What size prop for a 175 Merc

[sloopy]

Today while working at the "marina" a couple guys started to yell from a blue boat for a mechanic, unfortunately our marina does not have a mechanic so they then asked for someone who knows a little about OBs could come diagnose there problem. So I volunteered to do it..<br /><br />The guys on the boat said that there engine; a 1984 175 merc was recently rebuilt, and the mechanic installed a new prop on their boat for no extra charge. When they got the boat back from the repair shop, and took it out on the water it would not want to stay on plane. They said it cavitated (sp) like crazy. When they were done telling there story I had them raise the outboard trim up so I could look at the propeller. The propeller was way too small, the gear cases diameter was an inch larger than the propellers hub diameter. The prop size was 12.5 diameter and 21 pitch, this looked like a propeller for an engine in the 80-100 hp range. <br />So here is my question... What type of propeller and what size should be on this boat, I did not get a good look at the boat, but the owner said it would do 53mph before the rebuild.

 

[KCLOST]

Re: What size prop for a 175 Merc

It would be nice to know what boat they have and what they like to do with it..(skiing, fishing, howmany passangers, etc,) But a 175 merc, on let's say a 18ft bass boat should normally have a 24 pitch prop at 14-14.5" in diameter, 4-4.5" hub... With only a few people on board and hauling @ss....

 

[sloopy]

Re: What size prop for a 175 Merc

thanks

 

[m_bickle]

Re: What size prop for a 175 Merc

You need the boats length, weight and the engines rating. Get either a manual for the motor, prop manufactor or a west marine catalog and that will tell you which prop size is best for the application. Also when changing a prop the engine is going to need its idle RPM and max RPM set.