Mariner 40 hp.

[57 special]

I have a 1996 40 hp mariner I just put on a 16 ft smoker craft. It came with a. 12 pitch prop it was damaged a little. So I put a new 13 pitch prop on it. It’s running about 27 - 27 across the lake. My prob is my tac only reads 6000. And I can peg it with no problem. My question to bring rpm down to 5000 - 5500. What pitch prop should I get. 15 - 17 ??????!

 

[airshot]

What is the mfgr recommended max RPM at wot ?? Never exceed that or your motor will be short lived ! Remember every inch in pitch changes rpm about 200rpm..if your tach is accurate, do your math.

 

[chrisgt]

I have the same engine on a 14ft lund with a 15 pitch Michigan wheel and hit somewhere in the mid to high 5000's depending on load.
The engine has a progressive redline where it starts to retard ignition timing around 6000 and goes to complete spark cut after that, so while it's not amazing to rev these engines that high, you probably won't blow it up since it does have over rev protection.

Just based on my boat, I'd say a 15 pitch would be a good place to start, or maybe a cupped 14.

 

[airshot]

I have a 1996 40 hp mariner I just put on a 16 ft smoker craft. It came with a. 12 pitch prop it was damaged a little. So I put a new 13 pitch prop on it. It’s running about 27 - 27 across the lake. My prob is my tac only reads 6000. And I can peg it with no problem. My question to bring rpm down to 5000 - 5500. What pitch prop should I get. 15 - 17 ??????!

You need a 500 rpm drop, so add 2" of pitch to your prop to get you into that 5600 rpm range. If your testing the boat in its lightest weight setup you can exceed max rpm slightly......then you will be good when some weight is added. When running wot under a light load, watch your teach !
I have the Merc classic four cylinder motor on my 16' Sylvan side console, 13" pitch gets me around 56-5700 when weight is at minimum...gotta watch that tach...with two adults and fishing gear, right 0n 5500 rpm...