Boating "At elevation"...What's considered "high elevation"?!?!?

[2kwik4u]

I always thought I was fairly close to sea level. Been ding some research on the property my house was built on for another project and have located some topographical maps. Turns out I'm not all that close to sea level at home, or on the lake. House is somewhere around 875ft asl, and the lake is around 850f asl. I know some of the guys out west probably think this is nothing, but the guys on the coast clearly have a different perspective.

Looks like a drop of about .5 psi from sea level to my elevation. Roughly 1936ft elevation for every 1psi of pressure drop.

Air Pressure at Altitude Calculator <--easy calculator I found online.

At what point does this start to have realistic effects on boat performance? We're boating this summer on Douglas Lake which is about 920ft asl. I can do the math, but I'm looking for some real world examples/experiences. I doubt I have a problem compared to what I'm used to with only a few hundred feet difference in altitude, but I'm curious now when this starts to become an issue.

 

[chrisinslc]

I don't think you are going to be able to tell much at all. I live in Salt Lake City and my elevation is 4,200 ft. I did have Yamaha repitch my impeller to the high altitude setting of 4,500 ft. I am boating anywhere from 4,200 - 7,000 ft. I haven't tried the new impeller yet, but at a lake we frequent at 6,200 ft my 1.8L high output motor was a total dog.

 

[OrangeTJ]

For me, "elevation" means 4,000 feet or more. The lake we boat on most is at about 450 feet but we sometimes boat closer to 4,000 feet and other times on Lake Tahoe at 6,225 feet. On our SX210, power loss was noticeable but not a huge deal at 4,000 feet. At 6,225 feet, she took quite a while to get on plane (and if we had extra people in the boat some needed to move to the bow) but once up could run about 30 mph WFO. No such issues in our newer boat, but it is an entirely different animal.

 

[JBehrens]

TLDR, at Mohave (1600ft MSL) no power loss. At Powell (~3700ft MSL) there is a slight drop in power, say a good 5mph hit for both supercharged and NA 1.8's. At June (7600ft MSL) there is a significant power loss, boat might not get on plane, skis can but there is a very large loss of power.

Anything below 3000 should be fine, with little to no power loss. I usually boat on Lake Mohave (~1600ft MSL), that is my baseline for power numbers, when at Lake Powell (~3700ft MSL) there is a slight and noticeable difference in power, mostly at the top end. The supercharged version of the 1.8 will do better at elevation compared to the N/A version (I have had both in ski's at each elevation). Both have around the same level of power loss at elevation. Above 6000ft you can forget about performance. At June Lake (~7600ft MSL) it is more about hanging out and having a good time then making high performance runs. I would be interested to see how an impeller that is pitched for an elevation like Powell say 3800ft works at 1600ft, if you still loss power at a lower elevation.

 

[Gym]

The ECM for our engines will adjust the fuel/air mixture to compensat for elevation changes. I'm not sure of the top range but a few thousand feet is not an issue.

The real issue comes into play when high air temps combine with high elevations above sea level which is called density altitude. For example... at 1000 feet asl, with a temp of 85F, a barometric pressure of 28.92 and a dew point of 75F the density altitude would be 4422 feet. That means the boat engines would operate as if they were at 4422 feet asl. Now increase that temp only 5 degrees to 90F and the density altitude would now be 4725. Ask any pilot about this effect on his aircraft performance. Many pilots access density altitude calculators to determine how this adversely affects their aircraft performance, especially on takeoff.

 

[NORCAL-GAS]

While at Tahoe, water was cold so not pulling anyone. But we also had a lot of people in the boat. Seemed fine to me, didn’t notice much change. Tahoe is about 5k.

 

[2kwik4u]

The ECM for our engines will adjust the fuel/air mixture to compensat for elevation changes. I'm not sure of the top range but a few thousand feet is not an issue.

