Significant power loss at altitude??

[9094life]

I have a new to me 2007 Monterey 220 Explorer Sport deck boat. It has a Merc 5.0 MPI motor and Bravo3 drive. Last week at Lake Elsinore (California), elevation roughly 1,100 feet, it ran like a champ. Holeshot was incredible, planed in about 4 seconds, and cruised at about 45 mph. This was with 3 adults and 1 small kid.

Skip to yesterday, went to Big Bear Lake, elevation 6,700 feet, and there was a very noticeable decrease in power, especially when heading into the wind. It just didnt want to get up and go. The fastest I could get it to was 35 mph +/-, and it took forever to get on plane. This was with 4 adults, and 3 small kids. At first I thought it was load distribution with the occupants, so I rearranged that and it only slightly improved. This was only with 1/4 tank of fuel.

Will the altitude make that much of a difference? I did have both biminis up also, and it was real windy. The boat wasnt misfiring or running funny, just seemed to lack power. I didnt get any warning chimes or anything like that either. The boat sat in the driveway all week, so I dont think anything happened motor wise between the trips.

Please tell me that the high altitude could be causing all this! Some people rec a lower pitch prop for the altitude, nut honestly Ill probably never go back to that lake again, it was a last minute thing.

Thank you!

 

[achris]

Re: Significant power loss at altitude??

I have a new to me 2007 Monterey 220 Explorer Sport deck boat. It has a Merc 5.0 MPI motor and Bravo3 drive. Last week at Lake Elsinore (California), elevation roughly 1,100 feet, it ran like a champ. Holeshot was incredible, planed in about 4 seconds, and cruised at about 45 mph. This was with 3 adults and 1 small kid.

Skip to yesterday, went to Big Bear Lake, elevation 6,700 feet, and there was a very noticeable decrease in power, especially when heading into the wind. It just didnt want to get up and go. The fastest I could get it to was 35 mph +/-, and it took forever to get on plane. This was with 4 adults, and 3 small kids. At first I thought it was load distribution with the occupants, so I rearranged that and it only slightly improved. This was only with 1/4 tank of fuel.

Will the altitude make that much of a difference? I did have both biminis up also, and it was real windy. The boat wasnt misfiring or running funny, just seemed to lack power. I didnt get any warning chimes or anything like that either. The boat sat in the driveway all week, so I dont think anything happened motor wise between the trips.

Please tell me that the high altitude could be causing all this! Some people rec a lower pitch prop for the altitude, nut honestly Ill probably never go back to that lake again, it was a last minute thing.

Thank you!

Well, I've highlighted what jumped out at me... 1,100 feet + 3 adults and 1 child, versus 6,700 feet + 4 adults and 3 childs.... Yeah, I'd say you're going to notice some serious power loss...

And yes, the altitude will make that much difference. In the past, the recommendations was to change the carburetor jets. That got changed to changing to lower pitch props. Just put props on that will allow maximum recommended revs again....

Chris......
BTW, been to Big Bear Lake, really nice spot....

 

[Fun Times]

Re: Significant power loss at altitude??

Please tell me that the high altitude could be causing all this! Some people rec a lower pitch prop for the altitude, nut honestly Ill probably never go back to that lake again, it was a last minute thing.

Thank you!

Yes as Chris said, the altitude between the two lakes makes a big difference in power. You will also experience almost the same running condition if or when you go to lake Silverwood, lake Shasta, lake Tahoe, ETC. ETC. I'm in Moreno Valley, so I know them lakes pretty well.:behindsofa:


What size props are on your boat at the moment?

 

[9094life]

Re: Significant power loss at altitude??

Right now I have 26p props. Thanks for the input!

 

[fishrdan]

Re: Significant power loss at altitude??

You'll loose aaround 3% power for every 1000' elevation, so it was down about 15% on power. The power loss would seem even worse throwing in another adult and a couple of kids...

 

[9094life]

Re: Significant power loss at altitude??

You'll loose aaround 3% power for every 1000' elevation, so it was down about 15% on power. The power loss would seem even worse throwing in another adult and a couple of kids...

Maybe a dumb question, but with the wind as bad as it was, and both biminis up covering from bow to stern, would that also cause some power loss when heading into the wind?

 

[HT32BSX115]

Re: Significant power loss at altitude??

Maybe a dumb question, but with the wind as bad as it was, and both biminis up covering from bow to stern, would that also cause some power loss when heading into the wind?

Howdy,


A few years ago I took my FourWinns 211 Liberator to Lake Tahoe (approx 6000' MSL) .

I have a Mercruiser 7.4L (carbed) + [1.81:1 ratio]Bravo III running 26p Props. At sea level, 3 people, I can get 4600 RPM and 57 mph.

At Lake Tahoe, I put my 24p props on and with 8 people and (3) 80lb dogs, I was able to get 4200 RPM and about 40 mph and it was noticeably slower getting up on a plane.....

It's common to lose a little power at altitude and if you add additional (wind) drag you'll absolutely lose speed ....

 

[9094life]

Re: Significant power loss at altitude??

Thanks, all these responses are what I was hoping to hear. So may people, in person, most with Mag 350's are telling me it should perform the same at altitude and there is an engine problem. I didnt want to believe that because I had no warninglights or chimes, and the engine ran smooth, just lacked power, and on top of that, it ran like a champ the week prior at Elsinore. For al I know, they guys with the 350 may not lose as much power because its quite a bit more HP. I will be running it this weekend at Lake mead, and am anxious to see it perform at "normal" range again to put my worries to rest. Thank you!

 

[fishrdan]

Re: Significant power loss at altitude??

Last week at Lake Elsinore (California), elevation roughly 1,100 feet, it ran like a champ.

I will be running it this weekend at Lake mead, and am anxious to see it perform at "normal" range again to put my worries to rest.

My crystal ball says it will be running great, just like it did at Elsinore!

(Mead's current elevation is 1105' )

 

[9094life]

Re: Significant power loss at altitude??

Im hoping your prediction is on the money! Thanks!