is pretty low. I wanted to replace the aluminum prop on my Merc 50 (Tracker Classic XL boat) with a stainless one and all the online prop calculation sites told me I needed to go to a lower pitch due to altitude.

During my motor break-in and before I switched props, the OEM prop did seem to limit both RPMs and speed, but not by much. The replacement SS one gave an immediate boost to both - but that may also be due somewhat to the motor smoothing out as it gets used.

I also throttle back to 4000-4500 after getting on plane, btw. According to my Vessel View monitor, I burn only 2.5 to 3.0 gph at those settings and lose only about five mph from top speed versus 4.5 gph at top end. With Non-ethanol gas costing over $4/gal I consider it a worthy tradeoff.

[Mildog]

I agree with your throttle back comment. As I mentioned earlier I run the 50 Merc 4 stroke on a 17 ft aluminum Gregor. I can fish lake Powell with quite a bit of running around based off of a houseboat for 4 days and I only use about 12 Gallons of gas. I always have a spare 6 gallon can and I rarely ever need it. Once up on plane, by throttling back from full speed just a few MPH it increases the range and reduces the fuel consumption dramatically. Running full out is harder on the engine and much harder on your wallet $ as well.

[SkunkedAgain]

So I bought a motor out of a lower elevation area and have been having issues getting it on plane, I thought I would need to re-jet the carbs, but is it just a matter or changing the prop that I should be looking at? I'll have to look into this, it sounds a lot easier to accomplish... How do you size the props? I'm sure it has a lot to do with boat weight, motor size and etc... but do you have a good resource to check so you don't have to do an expensive game of parts changing? Thanks J

[BURLEY]

So I bought a motor out of a lower elevation area and have been having issues getting it on plane, I thought I would need to re-jet the carbs, but is it just a matter or changing the prop that I should be looking at?  I'll have to look into this, it sounds a lot easier to accomplish... How do you size the props?  I'm sure it has a lot to do with boat weight, motor size and etc... but do you have a good resource to check so you don't have to do an expensive game  of parts changing?  Thanks J

Call Iboats in Taylorsville and they will help you choose the right propeller for elevation. Give them boat and motor information along with your present prop info. (pitch, #splines, make). That said, they may suggest getting the jets changed since the motor is from a lower elevation. What elevation is it from?

[MrShane]

Jeff,
Carbed or efi?
Checking spark plug color is a good indicator if you are rich/lean.
Don’t ever run lean unless you like extra holes in your pistons.
Every inch of pitch you drop is good for about 100-200 increase in rpms.
First thing to do is find your manufacturers recommendation of where your motor should run at max rpm, then let’s talk.
Most motors are in high 5k range.
A high performance motor will be in low 6k range.
You need to be propped so at the lake you run the most your rpm is in the manufacturers rpm range.
If ran too low of rpm for long periods of time, damage will occur.
Remember, an outboard does not have a transmission, only a clutch.

[BURLEY]

Jeff, Iboats' website has a lot of information on understanding propellers size, pitch, diameter, and more that is really educational. If your motor is EFI, there are no jets to change.

[MrShane]

Every engine manufacturer also has a website that has a prop calculator.
You enter all the information it asks and it spits out the prop you need.
Finding the right prop is a very rewarding experience and gauranteed to put a  on your face.

[Gone Forever]

I had a 17" a 19" and a 21".
17 was for the Berry and over 7,000'. The 19 was my all around prop and worked most places. The 21 was for Powell.
My boat was probably underpowered (4 cyl I/O) for the area but that was harder to change than the prop was, which I could do in about 5 minutes and for a lot less money.
I also throttled back, a lot, most of the time. With the 17 on Willard I could get up on plane and then throttle back to 2,800 rpm and still be cruising right along on plane with 4 people on board sipping gas compared to the 4,400 I could have been running WOT. I could camp 3 days, pulling tubes, fishing, cruising and burn 20 gallons.
When shopping for props, many places have used "loaners" that you can take to test out and when you have it figured out which works best for you then you buy a new one of those.
When I had the Shamrock we towed it to a marina and they tried several props before finding the right combo of pitch, diameter and cup for it at the altitude it would be running rather than the sea level it was coming from. I will say that the prop decided on was not a slow speed prop by any means, idle was over 5mph, so no matter what, you were coming in hot. When you stood on it, that 351 Cleveland would push to 50 with 4 on board, no problems. Economy? Not so much.

[SkunkedAgain]

Hey Guys thanks so much for the info and discussion... my motor is carbureted and appears to be running rich by the color on the plugs. I know how touchy 2 strokes can be with fuel mixtures from past snowmobiling experiences... and I'll have to check your prop references, but I think first off I'll need to get a new tach, current one is an old dial gage and I'm not even sure it's accurate with the motor switch... Went from 4 cylinder to 3 cylinder, so pretty sure there is a setting there that needs to be changed, but it's so old I think a new digital tach would be a good call... Once I get that, I'll have to check out your references on new props... Actually glad to hear about this before I spent too much taking it into the shop to work on the motor, because it really sounds like this is what my issue is with the motor, it just won't pick up and pull like I think it should... So I'm excited to see what it can do for my boat... Thanks for pointing this out... Jeff

[klam]

If you aren't located too far from Orem The Prop Doc has helped me with prop selection on a couple of boats.

[Anglinarcher]

So I bought a motor out of a lower elevation area and have been having issues getting it on plane, I thought I would need to re-jet the carbs, but is it just a matter or changing the prop that I should be looking at?  I'll have to look into this, it sounds a lot easier to accomplish... How do you size the props?  I'm sure it has a lot to do with boat weight, motor size and etc... but do you have a good resource to check so you don't have to do an expensive game  of parts changing?  Thanks J

This can help you finds the right prop for your boat.  The more information you can fill in the better.

https://www.mercurymarine.com/en/us/prop...!/step-one