Re: Prop for Johnson DF 140 4 -stroke
Hi Steve,<br /><br />Your problem, or principially same problem, has been up here several times. It is true, that any prop is a compromise as it litterally works like a 'one-gear gearbox'. Rule of thumb is, that you are running the right prop if your rpm at wot is within the stated rnage for your motor. Rather near the upper limit. This should be decided when load and running conditions (trim) are as you most often use it. You don't want to setup your boat for conditins other than those, obviously.<br /><br />Staying within the stated rpm range ensures your motor's running conditions are best possible.<br /><br />Another concern when choosing a prop may be performance in general. Some experience some kind of problems with ventilation, lack of grip, bad trim properties etc.<br /><br />If your prop works OK but does not allow you to reach the rpm at wot range, you should change pitch DOWN by one inch per 200 rpm you want to achieve. This will even improve accelleration and may (probably) reduce top speed slightly (if the theoretical drop in top speed due to lower pitch is compensated by higher rpm, top speed will keep and become more stable).<br /><br />If you like, you can get a free Quicksilver booklet on props & more from my homepage.
