Suggestions on prop slection without a Tach?

I have a 1970 Glaspar 14' with a 79 Evinrude 75HP motor. There is no tachometer in the boat and i really don't feel like putting one in due to cutting into the dash. Currently there is a 14x17 on it and it looks like its cutting into the fin above the prop (obviously not good, previous owners must have done this.) My spare prop is a 13 1/4x17 but pretty beaten up. Also, I read in the owners guide that they recommend a 13x19. I'm new to the boating world and any info would be appreciated.

You really need to get a tach reading. The max RPM of your engine is 5500 RPM if memory serves. You want a prop that is going to get you as close to that max RPM with the boat loaded the way you use it. Some marinas will have a shop tach they can hook up to your outboard to see what you're turning. If not, there are cheap alternative such as an inductive pickup tach that works off of reading how many times your #1plug fires. You can find those on eBay pretty cheap. Make sure you get one that reads for two cycle engines. Actron makes a timing light that has a built in tach for around a hundred bucks that works really well. Or just scour eBay for a cheap OMC or aftermarket tach. Sometimes you can find used ones for around 20 bucks. Even if you don't mount the thing, you'll know what your engine is turning and thats important.

Sounds like the 14 x 17 is the wrong prop for that motor.------13 1/4 was the original equipment for diameter.