Don't install a hydrofoil without watching this 

Regarding your zinc trim tab. Your prop is likely right hand rotation. If you remove trim tab and run wot then let go of tiller handle it will go hard over to steering stop. This is prop torque. You adjust trim tab to counter-effect that torque. If done properly, you can run wot and release Tiller and it will remain centered. Hope this helps you understand.

The zinc tab is both a sacrificial metal and trim tab. The trim tab balances applied thrust forces between left and right by diverting thrust . The same amount of force should be required to turn the motor left or right and the motor should stay straight with no force holding it in place. A right hand rotating prop always wants to make the boat turn left by thrusting right - pushing motor left and nose of the boat left. . The tab catches the highest velocity thrust near the blade tip and diverts it left - counter balancing the right thrust forces holding the engine straight when both going straight and creating balanced turn forces while turning.

When a propeller is spining within a water column, the blades that dive (travel downwards) face a higher load than the blades that rise(travel upwards) because of the vicinity of the surface. In other words it´s easier to push water up, rather than down. Anyone can experience this, by using the palms of their hands while standing waist deep in a swimming pool or a beach. On any motor boat this fenomena creates a thrust differencial which will cause a slight veering to either port or starbord depending on the direction of rotation of the propeller. That´s the reason a trim tab has two purposes : the first, as a sacrificial anode to maintain galvanic cathodic protection on all submerged metal components of the engine , and the second, as a little rudder preset to compensate the course of the boat while underway due to that constant veering force. A boat with two outboards of opposed direction of rotation mounted on it`s transom wouldn`t need compensation because that veering would be cancelled by each engine.

Great tips. This is exactly the type of misstep that I would make. BTW the anode fin offset is intended to Counter any prop torque that might influence the steering resistance. It should be adjusted depending on your experience

I've found a right-angle attachment for my drill very useful for problems like this.

That fin is to push your motor to left or right to go in a circle if you fall overboard or loose control of your continuously till cavitation accord in hopes the bring your to a stop before causing damage

If you ever decide to replace this wing you might take a look at a Permatrim Cavitation Plate.....Just saying!!😎

The little fin coming out of the annoyed is she keep the prop from pulling the motor to one side or the other from the Prop

Regarding your 9.9 just so your aware soon as you get into a 9.9 it’s a inline 2 cylinder. 15 and 20 are the same motors just get a 9.9 sticker if your worried.

That plste is to adjust prop torque so your motor doesn't pull to hard either way

Trim tab to stop torque steer. I wish my 15hp merc had one.

Also have a 9.9 on my Gheenoe. Thanks for the heads up. BTW, Did the new plate have the desired effect?

Your comment about "catching air" when you start going faster with the motor raised, this is caused by the boat going on plane and lifting up higher in the water. Your motor will not be deep enough.

I used a different brand that worked great

I was interested in a Hydrofoil until the part I have to drill holes in the motor. Nope and nope.

torque rotation

Good morning, did you have to move the Sacrificial anode position when you instaled the hydrofoil??because when I instaled mine, the motor started to put pressure in one side, Heavilly

its off set to much , help keep boat straight from motor torgue

Oh yeah let’s make a “how to” video! We’ll read what the manufacturer has to say afterwards! 😅😅😅😅😂😂😂😂😂😂😂😂😂😂

It's a skeg not skag sorry that killed my ears.

Experience but still make mistakes, ummmmm