Prop Stupid

Looking at pic I,d say motor isn,t mounted low enough. Looks like it a short shaft motor on a long shaft transom. motor will push boat like that but you,ll never obtain max performance as your loseing flow from boat boat bottom. That's the slippage your probably feeling at full power. If mounting positon on transom can,t be lowered you may need to either cut transom down to get that skeg at least even with bottom to about 1/2" lower. An inch lower won,t hurt. Another option may be a set back plate that allows motor position to be lowered.
 
Can you get us pics of the entire transom and a side shot showing the cavitation plate in relation to the keel?
 
I agree with the others that the motor appears to be mounted too high. I suggest you take a yardstick or similar straightedge hold it against the bottom of the boat near the centerline extending it out toward the motor. This will simulate the waterline when the boat is on plane. The cav plate should be pretty near to this line.
I suspect that if all that stuff clamped to your lower unit is helping performance, it is only because the motor is set up very poorly. There have been more than 3 million outboard-powered boats sold in the USA since the year 2000. Of those, only a tiny fraction employs those big fins. Those things only help in very special circumstances on boats with unusual conditions. A 14’ jon boat is about the least special condition imaginable. The entire bottom is virtually one big straight-line planing surface. Before you start spending money on new propellers I suggest you seriously analyze the setup of the motor. And, again, use the wide-open-throttle RPM’s of your motor to guide any change in propeller if needed. Of course, all this assumes the powerhead is producing the expected horsepower.
 
Gordon Bartlett said:
A 14’ jon boat is about the least special condition imaginable. The entire bottom is virtually one big straight-line planing surface.
Click to expand...

Spot on for everything in your post, but the above is really right on.
 
I have not studied all the posts so if I am repeating sorry. First you should try to get a tach on that motor, even just a shop tach. Find out how fast your motor should run and prop into that RPM range. MORE pitch will make it slower to come on plane but higher speed once you get there. A lower pitch is like gearing down for more power. Try to get a tach. Oh yes, That plate will probably make the motor hard to turn.
 
Carl -- I will take more pics and post this weekend.

All -- appreciate the advice and suggestions. There clearly can be one or more issues at play and it's gonna take time and tinkering to get it right. More to follow on this one...
 
I will post another photo tomorrow with the straight edge coming back from the keep, but as far as I could tell by eyeballing it this evening, the cav plate is less than an inch above the keel. I should also note that I realized the angle of my motor might be a little too far trimmed up (not sure how much of a difference that makes, but one more thing to consider).

Folks have already chimed in about how the motor runs...I've kept up on motor fluids and no starting problems etc. since I bought it in 2009. I do NOT have a tachometer hooked to it and have not clocked the RPMs. On my previous 13' Boston Whaler, it pushed the boat about 28 mph, and I think I'm getting around 21-22 on this boat (significantly heavier than the BW). As I think I mentioned already, I have a jack plate that I'd gladly put on if the collective wisdom is that it would make a major difference based on the rest of the geometry.

I'm also willing to take off the hydrofoil; not trying to over complicate the setup, but it was something I tried--and have noticed an improvement by at least a few mph--when I started to question the performance of the motor setup.

In terms of my concern about performance, it struggles to get up on plane. It gets there, but I suspect it should have too much trouble pushing a 14' jon to plane, especially if not over loaded with gear. (I typically run it with a bow-mounted trolling motor, one battery, basic gear (life jackets and such), and me and my two boys.) Again, I greatly appreciate everyone's advice...
 
Thats a bit high, but not drastic.

Let us know how the new prop works.
 
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