Right prop for Yamaha 115

[CHANCE1234]

What prop are you using for your yamaha 2 stroke 115s on the 20s? Currently have 15 pitch but I'm pretty sure I need 17 pitch. I have not talked to prop gods yet. What works for you guys?

[Tiny]

Had the same engine but a 130. 19p yamaha semi clever was the best if i remember correctly. Search some of my posts, you'll find more specifics.

[FishStretcher]

I suspect that if you go 4 blade you will be happier in the snotty new england stuff with a 15P. I know the (Solas Amita Aluminum) 17P 4 blade is too much for the F100, even with more lower unit reduction(2.31 verus 2.00). It will run it, but hole shot is poor. If you can get the (expensive) yamaha stainless 16P 4 blade, that might be the ticket.

A $100 solas amita 4blade 17P might be cheap enough to try and an ok back up prop if it was a little too much for a fully loaded boat.

[CHANCE1234]

Maybe this helps narrow things down. I usually fish solo or with one other on board, at least 1/2 tank fuel, usually more. Fairly light load, no t top or canvas anywhere. 60 lbs of ice if fishing. I don't mind the slop at all or getting wet. My planning speed with the 15p is like 12-13 knots and I'll be adding trim tabs so bow rise is almost non existant. I'm trying to get better speed at cruise and economy more than anything. WOT with 15p is 29/30 kts and I def have to raise the engine a whole still.

[jpappleby]

You haven't said what rpm your engine is able to obtain at wide open throttle. If the prop is right, WOT rpm should reach at least the middle of the engines specified maximum rpm range with an average load. If rpm is too high, increase the pitch.

[CHANCE1234]

5800-6000 with the engine to low on the stern. I need to raise it up.

[Bushwacker]

Chance, I ran a 115 Evinrude on my boat for about 30 years and a 13 3/4 x 15 OMC SST was the perfect prop for it. That prop has a lot of cup in it and I was able to raise motor so AV plate was about 1" above keel. Motor had a 2.0:1 gear reduction and would turn about 5500 with a very heavy Bahama-trip type load, carrying about 80 gallons of gas. That was a 300 lb motor, so I could plane at about 12 mph with a heavy load and trim tabs, and run about 32-34 mph WOT depending on load.

However that was a 1975 vintage motor, back when they were rated at the powerhead, so it probably wasn't much more than 100 hp at the prop. Your newer motor is stronger since it's rated at the prop and your boat is probably lighter than my Seafari, so if you have a similar gear ratio, you should be able to run more than 15" pitch. You didn't say what specific prop you're running, but if you're turning 5800-6000 with it, you should be able to run 17" or maybe even 19" pitch, but I'd start with 17". If that motor isn't much over 300 lbs, I wouldn't think you'd need a 4B prop unless the boat is stern heavy for some other reason.

[CHANCE1234]

i'm currently running a 13 1/4 by 15 aluminum prop. i don't remember the brand. the engine is a 2001 yamaha 115 TXRZ (i believe) i'm not real mechanical so i don't know what the gear ratio is. i do have a line on a 17 pitch used alumium yamaha prop with a 13 1/4 diameter on ebay. i'm currently the high bidder, hopefully i can get it for cheap, as i'm the only bidder with a day left. i won't be in the water for about another month. when exactly do you determine your "on plane"? i have a video someplace of 13 my GPS at 13 knots which is what i determined to be on plane just be the feel and how the boat rode. but i'm not sure if there is a "book" answer for "on plane" i should not need a 4 blade as there is no weight back aft except for the engine, no livewell, etc... and there is no bow rise getting on plane.

[Bushwacker]

Originally Posted by CHANCE1234

. . . when exactly do you determine your "on plane"? . . .

I look at the wake . . . if water is coming cleanly off the bottom and flat for several feet behind the transom and water from around the sides is converging into sort of a rooster tail behind that, and you're at a point where you can rapidly pick up speed with additional power, I'd say you're on plane, even though the running angle continues to flatten out as you pick up speed. The Boating Magazine test on an I/O Seafari showed running angle continued to drop up to about 25 mph. It's optimum mpg was at 19 mph, where the running angle was relatively high, but it evidently didn't have as much hull in the water at that point!

[CHANCE1234]

Originally Posted by Bushwacker

I look at the wake . . . if water is coming cleanly off the bottom and flat for several feet behind the transom and water from around the sides is converging into sort of a rooster tail behind that, and you're at a point where you can rapidly pick up speed with additional power, I'd say you're on plane, even though the running angle continues to flatten out as you pick up speed. The Boating Magazine test on an I/O Seafari showed running angle continued to drop up to about 25 mph. It's optimum mpg was at 19 mph, where the running angle was relatively high, but it evidently didn't have as much hull in the water at that point!

good to know, thats how I measured it too. when i took my video it was with the previous engine a merc 115 before it blew up. i'll give it a shot in the pond hopefully late this month with both the 15 pitch and 17 pitch.