Prop

[CHANCE1234]

So I tried a few props today on not 20SF with a 2001 yamaha 115. The one I've been using is a 13 1/4 X 15 quicksilver aluminum. That got 5800 WOT and 34.9 knots. Then I tried a 13 1/4 X 17 yamaha semi clever and achieved the same exact numbers. 35 knots is just a hair over 40 mph but I figured I'd get a little better top end out of the yamaha prop. Any suggestions?

[Bushwacker]

Get the motor height correct before you conclude anything about props. A SS prop with more cup will typically allow motor to run higher on transom w/o losing grip and ventillating. Also make sure your tach is accurate as many analog tachs are notoriously inaccurate, and that could lead you into selecting wrong prop!

[McGillicuddy]

Originally Posted by CHANCE1234

So I tried a few props today on not 20SF with a 2001 yamaha 115. The one I've been using is a 13 1/4 X 15 quicksilver aluminum. That got 5800 WOT and 34.9 knots. Then I tried a 13 1/4 X 17 yamaha semi clever and achieved the same exact numbers. 35 knots is just a hair over 40 mph but I figured I'd get a little better top end out of the yamaha prop. Any suggestions?

That's pretty good Chance. You sound pretty dialed-in. like the others said in your engine height thread, the anti-vent plate might be running a bit low. Is that pic in other thread of the Yamaha prop? Are you sure the Quicksilver isn't 13-3/4 x 15?. Where you able to measure fuel burn? and did you measure speeds at specific rpms? And were you able to determine minimum sustained planing speed w/ either prop?

My guess is the hole-shot was better with the Quicksilver, and that you held a lower planing speed with the Quicksilver. Is that a 2-S or 4-S yammy?

The other thought - make sure you're testing with a maximum load. Like Fr. Frank suggests, make sure your able to achieve your top targeted RPM at WOT w/as full a load as you'll carry. Keep us posted. Thats a very common configuration and the question pops up often.

[CHANCE1234]

I'll raise the engine another hole before next trip. Both props are aluminum and used. The pic in the other thread is of the quicksilver prop and it's stamped 13 1/4 X 15. I don't have anyway installed on board to measure fuel burn. No, I did not compare sped of the different wheels at different speeds. Last year min planning speed was 12-13 kts, I did not think to check again this year after she's got a clean bottom. I'll do that next time out. It is a two stroke yamaha. She also has tabs now so she could potentially plane out at very low speed I would think. I generally fish solo so that is how I tested her today with a full load of fuel on board. The tach is digital. I didn't notice much bow rise at all with either prop and didn't touch the tabs at all. Would a 19 pitch be too much for this set up. I'm looking for a mix of fuel economy and good cruising speed around 25 kts roughly at 4200-4300 rpm I think. Thanks for any help.

[FishStretcher]

I think those numbers are good for a 2 stroke 115. I use the (draggy, but lift making) hydroshield with a F100. I think I hit 33MPH at WOT. I think a WOT of 40MPH is pretty good. I'd stick with the 15" pitch. If you find a cheap aluminum 19" pitch, you might have a prop shop hammer the cup out of it and it might get good cruise MPG empty, running solo, but loaded with gear, I bet holeshot and WOT RPM would suffer.

I can turn a 4 blade 17P, but the 15P is better. With more power and less weight and drag, I still suspect a 19P is too much for you, but a 3 blade aluminum 19P might not be.

[McGillicuddy]

Sorry about the presumptions.The stamp is the truth. Older model I guess with sleeker thinner blades.The late model Quicksilver Black Diamond QA2034X or Merc Black Max 48-77342A45 is 13-3/4 x 15. Bigger, rounder semi-cleaver blade. More lift, better push. Likely serve your 2 stroke well, even if you drop 200 rpm, I think you'll find economy gains at cruise and lower planing speed. You can find them on eby for $80 without hub and maybe $110 with. See if a friend or propshop has one laying around. they are very common. Dang good prop for the money. Your Yammy sounds very strong and might be able to spin up the 17p version, but I think you will lose overall going to 19 pitch as the wheel and blade area get smaller.