The real issue comes into play when high air temps combine with high elevations above sea level which is called density altitude. For example... at 1000 feet asl, with a temp of 85F, a barometric pressure of 28.92 and a dew point of 75F the density altitude would be 4422 feet. That means the boat engines would operate as if they were at 4422 feet asl. Now increase that temp only 5 degrees to 90F and the density altitude would now be 4725. Ask any pilot about this effect on his aircraft performance. Many pilots access density altitude calculators to determine how this adversely affects their aircraft performance, especially on takeoff.

Was having a discussion with a drag racing buddy of mine about this the other night. He brought up density altitude as well, and ran some quick numbers. Looks like a cool day at 1k ft elevation isn't much different than a hot day at 500ft.

Much to do about nothing on my end. Thanks guys!

 

[DavisAR195]

I live near Portland Oregon which is at 50’ elevation and sometimes boat at a lake in central Oregon which is at roughly 2,200’ in elevation. When I’m at 2,200’ I notice a drop in speed of roughly 2-3 mph. This is in a 2017 AR195.

 

[OrangeTJ]

While at Tahoe, water was cold so not pulling anyone. But we also had a lot of people in the boat. Seemed fine to me, didn’t notice much change. Tahoe is about 5k.

Tahoe is 6,220. That’s good that you still had solid performance!

 

[haknslash]

I would LOVE to boat at some of those higher elevation lakes with massive mountains in the background and clear beautiful water!

 

[OrangeTJ]

You mean like this kind of place?

 

[haknslash]

You mean like this kind of place?

Ugh. Now I'm even more depressed it's not summer yet, thanks a lot

 

[chrisinslc]

 

[chrisinslc]

Boating at 6,200 feet

 

[rjbdub]

I don't think you are going to be able to tell much at all. I live in Salt Lake City and my elevation is 4,200 ft. I did have Yamaha repitch my impeller to the high altitude setting of 4,500 ft. I am boating anywhere from 4,200 - 7,000 ft. I haven't tried the new impeller yet, but at a lake we frequent at 6,200 ft my 1.8L high output motor was a total dog.

Was at Panguitch my first time this weekend, 10-12 mph with passengers and 14-16 mph without.

 

[Troch1]

Was at Panguitch my first time this weekend, 10-12 mph with passengers and 14-16 mph without.

Nearly 10k feet above sea level!!! Holy crap, I’d be as much of a dog as your normally aspirated engines! I can’t even imagine (said the guy who has lived for 40+ years at a maximum of 40 ft above sea level).

 

[Robconn]

if you look up what the full pool is on a lake I thought that was the elevation relative to sea level. My local lake is approximately 1070 ft. And is located in the foothills of the Appalachian mountain chain. But there is no way in any part of the lake that it is that deep. Maybe 170 feet at the most. The full pool reading should be Near what the surrounding elevation of the land around it. So oxygen is always 21% at any altitude. It’s the pressure that drops. So at 10,000 ft the pressure drops from 760 mmHg (sea level) to 535mmHg at your location.

 

[Robconn]

Was at Panguitch my first time this weekend, 10-12 mph with passengers and 14-16 mph without.

What was your rpms with that speed? I’ll have to read up on elevation and effects on marine engines.

 

[rjbdub]

What was your rpms with that speed? I’ll have to read up on elevation and effects on marine engines.

It was 6500-6800

 

[Matt Phillips]

At sea level they will top out in the 7k+ range.
At Lake Tahoe (6225') it's about 6200rpm
The ECUs will adjust fuel mixture for elevation but there will also be a power loss unless you have super/turbo charging.

The formula I found online is: HP = elevation x .03 x horsepower @ sea level / 1000
So the formula for the standard 1800s at Lake Tahoe is: 6225 x.03 x 180 / 1000 = 33hp less per enging
Formula at 1000' is: 1000 x .03 x 180 / 1000 = 5.4hp loss per engine

Here's where I found it in case you're curious: How to Calculate the Horsepower Loss at Altitude for Snowmobiles