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Mx 16 with 112 Johnson spl and 13.5X20 raker

S

Skoolball23

New member
Hello forum I am a new checkmate boat owner. I absolutely love the boat it is a '72 mx 16 Checkmate with a Johnson 112 spl. It has the fins on the back of the motor that helps with cavitation. It came with a 14X19 aluminum prop and it went about 5300-5400 rpms at 45 mph. Now with the used 13.5X20 Raker prop it turns 5000 rpms at 52 mph. Are these good numbers? I'm just wondering if the motor is mounted up high enough and if my prop needs tweaking. I have no experience in tweaking theses boats, I just love speed.
 
Skoolball23 said:
This speed run was taken with 2 passengers and the exact speed was 51.6 taken by Garmin gps.
Click to expand...

I agree with bmw, not bad.

If youre going to get serious about it, you need to learn to use a prop calculator.
Mercury racing and others, offer free on-line versions.
Its the only way you ever really know what your doing and by using a GPS, which is a great sign that your using one.

The prop calculator takes your rpm x pitch x gear ratio x slip and tells you theoretical speed.
Slip is the big one (free speed by reducing it) to watch and youre after anything at 10% or less.

I think your motor has 2:1 gears but you need to verify.

So plug in red line for your motor, and start playing with different pitch and slip #'s.
Very educational.

Also a great lie detector ;)
When some one tells you a speed too good to be true, ask their pitch x rpm.
Plug in their numbers.
Math doesnt lie.
 
I remember reading that my gearing is 2.25x1. I appreciate all of the great information. I traded a gp 1300 for this boat last November. The interior has been redone and boat has been painted. I'm still working out all of the bugs. It wouldn't start without ether so I replaced the fuel pump. That fixed the first problem. My next issue is the boat will crank and run great, but will not crank up after riding it for awhile. It will crank up fine after letting it sit for 20-30 minutes. I believe the stator is bad. I ordered one from eBay last night. I will post pics after I get her cleaned up.
 
Skoolball23 said:
I remember reading that my gearing is 2.25x1. I appreciate all of the great information. I traded a gp 1300 for this boat last November. The interior has been redone and boat has been painted. I'm still working out all of the bugs. It wouldn't start without ether so I replaced the fuel pump. That fixed the first problem. My next issue is the boat will crank and run great, but will not crank up after riding it for awhile. It will crank up fine after letting it sit for 20-30 minutes. I believe the stator is bad. I ordered one from eBay last night. I will post pics after I get her cleaned up.
Click to expand...

Stator is a great guess.
 
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