advantage for setting prop CL high

[hopalong]

I have read that for improved mph/performance set the prop centerline about 3 to 4 inches below the bottom of boat/pad. What disadvantage would this have on an outboard motor ? I would suppose a forward nose water pick up would be needed since the stock pick up would be higher than a normal mounted outboard. Cav plate now is 1 3/4 in. above boat pad bottom. Doing the centerline prop method would raise the cav plate a total of 3 1/2 in. above the boat pad.
Outboard motor is a Suzuki 140, 2 stroke w/ carbs/ss 3 bladed cupped prop 13x19, mounted on a Maverick 18 ft. flats boat. The motor is mounted on an adjustable manual jack plate.
I imagine a prop change would be needed, to a 4 blade or other?
Your reply would be appreciated.

 

[WillyBWright]

Re: advantage for setting prop CL high

3-blades need to run mostly submerged. 4-blades can ride higher, but you have to be careful to keep the water pump intakes from sucking air. Sometimes the uppermost holes can be blocked if your gearcase would allow such a modification.

 

[hopalong]

Re: advantage for setting prop CL high

Thanks. Raising the cav plate to 3 1/4 in. above the bottom of boat would most likely create air into the upper water intake?
The motor is a 87 Suzuki 140, 2 stroke, 3 blade 13x19 ss prop w/ Bobs Machine manual jack plate, set off 5 1/2 in. from transom(btw the transom does not have the "pocket" cutout at the bottom like the newer models). I've used this present set up for since 1990 when I had my 86 115 Suzuki on the boat. Recently I've installed the 140 in its place (the 115 is still in very good condition, got the 140 "fresh water" for under $300 and now need to tweek the new set up)motor and realize I have too many rpms at top end and thinking of a remedy, including a possible prop change, when I read the article about the CL method. So trying to get educated as to what I need to do here. Any input would be great. Thanks

 

[bassboy1]

Re: advantage for setting prop CL high

Too many rpms? You need more prop pitch.

Raising the centerline is only to get as much of the gearcase out of the water, to reduce drag. The only boats in which I see finesse movements of the jackplate is on high performance bass rockets, where every bit of a mph counts.

 

[Dhadley]

Re: advantage for setting prop CL high

It has a lot to do with the marriage between hull design, gearcase design, prop design and balance. The whole idea of the theory is to "hide" the gearcase behind the transom. That way there is no gearcase drag except for the skeg. That's the theory. Obviously you cannot get there with every hull design / gearcase design / prop design combo.

If the 18 Maverick has a pad bottom you'll be able to run the motor higher than if it had a simple V. My 19 Hewes has a pad and a step. It looks and drives a lot like a Hydrostream. I have a 6" Bob's hydraulic plate. With a 13 3/4" diameter 4 blade or a 14 1/4" diameter 3 blade I can run the plate almost half way up and the prop is still hooked up.

Now, I have a 14 3/4" diameter 4 blade that I can run all the way up on the plate and still have an awesome holeshot and it stays hooked up at WOT. Stay tuned -- more on these props later.

 

[hopalong]

Re: advantage for setting prop CL high

Great info. Did you do any mods for the water pick up with your set up? and if so what. I have a low pick on each side up just above the gear box and an upper above the prop on bottom of cav plate.
What you have done sounds like the CL method, were the center of the prop shaft is about 3 1/2" below the bottom of the boat at transom

BTW. The Maverick has a radius V hull at the transom that is long sweeping radius at the V rather than a sharp V radius. And as the hull rises up toward the sides there are some chimes. The hull is not "flat" anywhere.
Does your hull at the rear have the slot cutout for improved water over the prop? I'm told this helps one move the motor higher above the V bottom as it provides a higher elevation of water to the prop and water inlet pick up.
Thanks
PS - Bobs Marine is about 20 miles from my house. He has some great stuff. I bought my manual jack plate from him in 1990 and had good success with my old set up: 86 115 Suzuki.....chnaged out recently with a 87 140 Suzuki. The 115 is still alive after 20 + years in "saltwater" well over 2000 hours on it. The 140 was a fresh water motor and looks brand new...no corrosion, all cyl 134 +- 2 # of ech opther. Who says Suzuki's don't last.

 

[Dhadley]

Re: advantage for setting prop CL high

I have the stock water pick ups on the 150. It's not fast enough to warrant a low water pick up nosecone. Yes, the Hewes has the transom "cutout" - that's the step. It does indeed allow the motor to run higher. It also has a pad bottom -- looks like a ski on the bottom.

Even though Bob isn't at Bob's Machine anymore they continue to make excellent products. Good stuff.

 

[hopalong]

Re: advantage for setting prop CL high

Yep I thought you may have that step. I'm thinking since the jack plate puts the motor back away from the transom and raising the motor up, I may get almost the same effect that the step would give for a motor that had no backset jack plate.
Yep, Bob's sure does make high quality items. I also have Bobs finned-aluminum plate over the cav plate. Below is a pic of the 140 (with the 115 cover/decal sleeper motor)after I painted with a different color skeem. You can barely see the plate.
Thanks for all the info. I will post some of what I know in time to give something back to the site in return. I'm into restoring muscle cars in my spare time, and moderate for a Nova/ChevyII site and know the value of people posting answers. Thanks much

http://new.photos.yahoo.com/plsmswain/photo/294928804437886024/1