Having trouble deciding if I need to raise this engine higher on the transom

[Asaracing21]

Having trouble mounting my Mercury engine Long shaft to what I believe is a short shaft transom.

My transom measures 16 inches along the edge which a true reading would be i believe 15 inches. I could not pass up on this engine its a 1996 9.9 ML Pro series tracker. There is a fin above the ventilation plate itself is this where my motor should be measured from the hull? No manual was with this engine and I would appreciate advice on how this motor should be correctly mounted.

This is my first boat....

 

[JB]

Re: Having trouble deciding if I need to raise this engine higher on the transom

Trade that engine for a short shaft.

 

[Asaracing21]

Re: Having trouble deciding if I need to raise this engine higher on the transom

I bought this engine for a steal and would love to make it work on this boat... I posted a pic for suggestions on how much should it be raised and the best possible way, also there is a fin above the ventilation plate that extends forward to the boat is this what i have to measure off of or do i still go by the vent plate?

 

[wired247]

Re: Having trouble deciding if I need to raise this engine higher on the transom

You need to go up a good 6 inches.

 

[Asaracing21]

Re: Having trouble deciding if I need to raise this engine higher on the transom

I just did a measurement roughly its 7 inches till its flush with the bottom of the hull from the vent plate.... Iv been searching it seems like hours for the best possible way on raising this thing let me know your 2 cents?
Here are some mods I found.

 

[wired247]

Re: Having trouble deciding if I need to raise this engine higher on the transom

A simple jack plate would suffice.

 

[Asaracing21]

Re: Having trouble deciding if I need to raise this engine higher on the transom

I read if you put the vent plate around 1 inch below the hull its possible for the engine to suck some air. So how high of a jack plate would be recommended?

 

[wired247]

Re: Having trouble deciding if I need to raise this engine higher on the transom

Hog wash. You can jack a motor so that the prop centerline is level with the hull. For what you have to work with I'd put the prop centerline 4-5 inches below the hull. Forget about the anti-ventilation plate They only work to keep the air out of the prop when the boat isnt moving. Once the boat is moving the anti ventilation plate does nothing. Heres a pic of my setup. This is by far the lowest Ive ever had this motor and its only there because the prop on there right now tends to vent if its any higher....

 

[Jim Hawkins]

Re: Having trouble deciding if I need to raise this engine higher on the transom

Just run it awhile.

I've done the same thing, small boat/ long motor.

Technically not the right setup but if this is your first boat just get the feel of things before doing mods your not familiar with. On a small boat the difference won't be big.

 

[Asaracing21]

Re: Having trouble deciding if I need to raise this engine higher on the transom

Iv just had some concerns of running this engine so deep in the water.

-Getting the engine trimed up far enough for shallow water
-Engine has to work harder due to increase drag, had seen one person only was getting 9 mph out of his 9.9 and then raised it up a bit and hit 23 mph
-Also heard the boat has a possibility of becoming unstable and flipping???

Boat is a 1972 Rich Line 14 feet long

 

[oldman570]

Re: Having trouble deciding if I need to raise this engine higher on the transom

The motor really needs to be moved up to get the best operation out of the motor. You can do as shown in the picture and build up the transom so the cavitation plate is even to up to 1 inch above the bottom of the boat. A aluminum 1/4" plate on the inside of the old transom and angles out farther should do the job. Use of a treated 2X8 is best for the wood. A thinner aluminum plate on the outside and every thing bolted and sealed with RTV sealer will hold it together. This is how I have done my 14 FT. flat boat, and I have run a 25hp motor on it for over 15 years with no trouble. Just keep the cavitation plate on the motor as it should be on the boat. JMO
Oldman570

 

[Asaracing21]

Re: Having trouble deciding if I need to raise this engine higher on the transom

If you have a chance could you take a pic and show a visual of how you did yours? Would be greatly appreciated

 

[oldman570]

Re: Having trouble deciding if I need to raise this engine higher on the transom

I will see if I can get a picture of it and will PM it if I can.
Oldman570

 

[Jim Hawkins]

Re: Having trouble deciding if I need to raise this engine higher on the transom

I would think moving the motor up 6" and by doing so raising the center of gravity on that little boat would do more to make it unstable than leaving it as is. Have fun, be careful.

 

[Jim Hawkins]

Re: Having trouble deciding if I need to raise this engine higher on the transom

I just re-read your original post. I missed that the boat is 14'. In the picture it looked like a smaller 10 or 12' aluminum boat so I can understand raising the transom. The main thing I have seen in all these mods is the 2 pieces of angle that connect the extension to the transom. In addition to that you can add a metal plate between or under the angle for added strength. As long as the extension is supported that way the rest is just whatever design you like.

 

[Asaracing21]

Re: Having trouble deciding if I need to raise this engine higher on the transom

I just pulled the transom its rotted to hell where going to start with a 4 inch rise, than the old transom to see the clearance it has on the vent plate to the hull. If it needs more Ill had 1 or 2 more inches of wood on top and screw them down into the transom. Once we get the clearance right Ill add aluminum plate to the transom covering it with a edge folded over giving it even more strength (also bolted going down from the top into the transom). After that's complete ill use 2 pieces of aluminum angle going from the top of the transom to the bottom completely bolting all the pieces with a few screws going completely through all layers.

Ill post some pics as we go.... The wood where using is used in home building, my buddy who is a contractor says it will last a very long time.

 

[CharlieB]

Re: Having trouble deciding if I need to raise this engine higher on the transom

Re-read and follow oldman's advise in his post #11. He spelled it out for you perfectly.

 

[Jim Hawkins]

Re: Having trouble deciding if I need to raise this engine higher on the transom

Re-read and follow oldman's advise in his post #11. He spelled it out for you perfectly.

Yes, I missed that post too. Don't mess with trying different heights and adding pieces of wood in increments, just set it like Oldman said.

 

[Alumarine]

Re: Having trouble deciding if I need to raise this engine higher on the transom

Just so you know I've heard some treated woods and aluminum boats don't mix well.