Temperatures affect on Performance

[jeffbare]

At what point does the ambient temperature begin to make any noticable affect on performance? I noticed in the May Powerboat that they tested the Laveycraft Evo on a 97 degree 21% humidity day, and was wondering how much of a difference it would be if it were 55, 65, or 75 degrees outside.

Cheers,

 

[cigdaze]

Per SAE J1349 Revision June1990, engine manufacture's have to rate their engines at 77 degrees F, 29.235 Inches Hg Barometer, 0 feet altitude, 0% relative humidity. Naturally, there are correction factors for being at different altitudes, temperatures, and humidity levels, but the above is the standard for which an engine has to make at least 100% of its rated horsepower.

All other things being equal, changes in temperature from 77* will yield the following % of rated horsepower:

110* 96.6%
100* 97.6%
90* 98.6%
80* 99.7%
77* 100.0%
70* 100.8%
60* 102.0%
50* 103.1%
40* 104.4%
30* 105.6%

 

[Perlmudder]

so at 30 degrees my boat makes 15 more horsepower which should equal about 1 mph! 56.5mph here I come!!

 

[phragle]

so at 30 degrees my boat makes 15 more horsepower which should equal about 1 mph! 56.5mph here I come!!

nope...you have to factor in the rest of the variables first.
as the temp change effects relative air density, so does barometric pressue, humidity and elevation, also consider other variable, at 30 degrees water should be frozen... if not frozen, the molecules being further apart give your boat less bouancy, increasing wetted surface and drag

 

[Ratickle]

so at 30 degrees my boat makes 15 more horsepower which should equal about 1 mph! 56.5mph here I come!!

at 30 degrees water should be frozen

30 degrees on the Salton Sea.......:sifone:

 

[cigdaze]

so at 30 degrees my boat makes 15 more horsepower which should equal about 1 mph! 56.5mph here I come!!

My numbers are for all other things being equal...in all likelihood, the humidity will be lower when colder, and the pressure may be higher as well. These are additional factors which will further boost horsepower.

For instance:
Say we're in FL, and it's 90*F, 80% Humidity, and 29.50" inches pressure.
If I make 500hp under these conditions, and then I do it again when it's 40*F, 10% humidity and the pressure is 30.00," HP would increase by almost 13%, to 564.

(theoretically - there are many more variables to consider, but this is all ballpark anyway).

 

[phragle]

30 degrees on the Salton Sea.......:sifone:

now see..your throwing another wrench in the fire altogether. the salton sea has a very high salinity value, that would have to be factored in against the increasing distance of water molecules as temp drips. thus the boat would have more bouancy than in fresh water........

 

[Perlmudder]

so pretty much my boat will run consistent from may-october...?

 

[jeffbare]

Per SAE J1349 Revision June1990, engine manufacture's have to rate their engines at 77 degrees F, 29.235 Inches Hg Barometer, 0 feet altitude, 0% relative humidity. Naturally, there are correction factors for being at different altitudes, temperatures, and humidity levels, but the above is the standard for which an engine has to make at least 100% of its rated horsepower.

All other things being equal, changes in temperature from 77* will yield the following % of rated horsepower:

110* 96.6%
100* 97.6%
90* 98.6%
80* 99.7%
77* 100.0%
70* 100.8%
60* 102.0%
50* 103.1%
40* 104.4%
30* 105.6%

Looks like everyone should move to the Pacific Northwest for thier summer boating, we are always in the 100% temperature range.

 

[Airpacker]

Blowers, the great weather equalizer

 

[Ratickle]

Blowers, the great weather equalizer

Well said.....

 

[Ratickle]

now see..your throwing another wrench in the fire altogether. the salton sea has a very high salinity value, that would have to be factored in against the increasing distance of water molecules as temp drips. thus the boat would have more bouancy than in fresh water........

That's why speed runs used to be there. Let me know the answer.....:sifone:

 

[phragle]

speed is classified...but I did do sound trials up there...

 

[BradH]

Noticeable with 2.5 outboards, very evident with turbines.

 

[MarylandMark]

Noticeable with 2.5 outboards, very evident with turbines.

Stock 300XS's as well- I run bigger props in the Spring and Fall than Summer. Cheapest upgrade one can do IMHO...

I remember MGR saying some thing like 1% for every 1 degree (NOT putting words in their mouth and NOT positive that is was that formula; just know it was a lot)

 

[Griff]

I've heard about 1% hp loss for every 10* above 70*. Of course, high humidity can also be a factor.

 

[4mulafastech]

Here's a handy calculator.:driving:

http://www.anycalculator.com/enginehorsepower.htm

 

[Sean Stinson]

30 degrees on the Salton Sea.......:sifone:

Salton Sea will never see 30 degrees very often!!!!!! But it is below sealevel by a few feet!!!!!