Another prop question?

[imported_JD__]

I have a Johnson/Suzuki 140 4-stroke on my bass type boat. Johnson/Suzuki advertises that because of the gear reduction(2.38:1) this engine can swing a larger prop. All the SS props offered for these engines by John/SU are 14" in diameter. I've been going the aftermarket prop route and can't seem to find the right combination. The closest to "right so far is a Merc Trophy 4-blade 13-3/4" X 23. All the others were 3-bladed 13.5" diameter X 21,22 and a raked & double-cupped 24. None but the Trophy would give me any bow lift. Mid-range and top end are good w/the Trophy but is slower out of the hole than the others. How much of this is attributed to the 4-blade design or do you feel the larger diameter comes into play? Should I be running a 14" diameter prop? I realize this is a hypothetical question but I would appreciate any knowledgeable input or advice. I don't mind buying a new prop but I hate to buy two or three hoping to get one out of the lot that works well. Are most of you guys running 14" diameter props on your 4-stroke John/Su 90's, 115's and 140,s?<br />JD

 

[Hooty]

Re: Another prop question?

Your best bet, JD, is find yourself a good prop shop that will work wth you. Usually they'll let you try different props and exchange them for free until you find one that'll work for you. <br /><br />c/6<br />Hooty

 

[LubeDude]

Re: Another prop question?

Hooties right if you can work it out. <br /><br />If you are like me, (and I have a Bass boat) You are WOT most of the time running here and there. The four blade is going to give you the best hole shot, and normally a three blade will give you the best top end. 13 1/2", 13 3/4", 14" isnt going to make a whole lot of difference. How does the boat perform at WOT and full trim? What RPMs and speed are we talking, do you experience any chine walk at WOT? Do you have a Jack plate?

 

[Dhadley]

Re: Another prop question?

You will need to play with the mounting height of the motor (X dimension). A 4 blade prop will run higher than a 3 blade of the same design. A larger diameter prop will run at a higher X dimension than a prop of the same design with less diameter. These 2 factors play a huge role in getting the proper set up.<br /><br />If you have a particular prop you like for top end but the hole shot is poor, I'd almost bet that you can use all the trim range and maybe more. These are classic signs that the motor needs to be raised to achieve maximum efficiency.<br /><br />There are some larger diameter props in the aftermarket like Turbo. Keep in mind that comparing props of different makes is comparing apples and oranges.<br /><br />Experiment with the X dimension and keep us posted.<br /><br />Good luck!

 

[imported_JD__]

Re: Another prop question?

LubeDude,<br />WOT is good @ around 6000-6100 RPM's, getting around 51 MPH, no chine walk. Engine rated WOT is 5600-6200 (gear ratio of 2.38:1).<br />Boat is a Tracker Avalanche, stretched-formed/welded hull w/ reverse chines, 1400 lbs. Transom sets back 15" and up 7" from keel. With engine all the way down (factory recommended position) the anti-ventilation plate is about 2.75"-3" above keel. I tried raising the engine one hole but the prop blows out pretty bad in turns. I just installed a Hi-Jacker 6" jack plate yesterday. I'll try approximating same engine height position as when the engine was bolted directly to the transom and let you know how it goes. How much should you move the engine and test? 1/4", 1/2", 1"?<br /><br />Dhadley,<br />Thank you, of all the boat dealers, prop tweekers and mechanics I've talked with you're the first that said diameter does have an affect. Most say it is just peculiar to the design of the particular prop/manufacturer. <br />JD

 

[Dhadley]

Re: Another prop question?

The set back will also affect your performance. It changes the center of gravity or lift point. This is usually a good thing. You may find some "cleaner" water back there too for a better bite.<br /><br />As far as the adjustments go, some folks prefer to go up a little at a time -- some go an inch at a time until they over do it and then come back down. Watch your water pressure. You know what it is now so thats your baseline. Some of todays props will grab water even when the water inlets dont. <br /><br />Let us know how you make out. Good luck!