Outboard Height In Relation To Hull

[a.j. scoggins]

What Are The Adverse Affects Of Lifting The Motor On The Transom,as Well As And/or Lowering It,also What Is The Proper Heiht Settings Based On.i Have An 85 Eliminator / Gmt Mod V Tunnel(centerpod Style) With A 2.4 Merc Bridgeport With Offshore Lower Unit ,just Curious ,the Boat Runs Good Now But Blows Out The Prop Really Easy,obviously It Should To A Certain Degree But ???,thanks And If You Are Coming To Havasu Pm Me??

[STV_Keith]

Is the motor on the transom or on a jackplate or some other setback bracket? If it is, how much setback? What is the current measurement from the bottom of the boat directly in front of the motor to the centerline of the propshaft? What prop are you running and has it been modified? What does the boat weigh? Offshore references the midsection, not the gearcase. Does your gearcase have a bullet nose or a blunt nose? Is it painted black or bare aluminum? How many water inlet holes in the nose?

Pics would help too. :)

[scud]

is it blow out or (as it sounds) ventilation ?

[Jay Smith]

A.J. ,

Firsts as a rule of thumb I've used my own formula over the years and its workd fine for me . Put the boat on a level drive way and use a 4' carpenter level on the rear of the center pad near the transom, level exactly the boat center pad with the trailor tonge jack. Next remove the prop and use a torpedo level on the prop shaft , use the trim to get the shaft perfectly level. Take a RIDGE straight edge and lay along the rear 2 to 3 feet of the pad perfectly flat and let the straight edge pertrude beyond the pad to the gear case. Calculate using the exact center of the drive shaft to establish how much you are truely above or below that pad bottom in corelation with the pad verses the center of the prop shaft. This is called in the racing world inches or tenths of inches on VEE bottoms high or low from "splitshaft" this is where that diminsion or plane strikes or runs from the exact flat bottom to the exact center of the shaft. If the center of the shaft is 1" above that plane your rig is 1" above split shaft and so on. In the THEROY I've used ( and this is a primitive starting point ) for evey one inch your jack plate is in length you can raise the gear case up 1/8 the of an inch from exact splitshaft and still remain in "clean" "hard" water.. If your engine is bolted directly to the transome I suggest no higher than exact split shaft high ..Example if a jack plate is 8 inches long ( deminision from the boat transom to where the motor bolts on to the other side of the jack plate ) you can in theroy go up 8 - 8ths of a inch or 1 "..All boats are different and have thier own sweet spots , alot has to do with the particular hull and or overall rig your working with. Raising a High Performance Engine ( or any engine as for as that goes ) with a low water pick up on the lower unit ( which is a must , if this is not a low water pick uped lower unit the engine being jacked will quickly run out of engine cooling water pressure and engine will be damaged BEFORE the optimal speed and handling can be achieved ) jacking to optimal and is the only way to get your ring to its ultimate potiential and to handle to an optimal set up . Dialing in these boats,motors, gearcases, and props combos are a trial and error game and must be done in small increments and the results of each change needs to be recorded for future movements and to see what helped and what hurt...

hope thats helped,
Good luck,

[a.j. scoggins]

Hey I Will Take Some Measurements To See Where It Is At It Does Have A Standoff Bracket That Sets The Motor Up And Back,i Will Measure It,as Far As The Lower Gearcase,it Is Aluminum In Colr With A Pointed Snout,low Water Pickups Are On Front Below Point And There Are Two Of Them,this Forumn Is Totally Awesome And Can't Wait To Hook Up With Some Fellow Performance Boaters,thanks For All Your Help,
A.j.

[drasticplastic]

The gearcase is an "2 hole" CLE., it will work well in your application. The way Jay described to measure the "X" dimention is the proper way to do it.

[Techno]

One tip is after you've zeroed this in either scribe 2 lines on the jack plate or stick on some kind of ruler for a direct read. Either eliminates the future need to level the boat and plumb the engine since you have a measuring point now.
If you don't have a jack plate its still worth noting what this measurement is on your set back plate so you can do any future changes with a ruler from the mounting holes.