Altitude verus Pitch ?

[SNye45]

Recently I bought my boat that came with a Suzuki DF 115 and a standard 21" prop. I bought it at a dealer 150 miles away who is at sea level but since I live at 3000 ft and intend on using on inland lakes he swapped the prop out for a 19" prop instead.

What main differences is this switch going to make ? and if I should visit friends (who still live @ sea level) should I switch back to a 21" for that short a time?

Any comments would be welcomed !!

Thanks

 

[steelespike]

Re: Altitude verus Pitch ?

The 19 allows the motor to rev easier at altitude. When at sea level its ok to use the 19 but don't exceed the max reccomended rpm.
When running at higher altitudes you should make sure the 19 is allowing it to run in its reccomended rpm range.
If you find it difficult to keep the rpm down at sea level you may want to go back to the 21.

 

[SNye45]

Re: Altitude verus Pitch ?

steelespike- Thank you for the reply

 

[Frank Acampora]

Re: Altitude verus Pitch ?

The reason for the switch is because at 3000 feet, the air is less dense. So the 115 horsepower engine (which is really nothing more than an air pump) can induct less air (and oxygen to burn) and produces less horsepower. At 3000 feet, your 115 is not making 115 horsepower, thus it can not swing the higher pitched prop at the recommended RPM.