In need of a jackplate genius

[Iron Horse]

I picked up a Ranger 451V that is being pushed by a 92 Merc 150 XR6( carbed motor). Prop a 4 blade stainless steel pitch unknown. No set-back on the transom but has a 6 inch manual jack-plate installed. What would be a good starting height for this combo. I know prop pitch is a consideration and plan on taking the prop to the prop shop tomorrow to have it pitched.

[nitro_rat]

How does the boat perform currently? Hole shot Ok? GPS top speed and RPM at that speed? Low water pickup? Water pressure gauge?

[Iron Horse]

Hey Rat
Do not know how well the boat performs it has been in dry dock for referb. Am pretty much starting from scratch. No low water pickup, boat has working water pressure gauge and tach. Boat will go in the water on the 14th for trial run.
Got a chance to go to the prop shop today. Prop is a 24 pitch Precision Turbo. I am afraid I will be over-propped at the start, but just want to get a starting point for this type setup. I am planning to do an initial run prior to making any changes unless the motor is so low that I should bring up to a nominal measurement. Jack-plate is currently set at the bottom of its travel.

[Merc 2.5]

Good rule of thumb is start with prop shaft 3in below pad,

[nitro_rat]

I would run it as is first. Who knows, it may be set up decent already. Plus it doesn't cost any effort. Once you have some base line numbers you will be able to decide which way to go...

[Merc 2.5]

Well reason I suggested that cause he said it's all the way down seems to me it's bout same height if it was on transom, with 6in plate I'd think it actually buried it more?

[Forkin' Crazy]

I would run it as is first. Who knows, it may be set up decent already. Plus it doesn't cost any effort. Once you have some base line numbers you will be able to decide which way to go...

Yep, and the prop may do just fine. Don't change things until you get a base line. And don't change but one thing at a time.

Just jack it up a bit at a time until you: A) run out of water pressure or B) starts driving funky and/or not coming out of the hole.

Your boat is very heavy, so it will never be rocket. I would say 10" of set back would be better.

Post a picture of the prop. I bet the size is on there somewhere.

[Iron Horse]

Ok here is how i checked it. Boat is not on a level surface but the cavitation plate was paralleled (leveled) to the transom. Bottom of cavitation plate to ground is 20 5/16 inches center of prop shaft to ground is 12 1/8 inches. Difference of 8 3/16 inch. Using 3 inches as a nominal starting point should I try to get all of it with the jack-plate or raise the motor on its mount and dial it in with the jack-plate? Does it matter where you take the measurement on the cavitation plate : leading edge, trailing edge or at the end of the prop shaft?

[Iron Horse]

Thanks Paul
Took the prop to the prop shop today and had the pitch checked. Prop guy say he is 99 percent sure it is a Precision Turbo. There are no marking on the prop that indicate OEM, diameter of the hub or the pitch. I couldn't find them and neither could the prop shop guy. He is basing his statement on experience.

Understood, I am not looking for a rocket just a good balance between hole shot and top speed that doesn't bog the engine down. Them fish will still be there whether I arrive at 0600 or 0610.

[Iron Horse]

All
Received and understood. I will leave the setup as is do the initial post maintenance run take notes and report back. I really appreciate the input from all who took the time to contribute.

[90 5.0]

Those boats with a 24p, xr-4 and a 6” plate liked between 3.5 and 3” under par depending on how heavy of a load

[Merc 2.5]

Don't measure to ground. Measure to lowest point on bottom of boat,, 3 to 3 1/2

[Iron Horse]

okay confusion has set in.











Just to clarify, with the prop shaft level to the lowest point on the pad that measurement should be 3.0 to 3.5. Correct??

[nitro_rat]

Yes, level propshaft 3-3.5" lower than bottom of pad.

[Iron Horse]

Copy
Thanks Rat

[Iron Horse]

Got a chance to do a run. Prop shaft 4.5" below pad. Boat ran 55mph on GPS at 4950rpm. Holeshot wasn't too bad. Water pressure 18psi. Boat rode and handled good. 20 gal of fuel on board and approx. half my normal gear.
Ready to make a move. Thinking of raising the motor up half an inch and doing another run or should I go a full inch to 3.5 below the pad?

[Merc 2.5]

3.5 and go from there

[nitro_rat]

3.5 and go from there

:iagree:

You’re really buried right now. Go to 3.5”

[Iron Horse]

414675414674
Does anyone know who manufactures this jack plate? It has no label or data plate to indicate who makes it.