CONTINUOUSWAVE

I am finishing a restore on a 1982 18' Guardian Outrage. I just purchased a Mercury 150 FOURSTROKE. I have no idea what propeller to put on it. Any help would be appreciated.

You will need instruments to measure engine speed and boat speed.

What is the transom height on the Guardian?

Have you mounted the engine already?

Three-blade propellers are good for general use. Try using the Mercury propeller selector to see their recommendation.

My wild guess: 17-pitch Enertia

I don't have a propeller at all to test it. Should I buy a cheap aluminum one and test, then decide what I need and invest in it? I have not mounted the engine yet. The transom height is exactly 25 inches

See if the dealer you bought the motor from will let you try props before you buy one. The downside is you'll be restricted to what he has in stock, and the props with the motor manufacturer's brand name on them tend to be the most expensive.

An aluminum prop won't tell you much about what type of stainless prop you'll need, so if you're going to want a good stainless prop on there in the end (and you should) then start with it. Aftermarket props tend to be a bit cheaper, and some brands (PowerTech) let you swap for the same prop in a different pitch for a nominal fee.

You are not the first to install a Mercury 150 FourStroke on a Outrage/Guardian 18.

The search feature on this site is very good. Here is a good thread (skip over the blather over engine brands) that compares the Mercury Enertia and Mirage prop.

Bottom Line - Enertia 18p prop is the way to go.

http://continuouswave.com/ubb/Forum4/HTML/007696.html

The archived discussion is quite a good review of propeller selection. I don't see any data from an ENERTIA 18-pitch, so I am not sure how that became the recommended outcome. Also, the testing was done in cold northern Pacific ocean water. Cold water is denser. Saltwater is denser. When making comparisons of performance the effect of cold saltwater testing should be considered if the comparison is for warm freshwater conditions.

I found all the discussion about the Mercury 150 FOURSTROKE not VERADO to be quite interesting. The usual FUD-meisters were active and trying to disseminate their usual negative waves.