20 masterangler

[DoozleD]

ok, I took the boat out yesterday and it got 5300rpm at wide open, my question it what is 2003 Yamaha 115 supost to tack out at? it has a 13 1/4 by 17 prop

[Normagain]

Is it a four stroke or two stroke? Stainless prop? My 20 with a four stroke F115 get's about 5800-2000 depending on load with a 15 pitch aluminum prop. If you have a 17 pitch stainless, that sounds close to what I might get. Some of the other guys are better than me with props here but they will want to know 2/4 stroke, prop material, brand and where your cav plate is in relation to the bottom of the boat. How much extra weight, fuel, etc. will make a difference also. The four stroke should tach out at close to 6000 when you are fully loaded.

[Bushwacker]

Originally Posted by Normagain

Is it a four stroke or two stroke? Stainless prop? . . .

Doozle, Norm is right . . . any advice you get will be meaningless if we don't even know what motor you have! 4-strokes typically have to rev higher than 2-strokes due to less mid-range torque on the 4S. When trying to select a prop, first make sure you've got the basic stuff right. (A tach of known accuracy, preferably a digital model tied into engine computer, and motor height correct (Top of AV plate above green water when on plane and trimmed out), and be sure to test with MAX load you intend to run, using water ballast if necessary.) And also check current prop to see what your min planing speed is with it. Some props will allow you to hang on plane at lower speeds than others, and that's just as important or maybe more so than WOT speed if you run offshore!

There is a lot more to to prop selection than just pitch and diameter! Two different props with the SAME pitch & diameter can behave much differently depending on blade shape, cup, rake and area, so if you want good advice, we also need to know what specific model prop and alloy type you're currently running. Stainless props typically have thinner blades so are easier to turn than an aluminum prop IF the blades are otherwise identical (but the blades are usually different too!) A prop for bass boats with lots of rake and bow lift for maximum speed will not stay on plane as well as a different (but same size) prop with larger blades and lots of stern lift! For example, if going from a BRP Raker (bass boat prop) to a BRP Rebel, one typically has to drop down about 2" in pitch even with the same diameter to get the same WOT rpm, because the Rebel blades are much larger and they slip less. If you're running a heavy motor (over about 300-350 lbs), you probably do NOT want a bow lifting prop! 4 blade props will provide more stern lift but may reduce top speed a bit due to more drag with the extra blade.

[DoozleD]

thanks guys its a 115 4-stroke, I know boats and its set up, (hight), and yes I know about trim...like I said I felt like the midrange was off...it could just be the way 4-strokes are?, im a e-tech guy so I might be used to awesome grunt?...I thought I saw a post someplace on here that someone put up with some numbers he got on his 20 with a 114 Yamaha 4-stroke?

[Normagain]

Originally Posted by DoozleD

thanks guys its a 115 4-stroke, I know boats and its set up, (hight), and yes I know about trim...like I said I felt like the midrange was off...it could just be the way 4-strokes are?, im a e-tech guy so I might be used to awesome grunt?...I thought I saw a post someplace on here that someone put up with some numbers he got on his 20 with a 114 Yamaha 4-stroke?

There may be others on here but here ya go.
http://www.classicseacraft.com/commu...ad.php?t=25526

I am trying a Powertech SCD4 in about a week and will report back on that when I get the prop. My dilemma is my motor is counter rotating so I am very limited on prop choices in the lower pitch range. When I tried a higher pitch prop and got similar high end RPMs to your numbers my low and mid range torque went out the window. Your motor should come alive if you get the RPMs where they should be, as close to 6000 as you can get.

[Ryan]

Were you trimmed out? If not that'll get you a few rpms.

[FishStretcher]

Originally Posted by DoozleD

ok, I took the boat out yesterday and it got 5300rpm at wide open, my question it what is 2003 Yamaha 115 supost to tack out at? it has a 13 1/4 by 17 prop

I would try a 13.25 x 15 P. It might be faster. It should have better holeshot. I bet 5700 to 5800 at WOT.

[dave s]

My 2005 F115 on a 18' SeaHunt gets 6000 rpm fully loaded with a PowerTech 3 blade stainless 13 1/4 x 17 pitch.

[DoozleD]

Bushwaker,,,its a alum 3blade 13 1/4 by 17...it gets on and stays on plane at a low rpm witch I like and agree with u on, but I feel like the migrange just sucks!...

[Bushwacker]

Originally Posted by DoozleD

Bushwaker,,,its a alum 3blade 13 1/4 by 17...it gets on and stays on plane at a low rpm witch I like and agree with u on, but I feel like the migrange just sucks!...

Sounds like you're about 700 rpm too low, so that's a lot, especially on a 4-stroke that has to be wound up pretty tight to make power! Don't know if dropping down to a 15" pitch would get you that much rpm but worth a try. A good shop can easily repitch an aluminum prop, so I'd try that first. Also check motor rigging to make sure throttle butterflies are fully open at WOT, that timing is correct and motor is otherwise healthy (compression check, fresh plugs & fuel, etc.)

I ran a 1975 115 V-4 300 lb 2-stroke on my Seafari that was probably only about 100 hp at the prop. (Motors were rated at powerhead back then.) It had a 2.0:1 gear reduction and a 13 3/4 X 15p SST prop was perfect. Gave me 32-35 mph WOT depending on load; cruised at 22-23 mph @ 4500 and would plane at 12 mph. Averaged 2.8 mpg on 6 Bahama trips with a very heavy load. Loud and smokey but otherwise a great motor that never quit on me once in over 30 years!