Why change pitch?
As we said from the beginning the propeller is the single most important part of your boat in regards
of performance. Changing the pitch is like changing the gear in a car. It alters the rpm of the engine
while maintaining the same speed. A change of one inch pitch is about 200 rpm.
But what is the pitch?
If the prop has a 19" pitch, in theory the propeller will in one revolution bring the boat forward 19".
But the truth is that because we are in water the prop will always slip a bit. In fact some props can
have more than 50% slip. In that case the boat will only travel say 9" in one revolution. We will not
go into why this happens but if you are interested to find out why, there is a lot of information on the
web about propeller technology.
The most important thing to know is that by changing the pitch you change the boats performance.
How do you know what pitch is right for your setup?
The best and most accurate way is to actually test different pitch settings.
With ProPulse it is very easy because you have up to nine different settings (depending on type of
prop) to choose from and you can easily change one inch at the time.
If you don't know what pitch your old prop has or if you have a new rig, it is best to start with the
middle pitch which is either 14 or 18 depending on what prop you have. The first test should be
done with the load you normally would have.
The first thing to check, is if the boat goes up on the plane easily, if you are struggling the pitch is
most likely to high so you need to try a lower pitch. The next test is at open throttle and you should
be in the engine manufacturers recommended rpm range. Most outboards have an rpm range of
about 1000 rpm. If your engines max rpm range is 5-6000 rpm and you easily reach 6000 you have
a pitch setting that would be good for a heavy load or waterskiing. You will not get particularly good
fuel economy with the load you have now.
If you are over reving you may damage your engine, so stop and go up in pitch. If you reach 5500
rpm you have a setting that gives good all-round qualities.
At 5000-5200 rpm you get good fuel economy at speeds up to cruising speed. If you try to push the
boat you may find an increase in fuel consumption.
The above are only guidelines. Every boat and engine combination is different, that's why it is so
important that you spend some time testing different pitch settings.
Remember that a marine engine is just like any other engine. If it gets overheated or uses more fuel
than normal, the engine is most likely working too hard and you may have the wrong pitch. If the
engine runs at the right temp and is easy on the fuel, you have the right pitch and the engine is
performing at its best. If you have any questions please don't hesitate to contact us we are more than
happy to be of assistance.
Four Seasons Marine Ltd
Marine Products For The 21st Century