Propeller Recommendation - 1998 Mercury Force 50 HP

[airshot]

In my years of experience with riveted aluminum boats it has worked better with the cav plate just below the hull mabey 1/2" up to 1" below. The keel and rivets tend to make lots of bubbles when traveling at speed and cause ventilation issues.. Just something to consider...

 

[QBhoy]

Prop looks just about the usual siort for that set up.
I’d almost bet

It is a Faria Tach, with the Deutsch Connector Case, setting 5 or 12-pole according to their instructions for that motor. See the attached PDF file.

setting 12 pole 92 and newer, I read. What’s the adapter thing you mention ?
Could your feed signal be off ? Or a bad ground ? 7k would be the gauge pinned max perhaps? Is it ? That will tell a story. If she was doing 7k for real. You’d know all about it for sure.
Give me 2 secs and I’ll show you the maths on how crazy 7k would show. If it was real.

 

[QBhoy]

Your upwards of 33/34% prop slip if your numbers are right. So either your tacho is wrong or something us slipping badly in the drivetrain.

 

[Steve Fournier]

View attachment 394532
This pic shows you engine mounted pretty much even with the Hull Bottom which is normally the correct height, but yours as a lot of Aluminium Hulls do, has a protruding Keel directly in front of the Motor. Perhaps that is creating a less than solid supply of water to the Prop, causing ventilation and higher revs. I can't tell by the pic if that Prop has any Cup. If not, a cupped blade will handle a bit of air a lot better

How far ahead of the Transom does the Keel, diminish?

Well, I wanted to give an update on my journey to find the right propeller for my restored 16' MirroCraft with the 1998 Mercury Force 50HP motor. The tachometer was correctly installed and set at 12-poles. The propeller was too small and replaced with a Michigan 11.25 x 17, RPM 5000, GPS Speed 32 MPH. Thank you everyone for your help!

 

[jimmbo]

A 2000 Rpm Drop from a 3 inch increase in Pitch? Is the New Prop cupped? Combined, that would account for about 800 rpm

 

[QBhoy]

Well, I wanted to give an update on my journey to find the right propeller for my restored 16' MirroCraft with the 1998 Mercury Force 50HP motor. The tachometer was correctly installed and set at 12-poles. The propeller was too small and replaced with a Michigan 11.25 x 17, RPM 5000, GPS Speed 32 MPH. Thank you everyone for your help!

Glad you got a result in the end. But if you’re at all bothered, it really doesn’t make sense at all.